/ /AGE, GROWTH, AND POPULATION STRUCTURE OF
JACK MACKEREL {Trachurus symmetricus)
FROM THE NORTHEASTERN
PACIFIC OC~/
A submitted to the faculty of San Francisco State University in partial fulfillment of the requirements for the degree
Master of Science in Marine Science
by
Deborah Ann Nebenzahl
San Francisco, California
May 1997 Copyright by Deborah Ann Nebenzahl 1997 All rights reserved Age, growth, and population structure of
Jack Mackerel (Trachurus symmetricus)
from the northeastern Pacific Ocean
Deborah Ann Nebenzahl San Francisco State University 1997
ABSTRACT
Jack mackerel (Trachurus symmetricus) are considered a highly underutilized nearshore commercial purse-seine fishery of the northeastern Pacific Ocean. In 1983, the majority of the jack mackerel commercial catch was fish younger than 3+ years (< 400 mm FL). Since then, no investigations of age and growth have been conducted (Mason 1989). Recently, there has been interest by domestic and international trawling fleets to develop a fishery in the offshore region of its range. In anticipation of this development, this study examines the age composition, growth rates, population structure, and possible migratory patterns of both nearshore and offshore components of the jack mackerel population collected from the northeastern Pacific Ocean, 1978-1993.
This study indicated that ages were best estimated from transverse thin-sectioned otoliths, and that growth was best described by the von Bertalanffy growth function (K = 0.159)
Marginal increment analysis was used to validate annual deposition of opaque and translucent otolith growth zones. Young jack mackerel were found nearshore and grew quickly until 400 mm FL, after which growth slowed in length but weight increased dramatically. Fish greater than 300 mm FL tend to move offshore into deeper, colder waters. This change in growth directly corresponds with their change in environment from nearshore waters to offshore waters. There is some indication that older members of the offshore portion of the population migrate to the north. It remains unclear whether the northern portion of the population is a resident stock, a migrating component, or both. Fish found in the northern limits may simply be displaced due to seasonal oceanographic warming trends or warming trends resulting from an El Nino event.
I certify that the Abstract is a correct representation of the content of this thesis. ACKNOWLEDGMENTS This work is a result of research sponsored in part by the Saltonstall-Kennedy Program, through the National Marine Fisheries Service, under grant number NA37FD0240. This project was also funded in part by LMR Fisheries Research, Inc., and in part by the Earl and Ethyl M. Myers Foundation and Packard Foundation grants. Otoliths were provided by the California Department of Fish and Game, Dan Kimura of the Alaska Fisheries Science Center, Sandy MacFarlane of the Department of Fisheries and Oceans, Canada, and LMR Fisheries Research Inc. I'd like to thank all those who assisted toward the completion of this project. My committee members, Greg Cailliet, who introduced me to the wild world of fish, the Baja Way, and Wayne's World (schwing); Richard Parrish for his invaluable guidance, intriguing "big picture" discussions, and for providing a stress outlet with adventurous trail rides; Ralph Larson for his inspiring support and encouragement, critical review, and ability to listen; Mary Yoklavich, the one and only "otolith queen", whose encouragement got me through. I thank the Moss Landing Marine Lab's faculty, staff, and students (with a special thank you to Gail Johnston, Sandie Yarborough, Sheila Baldridge, Sandie O'Neil, and Joan Parker) who kept me entertained and always laughing. Finally I'd like to thank my parents and family for all their love, support, and donations to my coffee fund.
VI TABLE OF CONTENTS
Page
LIST OF TABLES ...... ix
LIST OF FIGURES ...... x
INTRODUCTION ...... 12
MATERIALS AND METHODS ...... 20
Sites and sample collection ...... 20
Length frequency and length-weight relationships .... 22
Otolith morphometries ...... 23
Age and growth determination ...... 24
Marginal increment analysis ...... 28
Growth curves ...... 29
Age frequency and migratory patterns ...... 30
RESULTS ...... 31
Length frequency and length-weight relationships .... 31
Otolith morphometries ...... 3 3
Age and growth determination ...... 34
Marginal increment analysis ...... 36
Growth curves ...... 3 7
Age frequency and migratory patterns ...... 38
Inter study comparison ...... 40
DISCUSSION ...... 42
Length frequency and length-weight relationships .... 42
Otolith morphometries ...... 4 7 vii Page
Age and growth determination ...... 48
Marginal increment analysis ...... 49
Growth curves ...... 51
Age frequency and migratory patterns ...... 53
Interstudy comparison ...... 57
SUMMARY AND AFTERTHOUGHT ...... 59
REFERENCES CITED ...... 6 2
Vlll LIST OF TABLES
Table Page
1. Samples by geographical area and year ...... 71
2. Analysis of variance tables of age validation
data ...... 72
3. Mean and standard errors of length at
age from von Bertalanffy, Gompertz, and Logistic
growth functions ...... 73
4. Von Bertalannfy growth parameters of jack
mackerel from southern California and
Washington ...... 7 3
5. Interstudy comparison of ages and average fork-
lengths ...... 74
IX LIST OF FIGURES
Figure Page
1. Map of sampling area ...... 76
2. Length frequency histogram of all samples
combined and individual geographical sites ..... 77
3. Length frequency histogram of Washington samples
by year ...... 78
4. Length frequency histogram of nearshore southern
California samples from 1986-1990, 1992, and
1993 ...... 79
5. Fork length versus weight scatterplot of all fish
sampled ...... 80
6a. Fork length versus weight scatterplot of male
fish sampled ...... 81
6b. Fork length versus weight scatterplot of female
fish sampled ...... 81
7a. Scatterplot of nearshore samples, left otolith
length versus fork-length ...... 82
7b. Scatterplot of nearshore samples, left otolith
weight versus fork-length ...... 82
Sa. Scatterplot of offshore samples, left otolith
length versus fork-length ...... 83
Bb. Scatterplot of offshore samples, left otolith
weight versus fork-length ...... 83
X Figure Page 9. Scatterplot comparison of ageing techniques, whole otolith and transverse thin-section
readings ...... 84 10. Ageing precision histbgram between readers •.•.. 84 11. Marginal increment scatterplot of nearshore southern California samples from 1987, 1988,
and 1989 ...... 85 12. Von Bertalanffy growth function of all samples ... 86 13a.Von Bertalannfy growth function of male and
female samples ...... 8 6 13b.Von Bertalanffy growth function of male samples •. 87 13c.von Bertalanffy growth function of female samples •.•...... •..•...•...... •.•.. 88 14. Age frequency graph of nearshore and offshore southern California samples .....•..•...... ••.. 89 15. Age frequency graph of samples caught using trawling gear (southern California and Washington ..•..•...... ••.....•..•...... ••••• 9 0 16. Age frequency graph of southern California purse seine samples from 1986-1990, 1992 and
1993 ...... 91 17. Age frequency graph of Washington samples collected in 1978, 1981-1984 ••••....•.••.•••..• 92 18. Comparison of average fork lengths and age from this study and past studies ...... •.....•. 93
XI 12
INTRODUCTION
The northeastern Pacific jack mackerel (Trachurus symmetricus) is a pelagic fish whose population appears to have two distinct components, nearshore (NS) and offshore
(OS). A geographical boundary, in which sp,ecific size classes are taken by the fishery, separates the two components. The nearshore component consists of juvenile and young adult jack mackerel ( < 400 rnrn FL), found over shallow bottoms and sometimes over rocky outcrops (0-100 m depth, <
90 miles offshore) (MacCall et al. 1980). Offshore jack mackerel are greater than 400 mrn FL and typically are taken in waters deeper than 100m (Konno pers. comm.).
The economic importance of the northeastern Pacific jack mackerel fishery increased dramatically from 1940 through
1980 {MacCall et a1. 1980). Since then, commercial landings have decreased substantially, reaching a low of 3,129 MT in
1994 (Fisheries Review, CalCOFI Rep. 1995), and the fishery is currently considered highly underutilized. Nevertheless, little research on age structure and population dynamics has been conducted 1983-84 {Mason 1991). This is a concern because fishery management policies are based on biomass estimates and predictions, which in turn are derived from 13
demographic data of an individual species. Understanding the life history (age of recruitment into fishery, fertility, fecundity, longevity, growth, mortality, timing of reproduction, etc.) of a species is necessary to ensure viable fish are available to sustain the fished population.
Therefore it is important to continuously update records on the status of a specific population.
Traditionally, nearshore jack mackerel are landed using purse-seine techniques, which account for 90% of the total catch. The primary area of capture is in nearshore waters
( < 145 krn or 90 miles offshore) between Pt. Conception,
California and central Baja California, Mexico. Offshore fish ( > 400 rnrn FL) are usually considered bycatch, incidentally taken by salmon and albacore troll fisheries, and by the offshore Pacific whiting (Merluccius productus) trawl fishery (MacCall et al. 1980). This offshore fishery typically captures fish from 290 to 968 krn (180 to 600 miles) off southern California, but may do so as close as 5 krn (3 miles) off Oregon, Washington, and Canada where the continental shelf nears land (Neave and Hanavan 1960, Blunt
1969, MacCall et al. 1980, Mason 1991). Within the offshore fishery, jack mackerel have been found to reach up to 810 rnrn
(Miller and Lea 1972). 14
Presently, there are no catch restrictions or annual quotas on the jack mackerel fishery south of 39° N latitude, and a quota of 52,600 tons has been set (1991) north of 39° N latitude (U.S. Department of Commerce, 1991). Biomass estimates are made solely on the basis of nearshore landings by the purse-seine fleet in southern California. Recently, there has been great interest by domestic and international trawling fleets in developing a new targeted fishery for jack mackerel. Currently, a proposal to manage the fishery as two components, nearshore (purse-seine) and offshore (trawling), has been suggested (U.S. Department of Commerce, 1991). If this new fishery proposal is approved, it may potentially increase the annual yield of the jack mackerel fishery to
572,000 MT (MacCall and Stauffer 1983).
Age-specific parameters (mortality, fecundity, longevity, etc.) are the basis of any fisheries management program using dynamic population models (Brothers 1979,
Gulland 1983, Hilborn and Walters 1992). Scales and otoliths are commonly used for age determination in the demographic assessment of fish stocks. This approach is useful for investigations of growth rates, age distribution, mortality, and recruitment commercially exploited fish species. The data Provide necessary information for later analysis in 15
determining optimum sustainable yields of different stocks and setting quotas for a fishery. By determining validating ages from jack mackerel otoliths, such life history parameters may be used to determine differences in the population dynamics (i.e. growth, mortality, age at first reproduction, age-specific fecundity, timing and frequency of spawning, longevity, etc.) of the offshore and nearshore stocks throughout the species' range. For some fish species, differences in otolith morphology indicate variation in growth within component sites or that there may be more than one stock from which the fish were recruited (Ihssen et al.
