20152015 Final Final Report Report VirginiaVirginia ∼∼ ChesapeakeChesapeake Bay Bay FinfishFinfish Ageing Ageing andand PopulationPopulaPopulationtion Analysis Analysis

Hongsheng Liao, Cynthia M. Jones, & Jessica L. L. Gilmore

September 28, 2016

2015 Final Report Virginia and Chesapeake Bay Finfish Ageing and Population Analysis

Hongsheng Liao, Cynthia M. Jones, & Jessica L. Gilmore

September 28, 2016

Center for Quantitative Fisheries Ecology Old Dominion University 800 West 46th Street Norfolk, VA 23508

Funded by contract No. F-126-R-13 from the Virginia Saltwater Recreational Development Fund through the Virginia Marine Resources Commission

Contents

EXECUTIVE SUMMARY vii

ACKNOWLEDGEMENTS viii

1 ATLANTIC CROAKER Micropogonias undulatus 1 1.1 INTRODUCTION ...... 2 1.2 METHODS ...... 2 1.2.1 Sample size for ageing ...... 2 1.2.2 Handling of collections ...... 2 1.2.3 Preparation ...... 2 1.2.4 Readings ...... 3 1.2.5 Comparison tests ...... 4 1.3 RESULTS ...... 4 1.3.1 Sample size ...... 4 1.3.2 Reading precision ...... 4 1.3.3 Year class ...... 5 1.3.4 Age-length key ...... 5 1.4 REFERENCES ...... 5

2 BLACK DRUM Pogonias cromis 11 2.1 INTRODUCTION ...... 12 2.2 METHODS ...... 12 2.2.1 Handling of collections ...... 12 2.2.2 Preparation ...... 12 2.2.3 Readings ...... 12 2.2.4 Comparison tests ...... 13 2.3 RESULTS ...... 14 2.3.1 Reading precision ...... 14 2.3.2 Year class ...... 14 2.3.3 Age-length key ...... 14 2.4 REFERENCES ...... 15

3 BLUEFISH Pomatomus saltatrix 19 3.1 INTRODUCTION ...... 20

i CONTENTS

3.2 METHODS...... 20 3.2.1 Sample size for ageing ...... 20 3.2.2 Handling of collections ...... 20 3.2.3 Preparation ...... 20 3.2.4 Readings ...... 21 3.2.5 Comparison tests ...... 22 3.3 RESULTS ...... 23 3.3.1 Sample size ...... 23 3.3.2 Reading precision ...... 23 3.3.3 Year class ...... 23 3.3.4 Age-length key ...... 24 3.4 REFERENCES ...... 24

4 COBIA Rachycentron canadum 33 4.1 INTRODUCTION ...... 34 4.2 METHODS ...... 34 4.2.1 Handling of collections ...... 34 4.2.2 Preparation ...... 34 4.2.3 Readings ...... 34 4.2.4 Comparison tests ...... 35 4.3 RESULTS ...... 36 4.3.1 Reading precision ...... 36 4.3.2 Year class ...... 36 4.3.3 Age-length key ...... 36 4.4 REFERENCES ...... 37

5 RED DRUM Sciaenops ocellatus 41 5.1 INTRODUCTION ...... 42 5.2 METHODS ...... 42 5.2.1 Handling of collections ...... 42 5.2.2 Preparation ...... 42 5.2.3 Readings ...... 42 5.2.4 Comparison tests ...... 43 5.3 RESULTS ...... 44 5.3.1 Reading precision ...... 44 5.3.2 Year class ...... 44 5.3.3 Age-length key ...... 44 5.4 REFERENCES ...... 45

6 SHEEPSHEAD Archosargus probatocephalus 49 6.1 INTRODUCTION ...... 50 6.2 METHODS ...... 50 6.2.1 Handling of collections ...... 50 6.2.2 Preparation ...... 50 6.2.3 Readings ...... 50 6.2.4 Comparison tests ...... 51 6.3 RESULTS ...... 52 6.3.1 Reading precision ...... 52 ii CONTENTS

6.3.2 Year class ...... 52 6.3.3 Age-length key ...... 52 6.4 REFERENCES ...... 52

7 ATLANTIC SPADEFISH Chaetodipterus faber 57 7.1 INTRODUCTION ...... 58 7.2 METHODS ...... 58 7.2.1 Sample size for ageing ...... 58 7.2.2 Handling of collections ...... 58 7.2.3 Preparation ...... 58 7.2.4 Readings ...... 59 7.2.5 Comparison tests ...... 60 7.3 RESULTS ...... 60 7.3.1 Sample size ...... 60 7.3.2 Reading precision ...... 60 7.3.3 Year class ...... 61 7.3.4 Age-length key ...... 61 7.4 REFERENCES ...... 61

8 SPANISH MACKEREL Scomberomorous maculatus 65 8.1 INTRODUCTION ...... 66 8.2 METHODS ...... 66 8.2.1 Sample size for ageing ...... 66 8.2.2 Handling of collections ...... 66 8.2.3 Preparation ...... 66 8.2.4 Readings ...... 67 8.2.5 Comparison tests ...... 68 8.3 RESULTS ...... 68 8.3.1 Sample size ...... 68 8.3.2 Reading precision ...... 68 8.3.3 Year class ...... 69 8.3.4 Age-length key ...... 69 8.4 REFERENCES ...... 69

9 SPOT Leiostomus xanthurus 73 9.1 INTRODUCTION ...... 74 9.2 METHODS ...... 74 9.2.1 Sample size for ageing ...... 74 9.2.2 Handling of collections ...... 74 9.2.3 Preparation ...... 74 9.2.4 Readings ...... 75 9.2.5 Comparison tests ...... 76 9.3 RESULTS ...... 76 9.3.1 Sample size ...... 76 9.3.2 Reading precision ...... 76 9.3.3 Year class ...... 77 9.3.4 Age-length key ...... 77 9.4 REFERENCES ...... 77

iii CONTENTS

10 SPOTTED SEATROUT Cynoscion nebulosus 81 10.1 INTRODUCTION ...... 82 10.2 METHODS...... 82 10.2.1 Sample size for ageing...... 82 10.2.2 Handling of collections...... 82 10.2.3 Preparation...... 82 10.2.4 Readings ...... 83 10.2.5 Comparison tests...... 84 10.3 RESULTS ...... 84 10.3.1 Sample size ...... 84 10.3.2 Reading precision ...... 84 10.3.3 Year class ...... 85 10.3.4 Age-length key ...... 85 10.4 REFERENCES ...... 85

11 STRIPED BASS Morone saxatilis 89 11.1 INTRODUCTION ...... 90 11.2 METHODS ...... 90 11.2.1 Sample size for ageing ...... 90 11.2.2 Handling of collection ...... 90 11.2.3 Preparation ...... 91 11.2.4 Readings ...... 91 11.2.5 Comparison Tests ...... 94 11.3 RESULTS ...... 94 11.3.1 Sample size ...... 94 11.3.2 Scales ...... 95 11.3.3 Otoliths ...... 96 11.3.4 Comparison of scale and otolith ages ...... 96 11.3.5 Age-Length-Key (ALK) ...... 97 11.4 RECOMMENDATIONS ...... 97 11.5 REFERENCES ...... 97

12 SUMMER FLOUNDER Paralichthys dentatus 107 12.1 INTRODUCTION ...... 108 12.2 METHODS ...... 108 12.2.1 Sample size for ageing ...... 108 12.2.2 Handling of collection ...... 108 12.2.3 Preparation ...... 109 12.2.4 Readings ...... 109 12.2.5 Comparison Tests ...... 112 12.3 RESULTS ...... 112 12.3.1 Sample size ...... 112 12.3.2 Scales ...... 113 12.3.3 Otoliths ...... 114 12.3.4 Comparison of scale and otolith ages ...... 114 12.3.5 Age-Length-Key (ALK) ...... 115 12.4 REFERENCES ...... 115 iv CONTENTS

13 TAUTOG Tautoga onitis 123 13.1 INTRODUCTION ...... 124 13.2 METHODS...... 124 13.2.1 Sample size for ageing ...... 124 13.2.2 Handling of collection ...... 124 13.2.3 Preparation...... 125 13.2.4 Readings ...... 125 13.2.5 Comparison Tests...... 127 13.3 RESULTS ...... 127 13.3.1 Sample size ...... 127 13.3.2 Opercula ...... 127 13.3.3 Otoliths ...... 128 13.3.4 Comparison of operculum and otolith ages ...... 129 13.3.5 Age-Length-Key (ALK) ...... 130 13.4 REFERENCES ...... 130

14 WEAKFISH Cynoscion regalis 139 14.1 INTRODUCTION ...... 140 14.2 METHODS ...... 140 14.2.1 Sample size for ageing ...... 140 14.2.2 Handling of collections ...... 140 14.2.3 Preparation ...... 140 14.2.4 Readings ...... 141 14.2.5 Comparison tests ...... 142 14.3 RESULTS ...... 142 14.3.1 Sample size ...... 142 14.3.2 Reading precision ...... 142 14.3.3 Year class ...... 143 14.3.4 Age-length key ...... 143 14.4 REFERENCES ...... 143

v

EXECUTIVE SUMMARY

In this report we present the ageing results of 14 finfish species collected from commercial and recreational catches made in the Chesapeake Bay and Virginia waters of the Atlantic Ocean, U.S.A. in 2015. All fish were collected by the Virginia Marine Resources Commission’s (VMRC) Stock Assessment Program and the Center for Quantitative Fisheries Ecology (CQFE) at Old Dominion University in 2015 and aged in 2016 at the Age and Growth Laboratory of CQFE. This report is broken into chapters, one for each of the 14 species. We present measures of ageing precision, graphs of year-class distributions, and age-length keys for each species. Three calcified structures (hard-parts) are used in age determination. Specifically, two cal- cified structures were used for determining fish ages of the following three species: striped bass, Morone saxatilis, (n = 885); summer flounder, Paralichthys dentatus, (n = 884); and tautog, Tautoga onitis, (n = 279). Scales and otoliths were used to age striped bass and summer flounder, opercula and otoliths were used to age tautog. Comparing alterna- tive hard-parts allowed us to assess their usefulness in determining fish age as well as the relative precision of each structure. Ages were determined from otoliths only for the follow- ing species: Atlantic croaker, Micropogonias undulatus, (n = 357); black drum, Pogonias cromis, (n = 69); bluefish, Pomatomus saltatrix, (n = 442); cobia, Rachycentron canadum, (n = 342); red drum, Sciaenops ocellatus, (n = 31); sheepshead, Archosargus probato- cephalus, (n = 119); Atlantic spadefish, Chaetodipterus faber, (n = 135); Spanish mackerel, Scomberomorous maculates, (n = 231); spot, Leiostomus xanthurus, (n = 201); spotted seatrout, Cynoscion nebulosus, (n = 308); and weakfish, Cynoscion regalis, (n = 243). In total, we made 10,850 age readings from scales, otoliths and opercula collected during 2015. A summary of the age ranges for all species aged is presented in Table 1. In this report, we also present sample sizes and coefficient of variation (CV) for estimates of age composition for the following species: Atlantic croaker, bluefish, spadefish, Spanish mackerel, spot, spotted seatrout, striped bass, summer flounder, tautog, and weakfish. The sample sizes and the CVs enabled us to determine how many fish we needed to age in each length interval and to measure the precision for estimates of major age classes in each species, respectively, enhancing our efficiency and effectiveness on ageing those species. To support environmental and wildlife agencies, and charities, we donated more than 4800 pounds of dissected fish to the Salvation Army to feed the homeless, and the Wildlife Re- sponse, Inc., a local wildlife rescue agency which is responsible for saving injured animals found by the public. In 2015, we continued to upgrade our Age and Growth Laboratory website, which can be accessed at http://odu.edu/sci/research/cqfe/research/ageing-lab. The website includes an electronic version of this document and our previous VMRC final reports from 2001 to 2014. The site also provides more detailed explanations of the methods and structures we use in age determination.

In order to share the VMRC/ODU data and findings with the stakeholders and other fisheries biologists, in 2015, we developed two website applications (apps) and posted them at the CQFE website. The first one is called "Fish Age Estimator" and designed to estimate the probabilities of ages given a length of a fish (Click here to open the app). The second

vii one is called "Sample Size Estimator for Ageing" and designed to help fisheries biologists and educators to estimate necessary sample sizes with certain coefficients of variation (CV) (Click here to open the app).

Table 1: The minimum and maximum ages, number of fish and their hard-parts collected, number of fish aged, and age readings for the 14 finfish species in 2015. The hard-parts and age readings include both scales and otoliths for striped bass and summer flounder, and both opercula and otoliths for tautog.

Species Number Number Number Number Minimum Maximum of fish of hard- of fish of read- age age collected parts aged ings Atlantic Croaker 464 464 357 714 1 10 Black Drum 69 69 69 138 3 53 Bluefish 682 678 442 884 0 13 Cobia 350 343 342 684 2 11 Red Drum 31 31 31 62 1 6 Sheepshead 121 119 119 238 2 32 Spadefish 137 135 135 270 1 8 Spanish Mackerel 330 327 231 462 0 8 Spotted Seatrout 328 328 308 616 0 10 Spot 263 263 201 402 0 4 Striped Bass 1,081 1,387 885 2,432 3 22 Summer Flounder 1,095 1,386 884 2,356 1 15 Tautog 279 548 279 1,106 3 31 Weakfish 283 283 243 486 1 5 Totals 5,513 6,361 4,526 10,850 (Go back to text)

ACKNOWLEDGEMENTS

We thank Alicia Brown, Aris Horsey, Allison Roberts, Haxley Gomez Vigil, and James Black for their technical expertise in preparing otoliths, scales, and opercula for age determination. They all put in long hours processing "tons" of fish in our lab. A special note of appreciation is extended to Joe Grist, Joe Cimino, Adam Kenyon, and their technicians at the VMRC, including Richard Hancock, Myra Thompson, and Chris Williams for their many efforts in this cooperative project. We would like also to thank our graduate students Kathleen Kirch and Mike Schmidtke for their help in processing fish whenever we were short of hands.

viii Chapter 1

ATLANTIC CROAKER Micropogonias undulatus CHAPTER 1. ATLANTIC CROAKER MICROPOGONIAS UNDULATUS

1.1 INTRODUCTION be a number above which there is only a 1% CV reduction for the most major age in We aged a total of 357 Atlantic croaker, catch by ageing an additional 100 or more Micropogonias undulatus, collected by the fish. Finally, Al is A multiplied by the pro- VMRC’s Biological Sampling Program for portion of length interval l from the length age and growth analysis in 2015. Croaker distribution of the 2009 to 2013 catch. Al ages ranged from 1 to 10 years old with is number of fish to be aged for length in- an average age of 4.1, a standard deviation terval l in 2015. of 1.7, and a standard error of 0.09. Ten age classes (1 to 10) were represented, com- 1.2.2 Handling of collections prising fish of the 2005 to 2014 year-classes. The sample was dominated by fish from the year-class of 2012 with 52.4%. Otoliths were received by the Age & and Growth Laboratory in labeled coin en- velopes, were sorted by date of capture. 1.2 METHODS Their envelope labels were verified against VMRC’s collection data, and each fish was assigned a unique Age and Growth Labo- 1.2.1 Sample size for ageing ratory identification number. All otoliths were stored dry in their original labeled We estimated sample size for ageing coin envelopes. croaker in 2015 using a two-stage ran- dom sampling method (Quinn and Deriso 1999) to increase precision in estimates 1.2.3 Preparation of age composition from fish sampled effi- ciently and effectively. The basic equation Sagittal otoliths, hereafter, referred to as is: "otoliths", were processed for age deter- mination following the methods described Va A = 2 2 (1.1) in Barbieri et al. (1994) with a few θ CV + Ba/L a modifications. The left or right otolith where A is the sample size for ageing was randomly selected and attached, dis- croaker in 2015; θa stands for the propor- tal side down, to a glass slide with clear TM tion of age a fish in a catch. Va and Ba Crystalbond 509 adhesive or imbedded represent variance components within and in epoxy. The otoliths were viewed by eye between length intervals for age a, respec- and, when necessary, under a stereo micro- tively; CV is the coefficient of variation; L scope to identify the location of the core, was the total number of croaker used by and the position of the core was marked VMRC to estimate length distribution of using a pencil across the otolith surface. the catches from 2009 to 2013. θa, Va, Ba, At least one transverse cross-section (here- and CV were calculated using pooled age- after, referred to as "thin-section") was length data of croaker collected from 2009 then removed from the marked core of to 2013 and using equations in Quinn and each otolith using a Buehler IsoMetTM low- Deriso (1999). For simplicity, the equations speed saw equipped with two, 3-inch di- are not listed here. The equation (1.1) indi- ameter, Norton diamond grinding wheels cates that the more fish that are aged, the (hereafter, referred to as "blades"), sepa- smaller the CV (or higher precision) that rated by a stainless steel spacer of 0.5 mm will be obtained. Therefore, the criterion (diameter 2.5"). Thin-sections were placed to age A (number) of fish is that A should on labeled glass slides and covered with a

2 CHAPTER 1. ATLANTIC CROAKER MICROPOGONIAS UNDULATUS thin layer of Flo-texx mounting medium position period and before January 1, it is that not only fixed the sections to the slide, assigned an age class notation of "x+x", but more importantly, provided enhanced where "x" is the number of annuli in the contrast and greater readability by increas- thin-section. If the fish is captured be- ing light transmission through the thin- tween January 1 and the end of the species- sections. specific annulus deposition period, it is as- signed an age class notation of "x+(x+1)". Click here to obtain the protocol at Thus, any growth beyond the last annulus, the CQFE website on how to prepare after its "birthday" but before the end of otolith thin-section for ageing Atlantic annulus deposition period, is interpreted as croaker. being toward the next age class. For example, Atlantic croaker otolith an- 1.2.4 Readings nulus formation occurs between April and May (Barbieri et al. 1994a and b). A The CQFE system assigns an age class to croaker captured between January 1 and a fish based on a combination of number May 31, before the end of the species’ an- of annuli in a thin-section, the date of cap- nulus deposition period, with three visible ture, and the species-specific period when annuli and some translucent growth after the annulus is deposited. Each year, as the last annulus, would be assigned an age the fish grows, its otoliths grow and leave class of "x+(x+1)" or 3+(3+1), noted as behind markers of their age, called an an- 3+4. This is the same age-class assigned nulus. Technically, an otolith annulus is to a fish with four visible annuli captured the combination of both the opaque and after the end of May 31, the period of an- the translucent band. In practice, only the nulus deposition, which would be noted as opaque bands are counted as annuli. The 4+4. number of annuli replaces "x" in our nota- All thin-sections were aged by two different tion below, and is the initial "age" assign- readers using a Nikon SMZ1000 stereo mi- ment of the fish. croscope under transmitted light and dark- Second, the thin-section is examined for field polarization at between 8 and 20 times translucent growth. If no translucent magnification. Each reader aged all of the growth is visible beyond the last annulus, otolith samples. the otolith is called "even" and no modi- Due to discrepancy on identification of the fication of the assigned age is made. The first annulus of Atlantic croaker among At- initial assigned age, then, is the age class of lantic states, Atlantic States Marine Fish- the fish. Any growth beyond the last an- eries Commission (ASMFC) has decided nulus can be interpreted as either being to- not to count the smallest annulus at the ward the next age class or within the same center of the thin-section as the first an- age class. If translucent growth is visible nulus. Following ASMFC’s instruction, we beyond the last annulus, a "+" is added to didn’t count the smallest annulus at the the notation. center as the first annulus in 2015 (Figure 1.1). By convention all fish in the Northern Hemisphere are assigned a birth date of All samples were aged in chronological January 1. In addition, each species has order, based on collection date, without a specific period during which it deposits knowledge of previously estimated ages or the annulus. If the fish is captured after the specimen lengths. When the readers’ the end of the species-specific annulus de- ages agreed, that age was assigned to the

3 CHAPTER 1. ATLANTIC CROAKER MICROPOGONIAS UNDULATUS

within each reader. A figure of 1:1 equiv- alence was used to illustrate those differ- ences (Campana et al. 1995). All statistics analyses were performed in R 3.2.2 (R Core Team 2012).

1.3 RESULTS

Figure 1.1: Otolith thin-sections of a 8 year- old croaker without counting the smallest ring 1.3.1 Sample size and with the last annulus on the edge of the thin-section We estimated a sample size of 418 Atlantic croaker in 2015, ranging in length interval from 5 to 20 inches (Table 1.1). This sam- fish. When the two readers disagreed, both ple size provided a range in (CV) for age readers sat down together and re-aged the composition approximately from the small- fish, again without any knowledge of pre- est (CV) of 9% for age 4 and 5 to the largest viously estimated ages or lengths, and as- (CV) of 25% for age 1. In 2015, we ran- signed a final age to the fish. When the domly selected and aged 357 fish from 464 readers were unable to agree on a final age, croaker collected by VMRC. We fell short the fish was excluded from further analy- in our over-all collections for this optimal sis. length-class sampling estimate by 74 fish. Click here to obtain the protocol at However, we were short of some fish from the CQFE website on how to age At- the major length intervals (The interval re- lantic croaker using their otolith thin- quires 10 or more fish), as a result, the sections. precision for the estimates of major age groups would possibly be influenced signif- icantly. 1.2.5 Comparison tests

A symmetry test (Hoenig et al. 1995) 1.3.2 Reading precision and coefficient of variation (CV) analysis were used to detect any systematic differ- Both readers had high self-precision. ence and precision on age readings, respec- Specifically, there was no significant differ- tively, for the following comparisons: 1) be- ence between the first and second readings tween the two readers in the current year, for Reader 1 with an agreement of 96% and 2) within each reader in the current year, a CV of 1% (test of symmetry: χ2 = 2, df and 3) time-series bias between the current = 2, P = 0.3679), and there was no signif- and previous years within each reader. The icant difference between the first and sec- readings from the entire sample for the cur- ond readings for Reader 2 with an agree- rent year were used to examine the differ- ment of 96% and a CV of 0.7% (test of ence between two readers. A random sub- symmetry: χ2 = 2, df = 2, P = 0.3679). sample of 50 fish from the current year was There was no evidence of systematic dis- selected for second readings to examine the agreement between Reader 1 and Reader 2 difference within a reader. Fifty otoliths with an agreement of 94.96% and a CV of randomly selected from fish aged in 2003 0.9% (test of symmetry: χ2 = 5.29, df = 6, were used to examine the time-series bias P = 0.5077) (Figure 1.2).

4 CHAPTER 1. ATLANTIC CROAKER MICROPOGONIAS UNDULATUS

Figure 1.2: Between-reader comparison of Figure 1.3: Year-class frequency distribution otolith age estimates for Atlantic croaker col- for Atlantic croaker collected for ageing in lected in Chesapeake Bay and Virginia waters 2015. Distribution is broken down by sex. ’Un- of the Atlantic Ocean in 2015. known’ is for gonads that were not available for examination or were not examined for sex dur- ing sampling. There was no time-series bias for both read- ers. Reader 1 had an agreement of 100% with ages of fish aged in 2003. Reader 2 1.4 REFERENCES had an agreement of 100% . Barbieri, L. R., Chittenden, M.E. Jr., Lowerre-Barbieri, S.K. 1994a. Matu- 1.3.3 Year class rity, spawning, and ovarian cycle of At- lantic croaker, Micropogonias undula- Of the 357 fish aged with otoliths, 10 age tus, in the Chesapeake bay and adjacent classes (1 to 10) were represented (Table coastal waters. Fishery Bulletin 92:671- 1.2). The average age was 4.1 years, and 685. the standard deviation and standard error Barbieri, L. R., Chittenden, M.E. Jr., were 1.7 and 0.09, respectively. Year-class Lowerre-Barbieri, S.K. 1994b. Age, data show that the fishery was comprised of growth, and mortality of Atlantic 10 year-classes: fish from the 2005 to 2014 croaker, Micropogonias undulatus, in year-classes, with fish primarily from the the Chesapeake bay region, with a dis- year class of 2012 with 52.4%. The ratio of cussion of apparent geographic changes males to females was 1:2.91 in the sample in population dynamics. Fishery Bul- collected (Figure 1.3). letin 92:1-12.

Campana, S.E., M.C. Annand, and J.I. 1.3.4 Age-length key McMillan. 1995. Graphical and statis- tical methods for determining the con- sistency of age determinations. Trans. We developed an age-length-key (Table Am. Fish. Soc. 124:131-138. 1.3) that can be used in the conversion of numbers-at-length in the estimated catch Hoenig, J.M., M.J. Morgan, and C.A. to numbers-at-age using otolith ages. The Brown. 1995. Analysing differences be- table is based on VMRC’s stratified sam- tween two age determination methods pling of landings by total length inch inter- by tests of symmetry. Can. J. Fish. vals. Aquat. Sci. 52:364-368.

5 CHAPTER 1. ATLANTIC CROAKER MICROPOGONIAS UNDULATUS

Quinn, T. J. II, and R. B. Deriso. 1999. Quantitative Fish Dynamics. Oxford Univeristy Press. New York. R Core Team (2012). R: A lan- guage and environment for statistical computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org.

6 CHAPTER 1. ATLANTIC CROAKER MICROPOGONIAS UNDULATUS

Table 1.1: Number of Atlantic croaker collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 5 - 5.99 5 1 1 4 6 - 6.99 5 12 6 0 7 - 7.99 6 15 6 0 8 - 8.99 6 27 6 0 9 - 9.99 17 38 18 0 10 - 10.99 28 52 28 0 11 - 11.99 51 63 53 0 12 - 12.99 90 105 90 0 13 - 13.99 66 77 75 0 14 - 14.99 54 44 44 10 15 - 15.99 37 25 25 12 16 - 16.99 23 5 5 18 17 - 17.99 15 0 0 15 18 - 18.99 5 0 0 5 19 - 19.99 5 0 0 5 20 - 20.99 5 0 0 5 Totals 418 464 357 74 (Go back to text)

7 CHAPTER 1. ATLANTIC CROAKER MICROPOGONIAS UNDULATUS

Table 1.2: The number of Atlantic croaker assigned to each total length-at-age category for 357 fish sampled for otolith age determination in Virginia during 2015.

Age Interval 1 2 3 4 5 6 7 8 9 10 Totals 5 - 5.99 1 0 0 0 0 0 0 0 0 0 1 6 - 6.99 6 0 0 0 0 0 0 0 0 0 6 7 - 7.99 1 1 4 0 0 0 0 0 0 0 6 8 - 8.99 0 1 3 1 1 0 0 0 0 0 6 9 - 9.99 0 2 15 0 0 1 0 0 0 0 18 10 - 10.99 0 1 15 2 8 2 0 0 0 0 28 11 - 11.99 0 1 37 3 5 3 2 1 0 1 53 12 - 12.99 0 1 47 4 22 6 8 0 1 1 90 13 - 13.99 0 0 29 0 19 15 6 3 3 0 75 14 - 14.99 0 0 23 1 9 5 4 1 1 0 44 15 - 15.99 0 1 12 2 4 2 2 1 1 0 25 16 - 16.99 0 0 2 0 3 0 0 0 0 0 5 Totals 8 8 187 13 71 34 22 6 6 2 357 (Go back to text)

8 CHAPTER 1. ATLANTIC CROAKER MICROPOGONIAS UNDULATUS

Table 1.3: Age-Length key, as proportion-at-age in each 1-inch length interval, based on otolith ages for Atlantic croaker sampled for age determination in Virginia during 2015.

Age Interval 1 2 3 4 5 6 7 8 9 10 5 - 5.99 1 0 0 0 0 0 0 0 0 0 6 - 6.99 1 0 0 0 0 0 0 0 0 0 7 - 7.99 0.17 0.17 0.67 0 0 0 0 0 0 0 8 - 8.99 0 0.17 0.5 0.17 0.17 0 0 0 0 0 9 - 9.99 0 0.11 0.83 0 0 0.06 0 0 0 0 10 - 10.99 0 0.04 0.54 0.07 0.29 0.07 0 0 0 0 11 - 11.99 0 0.02 0.7 0.06 0.09 0.06 0.04 0.02 0 0.02 12 - 12.99 0 0.01 0.52 0.04 0.24 0.07 0.09 0 0.01 0.01 13 - 13.99 0 0 0.39 0 0.25 0.2 0.08 0.04 0.04 0 14 - 14.99 0 0 0.52 0.02 0.2 0.11 0.09 0.02 0.02 0 15 - 15.99 0 0.04 0.48 0.08 0.16 0.08 0.08 0.04 0.04 0 16 - 16.99 0 0 0.4 0 0.6 0 0 0 0 0 (Go back to text)

9

Chapter 2

BLACK DRUM Pogonias cromis CHAPTER 2. BLACK DRUM POGONIAS CROMIS

2.1 INTRODUCTION the position of the core marked using a pencil across the otolith surface. At We aged a total of 69 black drum, Pogonias least one transverse cross-section (hereafter cromis, collected by the VMRC’s Biologi- "thin-section") was then removed from the marked core of each otolith using a Buehler cal Sampling Program for age and growth TM analysis in 2015. Black drum ages ranged IsoMet low-speed saw equipped with from 3 to 53 years old with an average age two, three inch diameter, Norton Diamond of 14.9, a standard deviation of 12.5, and Grinding Wheels, separated by a stainless a standard error of 1.5. Twenty-five age steel spacer of 0.5 mm (diameter 2.5"). The classes (3 to 19, 21, 25, 38, 40, 42, 44 to position of the marked core fell within the 45, and 53) were represented, comprising 0.5 mm space between the blades, such that fish of the 1962, 1970 to 1971, 1973, 1975, the core was included in the removed thin- 1977, 1990, 1994, and 1996 to 2012 year- section. Otolith thin-sections were placed classes. The sample was dominated by fish on labeled glass slides and covered with a from the year-classes of 2011, 1999, and thin layer of Flo-texx mounting medium 2007 with 14.5%, 14.5%, and 11.6%, re- that not only fixed the sections to the spectively. slide, but more importantly, provided en- hanced contrast and greater readability by increasing light transmission through the 2.2 METHODS sections. Click here to obtain the protocol at the 2.2.1 Handling of collections CQFE website on how to prepare otolith thin-section for ageing black drum. Sagittal otoliths, hereafter, referred to as "otoliths", were received by the Age and 2.2.3 Readings Growth Laboratory in labeled coin en- velopes. In the lab they were sorted by date The CQFE system assigns an age class to of capture, their envelope labels were ver- a fish based on a combination of number ified against VMRC’s collection data, and of annuli in a thin-section, the date of cap- each fish was assigned a unique Age and ture, and the species-specific period when Growth Laboratory identification number. the annulus is deposited. Each year, as All otoliths were stored dry in their original the fish grows, its otoliths grow and leave labeled coin envelopes. behind markers of their age, called an an- nulus. Technically, an otolith annulus is 2.2.2 Preparation the combination of both the opaque and the translucent band. In practice, only the opaque bands are counted as annuli. The Otoliths were processed for age determi- number of annuli replaces "x" in our nota- nation following the methods described in tion below, and is the initial "age" assign- Bobko (1991) and Jones and Wells (1998). ment of the fish. The left or right sagittal otolith was ran- domly selected and attached, distal side Second, the thin-section is examined for down, to a glass slide with CrystalbondTM translucent growth. If no translucent 509 adhesive or embedded in epoxy. The growth is visible beyond the last annulus, otoliths were viewed by eye, and when the otolith is called "even" and no modi- necessary, under a stereo microscope to fication of the assigned age is made. The identify the location of the core, and initial assigned age, then, is the age class of

12 CHAPTER 2. BLACK DRUM POGONIAS CROMIS the fish. Any growth beyond the last an- nulus can be interpreted as either being to- ward the next age class or within the same age class. If translucent growth is visible beyond the last annulus, a "+" is added to the notation. By convention all fish in the Northern Figure 2.1: Otolith thin-section of a 3 year-old Hemisphere are assigned a birth date of black drum January 1. In addition, each species has a specific period during which it deposits the annulus. If the fish is captured after the specimen lengths. When the readers’ the end of the species-specific annulus de- ages agreed, that age was assigned to the position period and before January 1, it is fish. When the two readers disagreed, both assigned an age class notation of "x+x", readers sat down together and re-aged the where "x" is the number of annuli in the fish, again without any knowledge of pre- thin-section. If the fish is captured be- viously estimated ages or lengths, and as- tween January 1 and the end of the species- signed a final age to the fish. When the specific annulus deposition period, it is as- readers were unable to agree on a final age, signed an age class notation of "x+(x+1)". the fish was excluded from further analy- Thus, any growth beyond the last annulus, sis. after its "birthday" but before the end of Click here to obtain the protocol at the annulus deposition period, is interpreted as CQFE website on how to age black drum being toward the next age class. using their otolith thin-sections. For example, black drum otolith annulus formation occurs between May and June (Beckman et al. 1990; Bobko 1991; Jones 2.2.4 Comparison tests and Wells 1998). A black drum cap- tured between January 1 and June 30, be- A symmetry test (Hoenig et al. 1995) fore the end of the species’ annulus de- and coefficient of variation (CV) analysis position period, with three visible annuli were used to detect any systematic differ- and some translucent growth after the last ence and precision on age readings, respec- annulus, would be assigned an age class tively, for the following comparisons: 1) be- of "x+(x+1)" or 3+(3+1), noted as 3+4. tween the two readers in the current year, This is the same age-class assigned to a fish 2) within each reader in the current year, with four visible annuli captured after the and 3) time-series bias between the current end of May 31, the period of annulus depo- and previous years within each reader. The sition, which would be noted as 4+4. readings from the entire sample for the cur- rent year were used to examine the differ- All thin-sections were aged by two different ence between two readers. A random sub- readers using a Nikon SMZ1000 stereo mi- sample of 50 fish from the current year was croscope under transmitted light and dark- selected for second readings to examine the field polarization at between 8 and 20 times difference within a reader. Fifty otoliths magnification (Figure 2.1). Each reader randomly selected from fish aged in 2003 aged all of the otolith samples. were used to examine the time-series bias All samples were aged in chronological within each reader. A figure of 1:1 equiv- order, based on collection date, without alence was used to illustrate those differ- knowledge of previously estimated ages or ences (Campana et al. 1995). All statistics

13 CHAPTER 2. BLACK DRUM POGONIAS CROMIS analyses were performed in R 3.2.2 (R Core 2.3.2 Year class Team 2012). Of the 69 fish aged with otoliths, 25 age classes (3 to 19, 21, 25, 38, 40, 42, 44 to 2.3 RESULTS 45, and 53) were represented (Table 2.1). The average age was 14.9 years, and the 2.3.1 Reading precision standard deviation and standard error were 12.5 and 1.5, respectively. Year-class data Both readers had high self-precision. show that the fishery was comprised of 25 Specifically, there was no significant differ- year-classes: fish from the 1962, 1970 to ence between the first and second readings 1971, 1973, 1975, 1977, 1990, 1994, and for Reader 1 with an agreement of 70% and 1996 to 2012 year-classes, with fish primar- a CV of 3.8% (test of symmetry: χ2 = 13, ily from the year classes of 2011, 1999, and df = 14, P = 0.5265), and there was no 2007 with 14.5%, 14.5%, and 11.6%, re- significant difference between the first and spectively. The ratio of males to females second readings for Reader 2 with an agree- was 1:0.64 in the sample collected (Figure ment of 96% and a CV of 0.2% (test of 2.3). symmetry: χ2 = 2, df = 2, P = 0.3679). There was no evidence of systematic dis- agreement between Reader 1 and Reader 2 with an agreement of 89.86% and a CV of 0.3% (test of symmetry: χ2 = 7, df = 7, P = 0.4289) (Figure 2.2).

