Interstate Fisheries Management Program Implementation for North Carolina

INTERSTATE FISHERIES MANAGEMENT PROGRAM IMPLEMENTATION FOR NORTH CAROLINA

A. Blake Price and Jeff Gearhart

Completion Report for Cooperative Agreement No. NA 87FG0367 /3

Study II

DOCUMENTATION AND REDUCTION OF BYCATCH IN NORTH CAROLINA FISHERIES

JOB 4: Large Mesh (> 5-inch) Gillnet Discard Mortality of Spotted Seatrout (Cynoscion nebulosus), Weakfish (Cynoscion regalis), Southern Flounder (Paralichthys lethostigma), and Red Drum (Sciaenops ocellata) in Roanoke Sound, Core Sound, and the Neuse River, North Carolina

August 2002

ABSTRACT

A large mesh (> 5.0 in stretched mesh) gillnet discard mortality study was conducted in Pamlico Sound, Pungo River, and Hatteras Island at high and low salinity sites to determine delayed mortality estimates of red drum (Sciaenops ocellata) and striped bass (Morone saxatilis). Large mesh gillnets were soaked for approximately 12 hours. Upon retrieval, live fish were transferred to net pens located near the capture site and held for 72 hours. Mortalities and water quality data (temperature, dissolved oxygen, and salinity) were collected at 24 hr intervals. Delayed mortality estimates were 33% for red drum and 8% for striped bass. Logistic regression analysis was employed to model the effects of area (Outer Banks or River sites), mesh size, trial, fish length, dissolved oxygen, temperature, and salinity on mortality for each species. Temperature was related to mortality for both species. Salinity and mesh size were also related to red drum mortality. The results offer insights for fishery managers developing Fishery Management Plans (FMPs) and may assist in bycatch mortality estimates for each of these species. Recommendations include expansion of the study to fishery-dependent gillnet fisheries, establish more consistent observer coverage, implement control groups to measure the confounding effects of handling, transport and confinement stress in future delayed mortality studies.

4-ii TABLE OF CONTENTS

ABSTRACT ...... 4-ii

TABLE OF CONTENTS ...... 4-iii

LIST OF TABLES ...... 4-iv

LIST OF FIGURES ...... 4-v

INTRODUCTION ...... 4-6

METHODS ...... 4-7

PROJECT LIMITATIONS ...... 4-9

RESULTS ...... 4-9

Catches ...... 4-9 Total Mortality ...... 4-9 At Net Mortality ...... 4-10 Delayed Mortality ...... 4-10 Day of Death ...... 4-12 Water quality ...... 4-13 Statistical analyses...... 4-13 DISCUSSION ...... 4-16

CONCLUSION ...... 4-17

Striped Bass ...... 4-17 Red Drum ...... 4-17 RECOMMENDATIONS ...... 4-18

ACKNOWLEDGMENTS ...... 4-19

LITERATURE CITED ...... 4-20

4-iii LIST OF TABLES

Table 1. Number of striped bass and red drum caught by month in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted at sites located in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season...... 4-9

Table 2. Length frequency distributions of striped bass captured in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season...... 4-10

Table 3. Length frequency distributions of red drum captured in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season...... 4-11

Table 4. Percent mortality (at net delayed) of striped bass and red drum caught by mesh size in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound, and Roanoke Sound, NC during the 2001 fishing season...... 4-11

Table 5. Total mortality, at net mortality (upon capture), and delayed mortality of striped bass and red drum caught in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season...... 4-12

Table 6. At net mortality by month (Apr – Aug) of striped bass and red drum caught in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season...... 4-12

Table 7. Delayed mortality of striped bass and red drum caught in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season...... 4-12

Table 8. Water quality data collected during the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season. Data include mean water temperature (C), mean dissolved oxygen content (mg/L), and mean salinity (ppt) for the Outer banks and river sites by month...... 4-14

Table 9. Summary of stepwise logistic regression analyses of independent variables on 72-h discard mortality of striped bass caught in large mesh gillnets (5.0, 5.5, 6.0, 6.5 in. stretch mesh) in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season...... 4-15

Table 10. Summary of stepwise logistic regression analyses of independent variables on 72-h discard mortality of red drum in large mesh gillnets (5.0, 5.5, 6.0, 6.5 in. stretch mesh) in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season...... 4-15