1981) .
Little information exists about the differences between current size and age structure of the nearshore and offshore components of jack mackerel stocks throughout their entire range. Past studies have utilized whole otoliths to age fish taken primarily from nearshore commercial landings. Problems can arise with whole otolith ageing because outermost rings of the otolith can become very narrow and difficult to distinguish in older, long-living species (Beamish 1979b,
Cailliet et al. 1986). Irregularities in growth, faintness of growth zones, or presence of sub-annual growth patterns
(Pannella 1971) make the interpretation of zones difficult 16
and subjective (Williams and Bedford 1974, Chilton and
Beamish 1982), Thus, a basic investigation of the life history of jack mackerel is important relative to a proposal to subdivide the managed fishery into offshore and nearshore components.
In addition to past studies only ageing whole otoliths of nearshore fish, age determinations from those studies have not satisfactorily been validated (Knaggs and Sunada 1974).
Age verification (precision) and age validation (accuracy) are often overlooked and thus can cause serious management implications (Beamish and MacFarlane 1983). Invalid age estimates can lead to serious errors in predicting sustainable yield levels based on population models (Cailliet
1990, Hilborn and Walters 1992).
Marginal increment analysis, which has never been applied to jack mackerel, is one approach to determine the period and timing of band formation on an otolith, fin ray, bone, or scale (Blacker 1974, Bagenal and Tesch 1978). This procedure is carried out by a qualitative and quantitative examination of the margin of the scales, bones, or otoliths from samples taken throughout the year. Complications can arise when marks are found to be formed over a large part of
the year or when different age or size classes form them at 17
different times (Moe 1969, Williams and Bedford 1974, Beckman and Wilson 1995).
Knowledge of the life history of the northeastern
Pacific jack mackerel population from past studies is primarily limited to the exploited nearshore component of southern California. Jack mackerel range from the Gulf of
Alaska south to Baja California, Mexico, and as far west as
160° W Longitude (Ahlstrom and Ball 1954, Neave and Hanavan
1960) . The largest reported maximum length of jack mackerel is 813 mm (Miller and Lea 1972).
The reproductive biology of these fish has been briefly reviewed by Wine and Knaggs (1975) and MacCall and Stauffer
(1983). They are reproductively mature at age one ( < 230 mm
FL) and mature jack mackerel 1-8 years old ( < 400 mm FL) are typically found in nearshore waters (Roedel 1953, Wine and
Knaggs 1975). Little is known regarding feeding habits or physiology of jack mackerel. Fitch (1956) reported young jack mackerel (< 400 mm FL) found in nearshore waters of southern California, to feed on copepods, pteropods, euphausiids, juvenile squid, and anchovies. Larger fish
(320-600+ mm FL) examined during Spring 1977-1980, 400 miles offshore central and southern California, were found to have
fed on mysids, myctophids, and salps (Paschenko 1981). 18
Past studies inferred that the majority of the northeastern Pacific jack mackerel population was centered around "traditional" fishing areas: southern California and northern Baja California, Mexico, with relatively few fish or larvae found north of 46° N latitude (Ahlstrom and Ball 1954,
MacCall and Stauf 1983, MacCall and Prager 1988, Mason
1991). Juveniles and young adults constitute the majority of the Mexican stock, and young and mature adults dominate the northern portion of its range (Mason pers. comm.). This indicates that biological or physical factors may limit the recruitment and survivorship of the young or adults, and that there may be migratory patterns occurring at different stages of life.
This study examines the age composition, growth characteristics, population structure, and possible migratory patterns of both the nearshore and offshore components of the jack mackerel population collected from the north-eastern
Pacific Ocean, relative to management considerations.
Specific objectives of this study were to:
1. Use length frequency analysis and length to body weight relationships to examine size class distribution and allometric growth trends; 19
2. Determine ages of jack mackerel from otolith samples taken from nearshore and offshore components of the northeastern Pacific jack mackerel population from 1978-1993;
3. Evaluate the precision of age estimates derived from this structure among preparation techniques (whole, break and burn, sectioning) and between readers, and attempt to validate ages using marginal increment analysis;
4. Examine growth characteristics between the two population components;
5. Examine age composition within both components of the population;
6. Utilize results to evaluate possible migratory processes of nearshore and offshore jack mackerel populations; and
7. Compare these findings with existing data sets and past
Publications. 20
MATERIALS AND METHODS
Sites of sample collection
Samples of the nearshore component of the jack mackerel population were taken from commercial landings of fish taken with purse-seines from sites in northern Baja California,
Mexico (n = 118), southern California (n = 8,400), and central California (n = 119), (Figure 1). Mexican samples were collected in Summer 1990 and obtained from Ensenada
Harbor, Ensenada, Baja California, Mexico by LMR Fisheries
Research Inc. California samples were collected at fishing ports from Los Angeles-Long Beach Harbors (southern
California) between 1986 and 1993, and during 1993 at the
Monterey Harbor (central California) by California Department of Fish and Game (Figure 1). At all three sites, sampling of commercial landings of jack mackerel and processing of otoliths for analysis followed protocol set by California
Department of Fish and Game, i.e. sagittal otoliths were removed, rinsed with water, and stored dry (Wolf pers. comm.).
Offshore fish were taken with mid-water trawling gear over several years and from a wide north-south geographic range (southern California to southern British Columbia, 21
Canada) (Figure 1). Southern California samples were collected in 1991 (n = 592) by National Marine Fisheries
Service (NMFS). Washington samples, which included fish from northern California, Oregon and Washington, were taken between 1978 and 1984 (n = 320) by NMFS. Southern British
Columbia, Canada-northern Washington samples (denoted as
Canadian samples) were collected Fall 1993 (n = 148) by
Gordan MacFarlane (Department of Fisheries and Oceans,
Canada) . Sagittal otoliths were removed and stored in ethanol (southern California), dry (Washington), and in glycerin (Canada) .
All fish collected were measured to the nearest millimeter (mm) fork length (FL), weighed to the nearest 0.1 gram (g), and sexed when possible. Due to the large sample size of the southern California nearshore collection, a power analysis (Zar 1984) was conducted on the length and weight data to determine best sample size for later examination of growth patterns. The analysis indicated that a sample size of 18 pairs of otoliths per month of sampling should be adequate; however, to be certain, 21 pairs were randomly selected from each month available for a total of 1,384 pairs of otoliths. Southern California (NS) samples were analyzed
from available months between 1986 through 1993; no fish 22
were examined from 1991 due to lack of sampling.
Length frequency and length-weight relationships
A total of 2,681 jack mackerel was utilized for length frequency analysis, and of these 2,533 were used to investigate length-weight relationships. Length frequency analysis of fish populations is a useful technique for preliminary evaluation of age classes of fish. This analysis assumes the sizes of different year-classes will be distributed normally around a mean such that age groups become apparent in the form of a series of several normal curves. Two different sampling methods (purse-seine and trawling) were used to collect specimens, therefore length frequency analysis was conducted on samples by geographical area, population component (NS or OS), and year collected.
Fluctuations of length versus weight over time can indicate changes in the life history of a species. To analyze growth relationships between fork-length and body weight, the data were plotted for separate and combined
sexes. Males and females were separated to determine any
dimorphism between sexes. Length-frequency data were plotted
by geographical area and year collected to examine size class
distribution at 50 mm fork length (FL) intervals. 23
Otolith morphometries
To determine if otolith shape and weight vary ontogenetically, several morphometric variables were recorded and relationships among them analyzed. Length, height, and weight were compared between right and left otoliths among NS and OS fish. A subsample (n = 560) of small (101-350 mm FL), medium (350-500 mm FL), and large (500+ mm FL) right and left otolith pairs from southern California (nearshore and offshore), Monterey, and Washington (size classes resolved from length frequency histograms) were examined to determine if left and right otoliths varied with size of fish. To draw out extraneous moisture, otoliths were dried for 2 days at
90° F in a Blue M electronic oven after which they were immediately weighed on a Sartorius analytical balance to the nearest 0.0001 g. Otoliths were measured with calipers to the nearest 0.1 mm along the greatest anterior-posterior axis
(length) and dorsal-ventral axis (height) . Paired sample t tests (Zar 1984) were utilized to determine if any
significant differences existed between right and left
otolith variables. Left otolith weight and length measurements from the four sites were plotted against each
other by sampling method (purse-seine or trawling) and
geographical component (NS or OS) to note any morphological 24
differences among sites. Linear curves were fitted to left otolith scatterplots. Slopes andy-intercepts were analyzed using t-tests to note statistically significant differences.
Age and growth determination
Of the 2,681 fish examined, 2,495 sagittal otoliths were available for ageing. Several otoliths had been damaged, or stored in an unsuitable medium (glycerin) which cleared the otolith or made the otolith opaque, rendering it unreadable.
Otoliths were prepared for ageing in several ways: break and burn, whole otolith, and three thin sectioning techniques (longitudinal, sagittal, transverse) (Christensen
1964, Casselman 1982, Nielsen and Johnson 1983, Cailliet et al. 1986, Secor et al. 1991), and compared to determine the most precise and readable ageing strategy. For this analysis, the terms annulus (plural: annuli), band, banding pattern, check mark, core, ring, and zone follow definitions by Wilson et al. 1983, and Stevenson and Campana 1992.
The break and burn technique enhances contrast between opaque and translucent bands by burning the protein layer of
the translucent zone. Otoliths were broken through the core, heated by flame, placed in modeling clay with the burnt
surface facing upward, and coated with a drop of mineral oil 25
to enhance growth zone patterns. Burnt otoliths were examined using reflected light under a dissecting microscope with lOx oculars.
Whole otoliths were immersed in water and read using transmitted and/or reflected light through a WILD M5 Heerburg dissecting scope with lOx oculars. Thin sections were prepared in several steps. Otoliths were cast in resin
(Bondo polyester fiberglass resin) and mounted onto 1 in. x
1.5 in. cardboard cards. A variety of 0.5 rnrn sections
(transverse, sagittal, and longitudinal) were cut through the core with a Buehler Isomet low speed diamond blade saw. Thin sections were mounted on slides with Cytoseal 60 (low viscosity), then ground and polished on one side with 800 and
1200 grit paper and water on a Buehler Ecomet grinder until zones were clearly discernible.