Figure 2.3: Year-class frequency distribution for black drum collected for ageing in 2015. Distribution is broken down by sex. ’Unknown’ represents gonads that were not available for examination or were not examined for sex dur- ing sampling.

Figure 2.2: Between-reader comparison of otolith age estimates for black drum collected in Chesapeake Bay and Virginia waters of the Atlantic Ocean in 2015. 2.3.3 Age-length key

There was no time-series bias for both read- We developed an age-length-key (Table ers. Reader 1 had an agreement of 70% 2.2) that can be used in the conversion of with ages of fish aged in 2000 with a CV of numbers-at-length in the estimated catch 2% (test of symmetry: χ2 = 15, df = 15, P to numbers-at-age using otolith ages. The = 0.4514). Reader 2 had an agreement of table is based on VMRC’s stratified sam- 94%with a CV of 0.1% (test of symmetry: pling of landings by total length inch inter- χ2 = 3, df = 3, P = 0.3916). vals.

14 CHAPTER 2. BLACK DRUM POGONIAS CROMIS

2.4 REFERENCES

Beckman, D. W., C. A. Wilson, and A. L. Stanley. 1990. Age and growth of black drum in Louisiana waters of the Gulf of Mexico. Transactions of American Fish- eries Society 19:537-544. Bobko, S. J. 1991. Age, growth, and repro- duction of black drum, Pogonias cromis, in Virginia. M.S. thesis. Old Dominion University, Norfolk, VA. Campana, S.E., M.C. Annand, and J.I. McMillan. 1995. Graphical and statisti- cal methods for determining the consis- tency of age eterminations. Trans. Am. Fish. Soc. 124:131-138. Hoenig, J.M., M.J. Morgan, and C.A. Brown. 1995. Analysing differences be- tween two age determination methods by tests of symmetry. Can. J. Fish. Aquat. Sci. 52:364-368. Jones, C.J. and B.K. Wells. 1998. Age, growth, and mortality of black drum, Pogonias cromis, in the Chesapeake Bay region. Fish. Bull. 96:451-461. R Core Team (2012). R: A lan- guage and environment for statistical computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org.

15 CHAPTER 2. BLACK DRUM POGONIAS CROMIS (Go 2015. during T be21 h ubro lc rmasge oec oa egh(nh-taectgr o 9fihsmldfrooihaedtriaini Virginia in determination age otolith for sampled fish 69 for category (inch)-at-age length total each to assigned drum black of number The 2.1: able akt text) to back 9-4.900000000000000000000101002 5 2 0 1 1 0 1 0 2 3 1 0 1 2 0 0 0 0 3 0 0 0 1 0 6 0 0 0 1 0 5 0 0 1 0 0 0 3 1 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 4 0 0 1 0 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 5 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 1 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 1 0 0 49.99 0 0 0 0 0 0 0 - 0 0 0 0 49 0 0 0 0 0 0 45.99 0 0 0 0 0 0 - 0 0 0 0 45 0 0 0 2 0 0 44.99 0 0 0 0 0 0 - 0 0 0 44 0 0 0 0 0 0 42.99 0 0 0 0 0 0 - 0 0 0 42 0 0 0 0 0 41.99 0 0 0 1 0 0 - 0 0 2 41 0 0 0 0 40.99 0 0 0 0 0 0 - 0 1 0 40 0 0 0 0 39.99 0 0 0 1 0 - 0 1 0 39 0 0 0 0 38.99 0 0 0 0 0 - 0 4 0 38 0 0 0 0 37.99 0 0 0 1 - 0 2 0 37 0 0 0 0 36.99 0 0 0 0 - 0 0 36 0 0 0 0 35.99 2 0 0 0 - 0 0 35 0 0 0 34.99 1 0 0 0 - 0 0 34 0 0 33.99 0 0 0 0 - 0 0 33 0 1 32.99 0 0 0 - 0 0 32 4 0 31.99 0 0 0 - 0 31 3 0 29.99 0 0 0 - 29 1 0 27.99 0 2 - 27 2 0 26.99 0 - 26 0 25.99 0 - 25 24.99 1 - 24 22.99 - 22 21 In 19 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 21.99 - oas41 01111212113169 1 3 1 1 2 1 2 1 1 1 1 10 1 3 4 1 4 2 2 8 1 3 1 10 4 Totals evl34567891 11 31 51 71 92 53 04 44 3Totals 53 45 44 42 40 38 25 21 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 terval Age

16 CHAPTER 2. BLACK DRUM POGONIAS CROMIS Age terval 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 21 25 38 40 42 44 45 53 - 21.99 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 In 22 - 22.9924 - 24.9925 1 - 25.9926 0 - 26.99 027 0 - 0.4 27.99 129 0 - 0.6 29.99 131 0 0 - 31.99 0 0 0.832 0 0 - 32.99 0 0.233 0 0 - 0 33.99 0 034 0 0 - 0 34.99 0 0 035 0 0 0 - 35.99 0 0 036 0 0 - 36.99 0 1 0 0 0.4 037 0 0 - 37.99 0 0 038 0 0 0 - 0 38.99 0 0 0 0 039 0 0 - 0.2 39.99 0 0 0 0.4 0 040 0 0 - 0 40.99 0 0 0 0.8 041 0 0 0 - 0 41.99 0 0 0 0 0 0.2542 0 0 0 - 0 42.99 0 0 0 0 0 0.2 0.1744 0 0 0 - 0 44.99 0 0 0 0 0.33 045 0 0 0 - 0 0 0 45.99 0 0 0 0.25 0 049 0 0 0 - 0 0 49.99 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.33 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.17 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.2 0 0 0 0 0 0.33 0.17 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.25 0 0 0 0 0 0 0 0 0 0 0 0.25 0.2 0 0.17 0 0 0 0 0 0 0 0 0.33 0 0 0.2 0 0 0 0 0 0 0 0 0 0.33 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.17 0 0.67 0 0 0 0 0 0 0.2 0 0 0 0.17 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.67 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.2 0 0 0 0 0 0 0.33 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.33 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.33 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0.5 0 0 0 0 0 0 0 0 0 0 0 0 0 0.2 0 0 0 0 0 0.2 1 0 0 0 0 0 0.5 0 0 0 0 0 0 0.5 0 0.4 0.5 0 0.2 0 0 0 0 21 back to text) able 2.2: Age-Length key, as proportion-at-age in each 1-inch length interval, based on otolith ages for black drum sampled for age determination T (Go in Virginia during 2015.

17

Chapter 3

BLUEFISH Pomatomus saltatrix CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX

3.1 INTRODUCTION which there is only a 1% CV reduction for the most major age in catch by aging an We aged a total of 442 bluefish, Pomatomus additional 100 or more fish. Finally, Al is saltatrix, collected by the VMRC’s Biolog- A multiplied by the proportion of length in- ical Sampling Program for age and growth terval l from the length distribution of the analysis in 2015. Bluefish ages ranged from 2009 to 2013 catch. Al is number of fish to 0 to 13 years old with an average age of 3.1, be aged for length interval l in 2015. Based a standard deviation of 2.6, and a standard on VMRC’s request in 2010, we used 1-cm error of 0.12. Fourteen age classes (0 to length interval for bluefish, which differed 13) were represented, comprising fish of the from other species (1-inch). 2002 to 2015 year-classes. The sample was dominated by fish from the year-classes of 2013, 2014, and 2012 with 25.3%, 22.4%, 3.2.2 Handling of collections and 14.9%, respectively. Otoliths were received by the Age & Growth Laboratory in labeled coin en- 3.2 METHODS velopes, and were sorted by date of capture. Their envelope labels were verified against VMRC’s collection data, and each fish was 3.2.1 Sample size for ageing assigned a unique Age and Growth Labo- ratory identification number. All otoliths We estimated sample size for ageing blue- were stored dry in their original labeled fish in 2015 using a two-stage random sam- coin envelopes. pling method (Quinn and Deriso 1999) to increase precision in estimates of age com- position from fish sampled efficiently and 3.2.3 Preparation effectively. The basic equation is: We used our thin-section and bake tech- Va A = 2 2 (3.1) nique to process bluefish sagittal otoliths θ CV + Ba/L a (hereafter, referred to as "otoliths") for where A is the sample size for ageing blue- age determination (Robillard et al. 2009). fish in 2015; θa stands for the proportion of Otolith preparation began by randomly age a fish in a catch. Va and Ba represent selecting either the right or left otolith. variance components within and between Each whole otolith was placed in a ceramic length intervals for age a, respectively; CV "Coors" spot plate well and baked in a is the coefficient of variation; L was the to- Thermolyne 1400 furnace at 400 ◦C. Bak- tal number of bluefish used by VMRC to ing time was dependent on the otolith’s size estimate length distribution of the catches and gauged by color, with a light caramel from 2009 to 2013. θa, Va, Ba, and CV were color desired. Once a suitable color was calculated using pooled age-length data of achieved the baked otolith was embedded bluefish collected from 2009 to 2013 and us- in epoxy resin with its distal surface orien- ing equations in Quinn and Deriso (1999). tated downwards. The otoliths were viewed For simplicity, the equations are not listed by eye and, when necessary, under a stereo here. The equation (3.1) indicates that the microscope to identify the location of the more fish that are aged, the smaller the CV core. Then, the position of the core was (or higher precision) that will be obtained. marked using a permanent marker across Therefore, the criterion to age A (number) the epoxy resin surface. At least one trans- of fish is that A should be a number above verse cross-section (hereafter, referred to

20 CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX as "thin-section") was then removed from fication of the assigned age is made. The the marked core of each otolith using a initial assigned age, then, is the age class of Buehler IsoMetTM low-speed saw equipped the fish. Any growth beyond the last an- with two, 3-inch diameter, Norton diamond nulus can be interpreted as either being to- grinding wheels (hereafter, referred to as ward the next age class or within the same "blades"), separated by a stainless steel age class. If translucent growth is visible spacer of 0.5 mm (diameter 2.5"). The beyond the last annulus, a "+" is added to otolith was positioned so the blades strad- the notation. dled each side of the otolith focus. It was crucial that this cut be perpendicular to By convention all fish in the Northern the long axis of the otolith. Failure to do Hemisphere are assigned a birth date of so resulted in broad and distorted winter January 1. In addition, each species has growth zones. A proper cut resulted in a specific period during which it deposits annuli that were clearly defined and delin- the annulus. If the fish is captured after eated. Once cut, thin-sections were placed the end of the species-specific annulus de- on labeled glass slides and covered with a position period and before January 1, it is thin layer of Flo-texx mounting medium assigned an age class notation of "x+x", that not only fixed the sections to the slide, where "x" is the number of annuli in the but more importantly, provided enhanced thin-section. If the fish is captured be- contrast and greater readability by increas- tween January 1 and the end of the species- ing light transmission through the thin- specific annulus deposition period, it is as- section. signed an age class notation of "x+(x+1)". Click here to obtain the protocol at the Thus, any growth beyond the last annulus, CQFE website on how to prepare otolith after its "birthday" but before the end of thin-section for ageing bluefish. annulus deposition period, is interpreted as being toward the next age class.

3.2.4 Readings For example, bluefish otolith deposition oc- curs between March and June (Robillard The CQFE system assigns an age class to et al. 2009). A bluefish captured between a fish based on a combination of number January 1 and May 31, before the end of annuli in a thin-section, the date of cap- of the species’ annulus deposition period, ture, and the species-specific period when with three visible annuli and some translu- the annulus is deposited. Each year, as cent growth after the last annulus, would the fish grows, its otoliths grow and leave be assigned an age class of "x+(x+1)" or behind markers of their age, called an an- 3+(3+1), noted as 3+4. This is the same nulus. Technically, an otolith annulus is age-class assigned to a fish with four vis- the combination of both the opaque and ible annuli captured after the end of May the translucent band. In practice, only the 31, the period of annulus deposition, which opaque bands are counted as annuli. The would be noted as 4+4. number of annuli replaces "x" in our nota- tion below, and is the initial "age" assign- All thin-sections were aged by two different ment of the fish. readers using a Nikon SMZ1000 stereo mi- Second, the thin-section is examined for croscope under transmitted light and dark- translucent growth. If no translucent field polarization at between 8 and 20 times growth is visible beyond the last annulus, magnification (Figure 3.1). Each reader the otolith is called "even" and no modi- aged all of the otolith samples.

21 CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX

of age and older. This double-annulus for- mation was typically characterized by dis- tinct and separate annuli in extremely close proximity to each other. We do not know if the formation of these double annuli were two separate annuli, or in fact only one, but they seemed to occur during times of reduced growth after maturation. "Dou- Figure 3.1: Otolith thin-section of a 5 year-old ble annuli" were considered to be one an- bluefish with the last annulus on the edge of nulus when both marks joined to form a the thin-section central origin (the origin being the sulcal groove and the outer peripheral edge of the otolith). If these annuli did not meet to If an otolith was properly sectioned, the form a central origin they were considered sulcal groove came to a sharp point within two distinct annuli, and were counted as the middle of the focus. Typically the first such. year’s annulus was found by locating the focus of the otolith, which was character- All samples were aged in chronological ized as a visually distinct dark, oblong re- order, based on collection date, without gion found in the center of the otolith. The knowledge of previously estimated ages or first year’s annulus had the highest visibil- the specimen lengths. When the readers’ ity proximal to the focus along the edge ages agreed, that age was assigned to the of the sulcal groove. Once located, the fish. When the two readers disagreed, both first year’s annulus was followed outward readers sat down together and re-aged the from the sulcal groove towards the dorsal fish, again without any knowledge of pre- perimeter of the otolith. Often, but not viously estimated ages or lengths, and as- always, the first year was associated with signed a final age to the fish. When the a very distinct crenellation on the dorsal readers were unable to agree on a final age, surface and a prominent protrusion on the the fish was excluded from further analy- ventral surface. Both of these landmarks sis. had a tendency to become less prominent Click here to obtain the protocol at the in older fish. CQFE website on how to age bluefish using Even with the bake and thin-section tech- their otolith thin-sections. nique, interpretation of the growth zones from the otoliths of young bluefish was dif- ficult. Rapid growth within the first year 3.2.5 Comparison tests of life prevents a sharp delineation between opaque and translucent zones. When the A symmetry test (Hoenig et al. 1995) exact location of the first year was not and coefficient of variation (CV) analysis clearly evident, and the otolith had been were used to detect any systematic differ- sectioned accurately, a combination of sur- ence and precision on age readings, respec- face landscape (1st year crenellation) and tively, for the following comparisons: 1) be- the position of the second annuli were used tween the two readers in the current year, to help determine the position of the first 2) within each reader in the current year, annulus. and 3) time-series bias between the current and previous years within each reader. The What appeared to be "double annuli" were readings from the entire sample for the cur- occasionally observed in bluefish 4-7 years rent year were used to examine the differ-

22 CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX ence between two readers. A random sub- = 2, P = 0.1353). There was no evidence of sample of 50 fish from the current year was systematic disagreement between Reader 1 selected for second readings to examine the and Reader 2 with an agreement of 86.2% difference within a reader. Fifty otoliths and a CV of 3% (test of symmetry: χ2 = randomly selected from fish aged in 2003 19.09, df = 18, P = 0.3864) (Figure 3.2). were used to examine the time-series bias within each reader. A figure of 1:1 equiv- alence was used to illustrate those differ- ences (Campana et al. 1995). All statistics analyses were performed in R 3.2.2 (R Core Team 2012).

3.3 RESULTS

3.3.1 Sample size

We estimated a sample size of 459 bluefish in 2015, ranging in length interval from 14 Figure 3.2: Between-reader comparison of to 99 centimeters (Table 3.1). This sam- otolith age estimates for bluefish collected in Chesapeake Bay and Virginia waters of the At- ple size provided a range in (CV) for age lantic Ocean in 2015. composition approximately from the small- est (CV) of 6% for age 1 and 2 to the largest (CV) of 25% for age 8. In 2015, we There was no time-series bias for both read- randomly selected and aged 442 fish from ers. Reader 1 had an agreement of 94% 678 bluefish collected by VMRC. We fell with ages of fish aged in 2000 with a CV of short in our over-all collections for this op- 2.5% (test of symmetry: χ2 = 3, df = 3, P timal length-class sampling estimate by 71 = 0.3916). Reader 2 had an agreement of fish. However, we were short of no fish 94% with a CV of 4.2% (test of symmetry: from the major length intervals (The in- χ2 = 3, df = 3, P = 0.3916). terval requires more than 5 fish), as a re- sult, the precision for the estimates of ma- jor age groups would not be influenced sig- 3.3.3 Year class nificantly.

Of the 442 fish aged with otoliths, 14 age 3.3.2 Reading precision classes (0 to 13) were represented (Table 3.2). The average age was 3.1 years, and Reader 1 had high self-precision and Read the standard deviation and standard er- 2 had moderate self-precision. Specifically, ror were 2.6 and 0.12, respectively. Year- there was no significant difference between class data show that the fishery was com- the first and second readings for Reader 1 prised of 14 year-classes: fish from the 2002 with an agreement of 96% and a CV of 3% to 2015 year-classes, with fish primarily (test of symmetry: χ2 = 2, df = 2, P = from the year classes of 2013, 2014, and 0.3679), and there was no significant differ- 2012 with 25.3%, 22.4%, and 14.9%, re- ence between the first and second readings spectively. The ratio of males to females for Reader 2 with an agreement of 92% and was 1:1.66 in the sample collected (Figure a CV of 9.4% (test of symmetry: χ2 = 4, df 3.3).

23 CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX

guage and environment for statistical computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org. Robillard, E. M., C. S. Reiss, and C. M. Jones. 2009. Age-validation and growth of bluefish (Pomatomus saltatrix) along the East Coast of the United States. Fisheries Research 95:65-75.

Figure 3.3: Year-class frequency distribution for bluefish collected for ageing in 2015. Dis- tribution is broken down by sex. ’Unknown’ represents gonads that were not available for examination or were not examined for sex dur- ing sampling.

3.3.4 Age-length key

We developed an age-length-key (Table 3.3) that can be used in the conversion of numbers-at-length in the estimated catch to numbers-at-age using otolith ages. The table is based on VMRC’s stratified sam- pling of landings by total length cm inter- vals.

3.4 REFERENCES

Campana, S.E., M.C. Annand, and J.I. McMillan. 1995. Graphical and statis- tical methods for determining the con- sistency of age determinations. Trans. Am. Fish. Soc. 124:131-138. Hoenig, J.M., M.J. Morgan, and C.A. Brown. 1995. Analysing differences be- tween two age determination methods by tests of symmetry. Can. J. Fish. Aquat. Sci. 52:364-368. Quinn, T. J. II, and R. B. Deriso. 1999. Quantitative Fish Dynamics. Oxford Univeristy Press. New York. R Core Team (2012). R: A lan-

24 CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX

Table 3.1: Number of bluefish collected and aged in each 1-cm length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

(Go back to text) Interval Target Collected Aged Need 14 - 14.99 5 0 0 5 15 - 15.99 5 0 0 5 16 - 16.99 5 0 0 5 17 - 17.99 5 3 3 2 18 - 18.99 5 3 3 2 19 - 19.99 5 3 3 2 20 - 20.99 5 16 6 0 21 - 21.99 5 11 6 0 22 - 22.99 5 17 6 0 23 - 23.99 5 12 6 0 24 - 24.99 5 12 6 0 25 - 25.99 5 13 6 0 26 - 26.99 5 15 6 0 27 - 27.99 5 12 6 0 28 - 28.99 5 11 6 0 29 - 29.99 5 14 6 0 30 - 30.99 5 11 6 0 31 - 31.99 5 10 6 0 32 - 32.99 5 11 6 0 33 - 33.99 5 13 6 0 34 - 34.99 5 7 6 0 35 - 35.99 6 13 6 0 36 - 36.99 7 11 8 0 37 - 37.99 7 9 8 0 38 - 38.99 7 16 8 0 39 - 39.99 8 11 8 0 40 - 40.99 8 17 8 0 41 - 41.99 7 11 8 0 42 - 42.99 8 18 8 0 43 - 43.99 7 10 8 0 44 - 44.99 6 16 6 0 45 - 45.99 8 13 8 0 46 - 46.99 7 18 8 0 47 - 47.99 7 12 8 0 48 - 48.99 6 11 6 0 49 - 49.99 5 10 6 0 50 - 50.99 5 7 6 0 51 - 51.99 5 6 6 0 52 - 52.99 5 5 5 0 53 - 53.99 5 9 6 0 (To continue)

25 CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX

Table 3.1 (Continued) Interval Target Collected Aged Need 54 - 54.99 5 4 4 1 55 - 55.99 5 8 6 0 56 - 56.99 5 6 6 0 57 - 57.99 5 8 6 0 58 - 58.99 5 7 6 0 59 - 59.99 5 10 6 0 60 - 60.99 5 11 6 0 61 - 61.99 5 10 6 0 62 - 62.99 5 7 7 0 63 - 63.99 5 4 4 1 64 - 64.99 5 4 4 1 65 - 65.99 5 6 6 0 66 - 66.99 5 3 3 2 67 - 67.99 5 2 2 3 68 - 68.99 5 12 6 0 69 - 69.99 5 7 6 0 70 - 70.99 5 13 6 0 71 - 71.99 5 9 6 0 72 - 72.99 5 5 5 0 73 - 73.99 5 7 6 0 74 - 74.99 5 10 6 0 75 - 75.99 5 6 6 0 76 - 76.99 5 8 6 0 77 - 77.99 5 8 6 0 78 - 78.99 5 7 6 0 79 - 79.99 5 11 6 0 80 - 80.99 5 2 2 3 81 - 81.99 5 6 6 0 82 - 82.99 5 7 5 0 83 - 83.99 5 8 7 0 84 - 84.99 5 4 4 1 85 - 85.99 5 4 4 1 86 - 86.99 5 5 5 0 87 - 87.99 5 5 5 0 88 - 88.99 5 9 9 0 89 - 89.99 5 1 1 4 90 - 90.99 5 4 4 1 91 - 91.99 5 1 1 4 92 - 92.99 5 5 5 0 93 - 93.99 5 1 1 4 94 - 94.99 5 2 2 3 95 - 95.99 5 1 1 4 96 - 96.99 5 1 1 4 97 - 97.99 5 1 1 4 98 - 98.99 5 1 1 4 (To continue)

26 CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX

Table 3.1 (Continued) Interval Target Collected Aged Need 99 - 99.99 5 0 0 5 Totals 459 678 442 71

27 CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX

(Go back to text)

Table 3.2: The number of bluefish assigned to each total length (cm)-at-age category for 442 fish sampled for otolith age determination in Virginia during 2015.

Age Interval 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Totals 17 - 17.99 3 0 0 0 0 0 0 0 0 0 0 0 0 0 3 18 - 18.99 2 1 0 0 0 0 0 0 0 0 0 0 0 0 3 19 - 19.99 2 1 0 0 0 0 0 0 0 0 0 0 0 0 3 20 - 20.99 3 3 0 0 0 0 0 0 0 0 0 0 0 0 6 21 - 21.99 3 3 0 0 0 0 0 0 0 0 0 0 0 0 6 22 - 22.99 3 3 0 0 0 0 0 0 0 0 0 0 0 0 6 23 - 23.99 3 3 0 0 0 0 0 0 0 0 0 0 0 0 6 24 - 24.99 3 3 0 0 0 0 0 0 0 0 0 0 0 0 6 25 - 25.99 1 5 0 0 0 0 0 0 0 0 0 0 0 0 6 26 - 26.99 2 3 1 0 0 0 0 0 0 0 0 0 0 0 6 27 - 27.99 2 4 0 0 0 0 0 0 0 0 0 0 0 0 6 28 - 28.99 1 4 1 0 0 0 0 0 0 0 0 0 0 0 6 29 - 29.99 0 5 1 0 0 0 0 0 0 0 0 0 0 0 6 30 - 30.99 0 6 0 0 0 0 0 0 0 0 0 0 0 0 6 31 - 31.99 0 6 0 0 0 0 0 0 0 0 0 0 0 0 6 32 - 32.99 0 5 1 0 0 0 0 0 0 0 0 0 0 0 6 33 - 33.99 0 4 2 0 0 0 0 0 0 0 0 0 0 0 6 34 - 34.99 0 4 2 0 0 0 0 0 0 0 0 0 0 0 6 35 - 35.99 0 3 2 1 0 0 0 0 0 0 0 0 0 0 6 36 - 36.99 0 4 4 0 0 0 0 0 0 0 0 0 0 0 8 37 - 37.99 0 4 4 0 0 0 0 0 0 0 0 0 0 0 8 38 - 38.99 0 2 5 1 0 0 0 0 0 0 0 0 0 0 8 39 - 39.99 0 4 3 1 0 0 0 0 0 0 0 0 0 0 8 40 - 40.99 0 3 5 0 0 0 0 0 0 0 0 0 0 0 8 41 - 41.99 0 4 4 0 0 0 0 0 0 0 0 0 0 0 8 42 - 42.99 0 2 6 0 0 0 0 0 0 0 0 0 0 0 8 43 - 43.99 0 2 5 1 0 0 0 0 0 0 0 0 0 0 8 44 - 44.99 0 2 4 0 0 0 0 0 0 0 0 0 0 0 6 45 - 45.99 0 1 7 0 0 0 0 0 0 0 0 0 0 0 8 46 - 46.99 0 0 8 0 0 0 0 0 0 0 0 0 0 0 8 47 - 47.99 0 0 8 0 0 0 0 0 0 0 0 0 0 0 8 48 - 48.99 0 2 4 0 0 0 0 0 0 0 0 0 0 0 6 49 - 49.99 0 0 6 0 0 0 0 0 0 0 0 0 0 0 6 50 - 50.99 0 0 4 2 0 0 0 0 0 0 0 0 0 0 6 51 - 51.99 0 0 4 2 0 0 0 0 0 0 0 0 0 0 6 52 - 52.99 0 1 0 4 0 0 0 0 0 0 0 0 0 0 5 53 - 53.99 0 0 1 5 0 0 0 0 0 0 0 0 0 0 6 54 - 54.99 0 1 1 2 0 0 0 0 0 0 0 0 0 0 4 55 - 55.99 0 0 1 5 0 0 0 0 0 0 0 0 0 0 6 56 - 56.99 0 0 1 4 1 0 0 0 0 0 0 0 0 0 6 57 - 57.99 0 0 3 2 1 0 0 0 0 0 0 0 0 0 6 (To continue) 28 CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX

Table 3.2 (Continued) Age Interval 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Totals 58 - 58.99 0 0 2 4 0 0 0 0 0 0 0 0 0 0 6 59 - 59.99 0 1 2 1 2 0 0 0 0 0 0 0 0 0 6 60 - 60.99 0 0 3 3 0 0 0 0 0 0 0 0 0 0 6 61 - 61.99 0 0 2 3 1 0 0 0 0 0 0 0 0 0 6 62 - 62.99 0 0 3 2 2 0 0 0 0 0 0 0 0 0 7 63 - 63.99 0 0 0 1 2 1 0 0 0 0 0 0 0 0 4 64 - 64.99 0 0 0 3 1 0 0 0 0 0 0 0 0 0 4 65 - 65.99 0 0 1 5 0 0 0 0 0 0 0 0 0 0 6 66 - 66.99 0 0 1 1 1 0 0 0 0 0 0 0 0 0 3 67 - 67.99 0 0 0 0 2 0 0 0 0 0 0 0 0 0 2 68 - 68.99 0 0 0 3 1 2 0 0 0 0 0 0 0 0 6 69 - 69.99 0 0 0 2 3 1 0 0 0 0 0 0 0 0 6 70 - 70.99 0 0 0 3 2 1 0 0 0 0 0 0 0 0 6 71 - 71.99 0 0 0 1 4 0 1 0 0 0 0 0 0 0 6 72 - 72.99 0 0 0 3 1 1 0 0 0 0 0 0 0 0 5 73 - 73.99 0 0 0 0 1 3 2 0 0 0 0 0 0 0 6 74 - 74.99 0 0 0 1 1 2 1 1 0 0 0 0 0 0 6 75 - 75.99 0 0 0 0 2 2 2 0 0 0 0 0 0 0 6 76 - 76.99 0 0 0 0 0 5 1 0 0 0 0 0 0 0 6 77 - 77.99 0 0 0 0 1 3 2 0 0 0 0 0 0 0 6 78 - 78.99 0 0 0 0 1 3 2 0 0 0 0 0 0 0 6 79 - 79.99 0 0 0 0 1 0 5 0 0 0 0 0 0 0 6 80 - 80.99 0 0 0 0 0 1 1 0 0 0 0 0 0 0 2 81 - 81.99 0 0 0 0 0 0 2 3 1 0 0 0 0 0 6 82 - 82.99 0 0 0 0 0 1 0 3 1 0 0 0 0 0 5 83 - 83.99 0 0 0 0 0 1 3 3 0 0 0 0 0 0 7 84 - 84.99 0 0 0 0 0 0 2 1 1 0 0 0 0 0 4 85 - 85.99 0 0 0 0 0 0 1 1 1 1 0 0 0 0 4 86 - 86.99 0 0 0 0 0 0 1 2 0 1 0 1 0 0 5 87 - 87.99 0 0 0 0 0 0 0 4 0 0 1 0 0 0 5 88 - 88.99 0 0 0 0 0 0 2 0 0 3 4 0 0 0 9 89 - 89.99 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 90 - 90.99 0 0 0 0 0 0 0 2 1 1 0 0 0 0 4 91 - 91.99 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 92 - 92.99 0 0 0 0 0 0 0 0 0 1 2 1 1 0 5 93 - 93.99 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 94 - 94.99 0 0 0 0 0 0 0 0 0 0 1 1 0 0 2 95 - 95.99 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 96 - 96.99 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 97 - 97.99 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 98 - 98.99 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 Totals 28 99 112 66 31 27 28 20 5 8 11 5 1 1 442

29 CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX

(Go back to text)

Table 3.3: Age-Length key, as proportion-at-age in each 1-cm length interval, based on otolith ages for bluefish sampled for age determination in Virginia during 2015.