4-iv LIST OF FIGURES

Figure 1. Sample sites for the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico River and Pungo River (Map A), and Roanoke Sound (Map B), NC in the 2001 fishing season...... 4-8

Figure 2. Day of death for striped bass and red drum caught in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season...... 4-13

4-v INTRODUCTION

Large mesh gillnets (> 5.0 in stretched mesh) are common finfish gear used throughout the inshore waters of North Carolina. These nets are typically utilized in the flounder (Paralichthys spp.) fishery. There are many bycatch and discard mortality issues surrounding large mesh gillnet fisheries. Recovering stocks of striped bass are managed in the Albemarle Sound Management Area (ASMA) through harvest caps, size/slot limits, season, and mesh size restrictions. In the commercial striped bass fishery, 5 fish per person per day are allowed on a seasonal basis (Dilday, 2001). These restrictions are implemented to prevent targeting and overfishing of striped bass. However, in other large mesh gillnet fisheries (i.e., flounder fishery), key species such as striped bass and red drum are captured as bycatch and there may be significant discard mortalities. Yearly striped bass catches are primarily estimated through trip ticket data. The commercial landings were valued at greater than $ 450,000 in 2000. There are generally greater landings in the recreational striped bass fishery, and approximately 418,000 lbs of striped bass were landed recreationally in 2001, compared to 408,000 lbs landed commercially in 2000 (Dilday, 2001). Red drum are managed by regulations such as slot limit restrictions and daily creel limits. They are currently considered overfished, but recent stock assessments depict improved juvenile recruitment, a limiting factor for these species (Paramore, 2001). Bycatch of each of these species in estuarine gillnet fisheries are poorly estimated and are thought to be high. Furthermore, the discard mortality associated with this bycatch are unknown for these species and mortality estimates of gillnet discards needs further evaluation.

Research studies estimating discard mortality of finfish caught by hook and line gear are extensive (Harrell 1988; Childress 1989; Muoneke and Childress 1994; Swihart et al., 1996; Tomasso et al. 1996; Gearhart, 2002). These studies show that increased mortality is directly related to the location of the hook (i.e., gut or gills), hook type (i.e., straight, barbed) fight-time, and bait (live). Temperature and dissolved oxygen content has been correlated to finfish survival in many projects (Malchoff, 1997; Wilson, 1999; Price and Rulifson, 2000; Price and Gearhart, 2002; Gearhart, 2002;). Mortality estimates for red drum captured by hook and line gear have been high (50%) in deep hooked fish, but significantly lower (2% - 10%) in fish caught in the lip-jaw region (Va. Mar. Res. Bull., 2000/2001). Recent estimates of striped bass mortality with hook and line gear in Albemarle Sound are < 5% for all hook locations combined (Gearhart, 2002).

The objectives of this study were:

 Provide discard estimates for key species of finfish (red drum, and striped bass associated with the large mesh (> 5 inch stretched mesh) estuarine gillnet fisheries in estuarine waters of NC.

 Identify factors that affect the short-term release mortality of key species of finfish caught by large mesh gillnets in estuarine waters of NC.

 Provide management alternatives that reduce the mortality of discarded key species of finfish in estuarine waters of NC. METHODS

This study was conducted in the spring/summer (March – August) during the 2001 fishing season. Sample sites were chosen in tributaries of Pamlico Sound, Pungo River, Hatteras Island, and Oregon Inlet, North Carolina (Figure 1A, and 1B). Each area was sampled for three fishing days bimonthly, alternating between the Pamlico/Pungo River, and Roanoke Sound areas. All fish captured in this study were obtained independently with large mesh gill nets (5.0, 5.5, 6.0, 6.5 in stretched mesh), using commercial gears and practices commonly used in these locations. Four 100 yard replicate gillnets were deployed and consisted of four separate 25 yard panels of mesh. Each panel consisted of 5.0, 5.5, 6.0, or 6.5 inch stretched mesh. Each mesh size was randomly assigned to a position in each replicate net.