Sectioned otoliths were examined using reflected fiber optic lighting through a WILD M5 Heerburg dissecting scope with lOx oculars. To enhance banding patterns, otoliths were placed onto a black background plate on the stage of the
scope and both plate and otolith slide were moistened.
To standardize age readings, otolith cores were measured
to obtain an average core size at hatching. This established
a reference from which to enumerate bands and ensured that 26
thin section readings began from approximately the same area of the otolith. Cores were measured using a calibrated ocular micrometer, and determined by the following criteria.
Thin sections were grouped by fork-length from small to large. The otolith core was set in middle of cross hairs of an ocular micrometer, scope magnification was adjusted, and the micrometer calibrated. Cores were measured from small
(101-350 rnm FL), medium (351-500 mm FL), and large (500+ mm
FL) otoliths.
The core was found to range between 1.8-2.2 mm with a mean of 2.0 mm. After the core had been established, any full bands found outside the core were enumerated. Full bands were considered to be an opaque and transparent pair of rings occurring by side and detectable at least half-way around the otolith. Otoliths in random order were read by the same reader times with at least a two day interval between readings to eliminate temporal ageing bias. The criterion for accepting an age estimate was that at least two counts must agree for an age to be accepted. If none of the three counts agreed, the middle one was used provided that
the counts were only different by one age; otherwise, the otolith was not used in the analysis. 27
An examination of growth zones of whole and sectioned right and left otoliths was conducted to determine if differences in banding patterns between otoliths were present. Growth zones of left and right otoliths were analyzed for statistical differences using sample t-tests.
To evaluate discrepancies among ageing techniques and among readings, the average percent error (APE), coefficient of variation (V), and index of precision (D), considered the most conservative estimators of error (Beamish and Fournier
1981, as modified by Chang 1982), were used. The equations for APE, V, and Dare defined as:
APE = 1/N * L [1/R * 1:(lxij-Xjl/xj] ] ;
V = [S/average of x] * 100; D = V/sq. rt. R where N = number of fish aged, R = number of times each fish is aged, Xij = the ith age determination of the jth fish, Xj
= average age calculated for the jth fish, and S is the standard deviation in ageing the jth fish. These indices were calculated to examine precision among the ageing
techniques and among readings. To accept a precision index, a specified amount of error (< 5%) was arbitrarily used
(Beamish and Fournier 1981). Scatterplots average
readings from whole otolith and transverse thin sections were 28
also examined to determine similarity between techniques.
To verify reading precision of transversely sectioned samples among readers, approximately 10% (240) of the thin sectioned samples were examined by a second reader using the same criteria mentioned above. Reader discrepancy tests were used to test precision among readings and readers. In addition, discrepancy histograms were used to further evaluate reader disparity.
Marginal increment analysis
Marginal increment analysis (Baganel and Tesch 1978) was used as a validation (accuracy) technique for the southern
CaliforniaNS samples. Otolith sections (n = 700) from all fish caught throughout all seasons of three consecutive years, i.e. twenty otolith sections/month, were compared following techniques established by Brothers et al. (1976).
For each sample, edges of otoliths were measured and standardized to otolith length and fork length for that sample. A computer-aided image analysis system (Apple
Macintosh IICX with microscope, video camera, and video monitor) in conjunction with Bony Parts: Image analysis
Program (Brittnacher and Botsford 1991, Cailliet et al. 1996)
were used to measure otolith variables. Analysis of variance 29
tests (ANOVA) were used to detect statistical differences among the marginal increment monthly data for each year examined.
Growth curves
The three common growth equations (logistic, Gompertz, and von Bertalanffy) were fitted to the data and curves were plotted using the computer program FISHPARM (Prager et al.
1987). Mean square errors of these three growth functions were also calculated and compared to determine which growth function best described the data (Ricker 1975, Cailliet et al. 1986). To describe jack mackerel growth as realistically as possible, two hundred (100 male, 100 female) age 0 at 2 mm length fish (size at age of hatching for jack mackerel) were added to the data for the analysis.
The von Bertalanffy growth equation described the general growth better than other equations and was used for
further growth analysis. This equation is defined as:
L(t) = L (1- exp -K(t - to)
where L(t) = mean fork length at time t, L = mean asymptotic
length (mm), K =growth coefficient, and t = t 0 when L = 0.
Von Bertalanffy growth curves were fitted for age at size 30
data for separate and combined sexes, and combined sites.
Because little information exists on geographic stocks of jack mackerel and to help determine if the population is made up of more than one stock, two of the sites, southern
California (NS and OS) and Washington, were plotted individually for geographic growth analysis.
Ages and growth parameters determined in this study were compared with results from past studies for discrepancies.
Age frequency and migratory analysis
Age frequency histograms were used to reveal possible emigration and immigration movement trends of young and old jack mackerel. Combined and separate years of capture of jack mackerel age classes from southern California (NS and
OS) and Washington sites were plotted to examine cohort patterns, year class strength, and NS/OS-north/south spatial movements. Observing decreases of one component of the population followed by increases in latter components may give indication of movement patterns. 31
RESULTS
Length Frequency and Length-weight relationships
Fork length sizes of jack mackerel ranged from 142 to
670 mm FL (Figure 2, Table 1). Three size modes were evident. The mode of the small fish (101-350 mm FL) was fairly distinct from the medium fish (350-500 mm FL), while the large mode (500-670 mm FL) was less apparent.
Almost all fish examined from NS areas were small (101-
350 mm FL) (Figure 2) with a mode at 201-250+ mm FL. No jack mackerel greater than 400 mm FL were observed NS. Offshore samples were larger, with a primary mode at 401-450+ mm FL.
No fish smaller than 300 mm FL were observed in the OS samples.
Examination of individual sites revealed that fish appear to segregate according to geographic area (NS or OS) and/or year in which they were taken. Length frequency distributions for Central California and northern Baja
California, Mexico were dominated by fish less than 200 mm FL
(central California) and 300 mm FL (Mexico). Medium fish were seen NS in only one sample site, off southern
California. Large (500-670 mm FL) jack mackerel were
Predominately found in Washington, whereas medium size fish 32
constituted the majority of samples from Canada and southern
California (OS) (Figure 2).
Size composition varied somewhat over years for
Washington samples (Figure 3). Medium and large size classes were consistently the most abundant, but small fish were observed in 1982 and 1983.
Over the years examined, the sizes of NS jack mackerel declined in southern California (Figure 4). Small size classes dominated the catch in all years, although medium size fish were found from 1986 through 1989.
The relationship between fork length and weight for all fish was isometric, but showed scatter at fork lengths above
450 mm (Figure 5).
Male and female fish exhibited similar exponential length-weight relationships with no apparent dimorphism
(Figures 6a and 6b). However, because sex determination was unavailable for Mexican, central California, and many
Washington individuals, sample sizes for male (n = 844) and female (n = 1384) plots do not equal the sample size of the combined (n = 2533) length-weight plot. 33
Otolith morphometries
Left and right otoliths did not differ morphologically.
Paired sample t-tests did not show any significant differences between length (t = 0.054, p = 0.957, n = 437), or height (t = 0.065, p = 0.851, n = 400), of left and right otoliths. A statistically significant difference of less than 0.03% was detected between left and right otolith weight
(t = 3.98, p <<<< 0.0005, n = 437). This difference, while statistically significant, was probably due to human handling error. Otoliths were weighed as quickly as possible upon removal from the oven, but, as otoliths cool, they absorb moisture which may have caused the variance.
Some differences in otolith morphology between nearshore
(central and southern California) sample sites were seen
(Figure 7a and 7b) . Y-intercepts were found to be slightly statistically different for otolith length but not for otolith weight (t = 2.420, p = 0.01, n = 188 otolith length; t = 0.9468, p = 0.01, n = 188 otolith weight). Examining variation in slopes of otolith length and weight versus fork length between NS sites, revealed no significant differences between sites (t = 0.0035, p = 0.01, n = 188 otolith length; t = 1.0889, t = 0.9468 y-intercept, p = 0.01, n = 188 otolith weight) . 34
Empirical differences in otolith morphometries between
Washington and southern California (OS) were negligible.
Washington jack mackerel were larger than southern California
(OS) fish, so little overlap in otolith length or weight was observed between the sites (Figure Sa and Bb). However, no statistical differences could be detected between the slopes or y-intercepts of linear regression between OS sites (t =
1.6818 slope, t = 0.9952 y-intercept, p = 0.01, n = 372 otolith length; t = 1.0621 slope, t = 0.5011 y-intercept, p = 0.01, n = 372 otolith weight).
Age and growth determination
Of the three ageing techniques examined, one ageing technique (break and burn) proved inadequate because it revealed the smallest number of readable bands. Of the two remaining ageing techniques (whole otolith and sectioning) no statistical difference was found between the number of growth zones on right and left otoliths (t = 0.002, p = 0.05, n =
50). Therefore, for standardization, right otoliths were arbitrarily used for whole otolith counts and left otoliths for sectioning. 35
Transversely sectioned otoliths revealed more opaque and translucent zones than break and burn or whole otolith ageing techniques. Transverse sections also produced the lowest average percent error (APE) (3.30%), and greatest precision among readings. Coefficient of variation (0.043) and index of precision (D) (0.025) also indicated that sectioned otoliths gave more precise readings than whole otoliths.
Similar indices for whole otoliths were much higher at
12.15%, 0.165, and 0.095 respectively. Visual examination of average readings between whole and transverse sectioned otoliths also indicated that sectioning consistently produced higher counts (Figure 9). However, regression analysis examining the slope (0.922) andy-intercept {-0.241) of the data versus a 450 slope of 1 (y = x axis), revealed no significant differences indicating that both techniques may be satifactory for ageing jack mackerel but that thin sections are more consistent.
Discrepancies between the two readers verifying otolith ages were observed. Only reader 2, (the author) met all the aforementioned index of precision criteria (< 5% error).
Average percent error, coefficient of variation, and index of
Precision for Reader 1 were 0.42%, 0.149, and 0.086. From the coefficient of variation (0.066) and index of precision 36
values (0.038), Reader 2 gave a more precise reading.
However, Reader 2 had a similar APE value (0.41%) to Reader 1. Discrepancies between readers ranged from 0 to 8 years, with an average reading difference of 1.56 years, standard deviation 2.28 years {Figure 10).