Age Interval 0 1 2 3 4 5 6 7 8 9 10 11 12 13 17 - 17.99 1 0 0 0 0 0 0 0 0 0 0 0 0 0 18 - 18.99 0.67 0.33 0 0 0 0 0 0 0 0 0 0 0 0 19 - 19.99 0.67 0.33 0 0 0 0 0 0 0 0 0 0 0 0 20 - 20.99 0.5 0.5 0 0 0 0 0 0 0 0 0 0 0 0 21 - 21.99 0.5 0.5 0 0 0 0 0 0 0 0 0 0 0 0 22 - 22.99 0.5 0.5 0 0 0 0 0 0 0 0 0 0 0 0 23 - 23.99 0.5 0.5 0 0 0 0 0 0 0 0 0 0 0 0 24 - 24.99 0.5 0.5 0 0 0 0 0 0 0 0 0 0 0 0 25 - 25.99 0.17 0.83 0 0 0 0 0 0 0 0 0 0 0 0 26 - 26.99 0.33 0.5 0.17 0 0 0 0 0 0 0 0 0 0 0 27 - 27.99 0.33 0.67 0 0 0 0 0 0 0 0 0 0 0 0 28 - 28.99 0.17 0.67 0.17 0 0 0 0 0 0 0 0 0 0 0 29 - 29.99 0 0.83 0.17 0 0 0 0 0 0 0 0 0 0 0 30 - 30.99 0 1 0 0 0 0 0 0 0 0 0 0 0 0 31 - 31.99 0 1 0 0 0 0 0 0 0 0 0 0 0 0 32 - 32.99 0 0.83 0.17 0 0 0 0 0 0 0 0 0 0 0 33 - 33.99 0 0.67 0.33 0 0 0 0 0 0 0 0 0 0 0 34 - 34.99 0 0.67 0.33 0 0 0 0 0 0 0 0 0 0 0 35 - 35.99 0 0.5 0.33 0.17 0 0 0 0 0 0 0 0 0 0 36 - 36.99 0 0.5 0.5 0 0 0 0 0 0 0 0 0 0 0 37 - 37.99 0 0.5 0.5 0 0 0 0 0 0 0 0 0 0 0 38 - 38.99 0 0.25 0.62 0.12 0 0 0 0 0 0 0 0 0 0 39 - 39.99 0 0.5 0.38 0.12 0 0 0 0 0 0 0 0 0 0 40 - 40.99 0 0.38 0.62 0 0 0 0 0 0 0 0 0 0 0 41 - 41.99 0 0.5 0.5 0 0 0 0 0 0 0 0 0 0 0 42 - 42.99 0 0.25 0.75 0 0 0 0 0 0 0 0 0 0 0 43 - 43.99 0 0.25 0.62 0.12 0 0 0 0 0 0 0 0 0 0 44 - 44.99 0 0.33 0.67 0 0 0 0 0 0 0 0 0 0 0 45 - 45.99 0 0.12 0.88 0 0 0 0 0 0 0 0 0 0 0 46 - 46.99 0 0 1 0 0 0 0 0 0 0 0 0 0 0 47 - 47.99 0 0 1 0 0 0 0 0 0 0 0 0 0 0 48 - 48.99 0 0.33 0.67 0 0 0 0 0 0 0 0 0 0 0 49 - 49.99 0 0 1 0 0 0 0 0 0 0 0 0 0 0 50 - 50.99 0 0 0.67 0.33 0 0 0 0 0 0 0 0 0 0 51 - 51.99 0 0 0.67 0.33 0 0 0 0 0 0 0 0 0 0 52 - 52.99 0 0.2 0 0.8 0 0 0 0 0 0 0 0 0 0 53 - 53.99 0 0 0.17 0.83 0 0 0 0 0 0 0 0 0 0 54 - 54.99 0 0.25 0.25 0.5 0 0 0 0 0 0 0 0 0 0 55 - 55.99 0 0 0.17 0.83 0 0 0 0 0 0 0 0 0 0 56 - 56.99 0 0 0.17 0.67 0.17 0 0 0 0 0 0 0 0 0 57 - 57.99 0 0 0.5 0.33 0.17 0 0 0 0 0 0 0 0 0 (To continue) 30 CHAPTER 3. BLUEFISH POMATOMUS SALTATRIX

Table 3.3 (Continued) Age Interval 0 1 2 3 4 5 6 7 8 9 10 11 12 13 58 - 58.99 0 0 0.33 0.67 0 0 0 0 0 0 0 0 0 0 59 - 59.99 0 0.17 0.33 0.17 0.33 0 0 0 0 0 0 0 0 0 60 - 60.99 0 0 0.5 0.5 0 0 0 0 0 0 0 0 0 0 61 - 61.99 0 0 0.33 0.5 0.17 0 0 0 0 0 0 0 0 0 62 - 62.99 0 0 0.43 0.29 0.29 0 0 0 0 0 0 0 0 0 63 - 63.99 0 0 0 0.25 0.5 0.25 0 0 0 0 0 0 0 0 64 - 64.99 0 0 0 0.75 0.25 0 0 0 0 0 0 0 0 0 65 - 65.99 0 0 0.17 0.83 0 0 0 0 0 0 0 0 0 0 66 - 66.99 0 0 0.33 0.33 0.33 0 0 0 0 0 0 0 0 0 67 - 67.99 0 0 0 0 1 0 0 0 0 0 0 0 0 0 68 - 68.99 0 0 0 0.5 0.17 0.33 0 0 0 0 0 0 0 0 69 - 69.99 0 0 0 0.33 0.5 0.17 0 0 0 0 0 0 0 0 70 - 70.99 0 0 0 0.5 0.33 0.17 0 0 0 0 0 0 0 0 71 - 71.99 0 0 0 0.17 0.67 0 0.17 0 0 0 0 0 0 0 72 - 72.99 0 0 0 0.6 0.2 0.2 0 0 0 0 0 0 0 0 73 - 73.99 0 0 0 0 0.17 0.5 0.33 0 0 0 0 0 0 0 74 - 74.99 0 0 0 0.17 0.17 0.33 0.17 0.17 0 0 0 0 0 0 75 - 75.99 0 0 0 0 0.33 0.33 0.33 0 0 0 0 0 0 0 76 - 76.99 0 0 0 0 0 0.83 0.17 0 0 0 0 0 0 0 77 - 77.99 0 0 0 0 0.17 0.5 0.33 0 0 0 0 0 0 0 78 - 78.99 0 0 0 0 0.17 0.5 0.33 0 0 0 0 0 0 0 79 - 79.99 0 0 0 0 0.17 0 0.83 0 0 0 0 0 0 0 80 - 80.99 0 0 0 0 0 0.5 0.5 0 0 0 0 0 0 0 81 - 81.99 0 0 0 0 0 0 0.33 0.5 0.17 0 0 0 0 0 82 - 82.99 0 0 0 0 0 0.2 0 0.6 0.2 0 0 0 0 0 83 - 83.99 0 0 0 0 0 0.14 0.43 0.43 0 0 0 0 0 0 84 - 84.99 0 0 0 0 0 0 0.5 0.25 0.25 0 0 0 0 0 85 - 85.99 0 0 0 0 0 0 0.25 0.25 0.25 0.25 0 0 0 0 86 - 86.99 0 0 0 0 0 0 0.2 0.4 0 0.2 0 0.2 0 0 87 - 87.99 0 0 0 0 0 0 0 0.8 0 0 0.2 0 0 0 88 - 88.99 0 0 0 0 0 0 0.22 0 0 0.33 0.44 0 0 0 89 - 89.99 0 0 0 0 0 0 0 0 0 0 1 0 0 0 90 - 90.99 0 0 0 0 0 0 0 0.5 0.25 0.25 0 0 0 0 91 - 91.99 0 0 0 0 0 0 0 0 0 0 0 0 0 1 92 - 92.99 0 0 0 0 0 0 0 0 0 0.2 0.4 0.2 0.2 0 93 - 93.99 0 0 0 0 0 0 0 0 0 0 0 1 0 0 94 - 94.99 0 0 0 0 0 0 0 0 0 0 0.5 0.5 0 0 95 - 95.99 0 0 0 0 0 0 0 0 0 0 0 1 0 0 96 - 96.99 0 0 0 0 0 0 0 0 0 0 1 0 0 0 97 - 97.99 0 0 0 0 0 0 0 0 0 0 1 0 0 0 98 - 98.99 0 0 0 0 0 0 0 0 0 1 0 0 0 0

31

Chapter 4

COBIA Rachycentron canadum CHAPTER 4. COBIA RACHYCENTRON CANADUM

4.1 INTRODUCTION each otolith using a Buehler IsoMetTM low- speed saw equipped with two, three inch di- We aged a total of 342 cobia, Rachycentron ameter, Norton Diamond Grinding Wheels, canadum, collected by the VMRC’s Biolog- separated by a stainless steel spacer of ical Sampling Program for age and growth 0.5 mm (diameter 2.5"). The position of analysis in 2015. Cobia ages ranged from 2 the marked core fell within the 0.5 mm to 11 years old with an average age of 4.7, space between the blades, such that the a standard deviation of 1.6, and a stan- core was included in the removed thin sec- dard error of 0.09. Ten age classes (2 to tion. Otolith thin-sections were placed 11) were represented, comprising fish of the on labeled glass slides and covered with a 2004 to 2013 year-classes. The sample was thin layer of Flo-texx mounting medium dominated by fish from the year-classes of that not only fixed the sections to the 2010, 2012, and 2011 with 35.7%, 23.7%, slide, but more importantly, provided en- and 23.7%, respectively. hanced contrast and greater readability by increasing light transmission through the section. 4.2 METHODS Click here to obtain the protocol at the CQFE website on how to prepare otolith 4.2.1 Handling of collections thin-section for ageing cobia.

Sagittal otoliths, hereafter, referred to as 4.2.3 Readings "otoliths", were received by the Age and Growth Laboratory in labeled coin en- The CQFE system assigns an age class to velopes and were sorted by date of capture, a fish based on a combination of number their envelope labels were verified against of annuli in a thin-section, the date of cap- VMRC’s collection data, and each fish was ture, and the species-specific period when assigned a unique Age and Growth Labo- the annulus is deposited. Each year, as ratory identification number. All otoliths the fish grows, its otoliths grow and leave were stored inside of protective Axygen 2 behind markers of their age, called an an- ml micro-tubes within their original labeled nulus. Technically, an otolith annulus is coin envelopes. the combination of both the opaque and the translucent band. In practice, only the 4.2.2 Preparation opaque bands are counted as annuli. The number of annuli replaces "x" in our nota- tion below, and is the initial "age" assign- Otoliths were processed for age determina- ment of the fish. tion. The left or right otolith was ran- domly selected and embedded, distal side Second, the thin-section is examined for down, in epoxy resin and allowed to harden translucent growth. If no translucent overnight. The otoliths were viewed by eye, growth is visible beyond the last annulus, and when necessary, under a stereo micro- the otolith is called "even" and no modi- scope to identify the location of the core, fication of the assigned age is made. The and the position of the core marked us- initial assigned age, then, is the age class of ing a permanent marker across the epoxy the fish. Any growth beyond the last an- resin surface. At least one transverse nulus can be interpreted as either being to- cross-section (hereafter "thin-section") was ward the next age class or within the same then removed from the marked core of age class. If translucent growth is visible

34 CHAPTER 4. COBIA RACHYCENTRON CANADUM beyond the last annulus, a "+" is added to the notation.

By convention all fish in the Northern Hemisphere are assigned a birth date of January 1. In addition, each species has a specific period during which it deposits Figure 4.1: Otolith thin-section of a 4 year-old the annulus. If the fish is captured after cobia. the end of the species-specific annulus de- position period and before January 1, it is assigned an age class notation of "x+x", without any knowledge of previously esti- where "x" is the number of annuli in the mated ages or lengths, and assigned a final thin-section. If the fish is captured be- age to the fish. When the readers were un- tween January 1 and the end of the species- able to agree on a final age, the fish was specific annulus deposition period, it is as- excluded from further analysis. signed an age class notation of "x+(x+1)". Thus, any growth beyond the last annulus, after its "birthday" but before the end of Click here to obtain the protocol at the annulus deposition period, is interpreted as CQFE website on how to age cobia using being toward the next age class. their otolith thin-sections.

For example, cobia otolith annulus de- position occurs between June and July (Richards 1967 and modified by CQFE). A cobia captured between January 1 and 4.2.4 Comparison tests July 31, before the end of the species’ an- nulus deposition period, with three visible annuli and some translucent growth after A symmetry test (Hoenig et al. 1995) the last annulus, would be assigned an age and coefficient of variation (CV) analysis class of "x+(x+1)" or 3+(3+1), noted as were used to detect any systematic differ- 3+4. This is the same age-class assigned ence and precision on age readings, respec- to a fish with four visible annuli captured tively, for the following comparisons: 1) be- after the end of July 31, the period of an- tween the two readers in the current year, nulus deposition, which would be noted as 2) within each reader in the current year, 4+4. and 3) time-series bias between the current and previous years within each reader. The All thin-sections were aged by two different readings from the entire sample for the cur- readers using a Nikon SMZ1000 stereo mi- rent year were used to examine the differ- croscope under transmitted light and dark- ence between two readers. A random sub- field polarization at between 8 and 20 times sample of 50 fish from the current year was magnification (Figure 4.1). Each reader selected for second readings to examine the aged all of the otolith samples. All sam- difference within a reader. Fifty otoliths ples were aged in chronological order, based randomly selected from fish aged in 2003 on collection date, without knowledge of were used to examine the time-series bias previously estimated ages or the specimen within each reader. A figure of 1:1 equiv- lengths. When the readers’ ages agreed, alence was used to illustrate those differ- that age was assigned to the fish. When ences (Campana et al. 1995). All statistics the two readers disagreed, both readers sat analyses were performed in R 3.2.2 (R Core down together and re-aged the fish, again Team 2012).

35 CHAPTER 4. COBIA RACHYCENTRON CANADUM

4.3 RESULTS 4.3.2 Year class

Of the 342 fish aged with otoliths, 10 age 4.3.1 Reading precision classes (2 to 11) were represented (Table 4.1). The average age was 4.7 years, and the standard deviation and standard er- Both readers had high self-precision. ror were 1.6 and 0.09, respectively. Year- Specifically, there was no significant differ- class data show that the fishery was com- ence between the first and second readings prised of 10 year-classes: fish from the 2004 for Reader 1 with an agreement of 98% and to 2013 year-classes, with fish primarily a CV of 0.4% (test of symmetry: χ2 = 1, df from the year classes of 2010, 2012, and = 1, P = 0.3173), and there was no signif- 2011 with 35.7%, 23.7%, and 23.7%, re- icant difference between the first and sec- spectively. The ratio of males to females ond readings for Reader 2 with an agree- was 1:0.99 in the sample collected (Figure ment of 98% and a CV of 0.4% (test of 4.3). symmetry: χ2 = 1, df = 1, P = 0.3173). There was no evidence of systematic dis- agreement between Reader 1 and Reader 2 with an agreement of 94.74% and a CV of 0.8% (test of symmetry: χ2 = 2.83, df = 5, P = 0.7257) (Figure 4.2).

Figure 4.3: Year-class frequency distribution for cobia collected for ageing in 2015. Distri- bution is broken down by sex. ’Unknown’ rep- resents gonads that were not available for ex- amination or were not examined for sex during sampling.

Figure 4.2: Between-reader comparison of otolith age estimates for cobia collected in Chesapeake Bay and Virginia waters of the At- lantic Ocean in 2015. 4.3.3 Age-length key

There was no time-series bias for both read- We developed an age-length-key (Table ers. Reader 1 had an agreement of 82% 4.2) that can be used in the conversion of with ages of fish aged in 2000 with a CV of numbers-at-length in the estimated catch 1.8% (test of symmetry: χ2 = 9, df = 8, P to numbers-at-age using otolith ages. The = 0.3423). Reader 2 had an agreement of table is based on VMRC’s stratified sam- 88% with a CV of 1.5% (test of symmetry: pling of landings by total length inch inter- χ2 = 6, df = 5, P = 0.3062). vals.

36 CHAPTER 4. COBIA RACHYCENTRON CANADUM

4.4 REFERENCES

Campana, S.E., M.C. Annand, and J.I. McMillan. 1995. Graphical and statis- tical methods for determining the con- sistency of age determinations. Trans. Am. Fish. Soc. 124:131-138. Hoenig, J.M., M.J. Morgan, and C.A. Brown. 1995. Analysing differences be- tween two age determination methods by tests of symmetry. Can. J. Fish. Aquat. Sci. 52:364-368. R Core Team (2012). R: A lan- guage and environment for statistical computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org. Richards, C.E. 1967. Age, Growth, and Fecundity of the Cobia, Rachycentron canadum, from Chesapeake Bay and Adjacent Waters. Contribution No. 252, Virginia Institute of Marine Sci- ence, Gloucester Point, Virginia, 343- 350.

37 CHAPTER 4. COBIA RACHYCENTRON CANADUM

Table 4.1: The number of cobia assigned to each total length (inch)-at-age category for 342 fish sampled for otolith age determination in Virginia during 2015.

Age Interval 2 3 4 5 6 7 8 9 10 11 Totals 34 - 34.99 0 0 1 0 0 0 0 0 0 0 1 35 - 35.99 1 4 2 0 0 0 0 0 0 0 7 36 - 36.99 0 12 7 2 0 0 0 0 0 0 21 37 - 37.99 0 15 3 1 1 0 0 0 0 0 20 38 - 38.99 0 18 11 4 1 0 0 0 0 0 34 39 - 39.99 0 12 10 6 0 1 0 0 0 0 29 40 - 40.99 0 11 5 25 0 0 1 0 0 0 42 41 - 41.99 0 1 5 19 1 3 1 1 0 0 31 42 - 42.99 0 4 7 12 0 1 1 0 0 0 25 43 - 43.99 0 2 2 6 1 1 1 1 0 0 14 44 - 44.99 0 0 8 6 0 1 2 1 0 0 18 45 - 45.99 0 2 6 6 1 0 1 0 2 0 18 46 - 46.99 0 0 5 4 0 0 0 0 0 1 10 47 - 47.99 0 0 4 5 1 0 3 0 0 0 13 48 - 48.99 0 0 2 4 0 0 3 0 0 1 10 49 - 49.99 0 0 1 4 0 0 2 0 1 0 8 50 - 50.99 0 0 1 8 0 0 1 0 0 0 10 51 - 51.99 0 0 0 7 1 1 1 0 1 0 11 52 - 52.99 0 0 1 1 2 0 0 0 0 0 4 53 - 53.99 0 0 0 1 1 1 1 0 0 0 4 54 - 54.99 0 0 0 1 0 0 0 1 0 0 2 55 - 55.99 0 0 0 0 0 1 3 0 0 0 4 56 - 56.99 0 0 0 0 0 2 0 0 0 0 2 58 - 58.99 0 0 0 0 0 0 1 0 0 0 1 61 - 61.99 0 0 0 0 0 0 2 0 0 0 2 64 - 64.99 0 0 0 0 0 0 0 0 1 0 1 Totals 1 81 81 122 10 12 24 4 5 2 342 (Go back to text)

38 CHAPTER 4. COBIA RACHYCENTRON CANADUM

Table 4.2: Age-Length key, as proportion-at-age in each 1-inch length interval, based on otolith ages for cobia sampled for age determination in Virginia during 2015.

Age Interval 2 3 4 5 6 7 8 9 10 11 34 - 34.99 0 0 1 0 0 0 0 0 0 0 35 - 35.99 0.14 0.57 0.29 0 0 0 0 0 0 0 36 - 36.99 0 0.57 0.33 0.1 0 0 0 0 0 0 37 - 37.99 0 0.75 0.15 0.05 0.05 0 0 0 0 0 38 - 38.99 0 0.53 0.32 0.12 0.03 0 0 0 0 0 39 - 39.99 0 0.41 0.34 0.21 0 0.03 0 0 0 0 40 - 40.99 0 0.26 0.12 0.6 0 0 0.02 0 0 0 41 - 41.99 0 0.03 0.16 0.61 0.03 0.1 0.03 0.03 0 0 42 - 42.99 0 0.16 0.28 0.48 0 0.04 0.04 0 0 0 43 - 43.99 0 0.14 0.14 0.43 0.07 0.07 0.07 0.07 0 0 44 - 44.99 0 0 0.44 0.33 0 0.06 0.11 0.06 0 0 45 - 45.99 0 0.11 0.33 0.33 0.06 0 0.06 0 0.11 0 46 - 46.99 0 0 0.5 0.4 0 0 0 0 0 0.1 47 - 47.99 0 0 0.31 0.38 0.08 0 0.23 0 0 0 48 - 48.99 0 0 0.2 0.4 0 0 0.3 0 0 0.1 49 - 49.99 0 0 0.12 0.5 0 0 0.25 0 0.12 0 50 - 50.99 0 0 0.1 0.8 0 0 0.1 0 0 0 51 - 51.99 0 0 0 0.64 0.09 0.09 0.09 0 0.09 0 52 - 52.99 0 0 0.25 0.25 0.5 0 0 0 0 0 53 - 53.99 0 0 0 0.25 0.25 0.25 0.25 0 0 0 54 - 54.99 0 0 0 0.5 0 0 0 0.5 0 0 55 - 55.99 0 0 0 0 0 0.25 0.75 0 0 0 56 - 56.99 0 0 0 0 0 1 0 0 0 0 58 - 58.99 0 0 0 0 0 0 1 0 0 0 61 - 61.99 0 0 0 0 0 0 1 0 0 0 64 - 64.99 0 0 0 0 0 0 0 0 1 0 (Go back to text)

39

Chapter 5

RED DRUM Sciaenops ocellatus CHAPTER 5. RED DRUM SCIAENOPS OCELLATUS

5.1 INTRODUCTION "thin-section") was then removed from the marked core of each otolith using a Buehler TM We aged a total of 31 red drum, Sciaenops IsoMet low-speed saw equipped with ocellatus, collected by the VMRC’s Biolog- two, three inch diameter, Norton Diamond ical Sampling Program for age and growth Grinding Wheels, separated by a stainless analysis in 2015. Red drum ages ranged steel spacer of 0.5 mm (diameter 2.5"). The from 1 to 6 years old with an average age of position of the marked core fell within the 3.4, a standard deviation of 1, and a stan- 0.5 mm space between the blades, such that dard error of 0.18. Four age classes (1, 3 to the core was included in the removed thin- 4, and 6) were represented, comprising fish section. Otolith thin-sections were placed of the 2009, 2011 to 2012, and 2014 year- on labeled glass slides and covered with a classes. The sample was dominated by fish thin layer of Flo-texx mounting medium from the year-classes of 2011 and 2012 with that not only fixed the sections to the 48.4% and 38.7%, respectively. slide, but more importantly, provided en- hanced contrast and greater readability by increasing light transmission through the 5.2 METHODS sections. Click here to obtain the protocol at the 5.2.1 Handling of collections CQFE website on how to prepare otolith thin-section for ageing red drum. Sagittal otoliths, hereafter, referred to as "otoliths", were received by the Age and 5.2.3 Readings Growth Laboratory in labeled coin en- velopes, and were sorted by date of capture. The CQFE system assigns an age class to Their envelope labels were verified against a fish based on a combination of number VMRC’s collection data, and each fish was of annuli in a thin-section, the date of cap- assigned a unique Age and Growth Labo- ture, and the species-specific period when ratory identification number. All otoliths the annulus is deposited. Each year, as were stored dry in their original labeled the fish grows, its otoliths grow and leave coin envelopes. behind markers of their age, called an an- nulus. Technically, an otolith annulus is 5.2.2 Preparation the combination of both the opaque and the translucent band. In practice, only the opaque bands are counted as annuli. The Otoliths were processed for age determi- number of annuli replaces "x" in our nota- nation following the methods described tion below, and is the initial "age" assign- in Ross et al. (1993) and Jones and ment of the fish. Wells (1998) for red drum. The left or right sagittal otolith was randomly se- Second, the thin-section is examined for lected and attached, distal side down, to translucent growth. If no translucent a glass slide with CrystalbondTM 509 ad- growth is visible beyond the last annulus, hesive. The otoliths were viewed by eye, the otolith is called "even" and no modi- and when necessary, under a stereo micro- fication of the assigned age is made. The scope to identify the location of the core, initial assigned age, then, is the age class of and the position of the core marked us- the fish. Any growth beyond the last an- ing a pencil across the otolith surface. At nulus can be interpreted as either being to- least one transverse cross-section (hereafter ward the next age class or within the same

42 CHAPTER 5. RED DRUM SCIAENOPS OCELLATUS age class. If translucent growth is visible beyond the last annulus, a "+" is added to the notation. By convention all fish in the Northern Hemisphere are assigned a birth date of January 1. In addition, each species has a specific period during which it deposits the annulus. If the fish is captured after the end of the species-specific annulus de- position period and before January 1, it is Figure 5.1: Otolith thin-section of a 4 year-old red drum with the last annulus on the edge of assigned an age class notation of "x+x", the thin-section where "x" is the number of annuli in the thin-section. If the fish is captured be- tween January 1 and the end of the species- fish, again without any knowledge of pre- specific annulus deposition period, it is as- viously estimated ages or lengths, and as- signed an age class notation of "x+(x+1)". signed a final age to the fish. When the Thus, any growth beyond the last annulus, readers were unable to agree on a final age, after its "birthday" but before the end of the fish was excluded from further analy- annulus deposition period, is interpreted as sis. being toward the next age class. Click here to obtain the protocol at the For example, red drum annulus formation CQFE website on how to age red drum us- occurs between March and June (Ross et al. ing their otolith thin-sections. 1995 and modified by CQFE). A red drum captured between January 1 and June 30, before the end of the species’ annulus de- 5.2.4 Comparison tests position period, with three visible annuli and some translucent growth after the last A symmetry test (Hoenig et al. 1995) annulus, would be assigned an age class and coefficient of variation (CV) analysis of "x+(x+1)" or 3+(3+1), noted as 3+4. were used to detect any systematic differ- This is the same age-class assigned to a fish ence and precision on age readings, respec- with four visible annuli captured after the tively, for the following comparisons: 1) be- end of June 30, the period of annulus depo- tween the two readers in the current year, sition, which would be noted as 4+4. 2) within each reader in the current year, and 3) time-series bias between the current All thin-sections were aged by two different and previous years within each reader. The readers using a Nikon SMZ1000 stereo mi- readings from the entire sample for the cur- croscope under transmitted light and dark- rent year were used to examine the differ- field polarization at between 8 and 20 times ence between two readers. When the sam- magnification (Figure 5.1). Each reader ple size for the current year was smaller aged all of the otolith samples. than 50, the entire sample was read by each All samples were aged in chronological reader for the second time to examine the order, based on collection date, without difference within a reader. Fifty otoliths knowledge of previously estimated ages or randomly selected from fish aged in 2003 the specimen lengths. When the readers’ were used to examine the time-series bias ages agreed, that age was assigned to the within each reader. A figure of 1:1 equiv- fish. When the two readers disagreed, both alence was used to illustrate those differ- readers sat down together and re-aged the ences (Campana et al. 1995). All statistics

43 CHAPTER 5. RED DRUM SCIAENOPS OCELLATUS analyses were performed in R 3.2.2 (R Core 5.3.2 Year class Team 2012).

Of the 31 fish aged with otoliths, 4 age classes (1, 3 to 4, and 6) were represented (Table 5.1). The average age was 3.4 years, 5.3 RESULTS and the standard deviation and standard error were 1 and 0.18, respectively. Year- class data show that the fishery was com- 5.3.1 Reading precision prised of 4 year-classes: fish from the 2009, 2011 to 2012, and 2014 year-classes, with fish primarily from the year classes of 2011 Both readers had high self-precision. and 2012 with 48.4% and 38.7%, respec- Specifically, there was no significant dif- tively. The ratio of males to females was ference between the first and second read- 1:1.07 in the sample collected (Figure 5.3). ings for Reader 1 with an agreement of 100% , and there was no significant differ- ence between the first and second readings for Reader 2 with an agreement of 100%. There was no evidence of systematic dis- agreement between Reader 1 and Reader 2 with an agreement of 100% (Figure 5.2).

Figure 5.3: Year-class frequency distribution for red drum collected for ageing in 2015. Dis- tribution is broken down by sex. ’Unknown’ represents gonads that were not available for examination or were not examined for sex dur- ing sampling.

Figure 5.2: Between-reader comparison of otolith age estimates for red drum collected in Chesapeake Bay and Virginia waters of the At- lantic Ocean in 2015. 5.3.3 Age-length key

There was no time-series bias for both read- We developed an age-length-key (Table ers. Reader 1 had an agreement of 98% 5.2) that can be used in the conversion of with ages of fish aged in 2000 with a CV of numbers-at-length in the estimated catch 0.4% (test of symmetry: χ2 = 1, df = 1, P to numbers-at-age using otolith ages. The = 0.3173). Reader 2 had an agreement of table is based on VMRC’s stratified sam- 98% with a CV of 0.1% (test of symmetry: pling of landings by total length inch inter- χ2 = 1, df = 1, P = 0.3173). vals.

44 CHAPTER 5. RED DRUM SCIAENOPS OCELLATUS

5.4 REFERENCES

Campana, S.E., M.C. Annand, and J.I. McMillan. 1995. Graphical and statis- tical methods for determining the con- sistency of age determinations. Trans. Am. Fish. Soc. 124:131-138. Hoenig, J.M., M.J. Morgan, and C.A. Brown. 1995. Analyzing differences be- tween two age determination methods by tests of symmetry. Can. J. Fish. Aquat. Sci. 52:364-368. R Core Team (2012). R: A lan- guage and environment for statistical computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org. Ross, J., Stevens, T., Vaughan, D. 1995. Age, Growth, Mortality, and Reproduc- tive Biology of Red Drums in North Car- olina Waters. Trans. Amer. Fish. Soc. 124:37-54.

45 CHAPTER 5. RED DRUM SCIAENOPS OCELLATUS

Table 5.1: The number of red drum assigned to each total length (inch)-at-age category for 31 fish sampled for otolith age determination in Virginia during 2015.

Age Interval 1 3 4 6 Totals 18 - 18.99 1 0 0 0 1 19 - 19.99 2 0 0 0 2 21 - 21.99 0 2 0 0 2 22 - 22.99 0 2 0 0 2 23 - 23.99 0 3 1 0 4 24 - 24.99 0 3 2 0 5 25 - 25.99 0 2 1 0 3 26 - 26.99 0 0 4 0 4 27 - 27.99 0 0 3 0 3 28 - 28.99 0 0 3 0 3 30 - 30.99 0 0 1 0 1 36 - 36.99 0 0 0 1 1 Totals 3 12 15 1 31 (Go back to text)

46 CHAPTER 5. RED DRUM SCIAENOPS OCELLATUS

Table 5.2: Age-Length key, as proportion-at-age in each 1-inch length interval, based on otolith ages for red drum sampled for age determination in Virginia during 2015.

Age Interval 1 3 4 6 18 - 18.99 1 0 0 0 19 - 19.99 1 0 0 0 21 - 21.99 0 1 0 0 22 - 22.99 0 1 0 0 23 - 23.99 0 0.75 0.25 0 24 - 24.99 0 0.6 0.4 0 25 - 25.99 0 0.67 0.33 0 26 - 26.99 0 0 1 0 27 - 27.99 0 0 1 0 28 - 28.99 0 0 1 0 30 - 30.99 0 0 1 0 36 - 36.99 0 0 0 1 (Go back to text)

47

Chapter 6

SHEEPSHEAD Archosargus probatocephalus CHAPTER 6. SHEEPSHEAD ARCHOSARGUS PROBATOCEPHALUS

6.1 INTRODUCTION marker across the epoxy resin surface. At least one transverse cross-section (hereafter We aged a total of 119 sheepshead, Ar- "thin-section") was then removed from the marked core of each otolith using a Buehler chosargus probatocephalus, collected by TM the VMRC’s Biological Sampling Program IsoMet low-speed saw equipped with for age and growth analysis in 2015. two, three inch diameter, Norton Diamond Sheepshead ages ranged from 2 to 32 years Grinding Wheels, separated by a stainless old with an average age of 9.1, a standard steel spacer of 0.5 mm (diameter 2.5"). The deviation of 6.6, and a standard error of position of the marked core fell within the 0.61. Twenty age classes (2 to 4, 6 to 10, 0.5 mm space between the blades, such that 12 to 14, 17 to 19, 21, 23 to 25, 27, and the core was included in the removed thin 32) were represented, comprising fish of the section. Otolith thin-sections were placed 1983, 1988, 1990 to 1992, 1994, 1996 to on labeled glass slides and covered with a 1998, 2001 to 2003, 2005 to 2009, and 2011 thin layer of Flo-texx mounting medium to 2013 year-classes. The sample was dom- that not only fixed the sections to the inated by fish from the year-class of 2011 slide, but more importantly, provided en- with 48.7%. hanced contrast and greater readability by increasing light transmission through the section. 6.2 METHODS Click here to obtain the protocol at the CQFE website on how to prepare otolith 6.2.1 Handling of collections thin-section for ageing sheepshead.

Sagittal otoliths, hereafter, referred to as 6.2.3 Readings "otoliths", were received by the Age and Growth Laboratory in labeled coin en- The CQFE system assigns an age class to velopes,and were sorted by date of capture. a fish based on a combination of number Their envelope labels were verified against of annuli in a thin-section, the date of cap- VMRC’s collection data, and each fish was ture, and the species-specific period when assigned a unique Age and Growth Labo- the annulus is deposited. Each year, as ratory identification number. All otoliths the fish grows, its otoliths grow and leave were stored dry in their original labeled behind markers of their age, called an an- coin envelopes. nulus. Technically, an otolith annulus is the combination of both the opaque and 6.2.2 Preparation the translucent band. In practice, only the opaque bands are counted as annuli. The number of annuli replaces "x" in our nota- Otoliths were processed for age determi- tion below, and is the initial "age" assign- nation following the methods described in ment of the fish. Ballenger et al. (2011). The left or right otolith was randomly selected and Second, the thin-section is examined for embedded, distal side down, in epoxy resin translucent growth. If no translucent and allowed to harden overnight. The growth is visible beyond the last annulus, otoliths were viewed by eye, and when nec- the otolith is called "even" and no modi- essary, under a stereo microscope to iden- fication of the assigned age is made. The tify the location of the core, and the posi- initial assigned age, then, is the age class of tion of the core marked using a permanent the fish. Any growth beyond the last an-

50 CHAPTER 6. SHEEPSHEAD ARCHOSARGUS PROBATOCEPHALUS nulus can be interpreted as either being to- ward the next age class or within the same age class. If translucent growth is visible beyond the last annulus, a "+" is added to the notation. Figure 6.1: Otolith thin-section of a 5 year-old sheepshead By convention all fish in the Northern Hemisphere are assigned a birth date of January 1. In addition, each species has the two readers disagreed, both readers sat a specific period during which it deposits down together and re-aged the fish, again the annulus. If the fish is captured after without any knowledge of previously esti- the end of the species-specific annulus de- mated ages or lengths, and assigned a final position period and before January 1, it is age to the fish. When the readers were un- assigned an age class notation of "x+x", able to agree on a final age, the fish was where "x" is the number of annuli in the excluded from further analysis. thin-section. If the fish is captured be- tween January 1 and the end of the species- specific annulus deposition period, it is as- Click here to obtain the protocol at the signed an age class notation of "x+(x+1)". CQFE website on how to age sheepshead Thus, any growth beyond the last annulus, using their otolith thin-sections. after its "birthday" but before the end of annulus deposition period, is interpreted as being toward the next age class.

For example, sheepshead otolith annulus 6.2.4 Comparison tests formation occurs between May and June (Ballenger 2011). A sheepshead captured between January 1 and July 31, before A symmetry test (Hoenig et al. 1995) the end of the species’ annulus deposi- and coefficient of variation (CV) analysis tion period, with three visible annuli and were used to detect any systematic differ- some translucent growth after the last an- ence and precision on age readings, respec- nulus, would be assigned an age class of tively, for the following comparisons: 1) be- "x+(x+1)" or 3+(3+1), noted as 3+4. tween the two readers in the current year, This is the same age-class assigned to a fish 2) within each reader in the current year, with four visible annuli captured after the and 3) time-series bias between the current end of May 31, the period of annulus depo- and previous years within each reader. The sition, which would be noted as 4+4. readings from the entire sample for the cur- rent year were used to examine the differ- All thin-sections were aged by two different ence between two readers. A random sub- readers using a Nikon SMZ1000 stereo mi- sample of 50 fish from the current year was croscope under transmitted light and dark- selected for second readings to examine the field polarization at between 8 and 20 times difference within a reader. Fifty otoliths magnification (Figure 6.1). Each reader randomly selected from fish aged in 2003 aged all of the otolith samples. All sam- were used to examine the time-series bias ples were aged in chronological order, based within each reader. A figure of 1:1 equiv- on collection date, without knowledge of alence was used to illustrate those differ- previously estimated ages or the specimen ences (Campana et al. 1995). All statistics lengths. When the readers’ ages agreed, analyses were performed in R 3.2.2 (R Core that age was assigned to the fish. When Team 2012).

51 CHAPTER 6. SHEEPSHEAD ARCHOSARGUS PROBATOCEPHALUS

6.3 RESULTS 19, 21, 23 to 25, 27, and 32) were repre- sented (Table 6.1). The average age was 9.1 6.3.1 Reading precision years, and the standard deviation and stan- dard error were 6.6 and 0.61, respectively. Both readers had high self-precision. Year-class data show that the fishery was Specifically, there was no significant differ- comprised of 20 year-classes: fish from the ence between the first and second readings 1983, 1988, 1990 to 1992, 1994, 1996 to for Reader 1 with an agreement of 94% and 1998, 2001 to 2003, 2005 to 2009, and 2011 a CV of 0.5% (test of symmetry: χ2 = 3, df to 2013 year-classes, with fish primarily = 3, P = 0.3916), and there was no signif- from the year class of 2011 with 48.7%. The icant difference between the first and sec- ratio of males to females was 1:1.39 in the ond readings for Reader 2 with an agree- sample collected (Figure 6.3). ment of 92% and a CV of 0.5% (test of symmetry: χ2 = 4, df = 3, P = 0.2615). There was no evidence of systematic dis- agreement between Reader 1 and Reader 2 with an agreement of 84.03% and a CV of 1.1% (test of symmetry: χ2 = 13.67, df = 11, P = 0.252) (Figure 6.2).

Figure 6.3: Year-class frequency distribution for sheepshead collected for ageing in 2015. Distribution is broken down by sex. ’Unknown’ represents gonads that were not available for examination or were not examined for sex dur- ing sampling.