Upon capture, environmental data collections included soak time, mesh size, and twine size. The mesh size in which each fish species was captured was recorded. Fish that were not alive upon capture were measured and then discarded. Live fish were measured for total length (TL), and marked with numbered T-bar tags (FF-94 T-bar anchor tag, Floy Tag and Manufacturing Co., Seattle, Washington). These fish were then placed in a 378.5 L re-circulating live well and transferred to 1.25 m3 (1251 L) net- pens in open water located near the capture site. Net-pens were constructed of stainless steel rods enmeshed with purse seine webbing (1.25 in stretch mesh). Density within each pen was maintained at fewer than 15 fish to minimize incidental mortality caused by overcrowding.

Observers monitored pens for 72-hours. This period was chosen for logistic reasons and because previous studies reported the majority of mortality occurring within 72-hrs after release (Klein 1965; Plumb et al. 1988; Warner 1978; Matlock et al., 1993). Environmental data collected during pen monitoring included: water temperature (0C), salinity (ppt), and dissolved oxygen (mg/L). Data were collected at each pen at 24-hr intervals during the 72-hr holding period. During each 24-hr observation, dead fish were removed, identified by tag, and discarded.

For analyses, these data were grouped into two areas: 1) River sites (low salinity), and 2) Outer Banks sites (high salinity). To investigate whether any of several variables explain 72-hour postrelease mortality statistical methods outlined by Murphey et al. (1995) were utilized. Independent variables considered in the analysis were fish length, water temperature, salinity, dissolved oxygen, pen, site, mesh size, twine size and soak time. Each variable’s contribution to a linear logistic multiple regression. The model was fit with stepwise techniques (SAS Institute 1989) and will describe the probability of mortality (M) for individual fish as:

u u PMortality  e /1 e , where u is a linear function of the independent variables. The stepwise linear logistic regression had an acceptance level, based on a residual chi-square statistic (SAS Institute 1989), of 0.10 for incorporating a variable into the model and an acceptance level of 0.10 for retaining a variable. A log-likelihood statistic was used to assess significance of the model. Factors associated with delayed mortality of red drum, and striped bass were identified and estimates of delayed mortality provided by area, season, and gear.

4-7

Map A

Map B

Trials were conducted between April and August 2001. Water temperatures are generally higher, while dissolved oxygen content is relatively lower during this time, which may have contributed to mortality estimates. The sample size of striped bass (n = 35) and red drum (n = 55) was much lower than desired due to higher priority research needs that created a significantly shorter sampling regime. Also, bycatch numbers of these species were not as large as anticipated. Further, live fish captured were handled, transported and held in net pens, and associated physiological stressors may have influenced mortality. Importantly, these data should be used with caution as the effort herein was designed to obtain as many fish as possible and therefore does not accurately reflect bycatch in other fisheries (i.e., flounder) or discard mortality associated with other fisheries.

RESULTS

Catches

There were 90 finfish captured in large mesh gillnets during the study period. The total numbers of each species caught were similar between the sampling months. Catches were distributed evenly throughout the study period with 35 striped bass and 55 red drum captured (Table 1).

The majority of striped bass (89%, n = 31) were observed in April and May, while the bulk of red drum (53%, n = 29) were observed in August. However, there was a significant percentage (40%) of red drum observed in May and June (Table 1). Table 1. Number of striped bass and red drum caught by month in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted at sites located in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season.

SPECIES JAN FEB MAR APR MAY JUN JUL AUG SPE OCT NOV DEC striped bass . . . 19 12 2 2 . . . . .

red drum . . . 3 9 13 1 29 . . . .

The length frequency distributions for each mesh size (5.0 – 6.5 in stretched mesh) indicated minimal selectivity trends for each species. Striped bass ranged from 457 mm to 762 mm, and catches were dispersed evenly in each mesh size. However, there were fewer (n = 5) striped bass caught in the 6 in stretched mesh panels. Most striped bass (63%, n = 22) caught ranged from 584 mm to 686 mm (Table 2). Similarly, catches of red drum were dispersed evenly, and the majority (62%, n = 34) ranged from 584 mm to 660 mm (Table 3).