Marginal increment analysis
Both opaque and translucent zones were found around the edge of sectioned otoliths. However, opaque edges were found during any month, while translucent edges were only observed during the summer months. Further analysis of the opaque edge of the otolith sections from 1987, 1988, and 1989 revealed a distinct seasonality of occurrence {minima and maxima) during the year, suggesting NS southern California jack mackerel form one annulus each year. Minima around the edge of the otolith occurred in May (1987), June (1989), and
July (1988), while maxima, found around the edge, occurred December through February (Figure 11) . Analysis of variance (ANOVA) tests revealed statistically significant differences among the increment monthly data for each year examined
(Table 2). These differences verify the seasonality of occurrence (minima and maxima) of the opaque zone during the Year. 37
Growth Curves
Coefficient of determinat~on (r2l values indicated that all three growth functions described the data well, however mean square errors (MSE) calculated from growth curves indicated that the von Bertalanffy function most consistently had the best fit (Table 3). Visual examination of the three growth curves revealed that none truly descrihed the data satisfactorily. However among the three equations, the MSE and visual examination illustrated that the von Bertalanffy growth function (VBGF) best represented jack mackerel growth.
Examination of growth parameters for all jack mackerel sampled indicated that the VBGF greatly underestimated asymptotic length (552 mm FL) . Rate of growth is adequately described for small and medium fish, but is underestemated for very young (age 1) and older fish (ages 11+). Jack mackerel growth is relatively fast until age 6 and slows thereafter (Figure 12).
The differences in growth rate among geographic sites were slight and insignificant. Analysis of growth constants
(K) from all fish sampled (Figure 12) and from fish among geographical sites (Table 4) were very similar. Though fishing effort and method of capture of samples were different, and thus add bias for comparison, it is 38
interesting to note that growth coefficients for southern
California and Washington are ~lose (K = 0.193 soCal, and K
0.166 Wash.; Table 4). The southern California growth coefficient was slightly higher than all other sites due to inadequate sample sizes of older fish. Age at size to was high for Washington samples (to = -0.640) because of lack of small fish in the analysis. Individual K values between sites were also similar to the growth coefficient all jack mackerel sampled (K = 0.159). The similarities in growth rates between sites may indicate that jack mackerel are from one stock and not geographically independent.
Asymptotic length and t 0 values varied as individual sites do not include all age ranges.
Male and female jack mackerel appear to grow at similar
rates (Figure 13a) . Growth coefficients were not statistically different (K = 0.160 male, K = 0.177 female) (t
0.0027, p = 0.01, n = 2,695) which indicates that sexes can be combined to describe general growth (Figure 13b and 13c) .
Age Frequency and migratory patterns
Analysis of year classes strongly indicate an emigration
Pattern by southern California jack mackerel from NS to OS
(Figure 14) . Southern California fish segregate into two 39
components according to age. Young fish (1 to 6 years) were found in NS water, while olde~ fish were found offshore.
Three year olds dominated all NS samples and frequencies decreased sharply after age three. In association with the
NS components' decrease in number from 3 to 6 years, was an increase of OS fish 3 to 7 years.
Although OS southern California fish were only examined from one season (which may add bias to further conclusions drawn from this OS component), general trends are worth noting. Besides the increase of southern California jack mackerel OS around age 3, two age groups were apparent. The first group being age 6 through 8, and the second group ages
12 to 13 (Figure 14). Both age groups were spawned during El
Nino events (1985, 1984, 1983, and 1979, 1978 respectively) which may have influenced migration (NS to OS), survivability, or year-class strength.
Analysis of year classes of jack mackerel from OS southern California and Washington revealed no definitive migratory trend north or south (Figure 15). In general, young fish were uncommon in Washington, and older fish (21+) were observed more frequently from Washington than southern
California. However, because of unequal sampling over time, caution must be taken comparing the two OS components. 40
Even though evidence for northerly or southerly movement is inconclusive, migration of ~outhern California jack mackerel from NS to OS water was further supported by examining NS southern California cohorts (Figure 16) .
Different year classes dominated each year sampled. However, following cohorts over time revealed sharp declines after age
3 or 4. Among the seven years NS fish were sampled, few young of the year fish were observed and three and four year olds dominated catches.
Due to a small sample size, no strong trends were apparent among year-classes or cohorts in OS Washington data except for the novel appearance of young fish in 1982 and
1983 (Figure 17). The 1977 and 1976 year-classes formed the separate group taken in 1982, while three year-classes 1979,
1978, and 1977 compose the offset assemblage taken in 1983.
Interstudy Comparison
Scatterplots of ages and average fork-lengths were similar between this study and past studies (Wine and Knaggs
1975, Mason 1989) with most of the age discrepancies occurring among ages 1-7 (Figure 18, Table 5). In general,
Wine and Knaggs' (1975) and Mason's (1989) ages were within
the size at age range found for this study. Mason's study 41
(1989), consisting solely of the nearshore commercial fishery, demonstrated a strong dip in average fork-lengths at age 6 and 7. This variance \•las probably due to a small sample size for those ages (Table 5). Confidence intervals could not be calculated for past studies, therefore, interpretation of the data should be noted with some caution.
Wine and Knaggs (1975) calculated von Bertalanffy growth parameters for their data: L = 603 mm, K = 0.0935, and t 0 =
-3.2. Comparing these parameters to this study's southern
California data (Table 3), only growth rates are similar (K =
0. 094) . 42
DISCUSSION
Length Frequency and Length-weight relationships
Several studies have found that the majority of small, young jack mackerel concentrate mainly nearshore in warmer southern coastal waters, whereas larger, older fish dominate deeper, colder northern waters (Pachenko 1979, MacCall and
Stauffer 1983, Mason 1992). Typically the smaller jack mackerel (up to 400 mm FL) are found nearshore between central California and northern Baja California, Mexico
(Mason 1992), schooling near the surface over shallow rocky reefs. Length frequency histograms from the current study indicate that jack mackerel become available to the purse seine fishery around 140 mm FL and unavailable around 400 mm
FL. As most of the nearshore fish examined for this study fell into the 201-250 mm FL size class (53%) and were caught by purse-seine, this implies targeting by the fishery.
Over all years examined here, a large decrease in NS southern California fish was seen from 250+ mm FL, while an increase in the OS southern California component was observed around 300+ mm FL. By 400 mm FL, jack mackerel appear to be fully recruited to the offshore component of the population.
These large fish (> 400 mm FL) tend to be found solitary or 43
in loose aggregations and are incidentally caught by salmon and offshore albacore trollers! bottom and midwater trawls, and sport fishing party-boats (Blunt 1969, Mason 1991, Mason 1992) . Few studies have been able to examine a sizable data base of large (> 400 mm FL) jack mackerel, yet most of the samples were collected nearshore by commercial purse-seines, which target fish less than 400 mm FL (Mason 1992) . Examination of all the data for this study implied that the Northeastern Pacific population is made up of young fish found nearshore. However, the degree of effort of sampling was not reported, and since amount of fishing/sampling can highly influence population dynamic models, any definition of the population structure must be made with caution (Krebs 1989} . Even with unequal effort, inferences may be drawn regarding length frequency versus area. The largest and oldest fish were found in the northern sites, Washington and Canada, and in the OS southern California site. All these OS areas were collected by research trawlers. Trawlers have regularly caught jack mackerel in northern waters (Oregon, Washington, and southern Canada) in autumn when the Davidson current warms the surface waters (Blunt 1969, Hart 1973). 44
During unusual warming trends, i.e. El Nino events, a preponderance of small, medium, and large fish (as defined from the length frequency histogram) have been found in the extreme northern waters (through the Gulf of Alaska) (Larkins 1964, Neave and Hanavan 1960, Blunt 1969). Squire (1987) reports water temperatures were abnormally warm in the northeastern Pacific Ocean during 1982 and 1983, coincidentally the only two years in which smaller jack mackerel occurred in Washington study samples. In this study, jack mackerel cohorts were difficult to distinguish on the basis of size frequency distributions. As in all fish studies, this analysis is most reliable in younger size classes. Young jack mackerel grew faster than older fish, so sizes at age merged. Problems can also arise when frequency of spawning or timing between spawnings overlap, making cohorts hard to distinguish (Wooten 1991) . Jack mackerel have prolonged reproductive periods (February October) yielding several spawnings in one season. Unfortunately their spawning range and movement have not been fully established, rendering cohorts difficult to distinguish. 45
The jack mackerel spawning cycle begins in February in northern Baja California, Mexi90 and southern California.
They spawn in areas of 14-16° C sea surface temperature with spawning paralleling the 14-16° C isotherm as it moves northward with the Davidson current (Theilacker and Dorsey
1980). Thus, the spawning peak moves from southern California (May through July) progressively northward towards
Oregon (August through October) (Ahlstrom 1956, Farris 1961,
MacGregor 1976, and MacCall and Stauffer 1983). Macewicz and
Hunter (1993) examined ovaries from spawning females and found oocytes at various stages of development within a single female. This led them to conclude that jack mackerel are indeterminant spawners, capable of spawning up to 36 times over a reproductive season. Differences were not found between length versus weight scatterplots of male and female jack mackerel. Weight increases isometrically with fork length. There was an increase in deviation from the exponential curve after 450 mm FL which may result because of a change in lifestyle. As noted previously, 400+ mm FL jack mackerel tend to move offshore into colder, deeper waters. In this new habitat, feeding habits and metabolic rate may be different than in fish found NS. 46
Seasonality of weight gain or loss was not examined in this study. Mallicoate and Pa~rish (1981) reported mean weight changes of jack mackerel appeared to correspond with spawning season, and implied reproductive maturity at 3+. Examining nearshore southern California fish up to age 7 years, they found mean weight increased from late spring to late fall (peak increase in weight, July to September) in fish 3 years and older, followed by mean weight loss from winter to early spring. Conversely, Wine and Knaggs (1975) have shown that jack mackerel may be mature by the end of their first year. Thus, changes in weight may simply be seasonal; food is less available in winter as compared to spring. Changes in weight may therefore be due to a change in lifestyle and/or feeding habits as this study has shown that 3+ jack mackerel begin to move offshore. Fat reserves probably fluctuate seasonally with food availability and reproductive condition, although there is no information on fat reserves or physiology of the species. 47
Otolith morphometries
Use of calcified structubes for ageing is dependent on the assumption that growth increments are laid down with a predictable frequency. For some fishes (i.e. pleuronectids), left and right sagittal otoliths may grow at different rates (Ricker 1979, Campana 1984a and l984b). Therefore, it is necessary to establish which otolith is most reliable and standardize methods to help eliminate bias. In this study, left and right otoliths revealed no significant morphometric differences. Left otoliths were arbitrarily chosen for further otolith and ageing analysis in the interest of standardizing techniques. Otolith morphometry data indicate that jack mackerel from northern and southern sites may have originated from similar stocks. Differences in otolith length between nearshore sites was probably due to a lack of larger fish from central California. The small variation observed in otolith weight between nearshore sites may be due to several factors. Variances in calcium deposition may be caused bY differing physiological demands of the various environments. Environmental differences over time may also influence otolith growth; southern California (NS) samples were collected over several years whereas central California 48
samples came from one season of sampling.