Figure 6.2: Between-reader comparison of 6.3.3 Age-length key otolith age estimates for sheepshead collected in Chesapeake Bay and Virginia waters of the We developed an age-length-key (Table Atlantic Ocean in 2015. 6.2) that can be used in the conversion of numbers-at-length in the estimated catch There was no time-series bias for both read- to numbers-at-age using otolith ages. The ers. Reader 1 had an agreement of 92% table is based on VMRC’s stratified sam- with ages of fish aged in 2008 with a CV of pling of landings by total length inch inter- 2 0.3% (test of symmetry: χ = 2, df = 3, P vals. = 0.5724). Reader 2 had an agreement of 100% . 6.4 REFERENCES 6.3.2 Year class Campana, S.E., M.C. Annand, and J.I. Of the 119 fish aged with otoliths, 20 age McMillan. 1995. Graphical and statis- classes (2 to 4, 6 to 10, 12 to 14, 17 to tical methods for determining the con-

52 CHAPTER 6. SHEEPSHEAD ARCHOSARGUS PROBATOCEPHALUS

sistency of age determinations. Trans. Am. Fish. Soc. 124:131-138. Ballenger, J. 2011. Population dynam- ics of sheepshead (Archosargus probato- cephalus: Walbaum 1792) in the Chesa- peake Bay region: A comparison to other areas and an assessment of cur- rent status. Old Dominion University. Ph.D. Thesis. Hoenig, J.M., M.J. Morgan, and C.A. Brown. 1995. Analyzing differences be- tween two age determination methods by tests of symmetry. Can. J. Fish. Aquat. Sci. 52:364-368. R Core Team (2012). R: A lan- guage and environment for statistical computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org.

53 CHAPTER 6. SHEEPSHEAD ARCHOSARGUS PROBATOCEPHALUS (Go 2015. during T be61 h ubro hesedasge oec oa egh(nh-taectgr o 1 s ape o tlt g eemnto nVirginia in determination age otolith for sampled fish 119 for category (inch)-at-age length total each to assigned sheepshead of number The 6.1: able akt text) to back 5-2.9000000000010111000105 5 13 0 13 0 1 15 1 0 8 0 0 0 3 0 0 0 0 1 0 0 0 21 0 0 0 0 1 21 0 1 0 10 1 0 0 4 0 0 0 1 1 0 0 0 0 0 0 0 1 0 0 1 0 1 0 0 2 0 0 0 0 0 0 0 4 0 0 0 0 0 1 0 0 4 0 0 0 0 1 0 0 0 0 1 0 0 4 0 0 1 0 0 0 3 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 2 0 0 0 2 0 0 0 0 0 0 0 1 0 2 0 0 0 0 0 0 0 0 3 1 0 0 0 0 2 0 0 3 0 0 0 0 25.99 0 0 1 0 - 1 25 0 0 0 0 24.99 0 0 0 0 0 - 24 1 0 3 23.99 0 0 0 0 - 0 23 0 0 2 22.99 0 0 - 0 0 0 22 0 21.99 0 0 0 - 0 20 0 21 20.99 1 0 0 0 - 21 20 8 19.99 0 0 0 - 19 4 18.99 0 1 - 18 17.99 0 0 - 17 16.99 0 - 16 15.99 - 15 14 In 49 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 14.99 - oas115 22212111119 1 1 1 2 1 2 2 12 3 8 1 2 4 6 9 3 1 58 1 1 Totals evl23467891 21 41 81 12 42 73 Totals 32 27 25 24 23 21 19 18 17 14 13 12 10 9 8 7 6 4 3 2 terval Age

54 CHAPTER 6. SHEEPSHEAD ARCHOSARGUS PROBATOCEPHALUS Age terval 2 3 4 6 7 8 9 10 12 13 14 17 18 19 21 23 24 25 27 32 - 14.99 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 back to text) In 15 - 15.9916 - 0 16.9917 - 0 17.99 018 - 0.1 0 18.9919 - 0 19.99 0.8 1 020 - 0 0.1 20.99 021 - 0 0 21.99 0.95 1 022 - 0 0 22.99 0.67 023 0 - 0 0 0 23.99 0.38 024 - 0 0 0 24.99 025 0 0 0 - 0 0 25.99 0 0 0.05 0 0.12 0 0 0 0 0 0.38 0.33 0 0 0 0 0.12 0 0 0.13 0 0 0 0 0 0 0.2 0 0 0 0 0 0 0.13 0 0 0 0.08 0 0.13 0 0 0 0 0.15 0 0 0 0 0.08 0 0 0 0 0 0 0.15 0.08 0 0 0 0 0.08 0 0 0 0 0 0 0.07 0 0 0.08 0 0 0.2 0 0 0 0 0 0.07 0 0 0 0 0 0 0.31 0 0 0 0 0.31 0 0 0 0 0 0 0 0 0 0 0 0.2 0 0.08 0 0 0 0.31 0.2 0 0 0 0 0.08 0 0 0 0 0 0.07 0 0.2 0.08 0 0 0 0 0.4 0 0 0 0 0 0 0 0 0 0 0.2 0 0 0 0 0 0 0 0 0.2 0 0 0 0 0.08 0 0 0 0.2 0 0 0 0 0.2 0 0 0 0 0 0.08 0 0 0 0 0 0 0 0 0 0.2 0 0 14 able 6.2: Age-Length key, as proportion-at-age in each 1-inch length interval, based on otolith ages for sheepshead sampled for age determination in T (Go Virginia during 2015.

55

Chapter 7

ATLANTIC SPADEFISH Chaetodipterus faber CHAPTER 7. ATLANTIC SPADEFISH CHAETODIPTERUS FABER

7.1 INTRODUCTION should be a number above which there is only a 1% CV reduction for the most ma- We aged a total of 135 spadefish, jor age in catch by aging an additional 100 Chaetodipterus faber, collected by the or more fish. Finally, Al is A multiplied VMRC’s Biological Sampling Program for by the proportion of length interval l from age and growth analysis in 2015. Spade- the length distribution of the 2009 to 2013 fish ages ranged from 1 to 8 years old with catch. Al is number of fish to be aged for an average age of 3.6, a standard deviation length interval l in 2015. of 1.6, and a standard error of 0.14. Eight age classes (1 to 8) were represented, com- prising fish of the 2007 to 2014 year-classes. 7.2.2 Handling of collections The sample was dominated by fish from the year-classes of 2012 and 2010 with 34.1% Otoliths were received by the Age & and 27.4%, respectively. Growth Laboratory in labeled coin en- velopes, and were sorted by date of capture. Their envelope labels were verified against 7.2 METHODS VMRC’s collection data, and each fish was assigned a unique Age and Growth Labo- ratory identification number. All otoliths 7.2.1 Sample size for ageing were stored dry in their original labeled coin envelopes. We estimated sample size for ageing spade- fish in 2015 using a two-stage random sam- pling method (Quinn and Deriso 1999) to 7.2.3 Preparation increase precision in estimates of age com- position from fish sampled efficiently and We used our thin-section and bake tech- effectively. The basic equation is: nique to process spadefish sagittal otoliths (hereafter, referred to as "otoliths") for age Va A = 2 2 (7.1) determination. Otolith preparation began θ CV + Ba/L a by randomly selecting either the right or where A is the sample size for ageing spade- left otolith. Each whole otolith was placed fish in 2015; θa stands for the proportion in a ceramic "Coors" spot plate well and of age a fish in a catch. Va and Ba repre- baked in a Thermolyne 1400 furnace at sent variance components within and be- 400 ◦C. Baking time was dependent on the tween length intervals for age a, respec- otolith’s size and gauged by color, with a tively; CV is the coefficient of variation; L light caramel color desired. Once a suit- was the total number of spadefish used by able color was achieved the baked otolith VMRC to estimate length distribution of was embedded in epoxy resin with its dis- the catches from 2009 to 2013. θa, Va, Ba, tal surface orientated downwards and al- and CV were calculated using pooled age- lowed to harden overnight. The otoliths length data of spadefish collected from 2009 were viewed by eye and, when necessary, to 2013 and using equations in Quinn and under a stereo microscope to identify the Deriso (1999). For simplicity, the equations location of the core, and the position of the are not listed here. The equation (7.1) in- core was marked using a permanent marker dicates that the more fish that are aged, across the epoxy resin surface. At least the smaller the CV (or higher precision) one transverse cross-section (hereafter, re- that will be obtained. Therefore, the cri- ferred to as "thin-section") was then re- terion to age A (number) of fish is that A moved from the marked core of each otolith

58 CHAPTER 7. ATLANTIC SPADEFISH CHAETODIPTERUS FABER using a Buehler IsoMetTM low-speed saw initial assigned age, then, is the age class of equipped with two, 3-inch diameter, Nor- the fish. Any growth beyond the last an- ton diamond grinding wheels (hereafter, re- nulus can be interpreted as either being to- ferred to as "blades"), separated by a stain- ward the next age class or within the same less steel spacer of 0.5 mm (diameter 2.5"). age class. If translucent growth is visible The otolith was positioned so the blades beyond the last annulus, a "+" is added to straddled each side of the otolith focus. It the notation. was crucial that this cut be perpendicular to the long axis of the otolith. Failure to do By convention all fish in the Northern so resulted in broadening and distored win- Hemisphere are assigned a birth date of ter growth zones. A proper cut resulted in January 1. In addition, each species has annuli that were clearly defined and delin- a specific period during which it deposits eated. Once cut, thin-sections were placed the annulus. If the fish is captured after on labeled glass slides and covered with a the end of the species-specific annulus de- thin layer of Flo-texx mounting medium position period and before January 1, it is that not only fixed the sections to the slide, assigned an age class notation of "x+x", but more importantly, provided enhanced where "x" is the number of annuli in the contrast and greater readability by increas- thin-section. If the fish is captured be- ing light transmission through the thin- tween January 1 and the end of the species- section. specific annulus deposition period, it is as- signed an age class notation of "x+(x+1)". Click here to obtain the protocol at the Thus, any growth beyond the last annulus, CQFE website on how to prepare otolith after its "birthday" but before the end of thin-section for ageing Atlantic spade- annulus deposition period, is interpreted as fish. being toward the next age class.

For example, spadefish otolith annulus for- 7.2.4 Readings mation occurs between December and July (Hayse 1989 and modified by CQFE). A The CQFE system assigns an age class to spadefish captured between January 1 and a fish based on a combination of number July 31, before the end of the species’ an- of annuli in a thin-section, the date of cap- nulus deposition period, with three visible ture, and the species-specific period when annuli and some translucent growth after the annulus is deposited. Each year, as the last annulus, would be assigned an age the fish grows, its otoliths grow and leave class of "x+(x+1)" or 3+(3+1), noted as behind markers of their age, called an an- 3+4. This is the same age-class assigned nulus. Technically, an otolith annulus is to a fish with four visible annuli captured the combination of both the opaque and after the end of July 31, the period of an- the translucent band. In practice, only the nulus deposition, which would be noted as opaque bands are counted as annuli. The 4+4. number of annuli replaces "x" in our nota- All thin-sections were aged by two different tion below, and is the initial "age" assign- readers using a Nikon SMZ1000 stereo mi- ment of the fish. croscope under transmitted light and dark- Second, the thin-section is examined for field polarization at between 8 and 20 times translucent growth. If no translucent magnification (Figure 7.1). Each reader growth is visible beyond the last annulus, aged all of the otolith samples. All sam- the otolith is called "even" and no modi- ples were aged in chronological order, based fication of the assigned age is made. The on collection date, without knowledge of

59 CHAPTER 7. ATLANTIC SPADEFISH CHAETODIPTERUS FABER

7.3 RESULTS

7.3.1 Sample size

Figure 7.1: Otolith thin-section of a 2 year-old spadefish We estimated a sample size of 279 spade- fish in 2015, ranging in length interval from 4 to 25 inches (Table 7.1). This sample previously estimated ages or the specimen size provided a range in (CV) for age com- lengths. When the readers’ ages agreed, position approximately from the smallest that age was assigned to the fish. When (CV) of 6% for age 2 to the largest (CV) of the two readers disagreed, both readers sat 20% for age 1. In 2015, we spadefishaged down together and re-aged the fish, again all 135 collected by VMRC. We fell short without any knowledge of previously esti- in our over-all collections for this optimal mated ages or lengths, and assigned a final length-class sampling estimate by 150 fish. age to the fish. When the readers were un- However, we were short of many fish from able to agree on a final age, the fish was the major length intervals (The interval re- excluded from further analysis. quires 10 or more fish), as a result, the precision for the estimates of major age Click here to obtain the protocol at groups would definitely be influenced sig- the CQFE website on how to age At- nificantly. Therefore, precaution should be lantic spadefish using their otolith thin- used when developing ALK using these age sections. data.

7.2.5 Comparison tests 7.3.2 Reading precision A symmetry test (Hoenig et al. 1995) and coefficient of variation (CV) analysis Both readers had high self-precision. were used to detect any systematic differ- Specifically, there was no significant differ- ence and precision on age readings, respec- ence between the first and second readings tively, for the following comparisons: 1) be- for Reader 1 with an agreement of 94% and tween the two readers in the current year, a CV of 0.9% (test of symmetry: χ2 = 1, df 2) within each reader in the current year, = 2, P = 0.6065), and there was no signif- and 3) time-series bias between the current icant difference between the first and sec- and previous years within each reader. The ond readings for Reader 2 with an agree- readings from the entire sample for the cur- ment of 86% and a CV of 2.2% (test of rent year were used to examine the differ- symmetry: χ2 = 3, df = 3, P = 0.3916). ence between two readers. A random sub- There was no evidence of systematic dis- sample of 50 fish from the current year was agreement between Reader 1 and Reader 2 selected for second readings to examine the with an agreement of 86.67% and a CV of difference within a reader. Fifty otoliths 2.1% (test of symmetry: χ2 = 8.4, df = 6, randomly selected from fish aged in 2003 P = 0.2102) (Figure 7.2). were used to examine the time-series bias within each reader. A figure of 1:1 equiv- There was no time-series bias for both read- alence was used to illustrate those differ- ers. Reader 1 had an agreement of 86% ences (Campana et al. 1995). All statistics with ages of fish aged in 2003 with a CV of analyses were performed in R 3.2.2 (R Core 1.9% (test of symmetry: χ2 = 5, df = 6, P Team 2012). = 0.5438). Reader 2 had an agreement of

60 CHAPTER 7. ATLANTIC SPADEFISH CHAETODIPTERUS FABER

Figure 7.2: Between-reader comparison of Figure 7.3: Year-class frequency distribution otolith age estimates for spadefish collected in for spadefish collected for ageing in 2015. Dis- Chesapeake Bay and Virginia waters of the At- tribution is broken down by sex. ’Unknown’ lantic Ocean in 2015. represents gonads that were not available for examination or were not examined for sex dur- ing sampling. 94% with a CV of 1.2% (test of symmetry: 2 χ = 3, df = 3, P = 0.3916). 7.4 REFERENCES

Campana, S.E., M.C. Annand, and J.I. 7.3.3 Year class McMillan. 1995. Graphical and statis- tical methods for determining the con- Of the 135 fish aged with otoliths, 8 age sistency of age determinations. Trans. classes (1 to 8) were represented (Table Am. Fish. Soc. 124:131-138. 7.2). The average age was 3.6 years, and Hayse, J. W. 1989. Feeding habits, age, the standard deviation and standard error growth, and reproduction of Atlantic were 1.6 and 0.14, respectively. Year-class spadefish Chaetodipterus faber (Piscies: data show that the fishery was comprised of Ephippidae) in South Carolina. Fishery 8 year-classes: fish from the 2007 to 2014 Bulletin 88: 67-83. year-classes, with fish primarily from the year classes of 2012 and 2010 with 34.1% Hoenig, J.M., M.J. Morgan, and C.A. and 27.4%, respectively. The ratio of males Brown. 1995. Analyzing differences be- to females was 1:1.29 in the sample col- tween two age determination methods lected (Figure 7.3). by tests of symmetry. Can. J. Fish. Aquat. Sci. 52:364-368. Quinn, T. J. II, and R. B. Deriso. 1999. Quantitative Fish Dynamics. Oxford 7.3.4 Age-length key Univeristy Press. New York. R Core Team (2012). R: A lan- We developed an age-length-key (Table guage and environment for statistical 7.3) that can be used in the conversion of computing. R Foundation for Sta- numbers-at-length in the estimated catch tistical Computing, Vienna, Austria. to numbers-at-age using otolith ages. The ISBN 3-900051-07-0, URL http://www. table is based on VMRC’s stratified sam- R-project.org. pling of landings by total length inch inter- vals.

61 CHAPTER 7. ATLANTIC SPADEFISH CHAETODIPTERUS FABER

Table 7.1: Number of Atlantic spadefish collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 4 - 4.99 5 0 0 5 5 - 5.99 7 5 5 2 6 - 6.99 37 18 18 19 7 - 7.99 43 7 7 36 8 - 8.99 30 10 10 20 9 - 9.99 22 9 9 13 10 - 10.99 15 7 7 8 11 - 11.99 11 9 9 2 12 - 12.99 15 7 7 8 13 - 13.99 16 8 8 8 14 - 14.99 12 6 6 6 15 - 15.99 12 10 10 2 16 - 16.99 10 14 14 0 17 - 17.99 13 12 12 1 18 - 18.99 9 11 11 0 19 - 19.99 7 2 2 5 20 - 20.99 5 0 0 5 21 - 21.99 5 0 0 5 25 - 25.99 5 0 0 5 Totals 279 135 135 150 (Go back to text)

62 CHAPTER 7. ATLANTIC SPADEFISH CHAETODIPTERUS FABER

Table 7.2: The number of Atlantic spadefish assigned to each total length-at-age category for 135 fish sampled for otolith age determination in Virginia during 2015.

Age Interval 1 2 3 4 5 6 7 8 Totals 5 - 5.99 5 0 0 0 0 0 0 0 5 6 - 6.99 12 0 6 0 0 0 0 0 18 7 - 7.99 3 1 3 0 0 0 0 0 7 8 - 8.99 0 2 8 0 0 0 0 0 10 9 - 9.99 0 2 7 0 0 0 0 0 9 10 - 10.99 0 1 6 0 0 0 0 0 7 11 - 11.99 0 0 8 0 1 0 0 0 9 12 - 12.99 0 0 4 2 1 0 0 0 7 13 - 13.99 0 0 4 2 2 0 0 0 8 14 - 14.99 0 0 0 3 3 0 0 0 6 15 - 15.99 0 0 0 3 7 0 0 0 10 16 - 16.99 0 0 0 2 10 1 1 0 14 17 - 17.99 0 0 0 4 7 0 0 1 12 18 - 18.99 0 0 0 1 6 2 1 1 11 19 - 19.99 0 0 0 0 0 0 2 0 2 Totals 20 6 46 17 37 3 4 2 135 (Go back to text)

63 CHAPTER 7. ATLANTIC SPADEFISH CHAETODIPTERUS FABER

Table 7.3: Age-Length key, as proportion-at-age in each 1-inch length interval, based on otolith ages for Atlantic spadefish sampled for age determination in Virginia during 2015.

Age Interval 1 2 3 4 5 6 7 8 5 - 5.99 1 0 0 0 0 0 0 0 6 - 6.99 0.67 0 0.33 0 0 0 0 0 7 - 7.99 0.43 0.14 0.43 0 0 0 0 0 8 - 8.99 0 0.2 0.8 0 0 0 0 0 9 - 9.99 0 0.22 0.78 0 0 0 0 0 10 - 10.99 0 0.14 0.86 0 0 0 0 0 11 - 11.99 0 0 0.89 0 0.11 0 0 0 12 - 12.99 0 0 0.57 0.29 0.14 0 0 0 13 - 13.99 0 0 0.5 0.25 0.25 0 0 0 14 - 14.99 0 0 0 0.5 0.5 0 0 0 15 - 15.99 0 0 0 0.3 0.7 0 0 0 16 - 16.99 0 0 0 0.14 0.71 0.07 0.07 0 17 - 17.99 0 0 0 0.33 0.58 0 0 0.08 18 - 18.99 0 0 0 0.09 0.55 0.18 0.09 0.09 19 - 19.99 0 0 0 0 0 0 1 0 (Go back to text)

64 Chapter 8

SPANISH MACKEREL Scomberomorous maculatus CHAPTER 8. SPANISH MACKEREL SCOMBEROMOROUS MACULATUS

8.1 INTRODUCTION Therefore, the criterion to age A (number) of fish is that A should be a number above We aged a total of 231 Spanish mack- which there is only a 1% CV reduction for erel, Scomberomorous maculatus, collected the most major age in catch by aging an by the VMRC’s Biological Sampling Pro- additional 100 or more fish. Finally, Al is gram for age and growth analysis in 2015. A multiplied by the proportion of length in- Spanish mackerel ages ranged from 0 to 8 terval l from the length distribution of the years old with an average age of 1.4, a stan- 2009 to 2013 catch. Al is number of fish to dard deviation of 1, and a standard error of be aged for length interval l in 2015. 0.07. Seven age classes (0 to 5, and 8) were represented, comprising fish of the 2007, 8.2.2 Handling of collections and 2010 to 2015 year-classes. The sample was dominated by fish from the year-class of 2014 with 60.2%. Otoliths were received by the Age & Growth Laboratory in labeled coin en- velopes, and were sorted by date of capture. 8.2 METHODS Their envelope labels were verified against VMRC’s collection data, and each fish was assigned a unique Age and Growth Labo- 8.2.1 Sample size for ageing ratory identification number. All otoliths were stored dry in their original labeled We estimated sample size for ageing Span- coin envelopes. ish mackerel in 2015 using a two-stage ran- dom sampling method (Quinn and Deriso 1999) to increase precision in estimates 8.2.3 Preparation of age composition from fish sampled effi- ciently and effectively. The basic equation Sagittal otoliths, hereafter, referred to as is: "otolith", were processed for age determi- nation. The left or right otolith was ran- Va A = 2 2 (8.1) domly selected and embedded, distal side θ CV + Ba/L a down, in epoxy resin and allowed to harden where A is the sample size for ageing Span- overnight. The otoliths were viewed by eye, ish mackerel in 2015; θa stands for the pro- and when necessary, under a stereo micro- portion of age a fish in a catch. Va and Ba scope to identify the location of the core, represent variance components within and and the position of the core marked us- between length intervals for age a, respec- ing a permanent marker across the epoxy tively; CV is the coefficient of variation; L resin surface. At least one transverse was the total number of Spanish mackerel cross-section (hereafter "thin-section") was used by VMRC to estimate length distri- then removed from the marked core of bution of the catches from 2009 to 2013. each otolith using a Buehler IsoMetTM low- θa, Va, Ba, and CV were calculated using speed saw equipped with two, three inch di- pooled age-length data of Spanish mack- ameter, Norton Diamond Grinding Wheels, erel collected from 2009 to 2013 and us- separated by a stainless steel spacer of ing equations in Quinn and Deriso (1999). 0.5 mm (diameter 2.5"). The position of For simplicity, the equations are not listed the marked core fell within the 0.5 mm here. The equation (8.1) indicates that the space between the blades, such that the more fish that are aged, the smaller the CV core was included in the removed thin sec- (or higher precision) that will be obtained. tion. Otolith thin-sections were placed

66 CHAPTER 8. SPANISH MACKEREL SCOMBEROMOROUS MACULATUS on labeled glass slides and covered with a the end of the species-specific annulus de- thin layer of Flo-texx mounting medium position period and before January 1, it is that not only fixed the sections to the assigned an age class notation of "x+x", slide, but more importantly, provided en- where "x" is the number of annuli in the hanced contrast and greater readability by thin-section. If the fish is captured be- increasing light transmission through the tween January 1 and the end of the species- section. specific annulus deposition period, it is as- signed an age class notation of "x+(x+1)". Click here to obtain the protocol at the Thus, any growth beyond the last annulus, CQFE website on how to prepare otolith after its "birthday" but before the end of thin-section for ageing Spanish mack- annulus deposition period, is interpreted as erel. being toward the next age class.

For example, Spanish mackerel annulus 8.2.4 Readings formation occurs between May and June (Schmidt et al. 1993). A Spanish mack- The CQFE system assigns an age class to erel captured between January 1 and June a fish based on a combination of number 30, before the end of the species’ annulus of annuli in a thin-section, the date of cap- deposition period, with three visible annuli ture, and the species-specific period when and some translucent growth after the last the annulus is deposited. Each year, as annulus, would be assigned an age class the fish grows, its otoliths grow and leave of "x+(x+1)" or 3+(3+1), noted as 3+4. behind markers of their age, called an an- This is the same age-class assigned to a fish nulus. Technically, an otolith annulus is with four visible annuli captured after the the combination of both the opaque and end of May 31, the period of annulus depo- the translucent band. In practice, only the sition, which would be noted as 4+4. opaque bands are counted as annuli. The All thin-sections were aged by two different number of annuli replaces "x" in our nota- readers using a Nikon SMZ1000 stereo mi- tion below, and is the initial "age" assign- croscope under transmitted light and dark- ment of the fish. field polarization at between 8 and 20 times Second, the thin-section is examined for magnification (Figure 8.1). Each reader translucent growth. If no translucent aged all of the otolith samples. All sam- growth is visible beyond the last annulus, the otolith is called "even" and no modi- fication of the assigned age is made. The initial assigned age, then, is the age class of the fish. Any growth beyond the last an- nulus can be interpreted as either being to- ward the next age class or within the same age class. If translucent growth is visible Figure 8.1: Otolith thin-section of a 3 year-old beyond the last annulus, a "+" is added to Spanish mackerel with the last annulus on the edge of the thin-section the notation. By convention all fish in the Northern ples were aged in chronological order, based Hemisphere are assigned a birth date of on collection date, without knowledge of January 1. In addition, each species has previously estimated ages or the specimen a specific period during which it deposits lengths. When the readers’ ages agreed, the annulus. If the fish is captured after that age was assigned to the fish. When

67 CHAPTER 8. SPANISH MACKEREL SCOMBEROMOROUS MACULATUS the two readers disagreed, both readers sat composition approximately from the small- down together and re-aged the fish, again est (CV) of 4% for age 1 to the largest (CV) without any knowledge of previously esti- of 18% for age 3. In 2015, we randomly mated ages or lengths, and assigned a final selected and aged 231 fish from 327 Span- age to the fish. When the readers were un- ish mackerel collected by VMRC. We fell able to agree on a final age, the fish was short in our over-all collections for this op- excluded from further analysis. timal length-class sampling estimate by 44 fish. However, we were short of no fish from Click here to obtain the protocol at the the major length intervals (The interval re- CQFE website on how to age Span- quires 10 or more fish), as a result, the pre- ish mackerel using their otolith thin- cision for the estimates of major age groups sections. would not be influenced significantly.

8.2.5 Comparison tests 8.3.2 Reading precision

A symmetry test (Hoenig et al. 1995) Reader 1 had moderate self-precision and and coefficient of variation (CV) analysis Reader 2 had high self-precision. Specif- were used to detect any systematic differ- ically, there was a difference between the ence and precision on age readings, respec- first and second readings for Reader 1 with tively, for the following comparisons: 1) be- an agreement of 80% and a CV of 8.1% tween the two readers in the current year, (test of symmetry: χ2 = 10, df = 3, P = 2) within each reader in the current year, 0.0186), and there was no significant differ- and 3) time-series bias between the current ence between the first and second readings and previous years within each reader. The for Reader 2 with an agreement of 100% . readings from the entire sample for the cur- There was no evidence of systematic dis- rent year were used to examine the differ- agreement between Reader 1 and Reader 2 ence between two readers. A random sub- with an agreement of 95.24% and a CV of sample of 50 fish from the current year was 1.7% (test of symmetry: χ2 = 2.33, df = 4, selected for second readings to examine the P = 0.6747) (Figure 8.2). difference within a reader. Fifty otoliths randomly selected from fish aged in 2003 were used to examine the time-series bias within each reader. A figure of 1:1 equiv- alence was used to illustrate those differ- ences (Campana et al. 1995). All statistics analyses were performed in R 3.2.2 (R Core Team 2012).

8.3 RESULTS

8.3.1 Sample size Figure 8.2: Between-reader comparison of otolith age estimates for Spanish mackerel col- We estimated a sample size of 266 Spanish lected in Chesapeake Bay and Virginia waters of the Atlantic Ocean in 2015. mackerel in 2015, ranging in length interval from 10 to 30 inches (Table 8.1). This sam- ple size provided a range in (CV) for age There was no time-series bias for both read-

68 CHAPTER 8. SPANISH MACKEREL SCOMBEROMOROUS MACULATUS ers. Reader 1 had an agreement of 96% table is based on VMRC’s stratified sam- with fish aged in 2003 with a CV of 1.3% pling of landings by total length inch inter- (test of symmetry: χ2 = 2, df = 2, P = vals. 0.3679). Reader 2 had an agreement of 90% with a CV of 3.4% (test of symmetry: χ2 = 5, df = 3, P = 0.1718). 8.4 REFERENCES

8.3.3 Year class Campana, S.E., M.C. Annand, and J.I. McMillan. 1995. Graphical and statis- Of the 231 fish aged with otoliths, 7 age tical methods for etermining the consis- classes (0 to 5, and 8) were represented (Ta- tency of age terminations. Trans. Am. ble 8.2). The average age was 1.4 years, Fish. Soc. 124:131-138. and the standard deviation and standard Hoenig, J.M., M.J. Morgan, and C.A. error were 1 and 0.07, respectively. Year- Brown. 1995. Analyzing differences be- class data show that the fishery was com- tween two age determination methods prised of 7 year-classes: fish from the 2007, by tests of symmetry. Can. J. Fish. and 2010 to 2015 year-classes, with fish pri- Aquat. Sci. 52:364-368. marily from the year class of 2014 with 60.2%. The ratio of males to females was Quinn, T. J. II, and R. B. Deriso. 1999. 1:1.86 in the sample collected (Figure 8.3). Quantitative Fish Dynamics. Oxford Univeristy Press. New York. R Core Team (2012). R: A lan- guage and environment for statistical computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org. Schmidt, D., Collins, M., Wyanski, D. 1993. Age, growth, maturity, and spawning of Spanish mackerel from the Atlantic coast of the southeast- ern United States. Fishery Bulletin Figure 8.3: Year-class frequency distribution 91s. for Spanish mackerel collected for ageing in 2015. Distribution is broken down by sex. ’Un- known’ represents gonads that were not avail- able for examination or were not examined for sex during sampling.

8.3.4 Age-length key

We developed an age-length-key (Table 8.3) that can be used in the conversion of numbers-at-length in the estimated catch to numbers-at-age using otolith ages. The

69 CHAPTER 8. SPANISH MACKEREL SCOMBEROMOROUS MACULATUS

Table 8.1: Number of Spanish mackerel collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 10 - 10.99 5 0 0 5 11 - 11.99 5 0 0 5 12 - 12.99 5 0 0 5 13 - 13.99 5 1 1 4 14 - 14.99 19 30 23 0 15 - 15.99 38 61 38 0 16 - 16.99 41 64 41 0 17 - 17.99 36 50 36 0 18 - 18.99 21 35 22 0 19 - 19.99 17 27 18 0 20 - 20.99 13 19 14 0 21 - 21.99 13 15 14 0 22 - 22.99 8 9 8 0 23 - 23.99 5 6 6 0 24 - 24.99 5 5 5 0 25 - 25.99 5 1 1 4 26 - 26.99 5 2 2 3 27 - 27.99 5 1 1 4 28 - 28.99 5 0 0 5 29 - 29.99 5 1 1 4 30 - 30.99 5 0 0 5 Totals 266 327 231 44 (Go back to text)

70 CHAPTER 8. SPANISH MACKEREL SCOMBEROMOROUS MACULATUS

Table 8.2: The number of Spanish mackerel assigned to each total length-at-age category for 231 fish sampled for otolith age determination in Virginia during 2015.

Age Interval 0 1 2 3 4 5 8 Totals 13 - 13.99 0 1 0 0 0 0 0 1 14 - 14.99 6 17 0 0 0 0 0 23 15 - 15.99 6 31 1 0 0 0 0 38 16 - 16.99 7 34 0 0 0 0 0 41 17 - 17.99 0 32 4 0 0 0 0 36 18 - 18.99 0 15 7 0 0 0 0 22 19 - 19.99 0 5 11 2 0 0 0 18 20 - 20.99 0 3 10 1 0 0 0 14 21 - 21.99 0 1 9 1 2 1 0 14 22 - 22.99 0 0 4 4 0 0 0 8 23 - 23.99 0 0 3 1 1 1 0 6 24 - 24.99 0 0 2 3 0 0 0 5 25 - 25.99 0 0 1 0 0 0 0 1 26 - 26.99 0 0 0 1 1 0 0 2 27 - 27.99 0 0 0 0 0 1 0 1 29 - 29.99 0 0 0 0 0 0 1 1 Totals 19 139 52 13 4 3 1 231 (Go back to text)

71 CHAPTER 8. SPANISH MACKEREL SCOMBEROMOROUS MACULATUS

Table 8.3: Age-Length key, as proportion-at-age in each 1-inch length interval, based on otolith ages for Spanish mackerel sampled for age determination in Virginia during 2015.

Age Interval 0 1 2 3 4 5 8 13 - 13.99 0 1 0 0 0 0 0 14 - 14.99 0.26 0.74 0 0 0 0 0 15 - 15.99 0.16 0.82 0.03 0 0 0 0 16 - 16.99 0.17 0.83 0 0 0 0 0 17 - 17.99 0 0.89 0.11 0 0 0 0 18 - 18.99 0 0.68 0.32 0 0 0 0 19 - 19.99 0 0.28 0.61 0.11 0 0 0 20 - 20.99 0 0.21 0.71 0.07 0 0 0 21 - 21.99 0 0.07 0.64 0.07 0.14 0.07 0 22 - 22.99 0 0 0.5 0.5 0 0 0 23 - 23.99 0 0 0.5 0.17 0.17 0.17 0 24 - 24.99 0 0 0.4 0.6 0 0 0 25 - 25.99 0 0 1 0 0 0 0 26 - 26.99 0 0 0 0.5 0.5 0 0 27 - 27.99 0 0 0 0 0 1 0 29 - 29.99 0 0 0 0 0 0 1 (Go back to text)

72 Chapter 9

SPOT Leiostomus xanthurus CHAPTER 9. SPOT LEIOSTOMUS XANTHURUS

9.1 INTRODUCTION the most major age in catch by ageing an additional 100 or more fish. Finally, Al is A We aged a total of 201 spot, Leiostomus multiplied by the proportion of length in- xanthurus, collected by the VMRC’s Bi- terval l from the length distribution of the ological Sampling Program for age and 2009 to 2013 catch. Al is number of fish to growth analysis in 2015. spot ages ranged be aged for length interval l in 2015. from 0 to 4 years old with an average age of 1.3, a standard deviation of 0.7, and a standard error of 0.05. Five age classes (0 9.2.2 Handling of collections to 4) were represented, comprising fish of the 2011 to 2015 year-classes. The sample Otoliths were received by the Age & and was dominated by fish from the year-class Growth Laboratory in labeled coin en- of 2014 with 71.1%. velopes, were sorted by date of capture. Their envelope labels were verified against VMRC’s collection data, and each fish was 9.2 METHODS assigned a unique Age and Growth Labo- ratory identification number. All otoliths were stored dry in their original labeled 9.2.1 Sample size for ageing coin envelopes.