Total Mortality

Mortality of each species was characterized in three ways: 1) at net mortality, representing initial condition of fish upon retrieval of the net, 2) delayed mortality, consisting of fish mortality after being

4-9 held in the net pens for 72 hrs, and 3) total mortality, the sum of at net mortality and delayed mortality. Data were pooled for all sampling locations, and mortality was compared between the trial periods. Table 2. Length frequency distributions of striped bass captured in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season. Striped bass (number caught by mesh size) Size Class (in) 5 5.5 6 6.5

18 2 0 0 0 19 1 0 0 1 20 1 0 0 0 21 0 1 0 1 22 0 1 0 1 23 2 1 0 2 24 1 2 3 2 25 1 1 0 0

26 0 0 0 1 27 1 2 1 2 28 0 1 0 0 29 1 0 0 0 30 0 1 1 0

TOTALS 10 10 5 10

Total mortality was determined for each mesh size to discern trends between species and mesh size (Table 4). Striped bass exhibited relatively high mortality in all mesh sizes averaging 69%. The highest mortality (80%) in striped bass occurred in the 6.0 and 6.5 in stretched mesh panels. Decreased mortality (50%) was observed for striped bass caught in the 5.5 in stretched mesh. Red drum mortality averaged 76% across all mesh sizes, and the highest mortality (93%) occurred in the 6.0 in stretched mesh. There was an increasing trend in total mortality from the 5.0 to 6.0 in stretched mesh panels (54% to 93%, respectively), where mortality rates declined to 83%. The lowest mortality for red drum was 54% in the 5.0 in stretched mesh (Table 4).

At Net Mortality

Mortality was also characterized by at net mortality, the initial condition of fish upon capture. Mortality was 66% for both striped bass and red drum (Table 5). At net mortality was also characterized by month to discern seasonal variations (Table 6). The highest striped bass mortality (82%, n = 31) was observed in April and May. There were no striped bass collections in August. Likewise, of the red drum mortality at the net, the majority (86%, n = 42) was found in June and August (Table 6).

Delayed Mortality

Noteworthy, are the differences in delayed mortality for each species between areas: Outer Banks (high salinity) and River (low salinity) sites. Collection numbers of both species captured at River

4-10 sites were low, and no delayed mortality was observed in striped bass (0%, n = 2) or red drum (0%, n = 6) at these sites (Table 7). The delayed mortality of red drum was significantly higher (50%) compared to striped bass mortality (10%) in the Outer Banks sites. Table 3. Length frequency distributions of red drum captured in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season. Red Drum (number caught by mesh size) Size Class (in) 5 5.5 6 6.5

11 0 0 0 1 12 0 1 0 0 13 0 0 0 0 14 0 0 0 0 15 0 0 0 0 16 1 0 1 1 17 0 1 1 1 18 2 0 0 3 19 1 0 0 0 20 2 0 1 0 21 0 1 0 0 22 0 0 0 0 23 2 1 2 0 24 2 3 3 0 25 2 6 4 4 26 1 2 2 0 27 0 0 0 1 28 0 0 0 1 44 0 0 1 0

TOTALS 13 15 15 12 Table 4. Percent mortality (at net delayed) of striped bass and red drum caught by mesh size in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound, and Roanoke Sound, NC during the 2001 fishing season. Mesh Size 5.0 5.5 6.0 6.5 n % Mort n % Mort n % Mort n % Mort

striped bass 10 70 10 50 5 80 10 80

red drum 13 54 15 73 15 93 12 83

4-11 Table 5. Total mortality, at net mortality (upon capture), and delayed mortality of striped bass and red drum caught in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season.

Species Mortality Type Alive Dead % Mort striped bass Total 11 24 68.57

At Net 12 23 65.71 Delayed 11 1 8.33

red drum Total 13 42 76.36 At Net 19 36 65.45 Delayed 12 6 33.33 Table 6. At net mortality by month (Apr – Aug) of striped bass and red drum caught in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season. Species Month Alive Dead % Mort striped bass April 10 9 39 May 2 10 43 June 0 2 9 July 0 2 9 red drum April 2 1 3 May 6 3 8 June 3 10 28 July 0 1 3 August 8 21 58

Banks River

Dead Alive % Mort Dead Alive % Mort

striped bass 1 9 10 0 2 0 red drum 6 6 50 0 6 0

Day of Death

Net pens were monitored at 24-hr intervals for 3 days to determine the time of delayed mortality for each species. There were no mortality trends from day 1 to day 3 in either species. Striped bass mortality only occurred on day 2 (Figure 2). However, collection numbers were low (n = 12) for this species. The majority of red drum mortality (67%, n = 4) occurred on day 2. There were an equal

4-12 number of mortalities on day 1 and day 3 for red drum representing a combined 33% of the delayed mortality (Figure 2).