Otoliths from northern (W~shington) and southern (southern California OS) offshore samples were morphologically similar. Even though FL sizes did not overlap, changes in otolith length and weight were extremely similar between the sites, inferring that the population may be of one stock. Nevertheless it may be argued that otolith morphometry is insufficient evidence to conclude that all fish came from the same stock. Therefore, a genetic analysis throughout the geographic range of jack mackerel should better answer this population question.
Age and growth determination
This study tested the utility of ageing jack mackerel otoliths by break and burn, whole, and thin-sectioning methods. Break and burn otoliths were found to be difficult to read due to uneven surfaces and misleading banding patterns. This ageing technique can help reduce "check marks" (Chilton and Beamish 1982), but many times checks are still present and indistinguishable from true zones. Prior jack mackerel studies aged only whole otoliths
(~line and Knaggs 1975, Mason 1989) , but these are not as
Precise for ageing as thin sections. As jack mackerel gro\'1, 49
outermost zones become narrow and hard to distinguish. Whole otolith ageing can easily be used to age young fish (up to age 8-10), however ontogenetic changes in otolith morphometry occur as more material is deposited proximally (Beamish 1979b, Panella 1980). Of the methods tested, transverse sectioning revealed more annuli and greater ageing precision. Since jack mackerel otoliths grow in a three-dimensional allometric mode of calcium deposition, this suggests that thin-sectioning ageing techniques are optimal for analysis of the otoliths (Beamish 1979a and 1979b, Chilton and Beamish 1982, and Campana 1984b) .
Marginal increment analysis
This study was able to validate ages of nearshore southern California jack mackerel using marginal increment analysis techniques. Knaggs and Sunada (1974) attempted to validate nearshore southern California fish and found that both opaque and translucent zones could be found on the otolith edge in all months. They further examined percentage of jack mackerel with translucent edge over time and concluded that only one opaque and one translucent zone are formed during a year's growth. 50
Both Knaggs and Sunada's {1974) and this study's findings indicate that formatipn of translucent zones correspond to the spawning season of jack mackerel. The lowest amount of deposition occurred May through July, the peak of the fish's reproductive season (Ahlstrom and Ball 1954, Wine and Knaggs 1975, and Macewicz and Hunter 1993). Interestingly, deposition of growth rings, reproductive season, and seasonal growth in body weight may be interrelated for NS southern California fish, but not necessarily synchronized over time (i.e. variables are slightly out of phase with one another). Seasonal changes in body \"leight directly overlap with seasonal changes of otolith deposition and spawning season. Mallicoate and Parrish (1981) found mean weight loss in NS southern California jack mackerel to occur from late winter through early spring (December through March), followed by an increase in mean weight from late spring to early fall (peak increase in weight July through September) . Decrease in zone deposition (December through May) directly overlaps mean loss of body weight, where as, increase in body weight corresponds with an increase in otolith deposition. Increase in weight directly follows the peak spawning period for southern California jack mackerel. 51
These age validation results, however, are limited to
southern California nearshore fish. Only samples from nearshore southern California were collected over a
sufficient time period allowing validation. Since jack mackerel appear to be long lived, it may be useful in future validation studies to attempt radiometric validation
techniques (Smith et al. 1991).
Growth Curves
Growth curves describe age-at-length data, and are vital
to fishery management. Small and medium size jack mackerel growth was adequately described using the von Bertalanffy
(VBG) equation, but, as often happens, small young fish and older larger fish are under-represented for the growth model.
Lack of size ranges for age 0, 1 and ages 11+ account for much of the underestimation of growth by the VBG model. The
VBG equation is subject to bias if not enough samples are
examined from the entire size range (Ricker 1975 and 1979).
This study, however, is the only one to examine growth of a
substantial number and size range of jack mackerel throughout
the northeastern Pacific coast. 52
The largest jack mackerel collected in this study was
670 rom FL, but few fish exceed~d 600 rom FL. Age and growth of jack mackerel were also examined by Wine and Knaggs (1975). In their study, jack mackerel, ranging in size from
198 to 567 rom FL, were collected from southern California. Fish greater than 411 rom FL were greatly under-represented with number of samples ranging from 2 to 18. Mean asymptotic length was 603 rom FL, but their growth rate (K=0.094) was similar to that found in this study. Congruence of growth rates between Wine and Knaggs' study and this one indicates that estimation of growth rates were verified. Jack mackerel grow rapidly until 400 rom FL, at which time their growth slows, as can be seen by an inflection point in the growth curve. This change in growth rate corresponds to a change in its lifestyle, when jack mackerel move into deeper, colder offshore waters. Under laboratory conditions, fish living in colder waters grow at slower rates than conspecifics inhabiting warmer waters (Ricker 1979, Mccauley and Casselman 1981, Wootten 1991).
While in some species of fish, females tend to be larger than males (Fable et al. 1987, Smith and McFarlane 1990, and
Wilson and Seki 1994), this was not found in jack mackerel. Growth parameters, especially the shape of the growth curves 53
and/or grm.,rth rates, for each sex did not differ greatly.
Similarities in growth pattern~ between sexes may indicate that males and females follow similar life history patterns (i.e. migration, age at first reproduction, etc.).
Age frequency and migratory patterns Sampling site and fishing effort greatly affected the age composition observed in this study. This study offers support that the purse-seine fleet targets young fish near the water's surface and that older fish are not available to the fleet. The NS southern California jack mackerel caught by purse-seine were between ages 1 and 6 with the greatest proportion of fish being 3 years and younger. Purse-seine gear may be designed to target that age-class given three year olds are the most vulnerable to the mesh size of the net and that jack mackerel greater than 400 rom FL (age 5 to 8+) become unavailable (i.e. large fish are not found NS in southern California) to the purse-seine fleet (Mallicoate and Parrish 1981) . Jack mackerel have been economically important to the PUrse-seine fishery since 1947, with fish 3+ years (up to 400 mm FL) dominating the catch and fish older than age 6 being rare. As of 1965, the majority of the catch has been made up 54
of fish younger than 3 years { < 400 mm FL) (Mason 1991) . Fishing and natural mortality can only account for part of the decline in the catch for fish ages 3 through 6. Mason (1991) lists three possibilities: 1) larger fish were mainly caught in fall when the California Current diverges and sea surface temperatures drop, 2) after 1964, the contribution of biomass by the fall fishery decreased, and 3) strong year classes occurred more frequently since 1965. Although the persistence of strong year classes was seen in this study, the reasons listed cannot account for all changes in the catch since 1965. Changes in fishing effort or species targeting by the purse-seines add to the fluctuation of year class dominance from season to season. Environmental factors, such as changes in oceanic circulation or sea surface temperature, may cause jack mackerel to move offshore or northward into deeper colder waters at an earlier age. This movement would help to explain the sharp decrease observed by this study in nearshore fish. Since many fish are taken offshore, this would imply significant emigration from nearshore waters to offshore waters. Observations from this and previous studies {Blunt 1969, Pachenko 1979, MacCall and Stauffer 1983, Mason 1992) strongly suggests that southern California fish begin to move 55
offshore around age 3, but are not fully recruited to the offshore component until age 6.or 7. Even-though offshore southern California fish were only sampled over one season, some inferences can be made regarding the data. Two general year class groupings are apparent: 1) 1983, 1984, and 1985, and 2) 1978 and 1979. Interestingly, these age classes were all spawned during or directly following an El Nino event (Squire 1987), possibly implying that El Nines promote high survivorship of a year class spawned during or following a warm water event. Also noteworthy is the decline in fish older than age 7, and how the decrease smoothes over greater ages. Northward versus offshore emigration of OS southern California fish cannot be resolved with the data utilized in this study. It is plausible, however, that the decrease in numbers of OS southern California jack mackerel is due to increased emigration northward, as well as natural and fishing mortality {Neave and Hanavan 1960, Blunt 1969, MacCall and Stauffer 1983, and l4ason 1992) . Unusual water patterns, like warming events, tend to displace young "middle" aged stocks towards waters that meet the requirements of the species to sustain life, in this case, northwards {Squire 1987). Age frequency analysis of 56
Washington samples was interesting because young fish were indeed found in this area. Three possibilities explain the appearance of the offset group of age-classes (4 through 7): 1) the fish were an immigrants from southern waters, 2) the fish are recruits from an established stock in Washington area, or 3) a combination of 1 and 2. In support of an immigration theory, this separate group of young fish were caught in 1982 and 1983, both El Nino years. During these warming trends, jack mackerel have been found as far north as the Gulf of Alaska (Neave and Hanavan 1960, Larkins 1964). Blunt (1969) has especially noted that small jack mackerel have been found in northern waters during warming trends. With regard to replacement stock, all but one year-class from this group were spawned during an El Nino event (1976 and 1977). El Nino water patterns may meet the requirements needed for jack mackerel to spawn in northern waters. The inability to detect any trend in cohorts may be due to a sampling problem and inadequate sample size. Few fish were caught among the years sampled from Washington. It is therefore difficult to draw any conclusion regarding remaining year class strengths or trends within the cohorts of jack mackerel from Washington. 57
The importance of the jack mackerel offshore component for recruitment to the population, especially to southern California, is unknown. Since large fish are caught offshore of southern California, we know that not all jack mackerel emmigrate out of the region. Furthermore, as all OS samples, except OS southern California, were bycatch and not subjected to target sampling, it is necessary to conduct an intensive study of northern older, OS fish to help understand their importance with regard to the entire population. At this time no studies have been done to determine the percent contribution of eggs by the various regions, and no extensive tagging, tracking, or genetic studies have been conducted to determine the nature of the fish's migratory pattern.