We estimated sample size for ageing spot in 2015 using a two-stage random sampling 9.2.3 Preparation method (Quinn and Deriso 1999) to in- crease precision in estimates of age com- Sagittal otoliths, hereafter, referred to as position from fish sampled efficiently and "otoliths", were processed for age determi- effectively. The basic equation is: nation following the methods described in Barbieri et al. (1994) with a few modifi- Va A = 2 2 (9.1) cations. The left or right otolith was ran- θ CV + Ba/L a domly selected and embedded (distal side where A is the sample size for ageing spot down) in epoxy resin and allowed to harden in 2015; θa stands for the proportion of age overnight. The otoliths were viewed by a fish in a catch. Va and Ba represent eye and, when necessary, under a stereo variance components within and between microscope to identify the location of the length intervals for age a, respectively; CV core, and the position of the core was is the coefficient of variation; L was the marked using a permanent marker across total number of spot used by VMRC to the epoxy resin surface. At least one trans- estimate length distribution of the catches verse cross-section (hereafter, referred to from 2009 to 2013. θa, Va, Ba, and CV were as "thin-section") was then removed from calculated using pooled age-length data of the marked core of each otolith using a spot collected from 2009 to 2013 and us- Buehler IsoMetTM low-speed saw equipped ing equations in Quinn and Deriso (1999). with two, 3-inch diameter, Norton diamond For simplicity, the equations are not listed grinding wheels (hereafter, referred to as here. The equation (1.1) indicates that the "blades"), separated by a stainless steel more fish that are aged, the smaller the CV spacer of 0.5 mm (diameter 2.5"). Thin- (or higher precision) that will be obtained. sections were placed on labeled glass slides Therefore, the criterion to age A (number) and covered with a thin layer of Flo-texx of fish is that A should be a number above mounting medium that not only fixed the which there is only a 1% CV reduction for sections to the slide, but more importantly,

74 CHAPTER 9. SPOT LEIOSTOMUS XANTHURUS provided enhanced contrast and greater tween January 1 and the end of the species- readability by increasing light transmission specific annulus deposition period, it is as- through the thin-sections. signed an age class notation of "x+(x+1)". Thus, any growth beyond the last annulus, Click here to obtain the protocol at the after its "birthday" but before the end of CQFE website on how to prepare otolith annulus deposition period, is interpreted as thin-section for ageing spot. being toward the next age class.

For example, spot otolith annulus forma- 9.2.4 Readings tion occurs between May and July (Piner and Jones 2004). A spot captured between The CQFE system assigns an age class to January 1 and May 31, before the end a fish based on a combination of number of the species’ annulus deposition period, of annuli in a thin-section, the date of cap- with three visible annuli and some translu- ture, and the species-specific period when cent growth after the last annulus, would the annulus is deposited. Each year, as be assigned an age class of "x+(x+1)" or the fish grows, its otoliths grow and leave 3+(3+1), noted as 3+4. This is the same behind markers of their age, called an an- age-class assigned to a fish with four vis- nulus. Technically, an otolith annulus is ible annuli captured after the end of May the combination of both the opaque and 31, the period of annulus deposition, which the translucent band. In practice, only the would be noted as 4+4. opaque bands are counted as annuli. The number of annuli replaces "x" in our nota- All thin-sections were aged by two different tion below, and is the initial "age" assign- readers using a Nikon SMZ1000 stereo mi- ment of the fish. croscope under transmitted light and dark- field polarization at between 8 and 20 times Second, the thin-section is examined for magnification (Figure 9.1). Each reader translucent growth. If no translucent aged all of the otolith samples. Due to dis- growth is visible beyond the last annulus, the otolith is called "even" and no modi- fication of the assigned age is made. The initial assigned age, then, is the age class of the fish. Any growth beyond the last an- nulus can be interpreted as either being to- ward the next age class or within the same age class. If translucent growth is visible beyond the last annulus, a "+" is added to Figure 9.1: Otolith thin-section of a 2 year-old the notation. spot By convention all fish in the Northern Hemisphere are assigned a birth date of crepancy on identification of the first an- January 1. In addition, each species has nulus of spot among Atlantic states, At- a specific period during which it deposits lantic States Marine Fisheries Commission the annulus. If the fish is captured after (ASMFC) has decided not to count the the end of the species-specific annulus de- smallest annulus at the center of the thin- position period and before January 1, it is section as the first annulus. Following assigned an age class notation of "x+x", ASMFC’s instruction, we didn’t count the where "x" is the number of annuli in the smallest annulus at the center as the first thin-section. If the fish is captured be- annulus in 2015.

75 CHAPTER 9. SPOT LEIOSTOMUS XANTHURUS

All samples were aged in chronological 9.3 RESULTS order, based on collection date, without knowledge of previously estimated ages or 9.3.1 Sample size the specimen lengths. When the readers’ ages agreed, that age was assigned to the fish. When the two readers disagreed, both We estimated a sample size of 203 spot in readers sat down together and re-aged the 2015, ranging in length interval from 4 to fish, again without any knowledge of pre- 12 inches (Table 9.1). This sample size pro- viously estimated ages or lengths, and as- vided a range in (CV) for age composition signed a final age to the fish. When the approximately from the smallest (CV) of readers were unable to agree on a final age, 5% for age 1 to the largest (CV) of 11% for the fish was excluded from further analy- age 2. In 2015, we randomly selected and sis. aged 201 fish from 263 spot collected by VMRC. We fell short in our over-all collec- tions for this optimal length-class sampling Click here to obtain the protocol at the estimate by 11 fish. However, we were short CQFE website on how to age spot using of no fish from the major length intervals their otolith thin-sections. (The interval requires 10 or more fish), as a result, the precision for the estimates of major age groups would not be influenced significantly.

9.2.5 Comparison tests 9.3.2 Reading precision

Both readers had high self-precision. A symmetry test (Hoenig et al. 1995) Specifically, there was no significant differ- and coefficient of variation (CV) analysis ence between the first and second readings were used to detect any systematic differ- for Reader 1 with an agreement of 94% and ence and precision on age readings, respec- a CV of 4.3% (test of symmetry: χ2 = 3, df tively, for the following comparisons: 1) be- = 3, P = 0.3916), and there was no signif- tween the two readers in the current year, icant difference between the first and sec- 2) within each reader in the current year, ond readings for Reader 2 with an agree- and 3) time-series bias between the current ment of 98% and a CV of 0.9% (test of and previous years within each reader. The symmetry: χ2 = 1, df = 1, P = 0.3173). readings from the entire sample for the cur- There was no evidence of systematic dis- rent year were used to examine the differ- agreement between Reader 1 and Reader 2 ence between two readers. A random sub- with an agreement of 94.53% and a CV of sample of 50 fish from the current year was 2.1% (test of symmetry: χ2 = 7.57, df = 3, selected for second readings to examine the P = 0.0558) (Figure 9.2). difference within a reader. Fifty otoliths randomly selected from fish aged in 2003 There was no time-series bias for both read- were used to examine the time-series bias ers. Reader 1 had an agreement of 98% within each reader. A figure of 1:1 equiv- with ages of fish aged in 2003 with a CV of alence was used to illustrate those differ- 0.9% (test of symmetry: χ2 = 1, df = 1, P ences (Campana et al. 1995). All statistics = 0.3173). Reader 2 had an agreement of analyses were performed in R 3.2.2 (R Core 98% with a CV of 0.9% (test of symmetry: Team 2012). χ2 = 1, df = 1, P = 0.3173).

76 CHAPTER 9. SPOT LEIOSTOMUS XANTHURUS

9.3.4 Age-length key

We developed an age-length-key (Table 9.3) that can be used in the conversion of numbers-at-length in the estimated catch to numbers-at-age using otolith ages. The table is based on VMRC’s stratified sam- pling of landings by total length inch inter- vals.

Figure 9.2: Between-reader comparison of 9.4 REFERENCES otolith age estimates for spot collected in Chesapeake Bay and Virginia waters of the At- Campana, S.E., M.C. Annand, and J.I. lantic Ocean in 2015. McMillan. 1995. Graphical and statis- tical methods for determining the con- 9.3.3 Year class sistency of age determinations. Trans. Am. Fish. Soc. 124:131-138. Of the 201 fish aged with otoliths, 5 age Hoenig, J.M., M.J. Morgan, and C.A. classes (0 to 4) were represented (Table Brown. 1995. Analyzing differences be- 9.2). The average age was 1.3 years, and tween two age determination methods the standard deviation and standard error by tests of symmetry. Can. J. Fish. were 0.7 and 0.05, respectively. Year-class Aquat. Sci. 52:364-368. data show that the fishery was comprised of Piner, K. R., and C. M. Jones. 2004. Age, 5 year-classes: fish from the 2011 to 2015 growth and the potential for growth year-classes, with fish primarily from the overfishing of spot (Leiostomus xanthu- year class of 2014 with 71.1%. The ratio of rus) from the Chesapeake Bay, eastern males to females was 1:4.74 in the sample USA. Marine and Freshwater Research collected (Figure 9.3). 55: 553-560. Quinn, T. J. II, and R. B. Deriso. 1999. Quantitative Fish Dynamics. Oxford University Press. New York. R Core Team (2012). R: A lan- guage and environment for statistical computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org.

Figure 9.3: Year-class frequency distribution for spot collected for ageing in 2015. Distribu- tion is broken down by sex. ’Unknown’ is for gonads that were not available for examination or were not examined for sex during sampling.

77 CHAPTER 9. SPOT LEIOSTOMUS XANTHURUS

Table 9.1: Number of spot collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 4 - 4.99 5 2 2 3 5 - 5.99 5 12 6 0 6 - 6.99 5 15 6 0 7 - 7.99 23 40 24 0 8 - 8.99 44 50 44 0 9 - 9.99 61 78 62 0 10 - 10.99 46 60 51 0 11 - 11.99 9 6 6 3 12 - 12.99 5 0 0 5 Totals 203 263 201 11 (Go back to text)

78 CHAPTER 9. SPOT LEIOSTOMUS XANTHURUS

Table 9.2: The number of spot assigned to each total length-at-age category for 201 fish sampled for otolith age determination in Virginia during 2015.

Age Interval 0 1 2 3 4 Totals 4 - 4.99 2 0 0 0 0 2 5 - 5.99 2 3 1 0 0 6 6 - 6.99 0 6 0 0 0 6 7 - 7.99 0 22 2 0 0 24 8 - 8.99 0 31 12 1 0 44 9 - 9.99 0 36 14 11 1 62 10 - 10.99 0 40 5 6 0 51 11 - 11.99 0 5 1 0 0 6 Totals 4 143 35 18 1 201 (Go back to text)

79 CHAPTER 9. SPOT LEIOSTOMUS XANTHURUS

Table 9.3: Age-Length key, as proportion-at-age in each 1-inch length interval, based on otolith ages for spot sampled for age determination in Virginia during 2015.

Age Interval 0 1 2 3 4 4 - 4.99 1 0 0 0 0 5 - 5.99 0.33 0.5 0.17 0 0 6 - 6.99 0 1 0 0 0 7 - 7.99 0 0.92 0.08 0 0 8 - 8.99 0 0.7 0.27 0.02 0 9 - 9.99 0 0.58 0.23 0.18 0.02 10 - 10.99 0 0.78 0.1 0.12 0 11 - 11.99 0 0.83 0.17 0 0 (Go back to text)

80 Chapter 10

SPOTTED SEATROUT Cynoscion nebulosus CHAPTER 10. SPOTTED SEATROUT CYNOSCION NEBULOSUS

10.1 INTRODUCTION smaller the CV (or higher precision) that will be obtained. Therefore, the criterion We aged a total of 308 spotted seatrout, to age A (number) of fish is that A should Cynoscion nebulosus, collected by the be a number above which there is only a VMRC’s Biological Sampling Program for 1% CV reduction for the most major age in age and growth analysis in 2015. Spotted catch by aging an additional 100 or more seatrout ages ranged from 0 to 10 years old fish. Finally, Al is A multiplied by the pro- with an average age of 2.5, a standard de- portion of length interval l from the length viation of 2.1, and a standard error of 0.12. distribution of the 2009 to 2013 catch. Al Ten age classes (0 to 8, and 10) were rep- is number of fish to be aged for length in- resented, comprising fish of the 2005, and terval l in 2015. 2007 to 2015 year-classes. The sample was dominated by fish from the year-classes of 10.2.2 Handling of collections 2011, 2014, and 2015 with 27.6%, 26.9%, and 16.9%, respectively. Otoliths were received by the Age & Growth Laboratory in labeled coin en- 10.2 METHODS velopes. In the lab they were sorted by date of capture, their envelope labels were ver- ified against VMRC’s collection data, and 10.2.1 Sample size for ageing each fish was assigned a unique Age and Growth Laboratory identification number. We estimated sample size for ageing spot- All otoliths were stored dry in their original ted seatrout in 2015 using a two-stage ran- labeled coin envelopes. dom sampling method (Quinn and Deriso 1999) to increase precision in estimates of age composition from fish sampled effi- 10.2.3 Preparation ciently and effectively. The basic equation is: Sagittal otoliths, hereafter, referred to as "otoliths", were processed for age deter- Va A = 2 2 (10.1) mination. The left or right otolith was θ CV + Ba/L a randomly selected and attached, distal where A is the sample size for ageing spot- side down, to a glass slide with clear TM ted seatrout in 2015; θa stands for the pro- Crystalbond 509 adhesive. The otoliths portion of age a fish in a catch. Va and were viewed by eye and, when necessary, Ba represent variance components within under a stereo microscope to identify the and between length intervals for age a, re- location of the core, and the position of spectively; CV is the coefficient of varia- the core was marked using a pencil across tion; L was the total number of spotted the otolith surface. At least one trans- seatrout used by VMRC to estimate length verse cross-section (hereafter, referred to distribution of the catches from 2009 to as "thin-section") was then removed from 2013. θa, Va, Ba, and CV were calcu- the marked core of each otolith using a lated using pooled age-length data of spot- Buehler IsoMetTM low-speed saw equipped ted seatrout collected from 2009 to 2013 with two, 3-inch diameter, Norton diamond and using equations in Quinn and Deriso grinding wheels (hereafter, referred to as (1999). For simplicity, the equations are "blades"), separated by a stainless steel not listed here. The equation (10.1) indi- spacer of 0.5 mm (diameter 2.5"). Thin- cates that the more fish that are aged, the sections were placed on labeled glass slides

82 CHAPTER 10. SPOTTED SEATROUT CYNOSCION NEBULOSUS and covered with a thin layer of Flo-texx position period and before January 1, it is mounting medium that not only fixed the assigned an age class notation of "x+x", sections to the slide, but more importantly, where "x" is the number of annuli in the provided enhanced contrast and greater thin-section. If the fish is captured be- readability by increasing light transmission tween January 1 and the end of the species- through the thin-sections. specific annulus deposition period, it is as- signed an age class notation of "x+(x+1)". Click here to obtain the protocol at Thus, any growth beyond the last annulus, the CQFE website on how to prepare after its "birthday" but before the end of otolith thin-section for ageing spotted annulus deposition period, is interpreted as seatrout. being toward the next age class.

For example, spotted seatrout otolith an- 10.2.4 Readings nulus formation occurs between March and May (Ihde and Chittenden 2003). A spot- The CQFE system assigns an age class to ted seatrout captured between January 1 a fish based on a combination of number and May 31, before the end of the species’ of annuli in a thin-section, the date of cap- annulus deposition period, with three visi- ture, and the species-specific period when ble annuli and some translucent growth af- the annulus is deposited. Each year, as ter the last annulus, would be assigned an the fish grows, its otoliths grow and leave age class of "x+(x+1)" or 3+(3+1), noted behind markers of their age, called an an- as 3+4. This is the same age-class assigned nulus. Technically, an otolith annulus is to a fish with four visible annuli captured the combination of both the opaque and after the end of May 31, the period of an- the translucent band. In practice, only the nulus deposition, which would be noted as opaque bands are counted as annuli. The 4+4. number of annuli replaces "x" in our nota- All thin-sections were aged by two different tion below, and is the initial "age" assign- readers using a Nikon SMZ1000 stereo mi- ment of the fish. croscope under transmitted light and dark- Second, the thin-section is examined for field polarization at between 8 and 20 times translucent growth. If no translucent magnification (Figure 10.1). Each reader growth is visible beyond the last annulus, aged all of the otolith samples. All sam- the otolith is called "even" and no modi- fication of the assigned age is made. The initial assigned age, then, is the age class of the fish. Any growth beyond the last an- nulus can be interpreted as either being to- ward the next age class or within the same age class. If translucent growth is visible beyond the last annulus, a "+" is added to the notation. By convention all fish in the Northern Hemisphere are assigned a birth date of Figure 10.1: Otolith thin-section of a 4 year- January 1. In addition, each species has old spotted seatrout with the last annulus on a specific period during which it deposits the edge of the thin-section the annulus. If the fish is captured after the end of the species-specific annulus de- ples were aged in chronological order, based

83 CHAPTER 10. SPOTTED SEATROUT CYNOSCION NEBULOSUS on collection date, without knowledge of 10.3 RESULTS previously estimated ages or the specimen lengths. When the readers’ ages agreed, that age was assigned to the fish. When 10.3.1 Sample size the two readers disagreed, both readers sat down together and re-aged the fish, again without any knowledge of previously esti- We estimated a sample size of 342 spotted mated ages or lengths, and assigned a final seatrout in 2015, ranging in length interval age to the fish. When the readers were un- from 8 to 35 inches (Table 10.1). This sam- able to agree on a final age, the fish was ple size provided a range in (CV) for age excluded from further analysis. composition approximately from the small- est (CV) of 5% for age 1 to the largest (CV) of 24% for age 4. In 2015, we aged Click here to obtain the protocol at 308 of 328 spotted seatrout (The rest of the CQFE website on how to age spot- fish were either without otoliths or over- ted seatrout using their otolith thin- collected for certain length interval(s)) col- sections. lected by VMRC. We fell short in our over- all collections for this optimal length-class sampling estimate by 57 fish. However, we were short of some fish from the ma- jor length intervals (The interval requires 10 or more fish), as a result, the precision 10.2.5 Comparison tests for the estimates of major age groups would possibly be influenced significantly.

A symmetry test (Hoenig et al. 1995) and coefficient of variation (CV) analysis were used to detect any systematic differ- 10.3.2 Reading precision ence and precision on age readings, respec- tively, for the following comparisons: 1) be- tween the two readers in the current year, Both readers had high self-precision. 2) within each reader in the current year, Specifically, there was no significant differ- and 3) time-series bias between the current ence between the first and second readings and previous years within each reader. The for Reader 1 with an agreement of 98% and readings from the entire sample for the cur- a CV of 0.6% (test of symmetry: χ2 = 1, df rent year were used to examine the differ- = 1, P = 0.3173), and there was no signifi- ence between two readers. A random sub- cant difference between the first and second sample of 50 fish from the current year was readings for Reader 2 with an agreement of selected for second readings to examine the 100%. There was no evidence of systematic difference within a reader. Fifty otoliths disagreement between Reader 1 and Reader randomly selected from fish aged in 2003 2 with an agreement of 100% (Figure 10.2). were used to examine the time-series bias within each reader. A figure of 1:1 equiv- alence was used to illustrate those differ- There was no time-series bias for both read- ences (Campana et al. 1995). All statistics ers. Reader 1 had an agreement of 100% analyses were performed in R 3.2.2 (R Core with ages of fish aged in 2003. Reader 2 Team 2012). had an agreement of 100%.

84 CHAPTER 10. SPOTTED SEATROUT CYNOSCION NEBULOSUS

Figure 10.2: Between-reader comparison of Figure 10.3: Year-class frequency distribution otolith age estimates for spotted seatrout col- for spotted seatrout collected for ageing in lected in Chesapeake Bay and Virginia waters 2015. Distribution is broken down by sex. ’Un- of the Atlantic Ocean in 2015. known’ represents gonads that were not avail- able for examination or were not examined for sex during sampling. 10.3.3 Year class 10.4 REFERENCES

Of the 308 fish aged with otoliths, 10 age Campana, S.E., M.C. Annand, and J.I. classes (0 to 8, and 10) were represented McMillan. 1995. Graphical and statis- (Table 10.2). The average age was 2.5 tical methods for determining the con- years, and the standard deviation and stan- sistency of age determinations. Trans. dard error were 2.1 and 0.12, respectively. Am. Fish. Soc. 124:131-138. Year-class data show that the fishery was Hoenig, J.M., M.J. Morgan, and C.A. comprised of 10 year-classes: fish from the Brown. 1995. Analyzing differences be- 2005, and 2007 to 2015 year-classes, with tween two age determination methods fish primarily from the year classes of 2011, by tests of symmetry. Can. J. Fish. 2014, and 2015 with 27.6%, 26.9%, and Aquat. Sci. 52:364-368. 16.9%, respectively. The ratio of males to females was 1:0.77 in the sample collected Ihde, T., Chittenden, M. 2003. Vali- (Figure 10.3). dation of presumed annual marks on sectioned otoliths of spotted seatrout, Cynoscion nebulosus, in the Chesapeake Bay region. Bulletin of Marine Science, 72(1):77-87, 2003. 10.3.4 Age-length key Quinn, T. J. II, and R. B. Deriso. 1999. Quantitative Fish Dynamics. Oxford Univeristy Press. New York. We developed an age-length-key (Table R Core Team (2012). R: A lan- 10.3) that can be used in the conversion of guage and environment for statistical numbers-at-length in the estimated catch computing. R Foundation for Sta- to numbers-at-age using otolith ages. The tistical Computing, Vienna, Austria. table is based on VMRC’s stratified sam- ISBN 3-900051-07-0, URL http://www. pling of landings by total length inch inter- R-project.org. vals.

85 CHAPTER 10. SPOTTED SEATROUT CYNOSCION NEBULOSUS

Table 10.1: Number of spotted seatrout collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 8 - 8.99 5 0 0 5 9 - 9.99 5 0 0 5 10 - 10.99 5 0 0 5 11 - 11.99 8 1 1 7 12 - 12.99 21 29 29 0 13 - 13.99 17 19 18 0 14 - 14.99 15 16 16 0 15 - 15.99 23 24 24 0 16 - 16.99 31 31 31 0 17 - 17.99 33 31 31 2 18 - 18.99 27 27 27 0 19 - 19.99 27 13 13 14 20 - 20.99 22 25 25 0 21 - 21.99 11 16 12 0 22 - 22.99 12 13 12 0 23 - 23.99 10 14 10 0 24 - 24.99 9 11 10 0 25 - 25.99 7 11 8 0 26 - 26.99 6 8 6 0 27 - 27.99 7 9 8 0 28 - 28.99 6 7 6 0 29 - 29.99 5 8 6 0 30 - 30.99 5 9 9 0 31 - 31.99 5 4 4 1 32 - 32.99 5 1 1 4 33 - 33.99 5 0 0 5 34 - 34.99 5 1 1 4 35 - 35.99 5 0 0 5 Totals 342 328 308 57 (Go back to text)

86 CHAPTER 10. SPOTTED SEATROUT CYNOSCION NEBULOSUS

Table 10.2: The number of spotted seatrout assigned to each total length-at-age category for 308 fish sampled for otolith age determination in Virginia during 2015.

Age Interval 0 1 2 3 4 5 6 7 8 10 Totals 11 - 11.99 1 0 0 0 0 0 0 0 0 0 1 12 - 12.99 29 0 0 0 0 0 0 0 0 0 29 13 - 13.99 6 12 0 0 0 0 0 0 0 0 18 14 - 14.99 3 13 0 0 0 0 0 0 0 0 16 15 - 15.99 2 21 1 0 0 0 0 0 0 0 24 16 - 16.99 2 19 7 0 3 0 0 0 0 0 31 17 - 17.99 5 13 9 2 2 0 0 0 0 0 31 18 - 18.99 2 3 8 4 8 2 0 0 0 0 27 19 - 19.99 1 1 2 1 7 0 1 0 0 0 13 20 - 20.99 1 1 3 3 14 3 0 0 0 0 25 21 - 21.99 0 0 2 1 9 0 0 0 0 0 12 22 - 22.99 0 0 0 0 10 1 0 1 0 0 12 23 - 23.99 0 0 1 0 5 3 0 1 0 0 10 24 - 24.99 0 0 0 1 8 1 0 0 0 0 10 25 - 25.99 0 0 0 0 7 1 0 0 0 0 8 26 - 26.99 0 0 0 0 5 0 0 0 0 1 6 27 - 27.99 0 0 0 0 5 2 0 0 0 1 8 28 - 28.99 0 0 0 0 2 3 1 0 0 0 6 29 - 29.99 0 0 0 0 0 5 1 0 0 0 6 30 - 30.99 0 0 0 0 0 1 2 5 1 0 9 31 - 31.99 0 0 0 0 0 0 0 3 1 0 4 32 - 32.99 0 0 0 0 0 0 1 0 0 0 1 34 - 34.99 0 0 0 0 0 0 0 0 1 0 1 Totals 52 83 33 12 85 22 6 10 3 2 308 (Go back to text)

87 CHAPTER 10. SPOTTED SEATROUT CYNOSCION NEBULOSUS

Table 10.3: Age-Length key, as proportion-at-age in each 1-inch length interval, based on otolith ages for spotted seatrout sampled for age determination in Virginia during 2015.

Age Interval 0 1 2 3 4 5 6 7 8 10 11 - 11.99 1 0 0 0 0 0 0 0 0 0 12 - 12.99 1 0 0 0 0 0 0 0 0 0 13 - 13.99 0.33 0.67 0 0 0 0 0 0 0 0 14 - 14.99 0.19 0.81 0 0 0 0 0 0 0 0 15 - 15.99 0.08 0.88 0.04 0 0 0 0 0 0 0 16 - 16.99 0.06 0.61 0.23 0 0.1 0 0 0 0 0 17 - 17.99 0.16 0.42 0.29 0.06 0.06 0 0 0 0 0 18 - 18.99 0.07 0.11 0.3 0.15 0.3 0.07 0 0 0 0 19 - 19.99 0.08 0.08 0.15 0.08 0.54 0 0.08 0 0 0 20 - 20.99 0.04 0.04 0.12 0.12 0.56 0.12 0 0 0 0 21 - 21.99 0 0 0.17 0.08 0.75 0 0 0 0 0 22 - 22.99 0 0 0 0 0.83 0.08 0 0.08 0 0 23 - 23.99 0 0 0.1 0 0.5 0.3 0 0.1 0 0 24 - 24.99 0 0 0 0.1 0.8 0.1 0 0 0 0 25 - 25.99 0 0 0 0 0.88 0.12 0 0 0 0 26 - 26.99 0 0 0 0 0.83 0 0 0 0 0.17 27 - 27.99 0 0 0 0 0.62 0.25 0 0 0 0.12 28 - 28.99 0 0 0 0 0.33 0.5 0.17 0 0 0 29 - 29.99 0 0 0 0 0 0.83 0.17 0 0 0 30 - 30.99 0 0 0 0 0 0.11 0.22 0.56 0.11 0 31 - 31.99 0 0 0 0 0 0 0 0.75 0.25 0 32 - 32.99 0 0 0 0 0 0 1 0 0 0 34 - 34.99 0 0 0 0 0 0 0 0 1 0 (Go back to text)

88 Chapter 11

STRIPED BASS Morone saxatilis CHAPTER 11. STRIPED BASS MORONE SAXATILIS

11.1 INTRODUCTION where A is the sample size for ageing striped bass in 2015; θa stands for the pro- We aged a total of 885 striped bass, Mo- portion of age a fish in a catch. Va and Ba rone saxatilis, using their scales collected represent variance components within and by the VMRC’s Biological Sampling Pro- between length intervals for age a, respec- gram in 2015. Of 885 aged fish, 606 and tively; CV is the coefficient of variation; L 279 fish were collected in Chesapeake Bay was the total number of striped bass used (bay fish) and Virginia waters of the At- by VMRC to estimate length distribution lantic Ocean (ocean fish), respectively. The of the catches from 2009 to 2013. θa, Va, average bay fish age was 8.5 years with a Ba, and CV were calculated using pooled standard deviation of 4.3 and a standard age-length data of striped bass collected error of 0.17. Twenty age classes (3 to 22) from 2009 to 2013 and using equations in were represented in the bay fish, compris- Quinn and Deriso (1999). For simplicity, ing fish from the 1993 to 2012 year classes. the equations are not listed here. The equa- The bay fish sample in 2015 was dominated tion (11.1) indicates that the more fish that by the year class of 2011 with 22%. The av- are aged, the smaller the CV (or higher pre- erage ocean fish age was 11.7 years with a cision) that will be obtained. Therefore, standard deviation of 2.9 and a standard the criterion to age A (number) of fish is error of 0.17. Seventeen age classes (4, and that A should be a number above which 6 to 21) were represented in the ocean fish, there is only a 1% CV reduction for the comprising fish from the 1994 to 2009, and most major age in catch by aging an ad- 2011 year classes. The ocean fish sample in ditional 100 or more fish. Finally, Al is A 2015 was dominated by the year classes of multiplied by the proportion of length in- 2004, 2005, and 2003 with 17%, 16%, and terval l from the length distribution of the 16%, respectively. We also aged a total of 2009 to 2013 catch. Al is number of fish to 324 fish using their otoliths in addition to be aged for length interval l in 2015. ageing their scales. The otolith ages were compared to the scale ages to examine how close both ages were to one another (see details in Results).

11.2 METHODS 11.2.2 Handling of collection

11.2.1 Sample size for ageing Sagittal otoliths (hereafter, referred to as We estimated sample sizes for ageing "otoliths") and scales were received by the striped bass collected in both Chesapeake Age & Growth Laboratory in labeled coin Bay and Virginia waters of the Atlantic envelopes, and were sorted based on date Ocean in 2015, respectively, using a two- of capture. Their envelope labels were stage random sampling method (Quinn and verified against VMRC’s collection data, Deriso 1999) to increase precision in esti- and each fish assigned a unique Age and mates of age composition from fish sampled Growth Laboratory identification number. efficiently and effectively. The basic equa- All otoliths and scales were stored dry tion is: within their original labeled coin envelopes; Va otoliths were contained inside protective A = 2 2 (11.1) θaCV + Ba/L Axygen 2.0 ml microtubes.

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11.2.3 Preparation baked in a Thermolyne 1400 furnace at 400 ◦C. Baking time was dependent on the Scales otolith’s size and gauged by color, with a light caramel color desired. Once a suit- Striped bass scales were prepared for age able color was achieved the baked otolith and growth analysis by making acetate im- was embedded in epoxy resin with its dis- pressions of the scale microstructure. Due tal surface orientated downwards and al- to extreme variation in the size and shape lowed to harden overnight. The otoliths of scales from individual fish, we selected were viewed by eye and, when necessary, only those scales that had even margins under a stereo microscope to identify the and which were of uniform size. We se- location of the core, and the position of the lected a range of four to six preferred scales core was marked using a permanent marker (based on overall scale size) from each across the epoxy resin surface. At least fish, making sure that only non-regenerated one transverse cross-section (hereafter, re- scales were used. Scale impressions were ferred to as "thin-section") was then re- made on extruded clear acetate sheets (25 moved from the marked core of each otolith TM mm x 75 mm) with a Carver Laboratory using a Buehler IsoMet low-speed saw Heated Press (model "C"). The scales were equipped with two, 3-inch diameter, Nor- pressed with the following settings: ton diamond grinding wheels (hereafter, re- ferred to as "blades"), separated by a stain- Pressure: 15000 psi less steel spacer of 0.5 mm (diameter 2.5"). Temperature: 77 ◦C (170 ◦F) The otolith was positioned so the blades Time: 5 to 10 min straddled each side of the otolith focus. It was crucial that this cut be perpendicu- Striped bass scales that were the size of a lar to the long axis of the otolith. Failure quarter (coin) or larger, were pressed in- to do so resulted in broadening and dis- dividually for up to twenty minutes. Af- torted winter growth zones. A proper cut ter pressing, the impressions were viewed resulted in annuli that were clearly defined with a Bell and Howell microfiche reader and delineated. Once cut, thin-sections and checked again for regeneration and in- were placed on labeled glass slides and cov- complete margins. Impressions that were ered with a thin layer of Flo-texx mounting too light, or when all scales were regener- medium that not only fixed the sections to ated a new impression was made using dif- the slide, but more importantly, provided ferent scales from the same fish. enhanced contrast and greater readability Click here to obtain the protocol at the by increasing light transmission through CQFE website on how to prepare scale im- the thin-section. pression for ageing striped bass. Click here to obtain the protocol at the CQFE website on how to prepare otolith Otoliths thin-section for ageing striped bass.