Water quality

Water quality data were taken at 24-hr intervals at each pen and included temperature, dissolved oxygen, and salinity. Mean water temperatures were lower (22 C) at Outer Banks sites compared to 25 C at River sites (Table 8). Temperature ranged from 12 C to 27 C at Outer Banks sites. A smaller range of 21 C to 28 C was found in the River sites. There was a decreasing trend in dissolved oxygen from the Outer Banks sites when compared to the River sites. The mean dissolved oxygen content was 7 mg/L, and ranged from 6 mg/L to 9 mg/L at the Outer Banks sites, while the mean was 6 mg/L at River sites, with little variation (Table 8). High salinities occurred at the Outer Banks sites averaging 15 ppt and ranging from 12 ppt to 21 ppt. At the River sites, mean salinity was 7 ppt (Table 8). Figure 2. Day of death for striped bass and red drum caught in the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season.

Generally, the highest water temperatures, and lowest dissolved content were observed in the late summer months (Table 8). The highest mean water temperature (28 C) occurred in July at River sites, while the lowest dissolved oxygen content was 6 mg/L and occurred at this low level at both sites. There was little fluctuation in salinity at River sites, but at Outer Banks sites, the highest salinity was 21 ppt and occurred in August (Table 8).

Statistical analyses

To perform the logistic regression analyses, Outer Banks (high salinity) and River (low salinity) sites were pooled together to assess the influence of multiple variables on delayed mortality for each species. Chi Square tests were performed to determine if each independent variables relationship to

4-13 mortality was significant. Each significant variable was included in a logistic regression model. Additionally, variable interactions were tested for their relationship to mortality with a General Linear Model (GLM). Interactions with significant relationships were also included in the logistic regression model. The logistic model was fit with stepwise techniques (SAS Institute 1989) and describes the probability of mortality (PMortality) for each species as

u u PMortality  e /1 e , where u is a linear function of the independent variable. Independent variable considered in the analysis were fish length, water temperature (< 9 C, 9 – 18 C, > 18 C), trial (spring/summer, fall/winter), area (Outer Banks, River) dissolved oxygen (< 8 mg/L, > 8mg/L), salinity (< 10 ppt, 10 – 19 ppt, > 19 ppt), and mesh Size (5.0, 5.5, 6.0, 6.5 in stretch mesh). There were no significant variable interactions. Table 8. Water quality data collected during the large mesh (5.0, 5.5, 6.0, 6.5 in stretched mesh) gillnet discard mortality study conducted in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season. Data include mean water temperature (C), mean dissolved oxygen content (mg/L), and mean salinity (ppt) for the Outer banks and river sites by month.

Banks River TEMP DO SAL TEMP DO SAL JAN ...... FEB ...... MAR ...... APR 11.78 8.55 13.21 . . . MAY . . . 20.96 06.06 07.50 JUN 27.16 7.55 12.42 . . . JUL . . . 28.17 05.57 07.23

AUG 26.89 6.25 20.81 . . . SEP ...... OCT ...... NOV ...... DEC ......

Logistic regression analyses for striped bass contained the independent variable temperature. The mortality rate of striped bass was significantly (p < 0.04) related to temperature (Table 9). Combining the intercept and parameter estimates from Table 9 allow for the estimation of mortality using the following equation, where P(M) = the probability of mortality for striped bass as: e-2.251+1.8403(Temperature)

P(M) striped bass = 1+ e-2.251+1.8403(Temperature) where the following discrete values have been assigned to temperature:

Temperature 0 = < 9 C 1 = 9 - 18 C 2 = > 18 C

4-14 Table 9. Summary of stepwise logistic regression analyses of independent variables on 72-h discard mortality of striped bass caught in large mesh gillnets (5.0, 5.5, 6.0, 6.5 in. stretch mesh) in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season.

Striped Bass (Large Mesh)

Odds

Independent Variable df X2 P Estimate Ratioa

Temperature 1 4.3284 0.0375 1.8403 6.298

a Indicates the increase or decrease in the odds of mortality associated with a variable; a ratio of 1.0 indicates no difference.