Interstudy comparison
Although ageing discrepancies among this study, l!Jine and Knaggs' (1975), and Mason's (1989) were seen among the younger jack mackerel, all ages fell within the size at age range for this study. A more definite analysis could be made if confidence intervals were able to be calculated for the other studies. The differences observed may be due to sampling or ageing techniques. Both Wine and Knaggs (1975) and l
southern California. Even though all three studies used comparable ageing techniques, thin-sectioning of otoliths reveals finer more detailed structure than examination of whole otoliths (Secor et al. 1991, Stevenson and Campana 1992), and whole otolith ageing tends to underestimate ages (Secor et al. 1991). Inaccurate size-at-age data can contribute to wrong population estimates and age composition models from which a fishery yield may be based. Site-specific sampling may contribute to the size at age discrepancies among the studies. Since the majority of the younger fish examined for this study were also from southern California, it would be reasonable to rule out sampling site as a factor. Other factors may include temporal or sampling regimes, human error in ageing, and different or improper ageing criteria. Temporal differences in sampling may also contribute to the ageing discrepancies. Temporality of environmental events (i.e. El Nino) may have significant influence on the growth of young fish. To minimize ageing discrepancies, a more comprehensive age validation of the fish should be completed. Future validation studies should focus on the first year's growth (larval, and age 0-1) and older OS jack mackerel. 59
SUMMARY AND AFTERTHOUGHT
Several concepts from past studies were confirmed or questioned in this study. It was found that transverse thin sectioning is an optimal ageing technique for jack mackerel, and that growth zones were deposited annually in NS southern California fish. Further research is needed to confirm and validate ages of the older OS component and northern portion of the population. Von Bertalanffy growth curves show young jack mackerel, less than 400 mm FL, to grow relatively faster than larger fish. These smaller fish(> 400 mm FL), taken by purse-seine, are predominately caught in NS waters, and few of these young fish are found in the northern range of the population. Nearshore southern California fish move to OS areas between the ages of 3-6, but other migratory patterns remain uncertain. The consistency of ages found in the purse-seine catch implies that age structure of the NS component appears stable with strong age class recruitment (particularly 3 year olds); ho\'lever, stock abundance was not examined in this study. Survivorship and abundance of OS and northern portions of the population have not been researched. Evidence was lacking to confirm or dispute whether the northern portion of the 60
population is a separate stock. Genetic analysis would be the best tvay to deliminate sto.ck structure. Knowledge of the OS contribution to the NS population remains relatively unknown, and the preponderance of large fish in northern regions raises several questions: 1) since southern California is a primary spawning area and older fish are not commonly found in this region, do they return to spawn and/or what component (nearshore, offshore, northern, southern) contributes to the southern California stock; 2) is the northern segment of the population self-sustaining or does this group rely on migrating fish as replacements? Jack mackerel eggs and larvae have been found along southern Washington and Oregon's coast from August through October (Ahlstrom 1956, MacCall and Stauffer 1983). However, most studies state that eggs and larvae are rare north of Cape Mendocino, California (Kendall and Clark 1982, Doyle 1992, Doyle et al. 1993, Moser and Smith 1993). Ahlstrom and Ball (1954) concluded that 80% of the eggs and larvae are spawned between Point Conception, California, and Cape San Quintin, Baja California, Mexico, with dense concentrations found 1000 miles offshore (CalCOFI cruises 1951-present) . 61
MacCall and Stauffer (1983) argue that the northern and offshore areas have not received enough sampling effort and that the seasonality and geographic limits to spawning have not truly been determined. Past and present surveys have mainly been conducted from San Francisco to the southern tip of Baja and up to 1000 miles offshore (CalCOFI cruises 1951- present) . Larval surveys in northern California and north of the California/Oregon border have only concentrated on areas up to 200 miles offshore (Kendall and Clark 1982, Doyle 1992, Doyle et al. 1993). MacCall and Stauffer (1983) found larvae 600 miles off Washington's coast implying the far offshore northern regions have not been fully documented. The presence of juvenile jack mackerel in northern regions reveals another question that has not been investigated: if these northern spawnings are successful, where are the young fish and why are these fish not caught? Until questions regarding the OS regions are deliminated, the extent of the geographic limits of jack mackerel eggs and larvae must be interpreted in part as due to oceanic transport by currents and circulation. 62
REFERENCES CITED
Ahlstrom, E.H. 1956. Jack mackerel. CalCOFI Prog. Rpt. 1955-56: 17-19.
Ahlstrom, E.H., and O.P. Ball. 1954. Description of eggs and larvae of jack mackerel (Trachurus symmetricus) and distribution and abundance of larvae in 1950 and 1951. Fish. Bull 97, val. 56: 209-245.
Bagenal, T.B., and F.W. Tesch. 1978. Age and growth. In: T.B. Bagenal (ed). Methods for assessment of fish production in freshwater, 3rd edition. Blackwell Scientific Publications, Oxford, England, pp. 101-136.
Beamish, R.J. 1979a. New information on the longevity of Pacific Ocean perch (Sebastes alutus). J. Fish. Res. Board Can. 36: 1395-1400 .
...... 1979b. Differences in the age of Pacific hake (Merluccius productus) using whole otoliths and sections of otoliths. J. Fish. Res. Bd. Can. 36: 141-151.
Beamish, R.J. and D.A. Fournier. 1981. A method for comparing the precision of a set of age determinations. Can. J. Fish. Aquat. Sci. 38: 982-983.
Beamish, R.J. and G.A. MacFarlane. 1983. The forgotten requirement for age validation in fisheries biology. Trans. Am. Fish. Soc. 112: 735-743.
Beckman D.W. and C.A. Wilson. 1995. Seasonal timing of opaque zone formation in fish otoliths. In: Recent developments in fish otolith research, D.H. Secor, J.M. Dean and S.E. Campana (edsl. Belle w. Baruch Library in Marine Science, number 19.
Blacker, R.W. 1974. Recent advances in otolith studies. In: F.R. Harden Jones (ed). Sea Fisheries Research. Elek, London, pp. 67-90.
Blunt jr., C.E. 1969. The jack mackerel (Trachurus symmetricus) resource of the Eastern North Pacific. Calif. Mar. res. Comm., CalCOFI rept. 13: 45-52. 63
Brittnacher, J. and L. Botsford. 1991. Bony parts: an image program. University of California, Davis, 16p. Unpublished manuscript ..
Brothers, E.B. 1979. Age and growth studies on tropical fishes. In: Stock assessment for tropical small scale fisheries, Saila and Roedel (eds.), pp. 119-137.
Brothers, E.B., C.P. Mathews, and R. Lasker. 1976. Daily growth increments in otoliths from larval and adult fishes. Fish. Bull. 74(1): 1-8.
Cailliet, G.M., L.W. Botsford, J.G. Brittnacher, G. Ford, M. Matsubayashi, A. King, D.L. Watters, and R.G. Kope. 1996. Development of a computer-aided age determination system: evaluation based on otoliths of bank rockfish off California. Tran. Amer. Fish. Soc. 125: 874-888.
Cailliet, G.M. 1990. Elasmobranch age determination and verification: an updated review. In: w.s. Pratt, jr., T. Taniuchi, and S.H. Gruber (eds), United States-Japan workshop on Elasmobranch as living resources, NOAA Tech. Rep. NMFS 90: 157-166.
Cailliet, G.M., M.S. Love, and A.W. Ebeling. 1986. Fishes: A Field and Laboratory Manual on their Structure, Identification, and Natural History, Wadsworth Publishing Company, Belmont, California, 194 pp.
Campana, S.E. 1984a. Microstructural growth patterns in the otoliths of larval and juvenile flounder, Platichthys stellatus. Can. J. Zoo. 62: 1507-1512 .
...... 1984b. Comparison of age determination methods for the starry flounder, Platichthys stellatus. Tran. Amer. Fish. Soc. 113(3): 365-369.
Casselman, J.M. 1982. Age and growth assessment of fish from their calcified structures-Techniques and tools. In: Proceedings of the international workshop on age determination of oceanic pelagic fishes: Tunas, billfishes, sharks, ed. E. Prince and L. Pulos, pp. 157 65. NOAA Tech Rep/NMFS 8. 64
Chang, W.Y.B. 1982. A statistical method for evaluating the reproducibility of age determination. Can. J. Fish. Aquat. Sci. 39: 1208-1210.
Chilton, D.E., and R.J. Beamish. 1982. Age determination methods for fishes studied by the groundfish program at the Pacific Biological Station. Can. Spe. Publ. Fish. Aquat. Sci. no. 60, 102 pp.
Christensen, J.M. 1964. Burning of otoliths, a technique for age determination of soles and other fish. J. Cons. 29: 73-81.
Doyle, M.J. 1992. Patterns in distribution and abundance of Ichthyoplankton off Wash, Ore, and N Calif (1980-1987) . AFSC(Alaska Fisheries Science Center) Processed Rpt. 92 14. November 1992.
Doyle, M.J., W.W. Morse, and A.W. Kendall jr. 1993. A comparison of larval fish assemblages in the temperate zone of the northeast Pacific and northwest Atlantic Oceans. Bull. Mar. Sci., 53(2): 588-644.
Fable, W.A., A.G. Johnson, and L.E. Barger. 1987. Age and growth of spanish mackerel, Scomberomus maculatus, from Florida and the Gulf of Mexico. Fish. Bull. val. 85, no. 4: 777-783.
Farris, D.A. 1961. Abundance and distribution of eggs and larvae and survival of larvae of jack mackerel (Trachurus symmetricus) . Fish. Bull. 187, vol. 61: 247-279.
Fisheries Review: 1995. CalCOFI Rpt. 1995, vol. 36: 7-21.
Fitch, J.E. 1956. Jack mackerel. CalCOFI Prog. Rpt. 1955- 56: 27-28.
Gulland, J.A. 1983. Fish stock assessment: a manual of basic methods. FAO/Wiley Series on Food and Agriculture, Volume 1, John \·Jiley & Sons, Chichester, 223 pp.
Hart, J.L. 1973. Pacific fishes of Canada. Fish. Res. Bd. Can., Bull. 180, 740 pp. 65
Hilborn, R., and C.J. Walters. 1992. Quantitative fisheries stock assessment: choice, dynamics, and uncertainty. Routledge, Chapman and Hall, Inc. New York, 570 pp.
Ihssen, P.E., H.E. Booke, J.M. Casselman, J.M. McGlade, N.R. Payne, and F.M. Utter. 1981. Stock identification: Materials and methods. Can. J. Fish. Aquat. Sci. 38: 1838-1855.
Kendall jr., A.W., and J. Clark. 1982. Ichthyoplankton off Washington, Oregon, and Northern California, August 1980. NWAFC Processed rpt. 82-12.
Knaggs, E.H., and J.S. Sunada. 1974. Validity of otolith age determination for jack mackerel, Trachurus symmetricus, from southern California bight area. Calif. Dept. Fish and Game Mar. Res. Tech. Rep. 21: 1- 11.
Konno, E. pers. comrn. Department of Fish and Game, Marine resources division. Long Beach, California.