We used our thin-section and bake tech- nique to process spadefish sagittal otoliths 11.2.4 Readings (hereafter, referred to as "otoliths") for age determination. Otolith preparation began The CQFE system assigns an age class to by randomly selecting either the right or a fish based on a combination of reading left otolith. Each whole otolith was placed the information contained in its otolith, the in a ceramic "Coors" spot plate well and date of its capture, and the species-specific

91 CHAPTER 11. STRIPED BASS MORONE SAXATILIS period when it deposits its annulus. Each some translucent growth after the last an- year, as the fish grows, its otoliths grow and nulus, would be assigned an age class of leave behind markers of their age, called "x+(x+1)" or 3+(3+1), noted as 3+4. annuli. Technically, an otolith annulus is This is the same age-class assigned to a the combination of both the opaque and fish with four visible annuli captured af- the translucent bands. In practice, only the ter the end of June 30, the period of an- opaque bands are counted as annuli. The nulus formation, which would be noted as number of these visible dark bands replaces 4+4. "x" in our notation below, and is the initial Striped bass scales are also considered to "age" assignment of the fish. have a deposition between April and June Second, the otolith section is examined (Secor et al. 1995), and age class assign- for translucent growth. If no translucent ment using these hard-parts is conducted growth is visible beyond the last dark an- in the same way as otoliths. nulus, the otolith is called "even" and no All striped bass samples (scale pressings modification of the assigned age is made. and sectioned otoliths) were aged by two The initial assigned age, then, is the age different readers in chronological order class of the fish. Any growth beyond the based on collection date, without knowl- last annulus can be interpreted as either edge of previously estimated ages or the being toward the next age class or within specimen lengths. When the readers’ ages the same age class. If translucent growth agreed, that age was assigned to the fish. is visible beyond the last dark annulus, a When the two readers disagreed, both read- "+" is added to the notation. ers sat down together and re-aged the fish By convention all fish in the Northern again without any knowledge of previously Hemisphere are assigned a birth date of estimated ages or lengths, then assigned a January 1. In addition, each species has a final age to the fish. When the age readers specific period during which it deposits the were unable to agree on a final age, the fish dark band of the annulus. If the fish is cap- was excluded from further analysis. tured after the end of the species-specific annulus deposition period and before Jan- Scales uary 1, it is assigned an age class notation of "x+x", where "x" is the number of dark bands in the otolith. If the fish is cap- We determined fish age by viewing acetate tured between January 1 and the end of impressions of scales (Figure 11.1) with a the species-specific annulus deposition pe- standard Bell and Howell R-735 microfiche riod, it is assigned an age class notation reader equipped with 20 and 29 mm lenses. of "x+(x+1)". Thus, any growth beyond Annuli on striped bass scales are identi- the last annulus, after its "birthday", but fied based on two scale microstructure fea- before the dark band deposition period, is tures, "crossing over" and circuli disrup- interpreted as being toward the next age tion. Primarily, "crossing over" in the class. lateral margins near the posterior/ante- rior interface of the scale is used to deter- For example, striped bass otolith deposi- mine the origin of the annulus. Here com- tion occurs between April and June (Secor pressed circuli (annulus) "cross-over" the et al. 1995). A striped bass captured previously deposited circuli of the previous between January 1 and June 30, before year’s growth. Typically annuli of the first the end of the species’ annulus forma- three years can be observed transversing tion period, with three visible annuli and this interface as dark bands. These bands

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respect to the following annuli. For the an- nuli two through six, summer growth gen- erally decreases proportionally. For ages greater than six, a crowding effect of the annuli near the outer margins of the scale is observed. This crowding effect creates difficulties in edge interpretation. At this point it is best to focus on the straighten- ing of the circuli at the anterior margins of the scale. When ageing young striped bass, zero through age two, extreme caution must be Figure 11.1: Scale impression of a 3 year-old taken as not to over age the structure. In striped bass. young fish there is no point of reference to aid in the determination of the first year; this invariably results in over examination remain consistent throughout the posterior of the scale and such events as hatching or field and rejoin the posterior/anterior in- saltwater incursion marks (checks) may be terface on the opposite side of the focus. interpreted as the first year. Annuli can also be observed in the anterior lateral field of the scale. Here the annuli typically reveal a pattern of discontinuous Otoliths and suddenly breaking segmented circuli. This event can also be distinguished by the presence of concentric white lines, which All thin-sections were aged by two different are typically associated with the disruption readers using a Nikon SMZ1000 stereo mi- of circuli. croscope under transmitted light and dark- field polarization at between 8 and 20 times Annuli can also be observed bisecting the magnification (Figure 11.2). Each reader perpendicular plain of the radial striations aged all of the otolith samples. By conven- in the anterior field of the scale. Radii em- anate out from the focus of the scale to- wards the outer corner margins of the an- terior field. These radial striations consist mainly of segmented concave circuli. The point of intersection between radii and an- Figure 11.2: Otolith thin-section of a 4 year- nuli results in a "straightening out" of the old striped bass with the last annulus on the concave circuli. This straightening of the edge of the thin-section circuli should be consistent throughout the entire anterior field of the scale. This event tion an annulus is identified as the narrow is further amplified by the presence of con- opaque zone, or winter growth. Typically cave circuli neighboring both directly above the first year’s annulus can be determined and below the annulus. The first year’s by first locating the focus of the otolith. annulus can be difficult to locate on some The focus is generally located, depending scales. It is typically best identified in the on preparation, in the center of the otolith, lateral field of the anterior portion of the and is visually well defined as a dark oblong scale. The distance from the focus to the region. The first year’s annulus can be lo- first year’s annulus is typically larger with cated directly below the focus, along the

93 CHAPTER 11. STRIPED BASS MORONE SAXATILIS outer ridge of the sulcal groove on the ven- ences (Campana et al. 1995). All statistics tral and dorsal sides of the otolith. This analyses were performed in R 3.2.2 (R Core insertion point along the sulcal ridge re- Team 2012). sembles a check mark (not to be confused with a false annulus). Here the annulus can be followed outwards along the ventral and dorsal surfaces where it encircles the focus. 11.3 RESULTS Subsequent annuli also emanate from the sulcal ridge; however, they do not encir- cle the focus, but rather travel outwards to 11.3.1 Sample size the distal surface of the otolith. To be con- sidered a true annulus, each annulus must We estimated a sample size of 573 bay be rooted in the sulcus and travel with- striped bass in 2015, ranging in length in- out interruption to the distal surface of the terval from 17 to 50 inches (Table 11.1). otolith. The annuli in striped bass have a This sample size provided a range in CV for tendency to split as they advance towards age composition approximately from the the distal surface. As a result, it is criti- smallest CV of 11% for age 7 to the largest cal that reading path proceed in a direction CV of 23% for age 3 and 14 of the bay fish. down the sulcal ridge and outwards to the We randomly selected and aged 606 fish distal surface. from 784 striped bass collected by VMRC in Chesapeake Bay in 2015. We fell short Click here to obtain the protocol at the in our over-all collections for this optimal CQFE website on how to age striped bass length-class sampling estimate by 43 fish. using their otolith thin-sections. We were short of few fish from the major length intervals (The interval requires 10 or more fish), as a result, the precision for the 11.2.5 Comparison Tests estimates of major age groups would not be influenced significantly. A symmetry test (Hoenig et al. 1995) and coefficient of variation (CV) analysis were We estimated a sample size of 496 ocean used to detect any systematic difference striped bass in 2015, ranging in length in- and precision on age readings, respectively, terval from 26 to 56 inches (Table 11.2). for following comparisons: 1) between the This sample size provided a range in CV for two readers in the current year; 2) within age composition approximately from the each reader in the current year; 3) time- smallest CV of 1% for age 21 to the largest series bias between the current and previ- CV of 25% for age 6 of the ocean fish. ous years within each reader; and 4) be- We aged all 279 striped bass collected by tween scale and otoliths ages. The read- VMRC in Virginia waters of the Atlantic ings from the entire sample for the cur- Ocean in 2015. We fell short in our over- rent year were used to examine the differ- all collections for this optimal length-class ence between two readers. A random sub- sampling estimate by 231 fish. However, we sample of 50 fish from the current year was were short of many fish from in the major selected for second readings to examine the length intervals (The interval requires 10 or difference within a reader. Fifty otoliths more fish), as a result, the precision for the randomly selected from fish aged in 2000 estimates of major age groups would def- were used to examine the time-series bias initely be influenced significantly. There- within each reader. A figure of 1:1 equiv- fore, precaution should be used when de- alence was used to illustrate those differ- veloping ALK using these age data.

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11.3.2 Scales scales, 20 age classes (3 to 22) were rep- resented (Table 11.3). The average age for Reader 1 had high self-precision and Read 2 the sample was 8.5 years. The standard had moderate self-precision. Specifically, deviation and standard error were 4.3 and there was no significant difference between 0.17, respectively. Year-class data (Figure the first and second readings for Reader 11.4) indicates that recruitment into the 1 with an agreement of 60% (1 year or fishery in Chesapeake Bay begins at age 3, less agreement of 84%) and a CV of 4.7% which corresponds to the 2012 year-class (test of symmetry: χ2 = 18, df = 15, P = for striped bass caught in 2015. Striped 0.2627), and there was no significant differ- bass in the sample in 2015 was dominated ence between the first and second readings by the year class of 2011 with 22%. The for Reader 2 with an agreement of 38% (1 sex ratio of male to female was 1:1.51 for year or less agreement of 88%) and a CV of the bay fish. 6.4% (test of symmetry: χ2 = 14.73, df = 16, P = 0.5442). There was an evidence of systematic disagreement between Reader 1 and Reader 2 with an agreement of 42% (1 year or less agreement of 75%) and a CV of 7% (test of symmetry: χ2 = 256.54, df = 67, P < 0.0001) (Figure 11.3).

Figure 11.4: Year-class frequency distribution for striped bass collected in Chesapeake Bay, Virginia for ageing in 2015. Distribution is broken down by sex and estimated using scale ages. ’Unknown’ represents the fish gonads that were not available for examination or were not examined for sex during sampling.

Figure 11.3: Between-reader comparison of scale age estimates for striped bass collected Of the 279 ocean striped bass aged with in Chesapeake Bay and Virginia waters of the scales, 17 age classes (4, and 6 to 21) Atlantic Ocean in 2015. were represented (Table 11.4). The av- erage age for the sample was 11.7 years. The standard deviation and standard error Reader 1 had no time series bias while Read were 2.9 and 0.17, respectively. Year-class 2 does. Reader 1 had an agreement of 58% data (Figure 11.5) indicates that recruit- (1 year or less agreement of 95%) with ages ment into the fishery in Virginia waters of of fish aged in 2000 with a CV of 4.9% (test Atlantic ocean begins at age 4, which cor- of symmetry: χ2 = 11.33, df = 13, P = responds to the 2011 year-class for striped 0.5829). Reader 2 had an agreement of 50% bass caught in 2015. Striped bass in the (1 year or less agreement of 93%) with a sample in 2015 was dominated by the year CV of 5.9% (test of symmetry: χ2 = 22.67, classes of 2004, 2005, and 2003 with 17%, df = 12, P = 0.0307). 16%, and 16%, respectively. The sex ratio Of the 606 bay striped bass aged with of male to female was 1:2.24 for the ocean

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fish.

Figure 11.6: Between-reader comparison of otolith age estimates for striped bass collected Figure 11.5: Year-class frequency distribution in Chesapeake Bay and Virginia waters of the for striped bass collected in Virginia waters of Atlantic Ocean in 2015. the Atlantic Ocean for ageing in 2015. Distri- bution is broken down by sex and estimated using scale ages. ’Unknown’ represents the fish χ2 = 1, df = 2, P = 0.6065). gonads that were not available for examination or were not examined for sex during sampling. Of the 324 striped bass aged with otoliths, 24 age classes (2 to 23, and 25 to 26) were represented (Table 11.5). The average age for the sample was 11.3 years. The stan- 11.3.3 Otoliths dard deviation and standard error were 5.7 and 0.32, respectively. Both readers had high self-precision. Specifically, there was no significant differ- ence between the first and second readings for Reader 1 with an agreement of 94% and a CV of 0.4% (test of symmetry: χ2 = 3, df 11.3.4 Comparison of scale and = 3, P = 0.3916), and there was no signif- otolith ages icant difference between the first and sec- ond readings for Reader 2 with an agree- ment of 94% and a CV of 0.3% (test of We aged 324 striped bass using scales and symmetry: χ2 = 3, df = 3, P = 0.3916). otoliths. There was an evidence of system- There was no evidence of systematic dis- atic disagreement between otolith and scale 2 agreement between Reader 1 and Reader 2 ages (test of symmetry: χ = 130.63, df with an agreement of 90% (1 year or less = 55, P < 0.0001) with an average CV of agreement of 99%) and a CV of 0.7% (test 5.8%. There was an agreement of 48% be- of symmetry: χ2 = 15, df = 17, P = 0.5955) tween scale and otoliths ages whereas scales (Figure 11.6). were assigned a lower and higher age than otoliths for 44% and 8% of the fish, re- There was no time-series bias for both read- spectively (Figure 11.7). There was also an ers. Reader 1 had an agreement of 90% evidence of bias between otolith and scale with ages of fish aged in 2003 with a CV of ages using an age bias plot (Figure 11.8), 0.8% (test of symmetry: χ2 = 4, df = 5, P with scale generally assigned higher ages = 0.5494). Reader 2 had an agreement of for younger fish and lower ages for older 95% with a CV of 0.4% (test of symmetry: fish than otolith age estimates.

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11.4 RECOMMENDATIONS

We recommend that VMRC and ASMFC use otoliths for ageing striped bass. Al- though preparation time is greater for otoliths compared to scales, nonetheless as the mean age of striped bass increases in the recovering fishery, otoliths should pro- vide more reliable estimates of age (Liao et al. 2013; Secor et al. 1995). We will con- tinue to compare the age estimates between Figure 11.7: Comparison of scale and otolith otoliths and scales. age estimates for striped bass collected in Chesapeake Bay and Virginia waters of the At- lantic Ocean in 2015. 11.5 REFERENCES

Campana, S.E., M.C. Annand, and J.I. McMillan. 1995. Graphical and statisti- cal methods for determining the consis- tency of age eterminations. Trans. Am. Fish. Soc. 124:131-138. Hoenig, J.M., M.J. Morgan, and C.A. Brown. 1995. Analyzing differences be- tween two age determination methods by tests of symmetry. Can. J. Fish. Aquat. Sci. 52:364-368. Liao, H., A. F. Sharov, C. M. Jones, and Figure 11.8: Age-bias plot for striped bass scale and otolith age estimates in 2015. G. A. Nelson. 2013. Quantifying the Effects of Aging Bias in Atlantic Striped Bass Stock Assessment, Transactions of the American Fisheries Society, 142:1, 11.3.5 Age-Length-Key 193-207. (ALK) Secor, D. H., T. M. Trice, and H. T. Hor- nick. 1995. Validation of otolith-based ageing and a comparison of otolith and scale-based ageing in mark-recaptured We developed an age-length-key for both Chesapeake Bay summer flounder, Mo- bay (Table 11.6) and ocean fish (Table rone saxatilis. Fishery Bulletin 93: 186- 11.7) using scale ages, separately. The 190. ALK can be used in the conversion of Quinn, T. J. II, and R. B. Deriso. 1999. numbers-at-length in the estimated catch Quantitative Fish Dynamics. Oxford to numbers-at-age using scale ages. The Univeristy Press. New York. table is based on VMRC’s stratified sam- pling of landings by total length inch inter- R Core Team (2012). R: A lan- vals. guage and environment for statistical

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computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org.

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Table 11.1: Number of bay striped bass collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 17 - 17.99 5 0 0 5 18 - 18.99 9 18 14 0 19 - 19.99 20 39 27 0 20 - 20.99 22 51 31 0 21 - 21.99 28 46 29 0 22 - 22.99 29 41 30 0 23 - 23.99 30 37 30 0 24 - 24.99 32 43 30 2 25 - 25.99 28 39 28 0 26 - 26.99 27 29 27 0 27 - 27.99 23 33 28 0 28 - 28.99 18 22 18 0 29 - 29.99 15 23 19 0 30 - 30.99 14 26 14 0 31 - 31.99 16 31 17 0 32 - 32.99 20 31 30 0 33 - 33.99 20 25 25 0 34 - 34.99 24 21 21 3 35 - 35.99 29 22 21 8 36 - 36.99 34 31 31 3 37 - 37.99 31 23 23 8 38 - 38.99 17 26 18 0 39 - 39.99 12 16 11 1 40 - 40.99 11 25 18 0 41 - 41.99 8 10 8 0 42 - 42.99 9 12 9 0 43 - 43.99 7 11 8 0 44 - 44.99 5 18 13 0 45 - 45.99 5 15 9 0 46 - 46.99 5 13 12 0 47 - 47.99 5 4 4 1 48 - 48.99 5 2 2 3 49 - 49.99 5 1 1 4 50 - 50.99 5 0 0 5 Totals 573 784 606 43 (Go back to text)

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Table 11.2: Number of ocean striped bass collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 26 - 26.99 5 0 0 5 27 - 27.99 5 0 0 5 28 - 28.99 12 4 4 8 29 - 29.99 24 4 4 20 30 - 30.99 25 5 5 20 31 - 31.99 32 12 12 20 32 - 32.99 32 11 11 21 33 - 33.99 34 18 18 16 34 - 34.99 38 20 20 18 35 - 35.99 49 31 31 18 36 - 36.99 48 31 31 17 37 - 37.99 51 34 34 17 38 - 38.99 33 19 19 14 39 - 39.99 22 17 17 5 40 - 40.99 17 11 11 6 41 - 41.99 11 9 9 2 42 - 42.99 11 8 8 3 43 - 43.99 7 10 10 0 44 - 44.99 5 11 11 0 45 - 45.99 5 9 9 0 46 - 46.99 5 4 4 1 47 - 47.99 5 6 6 0 48 - 48.99 5 3 3 2 49 - 49.99 5 2 2 3 50 - 50.99 5 0 0 5 56 - 56.99 5 0 0 5 Totals 496 279 279 231 (Go back to text)

100 CHAPTER 11. STRIPED BASS MORONE SAXATILIS Age terval 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Totals Totals 23 135 60 38 29 37 38 46 52 60 17 10 14 13 9 11 6 3 3 2 606 - 18.99 7 4 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 14 In 18 19 - 19.9920 - 20.99 821 - 21.99 422 - 17 22.99 223 - 19 23.99 2 124 - 21 24.99 6 025 0 - 20 25.99 5 126 1 - 19 26.99 0 6 027 1 - 14 27.99 0 6 028 0 1 - 28.99 0 8 6 029 1 3 - 0 29.99 1 6 12 030 0 7 - 0 30.99 2 6 0 031 1 7 2 - 0 31.99 2 0 0 032 0 4 - 0 0 32.99 6 4 1 0 033 0 1 - 0 0 33.99 5 0 0 034 4 1 2 - 0 0 0 34.99 6 0 0 035 4 0 - 0 0 1 1 35.99 0 0 0 0 036 2 0 - 0 0 3 36.99 0 0 0 2 0 037 1 0 0 - 0 0 2 37.99 3 0 0 3 038 2 0 0 - 0 0 0 4 0 38.99 2 0 0 4 039 4 0 0 - 0 3 4 0 39.99 1 0 1 0 4 0 040 1 0 0 - 0 1 1 0 40.99 0 0 0 0 4 0 041 0 0 0 - 2 0 5 0 41.99 0 0 0 2 0 2 0 042 0 0 0 - 1 0 2 0 42.99 0 0 3 0 0 2 0 043 0 0 0 0 - 3 0 5 0 43.99 0 0 2 0 0 6 0 044 1 0 0 0 - 3 0 3 0 0 44.99 0 2 1 0 0 2 0 045 1 0 0 0 - 3 0 4 0 45.99 0 0 1 6 0 0 1 0 0 046 0 0 0 0 - 5 0 0 0 46.99 0 0 2 2 0 0 2 0 047 0 0 0 0 0 - 8 0 0 0 0 47.99 0 0 7 6 0 0 2 0 048 0 0 1 0 0 - 7 0 0 0 0 48.99 0 0 4 3 0 0 0 2 0 049 0 0 2 0 0 - 5 0 0 0 0 49.99 0 0 1 9 0 0 0 0 0 0 0 5 0 0 0 2 0 0 0 1 0 0 2 6 0 0 27 1 0 0 0 0 1 0 0 3 0 0 0 1 0 0 0 7 5 0 0 31 0 1 0 0 3 0 0 0 0 0 0 0 0 0 7 2 0 0 29 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 9 3 0 30 0 1 0 0 2 0 0 0 1 0 0 0 1 0 0 5 1 0 30 0 0 0 0 0 0 0 0 0 0 0 0 0 7 0 0 30 0 0 0 0 0 1 0 0 0 0 0 0 0 4 0 0 28 0 0 0 0 0 2 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 27 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 28 0 0 0 2 0 0 0 0 0 0 3 0 0 0 18 0 0 0 1 0 0 0 0 0 0 0 0 0 19 0 1 0 2 0 0 0 0 0 0 0 0 0 14 0 0 0 0 0 0 0 0 2 0 0 0 17 1 0 0 0 0 0 0 3 0 0 0 30 1 0 0 0 0 3 0 1 0 0 0 25 3 0 0 0 1 0 2 0 0 2 21 1 0 0 1 2 0 0 0 0 21 3 0 0 0 0 0 1 0 1 31 1 0 1 2 0 0 0 4 23 0 0 1 1 0 1 3 18 1 0 1 0 0 1 1 11 0 0 0 0 0 0 18 1 1 0 1 0 2 1 8 1 0 0 0 9 0 0 0 8 1 0 13 0 0 0 9 0 12 0 4 2 1 back to text) able 11.3: The number of striped bass assigned to each total length-at-age category for 606 fish sampled for scale age determination in Chesapeake T (Go Bay, Virginia during 2015.

101 CHAPTER 11. STRIPED BASS MORONE SAXATILIS (Go 2015. during ocean Atlantic of waters T be1.:Tenme fsrpdbs sindt ahttllnt-taectgr o 7 s ape o cl g eemnto nVirginia in determination age scale for sampled fish 279 for category length-at-age total each to assigned bass striped of number The 11.4: able akt text) to back 9-4.9000000000000101002 3 6 0 4 1 0 9 0 0 1 11 0 0 1 10 0 0 0 8 0 0 0 1 0 9 0 2 0 1 0 0 0 11 0 0 3 2 0 0 0 17 2 0 0 0 0 0 0 19 0 0 0 1 0 2 0 1 0 0 0 4 34 0 0 2 0 0 31 0 0 0 1 0 0 1 0 1 0 1 0 0 31 0 0 0 0 0 1 20 0 1 0 0 0 0 0 1 0 0 2 18 0 3 0 0 1 0 0 0 1 0 0 11 0 0 3 0 1 0 1 0 3 0 0 0 0 12 0 1 0 1 1 0 0 0 5 0 0 0 1 0 0 0 1 0 1 0 5 0 4 0 0 0 0 0 1 0 2 0 0 1 0 0 2 0 0 0 0 0 1 0 0 0 0 0 0 0 2 0 2 0 0 0 0 0 0 0 0 2 0 0 4 0 0 3 0 0 1 0 0 0 0 0 1 0 0 0 0 49.99 0 1 0 0 1 1 0 0 - 0 0 0 49 0 0 2 0 6 0 48.99 0 0 3 0 0 - 0 0 2 0 48 0 0 0 6 0 47.99 0 5 0 0 5 0 0 - 0 0 47 1 0 0 0 0 46.99 0 0 4 0 0 - 4 0 3 1 46 0 0 1 8 0 45.99 0 0 0 0 0 - 0 3 45 0 14 1 0 44.99 0 0 0 5 0 0 - 5 0 5 44 0 1 0 3 43.99 0 0 0 0 - 0 6 43 1 6 6 0 2 42.99 0 0 0 4 0 - 0 42 3 0 10 3 41.99 2 0 0 2 0 - 0 8 41 5 0 40.99 0 0 0 0 0 - 0 5 40 2 0 39.99 1 0 1 0 - 1 2 39 4 0 38.99 3 0 0 0 - 0 3 38 1 37.99 2 0 0 0 - 0 1 37 3 36.99 3 0 0 - 1 0 36 0 35.99 3 0 0 - 2 35 0 34.99 1 0 0 - 1 34 33.99 2 0 1 - 0 33 32.99 0 3 - 0 32 31.99 0 0 - 31 30.99 1 - 30 29.99 - 29 28 In 89 4 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 3 0 28.99 - oas1751 74 84 51 01 34221279 1 2 2 4 13 11 10 18 25 44 48 44 27 17 5 7 1 Totals evl467891 11 31 51 71 92 1Totals 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 4 terval Age

102 CHAPTER 11. STRIPED BASS MORONE SAXATILIS Age terval 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 25 26 Totals Totals 1 7 53 13 14 10 20 6 17 16 65 2 14 16 3 3 1 29 14 4 12 2 1 1 324 - 18.99 0 3 6 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 11 In 18 19 - 19.9920 - 20.99 021 - 21.99 0 222 - 22.99 0 1 1123 - 0 23.99 1 10 224 - 24.99 0 0 7 225 - 0 25.99 0 0 626 - 0 0 26.99 1 0 0 727 - 0 27.99 0 0 1 2 328 0 - 1 0 28.99 0 3 029 0 0 0 - 1 29.99 0 0 1 030 0 0 - 2 30.99 0 0 0 0 1 331 1 - 2 31.99 0 0 0 0 0 1 032 0 0 - 0 32.99 0 0 0 0 2 033 0 0 2 - 0 0 33.99 0 0 0 0 0 034 0 3 - 1 0 0 0 34.99 0 0 0 3 035 0 0 - 0 0 0 35.99 0 0 0 0 0 0 036 0 0 - 0 0 0 36.99 0 0 4 0 0 0 0 037 0 0 - 0 0 37.99 0 0 0 2 1 0 0 0 038 0 2 - 0 0 0 38.99 0 0 2 1 1 0 0 039 0 0 - 0 0 0 0 39.99 0 0 2 0 0 0 0 0 040 2 0 - 0 0 0 0 40.99 0 0 1 0 0 0 0 0 041 1 0 0 - 0 0 0 41.99 0 0 2 1 0 0 0 0 042 2 0 0 0 - 0 0 0 0 42.99 0 0 1 1 0 0 0 1 043 2 0 0 - 0 0 0 0 0 43.99 0 0 1 1 0 0 0 2 0 044 0 0 0 - 0 0 0 0 44.99 0 0 2 0 0 0 0 3 0 0 045 0 0 0 - 0 0 0 3 0 45.99 0 0 3 0 0 0 0 2 0 046 2 0 0 - 0 0 0 0 2 0 0 46.99 0 1 0 0 0 0 0 3 0 047 2 0 0 - 1 0 0 0 0 47.99 0 0 0 1 0 0 0 0 0 1 0 048 0 0 0 0 - 0 0 0 1 0 48.99 0 0 0 0 0 0 0 0 3 0 049 4 0 0 0 0 - 0 0 0 1 0 49.99 0 0 0 0 0 0 0 0 0 2 0 0 1 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0 1 0 0 0 2 0 0 2 0 0 0 0 0 0 0 0 2 6 0 0 0 0 0 0 0 0 1 0 0 0 2 14 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 2 0 0 0 0 0 0 0 0 8 0 0 0 1 0 0 0 0 0 0 0 1 10 0 0 0 0 0 0 0 15 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 15 0 0 0 4 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 3 1 0 0 0 0 0 0 0 9 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 10 0 4 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 5 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 1 0 0 0 0 0 0 0 7 3 0 0 0 0 0 0 0 0 0 0 0 0 1 0 7 1 0 0 0 0 0 0 1 0 0 0 0 1 0 9 0 0 0 0 2 0 0 0 0 0 0 0 7 1 0 0 0 0 0 0 0 10 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 11 2 0 0 0 0 0 1 0 0 0 0 0 10 8 0 1 3 0 0 0 0 0 1 3 0 0 0 8 1 0 0 1 10 6 0 0 0 0 4 0 0 0 0 11 2 1 3 0 0 2 0 13 3 0 0 2 0 18 0 0 1 0 2 1 0 0 1 14 0 3 0 21 0 0 0 0 2 0 0 0 11 1 1 1 0 10 0 1 0 0 11 0 0 0 14 0 0 10 0 0 13 0 6 5 2 back to text) able 11.5: The number of striped bass assigned to each total length-at-age category for 324 fish sampled for otolith age determination in Chesapeake T (Go Bay and Virginia waters of Atlantic Ocean during 2015.

103 CHAPTER 11. STRIPED BASS MORONE SAXATILIS (Go 2015. during Virginia T be1.:AeLnt e,a rprina-g nec -nhlnt nevl ae nsaeae o tie assmldi hspaeBay, Chesapeake in sampled bass striped for ages scale on based interval, length 1-inch each in proportion-at-age as key, Age-Length 11.6: able akt text) to back 9-4.900000000000001000000 0 0 0 0 0 0 0 0 0 0.5 0 0.08 0 0 0 0 0.22 0 0 0 0 0 0.08 0.25 1 0.08 0 0.25 0 0 0 0 0 0.08 0.11 0 0.25 0 0.08 0.44 0.25 0.25 0 0 0 0 0.12 0.5 0.08 0 0 0.17 0 0 0.12 0.08 0 0.25 0 0.12 0 0 0 0 0.15 0.11 0 0.17 0 0 0 0.23 0 0.11 0 0 0 0 0 0.22 0 0.12 0.23 0 0 0 0 0 0 0.33 0.12 0 0 0 0 0 0 0 0.11 0 0.25 0 0 0 0 0 0 0 0.25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.11 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.06 0 0 0.22 0 0 0 0 0 0 0 0 0 0 0.17 0 0 0 0 0 0 0 0 0 0 0 0.5 0 0 0 0.06 0 0 0 0 0 0 0 0 0 0 0 0 0.11 0 0 0.12 0 0 0 0 0 0 0 0 0 0 0 0.09 0 0 0.39 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.45 0.17 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.18 0 0 0 0 0 0 0 0 0 0.5 0 0 0 0 0 0 0.27 0 0 0 0.05 0 0 0 0 0.09 0 0 0 0.03 0.28 0 0 0 0.06 0.04 0 0 0.05 0 0 0.3 0 0 0 0 0 0 0 0 0.11 0 0 0 0 0 0 0 0.14 0 0 0 0 0 0 0.26 0.11 0 0 0 0 0.05 0 0.1 0 0 0 0 0 0 0.23 0 0.22 0 0 0 0 0 0.04 0 0 0.05 0 0 0 0 0 0.03 0.14 0 0.29 0.09 0 0 0 0.2 0 0.29 0 0 0 0 0 0 0 0.03 0.38 0.23 49.99 0 0 0 0 - 0 0 0 0 0.24 0 0 49 0 0 0.16 0 0.07 0.05 48.99 0.06 - 0 0 0 0 48 0.1 0 0 0 0 0.08 0 0 47.99 0.23 0.14 0.13 0.04 - 0 0 0 0 0 0 47 0 0 0 0.06 0 0.12 46.99 0.24 0.2 0 0.03 - 0 0 0 0 46 0 0.07 0 0.12 0 45.99 0 0.24 0 0 - 0 0 0 0 45 0.1 0 0 0 0 0 0 0.14 0.06 44.99 0.08 - 0 0 44 0 0 0 0 0.07 43.99 0.18 0 0.07 0 0 - 0 0 0 43 0 0 0 0 0 0 0.11 42.99 0 0.29 0.12 0.17 - 0 42 0 0 0 0 41.99 0.16 0.29 0.06 - 0 0.03 0 0.04 0 0 41 0 0 0 0 0 40.99 0.11 0.11 0 0.14 - 0.24 0.07 0 40 0 0 0 39.99 0 0.06 0.21 - 0 0.18 0 0 0 39 0 0 0 0 38.99 0.04 0 0.22 - 0.21 0 0 38 0 0 37.99 0 0 0.11 - 0.11 0.05 0 37 0 0 0 0 0 36.99 0 - 0.11 0 0.11 0 0 36 0 0 35.99 - 0.07 0 0.11 0.33 35 0 0 0 0 0 34.99 - 0.04 0.04 0.14 0 34 0.06 0.11 0 0 33.99 - 0.04 0 0.15 33 0.18 0 0.05 0 0 32.99 0 0 - 0.14 32 0.22 0 0.14 0 0 31.99 - 31 0.07 0.07 0.26 0.21 0 30.99 0.07 0 - 0 30 0.43 0.1 0.22 0 0 29.99 0.03 0.23 - 29 0.29 0 28.99 0.03 0.2 - 0.2 0.03 0 28 0 0 27.99 0.03 - 0 27 0.63 0.47 26.99 - 0.2 26 0.03 0 0.03 25.99 0 - 25 0.03 0.17 0.67 24.99 - 24 0.19 0.72 0.03 23.99 - 0.07 23 0.61 0.07 22.99 - 0.63 22 0.13 21.99 - 0.3 21 20.99 - 20 19.99 - 19 18 In 89 . .902 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.21 0.29 0.5 18.99 - evl34567891 11 31 51 71 92 122 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 terval Age

104 CHAPTER 11. STRIPED BASS MORONE SAXATILIS Age terval 4 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 - 28.99 0 0.75 0 0 0.25 0 0 0 0 0 0 0 0 0 0 0 0 In 28 29 - 29.9930 - 0.25 30.9931 - 31.9932 - 32.99 0 033 - 33.99 034 0.6 - 34.99 0 0.08 035 - 35.99 0 0.0836 0.5 0 - 36.99 0 0.25 037 - 0.2 37.99 0 0.25 0 0.1838 0 - 38.99 0 0.25 0 0.06 0.2739 - 39.99 0 0 0.08 0 0.11 0.0940 0 - 40.99 0 0 0.22 0.18 0 0.241 - 41.99 0 0 0.03 0.28 0 0 0.1542 - 0 42.99 0 0 0.11 0.03 043 0 0.1 - 43.99 0 0 0.11 0 0.16 0 0.27 044 - 0 44.99 0.4 0 0 0 0.06 0.3245 0 0.1 - 45.99 0 0 0 0.18 0.19 0 0 0 0.246 0.19 - 0 46.99 0 0 0.06 0 0.15 0.16 0 0.1547 0.16 0 - 47.99 0 0 0.06 0 0.41 0 0.05 0 048 0.1 0.26 - 0 48.99 0 0 0 0.12 0 0.06 0.1649 0 0.16 0 - 0.25 49.99 0 0 0 0.06 0 0.06 0.21 0 0 0 0.06 0 0 0 0 0.03 0 0.29 0.32 0 0 0 0 0 0 0 0 0.35 0.05 0 0 0 0 0 0 0 0 0 0.18 0.11 0 0 0 0 0.03 0 0 0 0 0 0.05 0 0 0.27 0 0 0 0 0 0 0 0 0 0.11 0 0 0.03 0 0 0 0 0 0.06 0 0 0 0.44 0.12 0 0 0 0 0 0.05 0 0 0.22 0 0.18 0 0.2 0 0 0 0 0 0 0 0 0 0.11 0 0.18 0 0 0 0 0 0.09 0 0 0.62 0 0 0 0 0 0 0 0 0 0 0 0 0.12 0.27 0 0 0.09 0 0.11 0 0 0.11 0.09 0 0 0 0 0 0 0 0 0 0.27 0.25 0 0.11 0 0 0 0 0 0.3 0.11 0.09 0 0 0.12 0 0 0 0 0.11 0.09 0 0 0 0 0 0.2 0 0 0.22 0.36 0 0.25 0 0 0 0 0.11 0 0 0 0 0.22 0 0 0 0 0 0.1 0 0 0 0 0.5 0 0 0 0 0.17 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.5 0 0 0.2 0 0 0.33 0 0.33 0 0 0.5 0 0 0 0.33 0 0 0 0 0.5 0 0.33 0 0 back to text) able 11.7: Age-Length key, as proportion-at-age in each 1-inch length interval, based on scale ages for striped bass sampled in Virginia waters of the T (Go Atlantic Ocean during 2015.