Logistic regression analyses for red drum contained the independent variables: temperature, salinity, and mesh size. The mortality rate of red drum was significantly (p < 0.08) related to all three variables (Table 10). Combining the intercept and parameter estimates from Table 9 allow for the estimation of mortality using the following equations, where P(M) = the probability of mortality for red drum as:

e-2.251+2.8608(Temperature) + 2.3157(Salinity) + 2.2635(Mesh Size)

P(M) red drum = 1+ e-2.251+2.8608(Temperature) + 2.3157(Salinity) + 2.2635(Mesh Size) where the following discrete values have been assigned to each variable:

Temperature 0 = < 9 C Sal 0 = < 10 ppt 1 = 9 - 18 C 1 = 10-19 ppt 2 = > 18 C 2 = > 19 ppt

Mesh Size 5.0 – 6.5 in stretch mesh Table 10. Summary of stepwise logistic regression analyses of independent variables on 72-h discard mortality of red drum in large mesh gillnets (5.0, 5.5, 6.0, 6.5 in. stretch mesh) in Pamlico Sound and Roanoke Sound, NC during the 2001 fishing season. Red Drum (Large Mesh)

Odds Independent Variable df X2 P Estimate Ratioa

Temperature 1 3.0738 0.0796 2.8608 17.476 Salinity 1 10.5792 0.0011 2.3157 10.132 Mesh Size 1 5.1643 0.0231 2.2635 9.617

a Indicates the increase or decrease in the odds of mortality associated with a variable; a ratio of 1.0 indicates no difference.

4-15 DISCUSSION

The delayed mortality of striped bass was comparatively low (8%, n = 12) to delayed mortality (33%, n = 18) of red drum (Table 5). The total and at net mortality were greater than 65% for striped bass and red drum (Table 5). The size selectivity of gillnets is such that larger mesh sizes tend to capture bigger fish (Reis and Pawson, 1999). Catch numbers of each species were evenly distributed in all mesh sizes (Tables 2, 3). However, a selectivity trend was apparent as larger sized fish (> 28 in for striped bass, > 27 in for red drum) were captured in larger mesh panels. Logistic regression analyses indicated mesh size significantly (p = 0.02) related to mortality in red drum (Table 10), and it is likely that an increased sample size would show similar significance in striped bass. Water temperature averaged 23 C (combined areas) and was higher (25 C) in River sites (Table 8). Temperature was directly related to mortality for striped bass (p = 0.04), and red drum (p = 0.08), and is possibly the best indicator for mortality in this study. The strongest indicator (p = 0.001) for red drum mortality was salinity (Table 10), which averaged 16 ppt at Outer Banks sites and 7 ppt at River sites. The highest temperature and salinity was recorded in July and August, and 61% (n = 30) of red drum mortality (at net) was observed at this time (Table 6). By contrast, the majority (82%, n = 31) of striped bass mortality was observed in April and May, but there were only four fish collected in the later months. No delayed mortality was observed at River sites, but samples were comparatively low at River sites, which may explain the lack of River mortalities (Table 7). There were no discernable trends in the day of death for either species, which could be interpreted as no effect of net pen, but these estimates should be used with caution. For both species, sample sizes were much lower than desired and precise conclusions cannot be drawn from these estimates.

Related research suggests a comparable total, and at net mortality for red drum from captures in small mesh (< 4.5 in stretched mesh) gillnets (Price and Gearhart, 2002). Delayed mortalities were greatly reduced in the small mesh gillnet study, but a superior sample size, and longer sampling duration accounted for this difference. In hook and line delayed mortality surveys, striped bass mortality was less than 5%, while red drum adjusted total mortality was 2.9% (Gearhart, 2002 A and B). Preliminary results from work in progress shows methodology that could be used to estimate striped bass discard mortality in flounder and shad nets (small and large mesh) with the use of 25% - 75% probability ranges (Dilday personal communication, 2002). Attempts to quantify discard mortality of finfish released from gillnets are currently limited to estimations based on an array of assumptions. While these are practical for preliminary assessments, these data should be used with caution in management of recreational and commercial fisheries due to the lack of large sample sizes, elimination of confounding variables, and implementation of control groups in project design. Discard mortality research needs extensive evaluation, and there are few studies in the literature that address this contentious issue. To effectively manage fisheries, quantifying post-capture finfish mortalities needs precise clarification. This information will allow mortality percentages to be applied to the discard numbers and result in more accurate stock assessments.