Krebs, C.J. 1989. Ecological methodology. HarperCollins Publishers, New York, 654 pp.
Larkins, H.A. 1964. Some epipelagic fishes of the North Pacific Ocean, Bering Sea, and Gulf of Alaska. Trans. Amer. Fish. Soc. 93: 286-290.
MacCall, A.D., H.W. Frey, D.D. Huppert, E.H. Knaggs, J. A. McMillan, and G.D. Stauffer. 1980. Biology and economics of the fishery for jack mackerel in the northeastern Pacific, NOAA Tech Memo. NMFS-SWFC-4.
MacCall, A.D., and M.H. Prager. 1988. Historical changes in abundance of six fish species off southern California, based on CalCOFI egg and larva samples. CalCOFI Rep 29: 91-101.
MacCall, A. D. and G. D. Stauffer. 1983. Biology and fishery potential of jack mackerel (Trachurus symmetricus) . CalCOFI Rep 24: 46-56. 66
Macewicz, B.J., and J.R. Hunter. 1993. Spawning frequency and batch fecundity of jack mackerel, Trachurus symmetricus, off Califernia during 1991. CalCOFI Rep., vol. 34: 112-121.
MacGregor, J.S. 1976. Ovarian development and fecundity of 5 species of California current fishes. CalCOFI Rpt. vol. XVIII: 181-188.
Mallicoate, D.L., and R.H. Parrish. 1981. Seasonal growth patterns of California stocks of northern anchovy (Engraulis mordax) , Pacific mackerel (Scomber japonicus) , and jack mackerel (Trachurus symmetricus) CalCOFI Rep. 22: 69-81.
Mason, J. E. 1989. The southern California jack mackerel fishery, and the age and length composition of the catch for the 1972-73 through 1983-84 seasons. Calif. Dept. Fish and Game, Mar. Res. Tech. Rep. 58: 1-39 .
...... 1991. Variations in the catch of jack mackerel on the southern California purse-seine fishery. CalCOFI Rep 32: 143-151 .
...... 1992. Jack mackerel. Pp 89-91 in W.S. Leet, C.M. Dewees, and C.W. Hauyen (eds) California living marine resources. Calif. Sea Grant Publication.
pers. comm. National Marine Fisheries Service (NMFS) . Pacific Grove, California.
McCauley, R.W., and J.M. Casselman. 1981. The final preferendum as an index of the temperature for optimum growth in fish. Proc. World Symp. on aquaculture in heated effluents and recirculation systems, Stavanger, May 28-30, 1980. vol. II. Berlin.
Miller, D.J., and R.N. Lea. 1972. Guide to the coastal marine fishes of California. State of Ca. Res. Agency. Dept. of Fish and Game Fish. Bull. 157.
Moe jr., M.A. 1969. Biology of the red grouper Epinephelus mario (Valenciennes) from the eastern Gulf of Mexico. Fla. Dept. Nat. Res. Prof. Paper Ser. 10: 1-95. 67
Moser, H.G., and P.E. Smith. 1993. Larval fish assemblages of the California current region and their horizontal and vertical distributions across a front. Bull. Mar. Sci., 53 (2) : 645-691.
Neave F., and M.G. Hanavan. 1960. Seasonal distribution of some epipelagic fishes in the Gulf of Alaska region. J. Fish. Res. Bd. Canada, 17 (2) : 221-233.
Nielsen, L. A. and D. L. Johnson, eds. 1983. Fisheries techniques. Bethesda, Md.: American Fisheries Society. 496 pp.
Pannella, G. 1971. Fish otoliths: daily growth layers and periodical patterns. Science, 173: 1124-1127 .
...... 1980. Growth patterns in fish sagittae. In: D.C. Rhoads and R.A. Lutz (eds), Skeletal growth of aquatic organisms: Biological records of environmental change, Plenum press, New York, 519-560 p.
Paschenko, V.M. 1979. Distribution, biology, and biomass assessment of the jack mackerel, Trachurus symmetricus. Presented to the 1979 U.S.-U.S.S.R. bilateral meeting on fisheries assessment in the North Pacific, Seattle, June 5-8, 1979 .
...... 1981. Biological characteristics of California jack mackerel. Pacific Institute of Fisheries and Oceanography (TINRO), unpubl. rep.
Prager,M.H., S.B. Sailia, and C.W. Reckseik. 1987. FISHPARM: A microcomputer program for parameter estimation of non-linear models in fishery science. Old Dominion Univ., Norfolk, Va., Tech. Rep. (87-10): 1-37.
Ricker, W.E. 1975. Computation and interpretation of biological statistics of fish populations. Bull. Fish. Res. Bd. Can. 191: 1-382 .
...... 1979. Growth rates and models. In: Hoar, W.S., D.J. Randall, and J.R. Brett (eds.). Fish physiology, vol. VIII. Bioenergetics and growth, pp. 677-743. 68
Roedel, P.M. 1953. The jack mackerel, Trachurus symmetricus: a review of the California fishery and of current biological knowledge. Calif. Fish and Game 39: 45-68.
Secor, D.H., J.M. Dean, and E.H. Laban. 1991. Manual for otolith removal and preparation for microstructural examination. Electric Power Research Institute and BelleW. Baruch Institute for Mar. Bio. and Coastal Res. 85 pp.
Smith, B.D., and G.A. McFarlane. 1990. Growth analysis of Strait of Geogia lingcod by use of length-frequency and length-increment data in combination. Trans. Am. Fish. Soc. vol. 119, no. 5: 802-812.
Smith, J.N., R. Nelson, and S.E. Campana. 1991. The use of Pb-210/Ra-226 and Th-228/Ra-228 dis-equilibria in the ageing of otoliths of marine fish. In: Radionuclides in the study of marine process. D. Woodhead (ed.). Elsevier Scientific Publication.
Stevenson, D.K., and S.E. Campana (ed.). 1992. Otolith microstructure examination and analysis. Can. Spec. Publ. Fish. Aquat. Sci. 117: 126 pp.
Squire, J.L. 1987. Relation of sea surface temperature changes during the 1983 El nino to the geographical distribution of some important recreational pelagic species and their catch temperature parameters. Mar. Fish. rev., 49 (2): 44-57.
Theilacker, G., and K. Dorsey. 1980. Larval fish diversity, a summary of laboratory and field research. In: Workshop on the effects of environmental variation on the survival of larval pelagic fishes. Intergov. Oceanogr. Comm. Rep. 28: 105-142 UNESCO, Paris.
U.S. Department of Commerce. 1991. Our Living Ocean. NOAA Tech. Memo. NMFS-F/SP0-1, 123 pp.
Williams, T., and B.C. Bedford. 1974. The use of otoliths for age determination. In: The ageing of fish. T.B. Bagenal (ed). Unwin Brothers Ltd., pp 114-123. 69
Wilson, C.A., Brothers, E.B., Casselman, J.M., Lavette-Smith, C., and A. Wild. 1983. Glossary. In: Proceedings of the international workshop on age determination of oceanic pelagic fishes: Tunas, billfishes, sharks (Prince E. and L. Pulos, eds). NOAA Tech. Rep./NMFS 8: 207-208.
Wilson, C.D., and M.P. Seki. 1994. Biology and population characteristics of Squalus mitsukurii from a seamount in the central Pacific Ocean. Fish. Bull. vol. 92, no. 4: 851-864.
Wine, V.L. and E.H. Knaggs. 1975. Maturation and growth of jack mackerel, Trachurus symmetricus. Calif. Fish and Game, Mar. Res. Tech. Rep. 32: 1-26.
Wolf, P. pers. comm. Department of Fish and Game. Menlo Park, California.
Wootten, R.J. 1991. Ecology of teleost fishes, Fish and Fisheries Series 1. Chapman and Hall: New York. 403 pp.
Zar, J.H. 1984. Biostatistical analysis, second edition. Prentice Hall, Inc. Englewood Cliffs, New Jersey. 781 pp. 70
TABLES 71
Table 1. Samples by geographical area and year.