105

Chapter 12

SUMMER FLOUNDER Paralichthys dentatus CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS

12.1 INTRODUCTION tion is:

Va A = 2 2 (12.1) We aged a total of 884 summer floun- θaCV + Ba/L der,Paralichthys dentatus, using their scales collected by the VMRC’s Biological where A is the sample size for ageing sum- Sampling Program in 2015. Of 884 aged mer flounder in 2015; θa stands for the pro- fish, 371 and 513 fish were collected in portion of age a fish in a catch. Va and Ba Chesapeake Bay (bay fish) and Virginia represent variance components within and waters of the Atlantic Ocean (ocean fish), between length intervals for age a, respec- respectively. The average bay fish age tively; CV is the coefficient of variation; L was 3.7 years with a standard deviation was the total number of summer flounder of 1.8 and a standard error of 0.09. Ten used by VMRC to estimate length distri- age classes (1 to 10) were represented in bution of the catches from 2009 to 2013. the bay fish, comprising fish from the 2005 θa, Va, Ba, and CV were calculated using to 2014 year classes. The bay fish sample pooled age-length data of summer floun- in 2015 was dominated by the year class der collected from 2009 to 2013 and us- of 2012 with 33%. The average ocean ing equations in Quinn and Deriso (1999). fish age was 4.9 years with a standard For simplicity, the equations are not listed deviation of 2 and a standard error of 0.09. here. The equation (12.1) indicates that Thirteen age classes (1 to 12, and 15) were the more fish that are aged, the smaller represented in the ocean fish, comprising the CV (or higher precision) that will be fish from the 2000, and 2003 to 2014 year obtained. Therefore, the criterion to age classes. The ocean fish sample in 2015 A (number) of fish is that A should be a was dominated by the year classes of 2010 number above which there is only a 1% CV and 2009 with 23% and 18%, respectively. reduction for the most major age in catch We also aged a total of 294 fish using by aging an additional 100 or more fish. Fi- their otoliths in addition to ageing their nally, Al is A multiplied by the proportion scales. The otolith ages were compared to of length interval l from the length distribu- the scale ages to examine how close both tion of the 2009 to 2013 catch. Al is num- ages were to one another (see details in ber of fish to be aged for length interval l Results). in 2015.

12.2.2 Handling of collection 12.2 METHODS Sagittal otoliths (hereafter, referred to as "otoliths") and scales were received by 12.2.1 Sample size for ageing the Age & Growth Laboratory in labeled coin envelopes, and were sorted based on We estimated sample sizes for ageing sum- date of capture, their envelope labels were mer flounder collected in both Chesapeake verified against VMRC’s collection data, Bay and Virginia waters of the Atlantic and each fish assigned a unique Age and Ocean in 2015, respectively, using a two- Growth Laboratory identification number. stage random sampling method (Quinn and All otoliths and scales were stored dry Deriso 1999) to increase precision in esti- within their original labeled coin envelopes; mates of age composition from fish sampled otoliths were contained inside protective efficiently and effectively. The basic equa- Axygen 2.0 ml microtubes.

108 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS

12.2.3 Preparation in a ceramic "Coors" spot plate well and baked in a Thermolyne 1400 furnace at Scales 400 ◦C. Baking time was dependent on the otolith’s size and gauged by color, with a Summer flounder scales were prepared for light caramel color desired. Once a suit- age and growth analysis by making ac- able color was achieved the baked otolith etate impressions of the scale microstruc- was embedded in epoxy resin with its dis- ture. Due to extreme variation in the size tal surface orientated downwards and al- and shape of scales from individual fish, lowed to harden overnight. The otoliths we selected only those scales that had even were viewed by eye and, when necessary, margins and which were of uniform size. under a stereo microscope to identify the We selected a range of four to six pre- location of the core, and the position of the ferred scales (based on overall scale size) core was marked using a permanent marker from each fish, making sure that only non- across the epoxy resin surface. At least regenerated scales were used. Scale im- one transverse cross-section (hereafter, re- pressions were made on extruded clear ac- ferred to as "thin-section") was then re- etate sheets (25 mm x 75 mm) with a moved from the marked core of each otolith TM Carver Laboratory Heated Press (model using a Buehler IsoMet low-speed saw "C"). The scales were pressed with the fol- equipped with two, 3-inch diameter, Nor- lowing settings: ton diamond grinding wheels (hereafter, re- ferred to as "blades"), separated by a stain- Pressure: 15000 psi less steel spacer of 0.5 mm (diameter 2.5"). Temperature: 77 ◦C (170 ◦F) The otolith was positioned so the blades Time: 5 to 10 min straddled each side of the otolith focus. It was crucial that this cut be perpendicu- summer flounder scales that were the size lar to the long axis of the otolith. Failure of a quarter (coin) or larger, were pressed to do so resulted in broadening and dis- individually for up to twenty minutes. Af- torted winter growth zones. A proper cut ter pressing, the impressions were viewed resulted in annuli that were clearly defined with a Bell and Howell microfiche reader and delineated. Once cut, thin-sections and checked again for regeneration and in- were placed on labeled glass slides and cov- complete margins. Impressions that were ered with a thin layer of Flo-texx mounting too light, or when all scales were regener- medium that not only fixed the sections to ated a new impression was made using dif- the slide, but more importantly, provided ferent scales from the same fish. enhanced contrast and greater readability Click here to obtain the protocol at the by increasing light transmission through CQFE website on how to prepare scale im- the thin-section. pression for ageing summer flounder. Click here to obtain the protocol at the CQFE website on how to prepare Otoliths otolith thin-section for ageing summer flounder. We used our thin-section and bake tech- nique to process spadefish sagittal otoliths (hereafter, referred to as "otoliths") for age 12.2.4 Readings determination. Otolith preparation began by randomly selecting either the right or The CQFE system assigns an age class to left otolith. Each whole otolith was placed a fish based on a combination of reading

109 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS the information contained in its otolith, the before the end of the species’ annulus for- date of its capture, and the species-specific mation period, with three visible annuli period when it deposits its annulus. Each and some translucent growth after the last year, as the fish grows, its otoliths grow and annulus, would be assigned an age class leave behind markers of their age, called of "x+(x+1)" or 3+(3+1), noted as 3+4. annuli. Technically, an otolith annulus is This is the same age-class assigned to a the combination of both the opaque and fish with four visible annuli captured af- the translucent bands. In practice, only the ter the end of June 30, the period of an- opaque bands are counted as annuli. The nulus formation, which would be noted as number of these visible dark bands replaces 4+4. "x" in our notation below, and is the initial Summer flounder scales are also consid- "age" assignment of the fish. ered to have a deposition between January Second, the otolith section is examined and June (Bolz et al. 1999 and modified for translucent growth. If no translucent by CQFE), and age class assignment using growth is visible beyond the last dark an- these hard-parts is conducted in the same nulus, the otolith is called "even" and no way as otoliths. modification of the assigned age is made. All summer flounder samples (scale press- The initial assigned age, then, is the age ings and sectioned otoliths) were aged by class of the fish. Any growth beyond the two different readers in chronological order last annulus can be interpreted as either based on collection date, without knowl- being toward the next age class or within edge of previously estimated ages or the the same age class. If translucent growth specimen lengths. When the readers’ ages is visible beyond the last dark annulus, a agreed, that age was assigned to the fish. "+" is added to the notation. When the two readers disagreed, both read- By convention all fish in the Northern ers sat down together and re-aged the fish Hemisphere are assigned a birth date of again without any knowledge of previously January 1. In addition, each species has a estimated ages or lengths, then assigned a specific period during which it deposits the final age to the fish. When the age readers dark band of the annulus. If the fish is cap- were unable to agree on a final age, the fish tured after the end of the species-specific was excluded from further analysis. annulus deposition period and before Jan- uary 1, it is assigned an age class notation Scales of "x+x", where "x" is the number of dark bands in the otolith. If the fish is cap- tured between January 1 and the end of We determined fish age by viewing acetate the species-specific annulus deposition pe- impressions of scales (Figure 12.1) with a riod, it is assigned an age class notation standard Bell and Howell R-735 microfiche of "x+(x+1)". Thus, any growth beyond reader equipped with 20 and 29 mm lenses. the last annulus, after its "birthday", but Annuli on summer flounder scales are iden- before the dark band deposition period, is tified based on two scale microstructure interpreted as being toward the next age features, "crossing over" and circuli dis- class. ruption. Primarily, "crossing over" in the lateral margins near the posterior/ante- For example, summer flounder otolith de- rior interface of the scale is used to deter- position occurs between January and April mine the origin of the annulus. Here com- (Bolz et al. 2000). A summer flounder pressed circuli (annulus) "cross-over" the captured between January 1 and April 30, previously deposited circuli of the previous

110 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS

entire anterior field of the scale. This event is further amplified by the presence of con- cave circuli neighboring both directly above and below the annulus. The first year’s annulus can be difficult to locate on some scales. It is typically best identified in the lateral field of the anterior portion of the scale. The distance from the focus to the first year’s annulus is typically larger with respect to the following annuli. For the an- nuli two through six, summer growth gen- erally decreases proportionally. For ages greater than six, a crowding effect of the annuli near the outer margins of the scale is observed. This crowding effect creates difficulties in edge interpretation. At this point it is best to focus on the straighten- ing of the circuli at the anterior margins of Figure 12.1: Scale impression of a 1 year-old the scale. summer flounder When ageing young summer flounder, zero through age two, extreme caution must be taken as not to over age the structure. In year’s growth. Typically annuli of the first young fish there is no point of reference to three years can be observed transversing aid in the determination of the first year; this interface as dark bands. These bands this invariably results in over examination remain consistent throughout the posterior of the scale and such events as hatching or field and rejoin the posterior/anterior in- saltwater incursion marks (checks) may be terface on the opposite side of the focus. interpreted as the first year. Annuli can also be observed in the anterior lateral field of the scale. Here the annuli typically reveal a pattern of discontinuous Otoliths and suddenly breaking segmented circuli. This event can also be distinguished by the All thin-sections were aged by two different presence of concentric white lines, which readers using a Nikon SMZ1000 stereo mi- are typically associated with the disruption croscope under transmitted light and dark- of circuli. field polarization at between 8 and 20 times magnification (Figure 12.2). Each reader Annuli can also be observed bisecting the aged all of the otolith samples. By conven- perpendicular plain of the radial striations in the anterior field of the scale. Radii em- anate out from the focus of the scale to- wards the outer corner margins of the an- terior field. These radial striations consist mainly of segmented concave circuli. The point of intersection between radii and an- nuli results in a "straightening out" of the Figure 12.2: Otolith thin-section of a 4 year- concave circuli. This straightening of the old summer flounder with the last annulus on circuli should be consistent throughout the the edge of the thin-section

111 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS tion an annulus is identified as the narrow ings from the entire sample for the cur- opaque zone, or winter growth. Typically rent year were used to examine the differ- the first year’s annulus can be determined ence between two readers. A random sub- by first locating the focus of the otolith. sample of 50 fish from the current year was The focus is generally located, depending selected for second readings to examine the on preparation, in the center of the otolith, difference within a reader. Fifty otoliths and is visually well defined as a dark oblong randomly selected from fish aged in 2000 region. The first year’s annulus can be lo- were used to examine the time-series bias cated directly below the focus, along the within each reader. A figure of 1:1 equiv- outer ridge of the sulcal groove on the ven- alence was used to illustrate those differ- tral and dorsal sides of the otolith. This ences (Campana et al. 1995). All statistics insertion point along the sulcal ridge re- analyses were performed in R 3.2.2 (R Core sembles a check mark (not to be confused Team 2012). with a false annulus). Here the annulus can be followed outwards along the ventral and dorsal surfaces where it encircles the focus. 12.3 RESULTS Subsequent annuli also emanate from the sulcal ridge; however, they do not encir- 12.3.1 Sample size cle the focus, but rather travel outwards to the distal surface of the otolith. To We estimated a sample size of 381 bay sum- be considered a true annulus, each annu- mer flounder in 2015, ranging in length in- lus must be rooted in the sulcus and travel terval from 12 to 29 inches (Table 12.1). without interruption to the distal surface of This sample size provided a range in CV for the otolith. The annuli in summer flounder age composition approximately from the have a tendency to split as they advance to- smallest CV of 6% for age 2 to the largest wards the distal surface. As a result, it is CV of 20% for age 6 of the bay fish. We critical that reading path proceed in a di- randomly selected and aged 371 fish from rection down the sulcal ridge and outwards 476 summer flounder collected by VMRC to the distal surface. in Chesapeake Bay in 2015. We fell short Click here to obtain the protocol at in our over-all collections for this optimal the CQFE website on how to age sum- length-class sampling estimate by 37 fish. mer flounder using their otolith thin- We were short of few fish from the major sections. length intervals (The interval requires 10 or more fish), as a result, the precision for the estimates of major age groups would not be 12.2.5 Comparison Tests influenced significantly. We estimated a sample size of 433 ocean A symmetry test (Hoenig et al. 1995) and summer flounder in 2015, ranging in length coefficient of variation (CV) analysis were interval from 11 to 33 inches (Table 12.2). used to detect any systematic difference This sample size provided a range in CV for and precision on age readings, respectively, age composition approximately from the for following comparisons: 1) between the smallest CV of 8% for age 3 to the largest two readers in the current year; 2) within CV of 22% for age 8 of the ocean fish. We each reader in the current year; 3) time- randomly selected and aged 513 fish from series bias between the current and previ- 615 summer flounder collected by VMRC ous years within each reader; and 4) be- in Virginia waters of the Atlantic Ocean in tween scale and otoliths ages. The read- 2015. We fell short in our over-all collec-

112 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS tions for this optimal length-class sampling of fish aged in 2000 with a CV of 3% (test of estimate by 32 fish. However, we were short symmetry: χ2 = 2.67, df = 3, P = 0.4459). of no fish from the major length intervals Reader 2 had an agreement of 68% (1 year (The interval requires 10 or more fish), as or less agreement of 88%) with a CV of a result, the precision for the estimates of 12.8% (test of symmetry: χ2 = 16, df = 9, major age groups would not be influenced P = 0.0669). significantly. Of the 371 bay summer flounder aged with scales, 10 age classes (1 to 10) were repre- 12.3.2 Scales sented (Table 12.3). The average age for the sample was 3.7 years. The standard Both readers had moderate self-precision. deviation and standard error were 1.8 and Specifically, there was no significant differ- 0.09, respectively. Year-class data (Figure ence between the first and second readings 12.4) indicates that recruitment into the for Reader 1 with an agreement of 64% (1 fishery in Chesapeake Bay begins at age 1, year or less agreement of 96%) and a CV of which corresponds to the 2014 year-class 5.9% (test of symmetry: χ2 = 9.8, df = 9, P for summer flounder caught in 2015. Sum- = 0.3669), and there was no significant dif- mer flounder in the sample in 2015 was ference between the first and second read- dominated by the year class of 2012 with ings for Reader 2 with an agreement of 64% 33%. The sex ratio of male to female was (1 year or less agreement of 92%) and a CV 1:48 for the bay fish. of 8.2% (test of symmetry: χ2 = 12.67, df = 10, P = 0.2429). There was an evidence of systematic disagreement between Reader 1 and Reader 2 with an agreement of 63% (1 year or less agreement of 91%) and a CV of 8.2% (test of symmetry: χ2 = 89.98, df = 32, P < 0.0001) (Figure 12.3).

Figure 12.4: Year-class frequency distribution for summer flounder collected in Chesapeake Bay, Virginia for ageing in 2015. Distribu- tion is broken down by sex and estimated using scale ages. ’Unknown’ represents gonads that were not available for examination or were not examined for sex during sampling.

Figure 12.3: Between-reader comparison of scale age estimates for summer flounder col- Of the 513 ocean summer flounder aged lected in Chesapeake Bay and Virginia waters with scales, 13 age classes (1 to 12, and of the Atlantic Ocean in 2015. 15) were represented (Table 12.4). The average age for the sample was 4.9 years. There was no time-series bias for both read- The standard deviation and standard error ers. Reader 1 had an agreement of 84% (1 were 2 and 0.09, respectively. Year-class year or less agreement of 100%) with ages data (Figure 12.5) indicates that recruit-

113 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS ment into the fishery in Virginia waters of Atlantic ocean begins at age 1, which cor- responds to the 2014 year-class for summer flounder caught in 2015. Summer flounder in the sample in 2015 was dominated by the year classes of 2010 and 2009 with 23% and 18%, respectively. The sex ratio of male to female was 1:1.15 for the ocean fish.

Figure 12.6: Between-reader comparison of otolith age estimates for summer flounder col- lected in Chesapeake Bay and Virginia waters of the Atlantic Ocean in 2015.

There was no time-series bias for both read- ers. Reader 1 had an agreement of 92% with ages of fish aged in 2003 with a CV of 1.9% (test of symmetry: χ2 = 4, df = 4, Figure 12.5: Year-class frequency distribution P = 0.406). Reader 2 had an agreement of for summer flounder collected in Virginia wa- ters of the Atlantic Ocean for ageing in 2015. 94% with a CV of 0.8% (test of symmetry: 2 Distribution is broken down by sex and esti- χ = 3, df = 3, P = 0.3916). mated using scale ages. ’Unknown’ represents Of the 294 summer flounder aged with gonads that were not available for examination or were not examined for sex during sampling. otoliths, 14 age classes (1 to 13, and 15) were represented (Table 12.5). The aver- age age for the sample was 4.9 years. The standard deviation and standard error were 2.3 and 0.13, respectively. 12.3.3 Otoliths

Both readers had high self-precision. 12.3.4 Comparison of scale and Specifically, there was no significant differ- otolith ages ence between the first and second readings for Reader 1 with an agreement of 90% and We aged 293 summer flounder using scales a CV of 1.6% (test of symmetry: χ2 = 5, df and otoliths (Excluding 1 fish with otolith- = 5, P = 0.4159), and there was no signif- age only). There was an evidence of sys- icant difference between the first and sec- tematic disagreement between otolith and ond readings for Reader 2 with an agree- scale ages (test of symmetry: χ2 = 33.91, ment of 88% and a CV of 1.6% (test of df = 20, P = 0.0267) with an average CV of symmetry: χ2 = 6, df = 5, P = 0.3062). 7.3%. There was an agreement of 61% be- There was no evidence of systematic dis- tween scale and otoliths ages whereas scales agreement between Reader 1 and Reader 2 were assigned a lower and higher age than with an agreement of 88% (1 year or less otoliths for 28% and 11% of the fish, re- agreement of 99%) and a CV of 1.8% (test spectively (Figure 12.7). There was also an of symmetry: χ2 = 14.14, df = 13, P = evidence of bias between otolith and scale 0.3639) (Figure 12.6). ages using an age bias plot(Figure 12.8),

114 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS with scale generally assigned higher ages 12.4 REFERENCES for younger fish and lower ages for older fish than otolith age estimates. Bolz, G., R. Monaghan, K. Lang, R. Gre- gory, and J. Burnett. 2000. Proceedings of the summer flounder ageing work- shop, 1-2 February 1999, Woods Hole, MA. Massachusetts. US Dep. Com- merce, NOAA Tech. Memo. NMFS NE 156; 15 p. Campana, S.E., M.C. Annand, and J.I. McMillan. 1995. Graphical and statis- tical methods for determining the con- sistency of age determinations. Trans. Am. Fish. Soc. 124:131-138. Figure 12.7: Comparison of scale and otolith Hoenig, J.M., M.J. Morgan, and C.A. age estimates for summer flounder collected in Brown. 1995. Analyzing differences be- Chesapeake Bay and Virginia waters of the At- tween two age determination methods lantic Ocean in 2015. by tests of symmetry. Can. J. Fish. Aquat. Sci. 52:364-368. Quinn, T. J. II, and R. B. Deriso. 1999. Quantitative Fish Dynamics. Oxford Univeristy Press. New York. R Core Team (2012). R: A lan- guage and environment for statistical computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org.

Figure 12.8: Age-bias plot for summer flounder scale and otolith age estimates in 2015.

12.3.5 Age-Length-Key (ALK)

We developed an age-length-key for both bay (Table 12.6) and ocean fish (Table 12.7) using scale ages, separately. The ALK can be used in the conversion of numbers-at-length in the estimated catch to numbers-at-age using scale ages. The table is based on VMRC’s stratified sam- pling of landings by total length inch inter- vals.

115 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS

Table 12.1: Number of bay summer flounder collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 12 - 12.99 5 0 0 5 13 - 13.99 6 0 0 6 14 - 14.99 70 86 75 0 15 - 15.99 58 70 60 0 16 - 16.99 45 64 45 0 17 - 17.99 39 73 39 0 18 - 18.99 31 53 36 0 19 - 19.99 28 45 31 0 20 - 20.99 21 29 29 0 21 - 21.99 22 19 19 3 22 - 22.99 15 14 14 1 23 - 23.99 11 9 9 2 24 - 24.99 5 9 9 0 25 - 25.99 5 2 2 3 26 - 26.99 5 2 2 3 27 - 27.99 5 0 0 5 28 - 28.99 5 1 1 4 29 - 29.99 5 0 0 5 Totals 381 476 371 37 (Go back to text)

116 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS

Table 12.2: Number of ocean summer flounder collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 11 - 11.99 5 0 0 5 12 - 12.99 5 0 0 5 13 - 13.99 5 1 1 4 14 - 14.99 34 54 43 0 15 - 15.99 56 97 72 0 16 - 16.99 58 81 62 0 17 - 17.99 47 71 64 0 18 - 18.99 34 45 45 0 19 - 19.99 24 26 26 0 20 - 20.99 23 32 29 0 21 - 21.99 17 30 19 0 22 - 22.99 21 37 27 0 23 - 23.99 21 35 30 0 24 - 24.99 17 30 26 0 25 - 25.99 14 25 18 0 26 - 26.99 11 23 23 0 27 - 27.99 10 13 13 0 28 - 28.99 6 8 8 0 29 - 29.99 5 4 4 1 30 - 30.99 5 2 2 3 31 - 31.99 5 0 0 5 32 - 32.99 5 1 1 4 33 - 33.99 5 0 0 5 Totals 433 615 513 32 (Go back to text)

117 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS

Table 12.3: The number of summer flounder assigned to each total length-at-age category for 371 fish sampled for scale age determination in Chesapeake Bay, Virginia during 2015.

Age Interval 1 2 3 4 5 6 7 8 9 10 Totals 14 - 14.99 24 22 20 7 1 1 0 0 0 0 75 15 - 15.99 3 20 28 7 2 0 0 0 0 0 60 16 - 16.99 0 7 28 2 5 2 1 0 0 0 45 17 - 17.99 0 5 16 6 8 3 1 0 0 0 39 18 - 18.99 0 1 12 8 9 3 2 1 0 0 36 19 - 19.99 0 1 10 7 6 4 3 0 0 0 31 20 - 20.99 0 1 4 10 8 4 1 0 1 0 29 21 - 21.99 0 0 3 2 4 5 3 1 1 0 19 22 - 22.99 0 0 0 0 5 6 2 1 0 0 14 23 - 23.99 0 0 0 3 2 3 1 0 0 0 9 24 - 24.99 0 0 0 1 0 2 2 3 1 0 9 25 - 25.99 0 0 0 0 0 0 0 1 1 0 2 26 - 26.99 0 0 0 0 0 1 1 0 0 0 2 28 - 28.99 0 0 0 0 0 0 0 0 0 1 1 Totals 27 57 121 53 50 34 17 7 4 1 371 (Go back to text)

118 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS

Table 12.4: The number of summer flounder assigned to each total length-at-age category for 513 fish sampled for scale age determination in Virginia waters of Atlantic ocean during 2015.

Age Interval 1 2 3 4 5 6 7 8 9 10 11 12 15 Totals 13 - 13.99 0 1 0 0 0 0 0 0 0 0 0 0 0 1 14 - 14.99 5 14 10 4 7 3 0 0 0 0 0 0 0 43 15 - 15.99 1 21 18 13 7 8 3 1 0 0 0 0 0 72 16 - 16.99 1 6 14 16 17 5 2 0 0 1 0 0 0 62 17 - 17.99 0 6 12 13 18 10 3 1 0 0 0 1 0 64 18 - 18.99 0 3 5 6 14 12 4 1 0 0 0 0 0 45 19 - 19.99 0 3 6 4 7 2 1 2 0 1 0 0 0 26 20 - 20.99 0 0 6 4 9 4 2 1 2 1 0 0 0 29 21 - 21.99 0 0 0 3 9 2 4 1 0 0 0 0 0 19 22 - 22.99 0 0 0 6 7 9 3 1 0 1 0 0 0 27 23 - 23.99 0 0 1 4 7 8 5 2 2 1 0 0 0 30 24 - 24.99 0 0 0 1 5 12 3 1 3 0 1 0 0 26 25 - 25.99 0 0 0 0 6 6 4 2 0 0 0 0 0 18 26 - 26.99 0 0 0 0 5 8 5 2 3 0 0 0 0 23 27 - 27.99 0 0 0 1 0 3 4 3 1 0 1 0 0 13 28 - 28.99 0 0 0 0 1 1 0 2 1 1 1 0 1 8 29 - 29.99 0 0 0 0 0 1 1 2 0 0 0 0 0 4 30 - 30.99 0 0 0 0 0 0 0 0 1 0 0 1 0 2 32 - 32.99 0 0 0 0 0 0 0 0 0 0 1 0 0 1 Totals 7 54 72 75 119 94 44 22 13 6 4 2 1 513 (Go back to text)

119 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS

Table 12.5: The number of summer flounder assigned to each total length-at-age category for 294 fish sampled for otolith age determination in Chesapeake Bay and Virginia waters of Atlantic Ocean during 2015.

Age Interval 1 2 3 4 5 6 7 8 9 10 11 12 13 15 Totals 14 - 14.99 8 8 5 2 1 0 0 1 0 0 0 0 0 0 25 15 - 15.99 1 13 12 4 1 5 2 2 1 1 0 0 0 0 42 16 - 16.99 0 5 12 8 5 4 3 0 0 0 0 0 1 0 38 17 - 17.99 0 5 11 4 7 4 4 0 0 0 0 0 0 0 35 18 - 18.99 0 0 5 4 2 8 3 2 1 1 0 0 0 0 26 19 - 19.99 0 1 8 1 0 2 1 2 0 0 0 0 0 0 15 20 - 20.99 0 0 3 4 6 3 1 0 0 0 0 0 0 0 17 21 - 21.99 0 0 1 2 3 3 5 0 1 0 0 0 0 0 15 22 - 22.99 0 0 0 2 5 7 1 2 0 0 0 0 0 0 17 23 - 23.99 0 0 0 3 3 7 2 0 0 0 0 0 0 0 15 24 - 24.99 0 0 0 2 2 5 2 2 1 0 1 0 0 0 15 25 - 25.99 0 0 0 0 0 4 0 3 1 0 0 0 0 0 8 26 - 26.99 0 0 0 0 0 4 2 2 0 0 0 0 0 0 8 27 - 27.99 0 0 0 0 0 2 2 3 0 0 0 1 0 0 8 28 - 28.99 0 0 0 0 0 1 0 2 1 0 2 0 0 1 7 29 - 29.99 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 30 - 30.99 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 32 - 32.99 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 Totals 9 32 57 36 35 59 28 23 6 2 4 1 1 1 294 (Go back to text)

120 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS

Table 12.6: Age-Length key, as proportion-at-age in each 1-inch length interval, based on scale ages for summer flounder sampled in Chesapeake Bay, Virginia during 2015.

Age Interval 1 2 3 4 5 6 7 8 9 10 14 - 14.99 0.32 0.29 0.27 0.09 0.01 0.01 0 0 0 0 15 - 15.99 0.05 0.33 0.47 0.12 0.03 0 0 0 0 0 16 - 16.99 0 0.16 0.62 0.04 0.11 0.04 0.02 0 0 0 17 - 17.99 0 0.13 0.41 0.15 0.21 0.08 0.03 0 0 0 18 - 18.99 0 0.03 0.33 0.22 0.25 0.08 0.06 0.03 0 0 19 - 19.99 0 0.03 0.32 0.23 0.19 0.13 0.1 0 0 0 20 - 20.99 0 0.03 0.14 0.34 0.28 0.14 0.03 0 0.03 0 21 - 21.99 0 0 0.16 0.11 0.21 0.26 0.16 0.05 0.05 0 22 - 22.99 0 0 0 0 0.36 0.43 0.14 0.07 0 0 23 - 23.99 0 0 0 0.33 0.22 0.33 0.11 0 0 0 24 - 24.99 0 0 0 0.11 0 0.22 0.22 0.33 0.11 0 25 - 25.99 0 0 0 0 0 0 0 0.5 0.5 0 26 - 26.99 0 0 0 0 0 0.5 0.5 0 0 0 28 - 28.99 0 0 0 0 0 0 0 0 0 1 (Go back to text)

121 CHAPTER 12. SUMMER FLOUNDER PARALICHTHYS DENTATUS

Table 12.7: Age-Length key, as proportion-at-age in each 1-inch length interval, based on scale ages for summer flounder sampled in Virginia waters of the Atlantic Ocean during 2015.

Age Interval 1 2 3 4 5 6 7 8 9 10 11 12 15 13 - 13.99 0 1 0 0 0 0 0 0 0 0 0 0 0 14 - 14.99 0.12 0.33 0.23 0.09 0.16 0.07 0 0 0 0 0 0 0 15 - 15.99 0.01 0.29 0.25 0.18 0.1 0.11 0.04 0.01 0 0 0 0 0 16 - 16.99 0.02 0.1 0.23 0.26 0.27 0.08 0.03 0 0 0.02 0 0 0 17 - 17.99 0 0.09 0.19 0.2 0.28 0.16 0.05 0.02 0 0 0 0.02 0 18 - 18.99 0 0.07 0.11 0.13 0.31 0.27 0.09 0.02 0 0 0 0 0 19 - 19.99 0 0.12 0.23 0.15 0.27 0.08 0.04 0.08 0 0.04 0 0 0 20 - 20.99 0 0 0.21 0.14 0.31 0.14 0.07 0.03 0.07 0.03 0 0 0 21 - 21.99 0 0 0 0.16 0.47 0.11 0.21 0.05 0 0 0 0 0 22 - 22.99 0 0 0 0.22 0.26 0.33 0.11 0.04 0 0.04 0 0 0 23 - 23.99 0 0 0.03 0.13 0.23 0.27 0.17 0.07 0.07 0.03 0 0 0 24 - 24.99 0 0 0 0.04 0.19 0.46 0.12 0.04 0.12 0 0.04 0 0 25 - 25.99 0 0 0 0 0.33 0.33 0.22 0.11 0 0 0 0 0 26 - 26.99 0 0 0 0 0.22 0.35 0.22 0.09 0.13 0 0 0 0 27 - 27.99 0 0 0 0.08 0 0.23 0.31 0.23 0.08 0 0.08 0 0 28 - 28.99 0 0 0 0 0.12 0.12 0 0.25 0.12 0.12 0.12 0 0.12 29 - 29.99 0 0 0 0 0 0.25 0.25 0.5 0 0 0 0 0 30 - 30.99 0 0 0 0 0 0 0 0 0.5 0 0 0.5 0 32 - 32.99 0 0 0 0 0 0 0 0 0 0 1 0 0 (Go back to text)

122 Chapter 13

TAUTOG Tautoga onitis CHAPTER 13. TAUTOG TAUTOGA ONITIS

13.1 INTRODUCTION is:

V We aged a total of 277 tautog,Tautoga oni- A = a (13.1) θ2CV 2 + B /L tis, using their opercula collected by the a a VMRC’s Biological Sampling Program in 2015. Of 277 aged fish, 220 and 57 fish where A is the sample size for ageing tau- were collected in Chesapeake Bay (bay fish) tog in 2015; θa stands for the proportion of and Virginia waters of the Atlantic Ocean age a fish in a catch. Va and Ba represent (ocean fish), respectively. The average age variance components within and between for the bay fish was 6.1 years with a stan- length intervals for age a, respectively; CV dard deviation of 1.6 and a standard er- is the coefficient of variation; L was the to- ror of 0.11. Eleven age classes (3 to 10, 13 tal number of tautog used by VMRC to to 14, and 18) were represented in the bay estimate length distribution of the catches fish, comprising fish from the 1997, 2001 to from 2009 to 2013. θa, Va, Ba, and CV were 2002, and 2005 to 2012 year classes. The calculated using pooled age-length data of bay fish sample in 2015 was dominated by tautog collected from 2009 to 2013 and us- the year class of 2009 with 46%. The av- ing equations in Quinn and Deriso (1999). erage age for the ocean fish was 10.4 years For simplicity, the equations are not listed with a standard deviation of 6.7 and a stan- here. The equation (13.1) indicates that dard error of 0.89. Eighteen age classes (4 the more fish that are aged, the smaller to 10, 12 to 13, 15, 17 to 18, 20, 22 to 24, 27, the CV (or higher precision) that will be and 31) were represented in the ocean fish, obtained. Therefore, the criterion to age comprising fish from the 1984, 1988, 1991 A (number) of fish is that A should be a to 1993, 1995, 1997 to 1998, 2000, 2002 to number above which there is only a 1% CV 2003, and 2005 to 2011 year classes. The reduction for the most major age in catch ocean fish sample in 2015 was dominated by aging an additional 100 or more fish. Fi- by the year class of 2009 with 25%. We nally, Al is A multiplied by the proportion also aged a total of 273 fish using their of length interval l from the length distribu- otoliths in addition to ageing their oper- tion of the 2009 to 2013 catch. Al is num- cula. The otolith ages were compared to ber of fish to be aged for length interval l the operculum ages to examine how close in 2015. both ages were to one another (see details in Results). 13.2.2 Handling of collection 13.2 METHODS Sagittal otoliths (hereafter, referred to as "otoliths") and opercula were received by 13.2.1 Sample size for ageing the Age & Growth Laboratory in labeled coin envelopes, and were sorted based on We estimated sample sizes for ageing tau- date of capture. Their envelope labels were tog collected in both Chesapeake Bay and verified against VMRC’s collection data, Virginia waters of the Atlantic Ocean in and each fish assigned a unique Age and 2015, respectively, using a two-stage ran- Growth Laboratory identification number. dom sampling method (Quinn and Deriso All otoliths and opercula were stored dry 1999) to increase precision in estimates within their original labeled coin envelopes; of age composition from fish sampled effi- otoliths were contained inside protective ciently and effectively. The basic equation Axygen 2.0 ml microtubes.

124 CHAPTER 13. TAUTOG TAUTOGA ONITIS

13.2.3 Preparation straddled each side of the otolith focus. It was crucial that this cut be perpendicu- Opercula lar to the long axis of the otolith. Failure to do so resulted in broadening and dis- Tautog opercula were boiled for several torted winter growth zones. A proper cut minutes to remove any attached skin and resulted in annuli that were clearly defined connective tissue. After boiling, opercula and delineated. Once cut, thin-sections were inspected for damage. If there were were placed on labeled glass slides and cov- no obvious flaws, the opercula was dried ered with a thin layer of Flo-texx mounting and then stored in a new, labeled enve- medium that not only fixed the sections to lope. the slide, but more importantly, provided enhanced contrast and greater readability Click here to obtain the protocol at the by increasing light transmission through CQFE website on how to prepare opercu- the thin-section. lum for ageing tautog. Click here to obtain the protocol at the CQFE website on how to prepare otolith Otoliths thin-section for ageing tautog.