4-16 CONCLUSION

Two important questions that are often unanswered during the development of FMPs are: 1) How much bycatch occurs in various fisheries, and 2) What is the mortality of the bycatch in these fisheries? Similar to the small mesh gillnet study (Price and Gearhart, 2002), this study was designed to answer the later question and identify predictors of mortality for red drum, and striped bass. Relevant discussion and suggestions from these data, which may assist in FMPs, are presented below for each species.

Striped Bass

The management of the striped bass dates back to the 1880s with early stocking programs (Rulifson and Laney, 1999). Despite past declines of the striped bass population in North Carolina due to such factors as dams, channelization of river systems, industrial water intakes, the striped bass are currently declared recovered by the federal government, NCWRC, and NCDMF (Carmichael, 2001). There is great incentive to maintain these recovered and economically vital stocks. Results from this discard mortality research, show about 8% striped bass mortality. As the striped bass population continues to grow this level of discard mortality may not be acceptable for sustaining the population. Importantly though, precise conclusions cannot be drawn from these mortality estimates. To verify these preliminary findings, it will be necessary to broaden this study, obtain an increased sample size, and utilize a control group in project design.

Red Drum

Red drum are primarily captured recreationally by hook and line gear and as bycatch in commercial gillnet fisheries. Stocks remain overfished, but current data suggests that recruitment may be increasing (Paramore, 2001). The red drum fishery is managed by slot-limit restrictions (< 18” and > 27”), a recreational bag limit of 1 fish per day, and a harvest quota of 50 lbs/day.

Compared to a small mesh (< 4.5 in stretched mesh) study (Price and Gearhart, 2002), total, at net, and delayed mortalities were higher in the large mesh (> 5.0 in stretched mesh) study. This likely reflects the smaller sample size (n = 18) relative to the increased numbers (n = 1236) captured in the small mesh study, which also was conducted for 1 year. Minimal trends were observed between independent variables and red drum mortality, however logistic regression analyses demonstrated that salinity, temperature and mesh size were significantly related (p < 0.08) to red drum mortality.

4-17 RECOMMENDATIONS

This study suggests that discard mortality rates of finfish captured in gillnet fisheries needs further examination. These data identify factors that influence mortality of fish caught in large mesh gillnets, but should be used with caution due to a small sample size, and the lack of clarification with potentially confounding variables (i.e., handling, transport, confinement) that may influence mortality.

 Expand the methodologies implemented in this project to other independent gillnet research compensating for the confounding affects of stress induced mortalities associated with handling, transport, and confinement.

 To eliminate confinement stressors and establish a control group, it may necessary to implement a radio-telemetry tagging and tracking regime to monitor the condition of released fish captured in gillnets. Compounded to eliminating confinement stressors, seasonal fish location data could also be obtained.

 Expand the methodologies implemented in this project to fishery-dependent gillnet research in North Carolina.

 In future research projects, establish a control group to compare the delayed mortality estimates of fish held in net pens, to those released after initial capture.

 Establish consistent observer coverage in gillnet fisheries throughout North Carolina to accurately assess bycatch numbers for each species. Compounded to more precise mortality estimates, this information will assist in the development of FMPs and maintaining sustainable stocks.

4-18 ACKNOWLEDGMENTS

The assistance of numerous individuals was instrumental in the work reported here. Thanks are extended to Parks Lewis, Matt Butzin, and many other NCDMF staff members that participated in data collections and equipment construction and maintenance.

4-19 LITERATURE CITED

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Dilday, Jason 2001. Stock status report on the striped bass. North Carolina Division of Marine Fisheries, Morehead City, North Carolina.NCDMF, 2001.

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4-20 Paramore, Lee. 2001. Stock status report of the red drum 2001. North Carolina Division of Marine Fisheries, Morehead City, North Carolina.

Personal communication 2002. Jason Dilday. Preliminary results of: Striped bass discard mortality in the unattended and attended multispecies gill net fishery in the Albemarle Sound Management Area. North Carolina Division of Marine Fisheries, Elizabeth City, North Carolina.NCDMF, 2002.

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4-21 Wilson, C.J. 1999. Mesh size selectivity of gill nets in western Pamlico Sound, North Carolina. Masters Thesis, East Carolina University, Greenville, NC.

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