Northern Baja California, f\.Iexico - 118 Nearshore Purse Sehte YJ;;y: Total Collected Fork Length (mml Range Fork Length Southern California 1,384 Nearshore Purse Seine YJ;;y: Ig!ul CalleQt!:d Fork Length (mm) Range Fork Length (mm) A verag~ 1986 226 178-362 291 ±44.20 1987 237 172-321 237 ±30.94 1988 243 144-323 247 ±42.09 1989 253 169-323 222 ot27.84 1990 (Spring) 84 195-280 243 ±22.09 1992 174 141-271 207 ±25.59 1993 (Summer and 167 149-294 209 ±30.24 Fall) Southern California - 592 Offshore Trawling YJ;;y: Total Collected Fork Length (rum) Range Fork Length {rom) A vernge 1991 (Spring) 592 245-618 424 ot48.91 Central California - 119 Nearshore Purse Seine YJ;;y: Total Collected Fork Length fmm) Range Fork Length Northern Washington • 320 Offshore Trawling Year Total Collected Fork Length from) Ran~e Fork Length (rom} Averm!e 1978 (July) 40 460-600 536 ±42.82 1981 (Fall) 69 450-600 554 ot27.99 1982 (Fall) 70 330-670 524 ±74.63 1983 (Summer) 96 290-630 477 otl21.69 1984 (August) 45 380-600 551 ±40.12 Southern British Columbia, Canada -148 Offshore Trawling YJ;;y: Total Collected Fork Length (rom) Range Fork Length from) A veruge 1993 (Fall) 148 (7) 380-530 441 ot31.39 i<**Numbcrs in parentheses ( ) arc number of otolilhs aged if different from number collected, and± are Standard Deviation. Table 2. ANOVA tables of age validation data of jack mackerel from: 72 A (1987), B (1988), and C (1989), testing significance of marginal increment otolith data among months examined (refer to Figure 11 ). A (1987) Source of Variation ss df F P<0.5 Among months l.97E-07 !0 3.48 ****** Error l.24E-06 219 B(l988) Source of Variation ss df F P<0.5 Among months 6.90E-07 II 25.8 ****** Error 5.80E-07 239 c (!989) Source of Variation ss df F P<0.5 Among months 2.91E-07 !I 4.27 ****** Error 1.38E-06 239 73 Table 3. Mean square errors and coefficient of detennination (r2) from von Bertalannfy, Gompertz, and Logistic growth equations. Jack mackerel samples von Bertalannfy Gompertz Logistic ..!!.. MS .12 MS J.2 MS .x2 All jack mackerel 2,695 464.6 o:968 557.3 0.946 654.4 0.955 Male jack mackerel 892 479.4 0.974 573.2 0.962 689.4 0.955 Female jack mackerel 1,409 456.5 0.967 506.1 0.946 582.9 0.951 ***not all samples were sexed, therefore male and female (n) do not equal total number of samples aged. Note for size at age analyses, 200 (I 00 male, I 00 female) age 0 at size 2 mm length fish were added. Table 4. Von Bertalannfy growth parameters of jack mackerel taken from southern California and Washington. von Bertalannfy Growth Parameters Sample site L K to R2 Southern California purse-seine 525.9 0.193 -0.283 0.961 and trawl data (sexes combined) Washington trawl data 577.1 0.166 -0.640 0.992 (sexes combined) 1·11 bJeS Imerstudy comparison of ages and average fork-lengths among this study, Wine and Knaggs (1975), and Mason (1989). Age Average fork~feugtlt, tit is study Average fork·leugtlr, Wine and Knaggs (1975) Average jork.. /engllt, Mason (1989) 0 0 (0) 0 (0) 180 (3813) I 156 (39) 199(100) 237 (10,343) ll 181 (258) 235 (100) 267 (8912) lli 229 (588) 268 (100) 293 (2221) IV 288 (289) 288 (100) 323 (596) v 349 (72) 328 (100) 344 (196) VI 379 (100) 350 (100) 297 (41) VII 404 (93) 374 (100) 320(13) llX 415 (77) 392 (52) 426 (3) IX 424 (38) 404 (18) X 432 (16) 419 (8) X1 443 (20) 465 (6) Xll 456 (31) 450(11) XIII 473 (31) 465 (6) XIV 489 (23) 492 (2) XV 498 (11) 500 (II) XVI 512 (12) 505 (9) XVII 525 (19) 5!4 (10) !IXX 521 (14) 534 (13) lXX 533 (7) 531 (15) XX 550 (5) 54! (ll) XXI 546 (9) 538 (14) XX!l 556 (15) 537 (11) xxm 558 (17) 553 (7) XXIV 562 (!0) 553 (3) XXV 572 (10) 552 (2) XXV! 574 (14) 540 (2) XXVIJ 574 (7) 533 (2) llXXX 582 (14) lXXX 590 (8) XXX 590 (7) XXXI 602 (5) XXXII 604 (5) xxxm 600 (l) XXXIV 609 (3) XXXV 0 (0) XXXVI 620 (l) XXXVII 0(0) HXXXX 670 (I) **Sample sizes in parentheses () 75 FIGURES 130°W 120° 110° 76 50°N British. Columbia; Canada Legend ofsamples: A. Gari~da B1. Washil1g!on 19.78 B?; Washington 1981 B3. Washington 1982 B4.V\fashlngton 1983 B5 B5. Washlngton·i984 45° Monte~y . . . · c, Cape Blanco,QR · D. Nearshore southern California 1986-1993 B2~/WI'L E. OffshorE, southern California F: Northern Baja · California B1 40° Pacific Ocean 35° D ~ 30° -f Figure 2. Length frequency histogram of jack mackerel sampled by geographical site. (NS) and (OS) denote nearshore and offshore. Boo 7oo 600 sao 4DO aoo 2oo 1oo Length frequency histogram of jack mackerel sampled from Washington m Figure 3. 1978, and 1981 through 1984. 35 3Q 25 10 5 Figure 4. Length frequency histogram of jack mackerel sampled from southern California in 1986-1989, Spring 1990, full season 1992, Summer and Fall 1993. 180 160 lao 16() 14() ~~o lao i; eo .() 6Q ~ 40 ~ 80 Figure 5. Relationship between weight and fork-length of jack mackerel sampled except Canadian specimens. 3000 ••• 2500 n = 2533 • 2000 ~ 1:>1) ~.., ..t:: 1500 1:>1) ·-~ 1000 500 f(x) = 7.044E-6 • (x"3.076) R"2 =0.988 o~~~~--..• ~~~--~--~~~~~~~~~~~~ 0 100 200 300 400 500 600 700 Fork Length (mm) 81 Figure 6a. Relationship between weight and fork-length of male jack mackerel sampled. 3000 2500 • n=844 2000 ~ biJ ~ 1500 .c:... biJ ·~ :;-:QJ 1000 500 f(x) = 1.1 05E-5 • (x"3.001 ) R-'2 = 0.993 0 0 100 200 300 400 500 600 700 Fork Length (mm) Figure 6b. Relationship between weight and fork-length of female jack mackerel sampled. n=1389 f(x) = 1.081 E-5 ' (X''3.005) R"2 = 0.99 0 100 200 300 400 500 600 700 Fork Length (mm) 82 Figure 7a. Comparison of fork length and left otolith length of nearshore samples from southern and central California. Significant differences were observed between y-intercepts of NS sites, but not between slopes for otolith length (p=O.OI). 7 6 15 ~ t4 = ....."' 3 f(x) = 0.013'x + 2.575 .!:1 .- RA2 = 0.21 central California .....·~ .-0 2 * Central California 0 f(x) = 0.0265'x + 0.511 ...... 1 RA2 =0. 782 southern California '1 Southern California ..:::! 0 100 125 150 175 200 225 250 Fork Length (mm) Figure 7b. Comparison of natural log (In) fork length and natural log (ln) left otolith weight of nearshore samples from southern and central California. No significant differences were observed between NS sites for otolith weight (p=O.Ol). -2 -2.5 * Central California -3 v Southern California 00 ~.- .!:l -3.5 ·-..,00 ~ ·4 f(x) = 1 .420'x + -12.394 .!:1.- Rll2 =0.317 central California ~ -4.5 ·-.-0 f(x) =1.566*x + -12.955 0 ... -5 R"2 =0.724 southern California ""'"), -.8 -5.5 -6 2 2.5 3 3.5 4 4.5 5 5.5 6 In Fork Length (mm) 83 Figure Sa. Comparison of fork length and lel't otoliti1length of offshore southern California and Washington samples. No significant differences were observed between OS sites for otolith length (p=O.Ol). 14- i2 10 s13 . ~ ..cl... 8 ""~ (l) 6 l(x) = 1.038E·2'x + 4.792 ..cl-... ;;. Washington R'2 = 0.627 Washington ·~ 0 4 - l(x) =8.525E·3'x + 5.513 ...0 \ Southern California i!: 2 RA2 = 0.383 southern California (l) ~ 0 ' I I 200 300 400 500 600 700 Fork Length (mm) Figure Sb. Comparison of natural log (In) fork length and natural log (In) left otolith weight of offshore southern California and Washington samples. No significant differences were observed between OS sites for otolith weight (p=O.Ol). -1 -1.5 * Washington Southern California .... ~ -~ -2.5 l(x) = 2.120'x + ·16.162 -i3 ·3 ;::: R'2 = 0.869 Washington ....0 0 ·3.5 f(x) =2.155"x+ -16.468 .:;:::: AA2 = 0.805 southern California !l -4 ..E 1 2 3 4 5 6 7 In Fork Length (mm) 84 Figure 9. Scatterplot of ageing techniques, whole otolith and transverse thin-section readings, indicating good agreement between techniques. 16 14 "' ..="" 12 "d • .." 10 • -= ·-.... 8 -"' -"' 6 • -" 4 -="' f(x) = 0.922*x + -0.241 ~ 2 R"2 = 0.948, n = so 0 0 2 4 6 8 10 12 14 16 Thin-section otolith readings Figure 10. Otolith ageing precision histogram, comparing frequency of discrepancies (positive and negative differences) between reader l and reader 2. 50 45 40 II n =240 35 >. 30 u 25 ;=jE g' 20 J:: 15 10 5 o~~~~~~~~ -10 -9 -8 ·7 ·6 -5 -4 -3 ·2 -1 0 1 2 3 4 5 6 7 8 9 10 Age Discrepancy 85 Figure 11. Mean monthly marginal increment of jack mackerel sampled from nearshore southern California in 1987, 1988, and 1989; (bars indicate one standard deviation, n=20 otoliths per month/year}. Significant differences were observed among peaks and valleys for each year examined (refer to Table 2). 0.000500- 0.000450- ~ f 8 8 0.000400- ~.., c: 0.000350- ! i f !I) ! f r f 8 0.000300-: t ! f !I) I i 1-< u 0.000250- ! i f .: f t 1 ~ ·- 0.000200- 1lf f -c:ell I ·- 0.000150- ~ ' 8 0.000100- • 1987 'I' 1989 a 0.000050-: 1988 !I) * ~ 0.000000 I I I I I I I I I I I I 0 1 2 3 4 5 6 7 8 9 10 11 12 Month (l January, 12 = December) 86 Figure 12. Growth curve of all jack mackerel sampled, with von Bertalannfy parameters lis ted. X ' X X 500 ~ ~~ ..<:I ~ a' 300 - Figure 13a. Comparison of von Bertalannfy growth curves of male and female jack mackereL 700 600 500 1400-: ~ . -::! a' 300 - 0 I I ' 0 5 10 15 20 25 30 35 40 Age 87 Figure 13b. Growth curve or all male jack mackerel sampled, will1 von Bertalann(y parameters listed. BB Figure l3c. Growth curve of all female jack mackerel sampled, with von llertalannfy parameters listed. 700 600 X ~ 500 ~ ~ 400 -ac.o s0 300 ~ 1-< 200 0 r.;., 100 L00 ~552, K=0.177, t0 ~-0.169 R"2~ 0.967 0 0 5 10 15 20 25 30 35 40 Age Figure 14. Age frequency graph of jack mackerel caught using purse-seine (nearshore) and trawling (offshore) gear from southern California. 700 600 • Nearshore 500 ~ Offshore ;... Q) 400 ..0 E ;! z 300 200 100 0 Age Figure 15. Age frequency graph of jack mackerel caught using trawling gear offshore from southern California (1991) and Washington (all years sampled). 100 90 80 II s. California 70 fil Washington ... 60 Cl) ..c 8 50 ;:l z 4(l 30 20 Age \.0 0 Figure 16. Age frequency and cohorts of jack mackerel caught using purse-seine gear nearshore from southern California (1986-1990, 1992, and 1993). Figure 17. Age frequency graph of jack mackerel sampled from Washington, 1978 and 1981 through 1984. 16 1e ~ 14 ~ ~ 12 10 a 6 4 2 I lD tv I 93 Figure 18. Comparison of average fork·lengths and ages of jack mackerel from this study, Wine and Knaggs (1975), and Mason {1989). 600 500 E1 E1 ~ 400 ..c::...., t>O E1 ..... Age