We used our thin-section and bake tech- 13.2.4 Readings nique to process spadefish sagittal otoliths (hereafter, referred to as "otoliths") for age The CQFE system assigns an age class to determination. Otolith preparation began a fish based on a combination of reading by randomly selecting either the right or the information contained in its otolith, the left otolith. Each whole otolith was placed date of its capture, and the species-specific in a ceramic "Coors" spot plate well and period when it deposits its annulus. Each baked in a Thermolyne 1400 furnace at year, as the fish grows, its otoliths grow and 400 ◦C. Baking time was dependent on the leave behind markers of their age, called otolith’s size and gauged by color, with a annuli. Technically, an otolith annulus is light caramel color desired. Once a suit- the combination of both the opaque and able color was achieved the baked otolith the translucent bands. In practice, only the was embedded in epoxy resin with its dis- opaque bands are counted as annuli. The tal surface orientated downwards and al- number of these visible dark bands replaces lowed to harden overnight. The otoliths "x" in our notation below, and is the initial were viewed by eye and, when necessary, "age" assignment of the fish. under a stereo microscope to identify the location of the core, and the position of the Second, the otolith section is examined core was marked using a permanent marker for translucent growth. If no translucent across the epoxy resin surface. At least growth is visible beyond the last dark an- one transverse cross-section (hereafter, re- nulus, the otolith is called "even" and no ferred to as "thin-section") was then re- modification of the assigned age is made. moved from the marked core of each otolith The initial assigned age, then, is the age using a Buehler IsoMetTM low-speed saw class of the fish. Any growth beyond the equipped with two, 3-inch diameter, Nor- last annulus can be interpreted as either ton diamond grinding wheels (hereafter, re- being toward the next age class or within ferred to as "blades"), separated by a stain- the same age class. If translucent growth less steel spacer of 0.5 mm (diameter 2.5"). is visible beyond the last dark annulus, a The otolith was positioned so the blades "+" is added to the notation.

125 CHAPTER 13. TAUTOG TAUTOGA ONITIS

By convention all fish in the Northern or lengths, then assigned a final age to the Hemisphere are assigned a birth date of fish. When the age readers were unable to January 1. In addition, each species has a agree on a final age, the fish was excluded specific period during which it deposits the from further analysis. dark band of the annulus. If the fish is cap- tured after the end of the species-specific annulus deposition period and before Jan- Opercula uary 1, it is assigned an age class notation of "x+x", where "x" is the number of dark All prepared opercula were aged by two dif- bands in the otolith. If the fish is cap- ferent readers in chronological order based tured between January 1 and the end of on collection date, without knowledge of the species-specific annulus deposition pe- previously estimated ages or the specimen riod, it is assigned an age class notation lengths. Opercula were aged on a light of "x+(x+1)". Thus, any growth beyond table with no magnification (Figure 13.1). the last annulus, after its "birthday", but before the dark band deposition period, is interpreted as being toward the next age class.

For example, tautog otolith deposition oc- curs between May and July (Hostetter and Munroe 1993). A tautog captured between January 1 and July 31, before the end of the species’ annulus formation period, with three visible annuli and some translu- cent growth after the last annulus, would be assigned an age class of "x+(x+1)" or 3+(3+1), noted as 3+4. This is the same age-class assigned to a fish with four visi- ble annuli captured after the end of June 30, the period of annulus formation, which would be noted as 4+4. Figure 13.1: Operculum of a 7 year-old tautog Tautog opercula are also considered to have a deposition period of May through July (Hostetter and Munroe 1993), and age class assignment using these hard-parts is con- Otoliths ducted in the same way as otoliths. All otolith thin-sections were aged by two All tautog samples (opercula and sectioned different readers using a Nikon SMZ1000 otoliths) were aged by two different readers stereo microscope under transmitted light in chronological order based on collection and dark-field polarization at between 8 date, without knowledge of previously esti- and 20 times magnification (Figure 13.2). mated ages or the specimen lengths. When Each reader aged all of the otolith samples. the readers’ ages agreed, that age was as- signed to the fish. When the two read- ers disagreed, both readers sat down to- Click here to obtain the protocol at the gether and re-aged the fish again without CQFE website on how to age tautog using any knowledge of previously estimated ages their otolith thin-sections.

126 CHAPTER 13. TAUTOG TAUTOGA ONITIS

for age 2 of the bay fish. We aged all 220 tautog collected by VMRC in Chesapeake Bay in 2015. We fell short in our over- all collections for this optimal length-class sampling estimate by 194 fish. However, we were short of many fish from the major length intervals (The interval requires 10 or Figure 13.2: Otolith thin-section of 6 year-old more fish), as a result, the precision for the tautog estimates of major age groups would def- initely be influenced significantly. There- 13.2.5 Comparison Tests fore, precaution should be used when de- veloping ALK using these age data. A symmetry test (Hoenig et al. 1995) and We estimated a sample size of 398 ocean coefficient of variation (CV) analysis were tautog in 2015, ranging in length interval used to detect any systematic difference from 11 to 30 inches (Table 13.2). This and precision on age readings, respectively, sample size provided a range in CV for age for following comparisons: 1) between the composition approximately from the small- two readers in the current year; 2) within est CV of 10% for age 4 to the largest CV of each reader in the current year; 3) time- 21% for age 13 of the ocean fish. We aged series bias between the current and previ- all 57 tautog collected by VMRC in Vir- ous years within each reader; and 4) be- ginia waters of the Atlantic Ocean in 2015. tween operculum and otoliths ages. The We fell short in our over-all collections for readings from the entire sample for the cur- this optimal length-class sampling estimate rent year were used to examine the dif- by 342 fish. However, we were short of ference between two readers. A random many fish from the major length intervals sub-sample of 50 fish from the current year (The interval requires 10 or more fish), as was selected for second readings to examine a result, the precision for the estimates of the difference within a reader.Fifty otoliths major age groups would definitely be influ- randomly selected from fish aged in 2000 enced significantly. Therefore, precaution were used to examine the time-series bias should be used when developing ALK us- within each reader. A figure of 1:1 equiv- ing these age data. alence was used to illustrate those differ- ences (Campana et al. 1995). All statistics analyses were performed in R 3.2.2 (R Core 13.3.2 Opercula Team 2012).

Both readers had high self-precision. 13.3 RESULTS Specifically, there was no significant differ- ence between the first and second readings for Reader 1 with an agreement of 74% (1 13.3.1 Sample size year or less agreement of 96%) and a CV of 3.1% (test of symmetry: χ2 = 5.8, df We estimated a sample size of 414 bay tau- = 6, P = 0.446), and there was no signifi- tog in 2015, ranging in length interval from cant difference between the first and second 12 to 27 inches (Table 13.1). This sample readings for Reader 2 with an agreement of size provided a range in CV for age compo- 64% (1 year or less agreement of 94%) and sition approximately from the smallest CV a CV of 4.5% (test of symmetry: χ2 = 8.33, of 1% for age 16 to the largest CV of 22% df = 10, P = 0.5963). There was no evi-

127 CHAPTER 13. TAUTOG TAUTOGA ONITIS dence of systematic disagreement between Reader 1 and Reader 2 with an agreement of 70% (1 year or less agreement of 97%) and a CV of 3.5% (test of symmetry: χ2 = 26.73, df = 20, P = 0.143) (Figure 13.3).

Figure 13.4: Year-class frequency distribution for tautog collected in Chesapeake Bay, Vir- ginia for ageing in 2015. Distribution is bro- ken down by sex and estimated using opercu- lum ages. ’Unknown’ represents the fish go- nads that were not available for examination or were not examined for sex during sampling. Figure 13.3: Between-reader comparison of op- erculum age estimates for tautog collected in 18 age classes (4 to 10, 12 to 13, 15, 17 to Chesapeake Bay and Virginia waters of the At- lantic Ocean in 2015. 18, 20, 22 to 24, 27, and 31) were repre- sented (Table 13.4). The average age for the sample was 10.4 years. The standard There was no time-series bias for both read- deviation and standard error were 6.7 and ers. Reader 1 had an agreement of 68% (1 0.89, respectively. Year-class data (Figure year or less agreement of 90%) with ages of 13.5) indicates that recruitment into the fish aged in 2000 with a CV of 5.3% (test of fishery in Virginia waters of Atlantic ocean symmetry: χ2 = 6, df = 10, P = 0.8153). begins at age 4, which corresponds to the Reader 2 had an agreement of 80% (1 year 2011 year-class for tautog caught in 2015. or less agreement of 98%) with a CV of Tautog in the sample in 2015 was domi- 2.9% (test of symmetry: χ2 = 6, df = 6, P nated by the year class of 2009 with 25%. = 0.4232). The sex ratio of male to female was 1:1.71 Of the 220 bay tautog aged with opercula, for the ocean fish. 11 age classes (3 to 10, 13 to 14, and 18) were represented (Table 13.3). The av- 13.3.3 Otoliths erage age for the sample was 6.1 years. The standard deviation and standard error Both readers had high self-precision. were 1.6 and 0.11, respectively. Year-class Specifically, there was no significant differ- data (Figure 13.4) indicates that recruit- ence between the first and second readings ment into the fishery in Chesapeake Bay for Reader 1 with an agreement of 90% and begins at age 3, which corresponds to the a CV of 0.8% (test of symmetry: χ2 = 5, df 2012 year-class for tautog caught in 2015. = 5, P = 0.4159), and there was no signifi- Tautog in the sample in 2015 was domi- cant difference between the first and second nated by the year class of 2009 with 46%. readings for Reader 2 with an agreement The sex ratio of male to female was 1:0.93 of 88% and a CV of 1.2% (test of symme- for the bay fish. try: χ2 = 3.33, df = 4, P = 0.5037). There Of the 57 ocean tautog aged with opercula, was no evidence of systematic disagreement

128 CHAPTER 13. TAUTOG TAUTOGA ONITIS

0.2231).

Of the 273 tautog aged with otoliths, 19 age classes (4 to 16, 18 to 19, 22 to 23, 25, and 31) were represented (Table 13.5). The average age for the sample was 6.9 years. The standard deviation and standard error were 3.8 and 0.23, respectively.

Figure 13.5: Year-class frequency distribution 13.3.4 Comparison of operculum for tautog collected in Virginia waters of the and otolith ages Atlantic Ocean for ageing in 2015. Distribu- tion is broken down by sex and estimated using operculum ages. ’Unknown’ represents the fish We aged 273 tautog using opercula and gonads that were not available for examination or were not examined for sex during sampling. otoliths. There was no evidence of sys- tematic disagreement between otolith and operculum ages (test of symmetry: χ2 = between Reader 1 and Reader 2 with an 38.46, df = 28, P = 0.0899) with an aver- agreement of 88% (1 year or less agreement age CV of 5%. There was an agreement of of 97%) and a CV of 1.2% (test of symme- 61% between operculum and otoliths ages try: χ2 = 18.2, df = 20, P = 0.5742) (Fig- whereas opercula were assigned a lower and ure 13.6). There was no time-series bias higher age than otoliths for 18% and 21% of the fish, respectively (Figure 13.7). There was also little evidence of bias between otolith and operculum ages using an age bias plot(Figure 13.8), with no trend of ei- ther over-ageing younger or under-ageing older fish.

Figure 13.6: Between-reader comparison of otolith age estimates for tautog collected in Chesapeake Bay and Virginia waters of the At- lantic Ocean in 2015. for both readers. Reader 1 had an agree- ment of 94% with ages of fish aged in 2003 Figure 13.7: Comparison of operculum and otolith age estimates for tautog collected in with a CV of 0.6% (test of symmetry: χ2 Chesapeake Bay and Virginia waters of the At- = 3, df = 2, P = 0.2231). Reader 2 had lantic Ocean in 2015. an agreement of 94% with a CV of 0.7% (test of symmetry: χ2 = 3, df = 2, P =

129 CHAPTER 13. TAUTOG TAUTOGA ONITIS

Quinn, T. J. II, and R. B. Deriso. 1999. Quantitative Fish Dynamics. Oxford University Press. New York. R Core Team (2012). R: A lan- guage and environment for statistical computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org.

Figure 13.8: Age-bias plot for tautog opercu- lum and otolith age estimates in 2015.

13.3.5 Age-Length-Key (ALK)

We developed an age-length-key for both bay (Table 13.6) and ocean fish (Table 13.7) using operculum ages, separately. The ALK can be used in the conversion of numbers-at-length in the estimated catch to numbers-at-age using operculum ages. The table is based on VMRC’s stratified sampling of landings by total length inch intervals.

13.4 REFERENCES

Campana, S.E., M.C. Annand, and J.I. McMillan. 1995. Graphical and statis- tical methods for determining the con- sistency of age determinations. Trans. Am. Fish. Soc. 124:131-138. Hoenig, J.M., M.J. Morgan, and C.A. Brown. 1995. Analyzing differences be- tween two age determination methods by tests of symmetry. Can. J. Fish. Aquat. Sci. 52:364-368. Hostetter, E. B., and T. A. Munroe. 1993. Age, growth, and reproduction of tautog Tautoga onitis (Labridae: Perciformes) from coastal waters of Virginia. Fishery Bulletin 91: 45-64.

130 CHAPTER 13. TAUTOG TAUTOGA ONITIS

Table 13.1: Number of bay tautog collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 12 - 12.99 5 1 1 4 13 - 13.99 23 0 0 23 14 - 14.99 66 17 17 49 15 - 15.99 77 68 68 9 16 - 16.99 68 51 51 17 17 - 17.99 58 46 46 12 18 - 18.99 40 18 18 22 19 - 19.99 30 13 13 17 20 - 20.99 12 4 4 8 21 - 21.99 5 1 1 4 22 - 22.99 5 0 0 5 23 - 23.99 5 0 0 5 24 - 24.99 5 0 0 5 25 - 25.99 5 0 0 5 26 - 26.99 5 1 1 4 27 - 27.99 5 0 0 5 Totals 414 220 220 194 (Go back to text)

131 CHAPTER 13. TAUTOG TAUTOGA ONITIS

Table 13.2: Number of ocean tautog collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 11 - 11.99 5 0 0 5 13 - 13.99 10 0 0 10 14 - 14.99 35 0 0 35 15 - 15.99 63 1 1 62 16 - 16.99 79 6 6 73 17 - 17.99 35 3 3 32 18 - 18.99 31 6 6 25 19 - 19.99 21 4 4 17 20 - 20.99 21 7 7 14 21 - 21.99 14 7 7 7 22 - 22.99 16 4 4 12 23 - 23.99 17 3 3 14 24 - 24.99 7 2 2 5 25 - 25.99 5 3 3 2 26 - 26.99 19 3 3 16 27 - 27.99 5 6 6 0 28 - 28.99 5 2 2 3 29 - 29.99 5 0 0 5 30 - 30.99 5 0 0 5 Totals 398 57 57 342 (Go back to text)

132 CHAPTER 13. TAUTOG TAUTOGA ONITIS

Table 13.3: The number of tautog assigned to each total length-at-age category for 220 fish sampled for operculum age determination in Chesapeake Bay, Virginia during 2015.

Age Interval 3 4 5 6 7 8 9 10 13 14 18 Totals 12 - 12.99 0 0 1 0 0 0 0 0 0 0 0 1 14 - 14.99 0 6 7 3 1 0 0 0 0 0 0 17 15 - 15.99 1 10 21 33 3 0 0 0 0 0 0 68 16 - 16.99 0 4 9 27 10 1 0 0 0 0 0 51 17 - 17.99 0 0 4 26 14 1 0 0 1 0 0 46 18 - 18.99 0 0 2 10 0 4 0 2 0 0 0 18 19 - 19.99 0 2 0 2 4 3 2 0 0 0 0 13 20 - 20.99 0 0 0 0 1 0 0 2 0 1 0 4 21 - 21.99 0 0 0 0 0 0 0 1 0 0 0 1 26 - 26.99 0 0 0 0 0 0 0 0 0 0 1 1 Totals 1 22 44 101 33 9 2 5 1 1 1 220 (Go back to text)

133 CHAPTER 13. TAUTOG TAUTOGA ONITIS (Go 2015. during ocean Atlantic of T be1.:Tenme ftuo sindt ahttllnt-taectgr o 7fihsmldfroeclmaedtriaini ignawaters Virginia in determination age operculum for sampled fish 57 for category length-at-age total each to assigned tautog of number The 13.4: able akt text) to back 8-2.90000000000000100012 6 3 1 3 0 0 2 0 1 3 0 0 0 4 1 0 0 0 7 0 1 0 1 0 7 0 1 0 0 0 4 0 0 0 0 0 0 6 0 0 0 0 0 0 0 3 1 0 0 0 0 0 1 0 6 0 0 1 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 28.99 1 0 0 0 0 - 0 28 0 0 0 0 27.99 0 0 0 2 0 - 0 27 0 0 0 26.99 0 0 0 2 0 - 0 26 0 2 25.99 0 1 0 0 0 - 1 25 0 3 24.99 0 2 0 0 0 - 0 24 3 23.99 0 0 0 1 0 - 0 23 3 22.99 1 0 1 2 - 0 22 2 21.99 1 0 0 0 - 21 1 20.99 1 0 1 - 20 0 19.99 1 0 - 19 18.99 0 4 - 18 17.99 1 - 17 16.99 - 16 15 In 59 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 15.99 - oas281 57 1 1 1 2 2 1 2 1 4 2 1 2 1 6 6 14 8 2 Totals evl4567891 21 51 82 22 42 1Totals 31 27 24 23 22 20 18 17 15 13 12 10 9 8 7 6 5 4 terval Age

134 CHAPTER 13. TAUTOG TAUTOGA ONITIS Age terval 4 5 6 7 8 9 10 11 12 13 14 15 16 18 19 22 23 25 31 Totals Totals 40 34 112 47 9 4 4 2 2 1 1 4 2 3 1 3 1 2 1 273 - 12.99 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 In 12 14 - 14.9915 - 15.99 816 - 18 16.9917 - 5 17.99 17 718 - 18.99 2 2719 4 - 7 19.99 220 - 4 5 20.99 0 35 221 - 0 0 21.99 0 27 022 7 - 0 0 22.99 0 12 13 023 1 - 1 23.99 0 0 024 0 6 8 0 - 0 24.99 0 025 1 1 0 - 0 0 25.99 4 0 026 0 1 1 - 0 26.99 5 2 0 0 027 0 0 - 0 27.99 3 1 1 0 0 028 0 - 0 0 28.99 0 3 2 0 0 0 0 0 1 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 1 0 0 1 0 0 0 67 0 17 1 0 0 0 0 0 0 0 0 0 0 0 57 0 0 0 0 0 48 0 2 0 0 1 0 0 0 1 0 24 0 0 0 0 0 0 1 0 16 0 0 0 0 0 11 0 2 0 0 0 1 8 0 0 1 4 0 0 1 3 0 0 2 0 3 1 4 6 2 back to text) able 13.5: The number of tautog assigned to each total length-at-age category for 273 fish sampled for otolith age determination in Chesapeake Bay T (Go and Virginia waters of Atlantic Ocean during 2015.

135 CHAPTER 13. TAUTOG TAUTOGA ONITIS

Table 13.6: Age-Length key, as proportion-at-age in each 1-inch length interval, based on operculum ages for tautog sampled in Chesapeake Bay, Virginia during 2015.

Age Interval 3 4 5 6 7 8 9 10 13 14 18 12 - 12.99 0 0 1 0 0 0 0 0 0 0 0 14 - 14.99 0 0.35 0.41 0.18 0.06 0 0 0 0 0 0 15 - 15.99 0.01 0.15 0.31 0.49 0.04 0 0 0 0 0 0 16 - 16.99 0 0.08 0.18 0.53 0.2 0.02 0 0 0 0 0 17 - 17.99 0 0 0.09 0.57 0.3 0.02 0 0 0.02 0 0 18 - 18.99 0 0 0.11 0.56 0 0.22 0 0.11 0 0 0 19 - 19.99 0 0.15 0 0.15 0.31 0.23 0.15 0 0 0 0 20 - 20.99 0 0 0 0 0.25 0 0 0.5 0 0.25 0 21 - 21.99 0 0 0 0 0 0 0 1 0 0 0 26 - 26.99 0 0 0 0 0 0 0 0 0 0 1 (Go back to text)

136 CHAPTER 13. TAUTOG TAUTOGA ONITIS Age terval 4 5 6 7 8 9 10 12 13 15 17 18 20 22 23 24 27 31 - 15.99 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 In 15 16 - 16.9917 - 17.99 0.1718 - 18.99 0.6719 - 0.17 19.99 020 - 20.99 0.17 021 - 21.99 0.33 0 0.17 022 - 22.99 0.17 0 0.3323 - 23.99 0.17 0 0.29 0 0.33 024 - 24.99 0 0.43 0.75 0.3325 - 25.99 0 0.29 0 0 026 - 26.99 0 0 0.43 0 027 - 27.99 0 0 0.14 0 0 028 0.5 - 28.99 0 0 0.29 0 0 0 0 0 0 0 0.25 0 0 0 0 0 0 0 0.5 0 0 0.14 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.33 0 0 0 0 0.33 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.33 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.5 0 0 0.33 0.67 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.17 0.33 0 0 0 0 0 0 0 0 0 0 0 0 0.33 0 0 0 0 0 0.33 0.5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.33 0 0.17 0 0 0 0.17 0 0 0 0.5 0 0.17 0 0 0 0 0 0 0 0 0 0 0 0.5 back to text) able 13.7: Age-Length key, as proportion-at-age in each 1-inch length interval, based on operculum ages for tautog sampled in Virginia waters of T (Go the Atlantic Ocean during 2015.

137

Chapter 14

WEAKFISH Cynoscion regalis CHAPTER 14. WEAKFISH CYNOSCION REGALIS

14.1 INTRODUCTION only a 1% CV reduction for the most ma- jor age in catch by aging an additional 100 We aged a total of 243 weakfish, Cynoscion or more fish. Finally, Al is A multiplied regalis, collected by the VMRC’s Biologi- by the proportion of length interval l from cal Sampling Program for age and growth the length distribution of the 2009 to 2013 analysis in 2015. The weakfish ages ranged catch. Al is number of fish to be aged for from 1 to 5 years old with an average age length interval l in 2015. of 2.1, a standard deviation of 0.8, and a standard error of 0.05. Five age classes (1 to 5) were represented, comprising fish of 14.2.2 Handling of collections the 2010 to 2014 year-classes. The sample was dominated by fish from the year-class Otoliths were received by the Age & of 2013 with 60.1%. Growth Laboratory in labeled coin en- velopes, and were sorted by date of capture. Their envelope labels were verified against 14.2 METHODS VMRC’s collection data, and each fish was assigned a unique Age and Growth Labo- ratory identification number. All otoliths 14.2.1 Sample size for ageing were stored dry in their original labeled coin envelopes. We estimated sample size for ageing weak- fish in 2015 using a two-stage random sam- pling method (Quinn and Deriso 1999) to 14.2.3 Preparation increase precision in estimates of age com- position from fish sampled efficiently and Sagittal otoliths, hereafter, referred to as effectively. The basic equation is: "otoliths", were processed for age deter- mination following the methods described Va A = 2 2 (14.1) in Lowerre-Barbieri et al. (1994) with a θ CV + Ba/L a few modifications. The left or right otolith where A is the sample size for ageing weak- was randomly selected and attached, dis- fish in 2015; θa stands for the proportion tal side down, to a glass slide with clear TM of age a fish in a catch. Va and Ba repre- Crystalbond 509 adhesive. The otoliths sent variance components within and be- were viewed by eye and, when necessary, tween length intervals for age a, respec- under a stereo microscope to identify the tively; CV is the coefficient of variation; L location of the core, and the position of was the total number of weakfish used by the core was marked using a pencil across VMRC to estimate length distribution of the otolith surface. At least one trans- the catches from 2009 to 2013. θa, Va, Ba, verse cross-section (hereafter, referred to and CV were calculated using pooled age- as "thin-section") was then removed from length data of weakfish collected from 2009 the marked core of each otolith using a to 2013 and using equations in Quinn and Buehler IsoMetTM low-speed saw equipped Deriso (1999). For simplicity, the equations with two, 3-inch diameter, Norton diamond are not listed here. The equation (14.1) in- grinding wheels (hereafter, referred to as dicates that the more fish that are aged, "blades"), separated by a stainless steel the smaller the CV (or higher precision) spacer of 0.5 mm (diameter 2.5"). Thin- that will be obtained. Therefore, the cri- sections were placed on labeled glass slides terion to age A (number) of fish is that A and covered with a thin layer of Flo-texx should be a number above which there is mounting medium that not only fixed the

140 CHAPTER 14. WEAKFISH CYNOSCION REGALIS sections to the slide, but more importantly, thin-section. If the fish is captured be- provided enhanced contrast and greater tween January 1 and the end of the species- readability by increasing light transmission specific annulus deposition period, it is as- through the thin-sections. signed an age class notation of "x+(x+1)". Thus, any growth beyond the last annulus, Click here to obtain the protocol at the after its "birthday" but before the end of CQFE website on how to prepare otolith annulus deposition period, is interpreted as thin-section for ageing weakfish. being toward the next age class. For example, weakfish annulus formation 14.2.4 Readings occurs between April and July (Lowerre- Barbieri et al. 1994 and modified by The CQFE system assigns an age class to CQFE). A weakfish captured between Jan- a fish based on a combination of number uary 1 and July 31, before the end of the of annuli in a thin-section, the date of cap- species’ annulus deposition period, with ture, and the species-specific period when three visible annuli and some translucent the annulus is deposited. Each year, as growth after the last annulus, would be the fish grows, its otoliths grow and leave assigned an age class of "x+(x+1)" or behind markers of their age, called an an- 3+(3+1), noted as 3+4. This is the same nulus. Technically, an otolith annulus is age-class assigned to a fish with four vis- the combination of both the opaque and ible annuli captured after the end of July the translucent band. In practice, only the 31, the period of annulus deposition, which opaque bands are counted as annuli. The would be noted as 4+4. number of annuli replaces "x" in our nota- All thin-sections were aged by two different tion below, and is the initial "age" assign- readers using a Nikon SMZ1000 stereo mi- ment of the fish. croscope under transmitted light and dark- field polarization at between 8 and 20 times Second, the thin-section is examined for magnification (Figure 14.1). Each reader translucent growth. If no translucent aged all of the otolith samples. All sam- growth is visible beyond the last annulus, the otolith is called "even" and no modi- fication of the assigned age is made. The initial assigned age, then, is the age class of the fish. Any growth beyond the last an- nulus can be interpreted as either being to- ward the next age class or within the same age class. If translucent growth is visible beyond the last annulus, a "+" is added to the notation. Figure 14.1: Otolith thin-section of 4 year-old By convention all fish in the Northern weakfish Hemisphere are assigned a birth date of January 1. In addition, each species has ples were aged in chronological order, based a specific period during which it deposits on collection date, without knowledge of the annulus. If the fish is captured after previously estimated ages or the specimen the end of the species-specific annulus de- lengths. When the readers’ ages agreed, position period and before January 1, it is that age was assigned to the fish. When assigned an age class notation of "x+x", the two readers disagreed, both readers sat where "x" is the number of annuli in the down together and re-aged the fish, again

141 CHAPTER 14. WEAKFISH CYNOSCION REGALIS without any knowledge of previously esti- we aged 243 of 283 weakfish (The rest of mated ages or lengths, and assigned a final fish were either without otoliths or over- age to the fish. When the readers were un- collected for certain length interval(s)) col- able to agree on a final age, the fish was lected by VMRC. We fell short in our over- excluded from further analysis. all collections for this optimal length-class sampling estimate by 77 fish. However, we Click here to obtain the protocol at the were short of no fish from the major length CQFE website on how to age weakfish us- intervals (The interval requires 10 or more ing their otolith thin-sections. fish), as a result, the precision for the es- timates of major age groups would not be 14.2.5 Comparison tests influenced significantly.

A symmetry test (Hoenig et al. 1995) 14.3.2 Reading precision and coefficient of variation (CV) analysis were used to detect any systematic differ- Both readers had high self-precision. ence and precision on age readings, respec- Specifically, there was no significant differ- tively, for the following comparisons: 1) be- ence between the first and second readings tween the two readers in the current year, for Reader 1 with an agreement of 96% and 2) within each reader in the current year, a CV of 1.9% (test of symmetry: χ2 = 2, df and 3) time-series bias between the current = 1, P = 0.1573), and there was no signifi- and previous years within each reader. The cant difference between the first and second readings from the entire sample for the cur- readings for Reader 2 with an agreement rent year were used to examine the differ- of 96% and a CV of 1.9% (test of symme- ence between two readers. A random sub- try: χ2 = 2, df = 1, P = 0.1573). There sample of 50 fish from the current year was was no evidence of systematic disagreement selected for second readings to examine the between Reader 1 and Reader 2 with an difference within a reader. Fifty otoliths agreement of 100% (Figure 14.2). randomly selected from fish aged in 2003 were used to examine the time-series bias within each reader. A figure of 1:1 equiv- alence was used to illustrate those differ- ences (Campana et al. 1995). All statistics analyses were performed in R 3.2.2 (R Core Team 2012).

14.3 RESULTS

14.3.1 Sample size Figure 14.2: Between-reader comparison of We estimated a sample size of 318 for age- otolith age estimates for weakfish collected in ing weakfish in 2015, ranging in length in- Chesapeake Bay and Virginia waters of the At- lantic Ocean in 2015. terval from 6 to 35 inches (Table 14.1). This sample size provided a range in (CV) for age composition approximately from There was no time-series bias for both read- the smallest (CV) of 6% for age 2 to the ers. Reader 1 had an agreement of 98% largest (CV) of 11% for age 1. In 2015, with ages of fish aged in 2003 with a CV of

142 CHAPTER 14. WEAKFISH CYNOSCION REGALIS

0.2% (test of symmetry: χ2 = 1, df = 1, P 14.4 REFERENCES = 0.3173). Reader 2 had an agreement of 100%. Campana, S.E., M.C. Annand, and J.I. McMillan. 1995. Graphical and statis- tical methods for determining the con- 14.3.3 Year class sistency of age determinations. Trans. Am. Fish. Soc. 124:131-138. Of the 243 fish aged with otoliths, 5 age classes (1 to 5) were represented (Table Hoenig, J.M., M.J. Morgan, and C.A. 14.2). The average age was 2.1 years, and Brown. 1995. Analyzing differences be- the standard deviation and standard error tween two age determination methods were 0.8 and 0.05, respectively. Year-class by tests of symmetry. Can. J. Fish. data show that the fishery was comprised of Aquat. Sci. 52:364-368. 5 year-classes: fish from the 2010 to 2014 Lowerre-Barbieri, S.K., M.E. Chittenden year-classes, with fish primarily from the Jr., and C.M. Jones. 1994. A com- year-class of 2013 with 60.1%. The ratio of parison of a validated otolith method males to females was 1:4.06 in the sample to age weakfish, Cynoscion regalis, with collected (Figure 14.3). the traditional scale method. Fish Bull. 92:555-568. Quinn, T. J. II, and R. B. Deriso. 1999. Quantitative Fish Dynamics. Oxford University Press. New York. R Core Team (2012). R: A lan- guage and environment for statistical computing. R Foundation for Sta- tistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www. R-project.org.

Figure 14.3: Year-class frequency distribution for weakfish collected for ageing in 2015. Dis- tribution is broken down by sex. ’Unknown’ represents gonads that were not available for examination or were not examined for sex dur- ing sampling.

14.3.4 Age-length key

We developed an age-length-key (Table 14.3) that can be used in the conversion of numbers-at-length in the estimated catch to numbers-at-age using otolith ages. The table is based on VMRC’s stratified sam- pling of landings by total length inch inter- vals.

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Table 14.1: Number of weakfish collected and aged in each 1-inch length interval in 2015. ’Target’ represents the sample size for ageing estimated for 2015, and ’Need’ represents number of fish shorted in each length interval compared to the optimum sample size for ageing and number of fish aged.

Interval Target Collected Aged Need 6 - 6.99 5 0 0 5 7 - 7.99 5 1 1 4 8 - 8.99 5 6 6 0 9 - 9.99 30 38 30 0 10 - 10.99 60 70 60 0 11 - 11.99 42 42 42 0 12 - 12.99 27 27 27 0 13 - 13.99 19 35 20 0 14 - 14.99 14 21 14 0 15 - 15.99 15 14 14 1 16 - 16.99 12 12 12 0 17 - 17.99 8 8 8 0 18 - 18.99 6 4 4 2 19 - 19.99 5 1 1 4 20 - 20.99 5 1 1 4 21 - 21.99 5 1 1 4 22 - 22.99 5 0 0 5 23 - 23.99 5 0 0 5 24 - 24.99 5 1 1 4 25 - 25.99 5 0 0 5 26 - 26.99 5 1 1 4 27 - 27.99 5 0 0 5 28 - 28.99 5 0 0 5 29 - 29.99 5 0 0 5 31 - 31.99 5 0 0 5 34 - 34.99 5 0 0 5 35 - 35.99 5 0 0 5 Totals 318 283 243 77 (Go back to text)

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Table 14.2: The number of weakfish assigned to each total length-at-age category for 243 fish sampled for otolith age determination in Virginia during 2015.

Age Interval 1 2 3 4 5 Totals 7 - 7.99 1 0 0 0 0 1 8 - 8.99 1 5 0 0 0 6 9 - 9.99 5 24 1 0 0 30 10 - 10.99 6 50 4 0 0 60 11 - 11.99 14 27 1 0 0 42 12 - 12.99 6 14 5 2 0 27 13 - 13.99 9 4 5 2 0 20 14 - 14.99 1 8 5 0 0 14 15 - 15.99 2 3 5 3 1 14 16 - 16.99 1 4 3 3 1 12 17 - 17.99 1 5 1 1 0 8 18 - 18.99 0 2 1 1 0 4 19 - 19.99 0 0 0 1 0 1 20 - 20.99 0 0 0 1 0 1 21 - 21.99 0 0 0 1 0 1 24 - 24.99 0 0 0 1 0 1 26 - 26.99 0 0 0 1 0 1 Totals 47 146 31 17 2 243 (Go back to text)

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Table 14.3: Age-Length key, as proportion-at-age in each 1-inch length interval, based on otolith ages for weakfish sampled for age determination in Virginia during 2015.

Age Interval 1 2 3 4 5 7 - 7.99 1 0 0 0 0 8 - 8.99 0.17 0.83 0 0 0 9 - 9.99 0.17 0.8 0.03 0 0 10 - 10.99 0.1 0.83 0.07 0 0 11 - 11.99 0.33 0.64 0.02 0 0 12 - 12.99 0.22 0.52 0.19 0.07 0 13 - 13.99 0.45 0.2 0.25 0.1 0 14 - 14.99 0.07 0.57 0.36 0 0 15 - 15.99 0.14 0.21 0.36 0.21 0.07 16 - 16.99 0.08 0.33 0.25 0.25 0.08 17 - 17.99 0.12 0.62 0.12 0.12 0 18 - 18.99 0 0.5 0.25 0.25 0 19 - 19.99 0 0 0 1 0 20 - 20.99 0 0 0 1 0 21 - 21.99 0 0 0 1 0 24 - 24.99 0 0 0 1 0 26 - 26.99 0 0 0 1 0 (Go back to text)

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