Sea Turtle Bycatch in a Demersal Gillnet Fishery in Pamlico Sound, North Carolina
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Sea Turtle Bycatch in a Demersal Gillnet Fishery in Pamlico Sound, North Carolina Alan Bianchi, North Carolina State University, Department of Zoology, Campus Box 7617, Raleigh, NC 27695-7617 Introduction The southern flounder (Paralichthys lethostigma) fishery is one of the most valuable finfish fisheries along the coast of North Carolina; landings of this fishery were valued at over $7 million in 1995 (NCDMF 1997). A large portion of this fishery is conducted in Pamlico Sound, North Carolina during the annual flounder fall migrations (September 15 to December 15). The increase in gillnet abundance utilized in this fishery over the past 10 years has begun to raise concerns among conservationists and fisheries managers. Not only has the concentration of gillnets increased, so has the number of sea turtle strandings in the southeastern portion of Pamlico Sound (NCDMF 2000; Gearhart 2001; NCDMF 2001a). The increase in sea turtle strandings prompted the North Carolina Division of Marine Fisheries (NCDMF) and the National Marine Fisheries Service (NMFS) to conduct observer trips on two gillnet fisheries, the spotted trout (Cynoscion nebulosus) and southern flounder fisheries, operating in the area in the fall of 1999 (NCDMF 2000; Gearhart 2001; NCDMF 2001). Observes implicated the southern flounder gillnets as a possible cause to the increase in strandings when two Kemp’s ridley (Lepidochelys kempii) sea turtles were observed taken on flounder trips and no sea turtle interactions were recorded during spotted trout trips (NCDMF 2000; Gearhart 2001; NCDMF 2001). The goal of this study was to determine the impact that southern flounder gillnets could be having on sea turtles in Pamlico Sound, NC. Examination of the catch-per-unit-effort of sea turtles were compared among the deep and shallow areas of Pamlico Sound, the first and second halves of the season, gear parameters, soak time, and gear configurations. The objectives of this study are: 1). To characterize the sea turtle bycatch composition and distribution, 2). To suggest reasonable and prudent regulations for the fishery and 3). To test experimental gillnet configurations in an effort to reduce sea turtle bycatch. Study Area The southern flounder gillnet fishery of Pamlico Sound, North Carolina is operated in two primary areas of the sound, which are separated by a sandbar (Figure 1). The shallow area is on the barrier island side of the sandbar while the deep area is located on the mainland side of the sandbar (Figure 1). Water depth in the shallow area rarely exceeds 3 m while the deep area ranges from 3-7 m. Figure 1 Deep and shallow water southern flounder gillnet fisheries of Pamlico Sound, North Carolina (Map Generated by the NCDMF). Methods •Data was collected from observer trips during the 2000 and 2001 seasons •Gear testing was conducted during the 2001 season and consisted of testing a control, double lead-line, and low profile configured gillnets in the deep water area •Catch-per-unit-effort = number of sea turtles / (100 meters * soak time) •Analysis divided into fishing practices (area, season, effort) and gear parameters (mesh size, length, twine size, etc.) •Logistical Regression analysis utilizing a backward model selection was employed to detect which variables were significant in the fishing practices and gear parameters analysis Species Alive Dead Total CPUE * Green 6 4 10 2.65 -2 Loggerhe ad 6 2 8 2.12 -2 Kemp’s Ridley 2 2 4 1.06 -2 Total 14 8 22 5.83 -2 Table 1 Total number of sea turtle interactions observed in the 2000 southern flounder gillnet fishery of Pamlico Sound, NC. *CPUE = Total number of sea turtles / total number of nets employed Table 2 Paired t-test analysis between sea turtle CPUE for 2000 southern flounder gillnet fishery of Pamlico Sound, NC. Test t-value p-value Green-Kemp’s 2.05 0.0408 Green- Loggerhead 1.75 0.0814 Loggerhead- Kemp’s 0.81 0.4205 Figure 2 Proportion of Sea Turtle Interactions ( std. error) vs. Area during the 2000 southern flounder gillnet fishery of Pamlico Sound, NC. A rea -0.01 0.04 0.09 0.14 1 2 A rea (A rea 1=shallow ,2=deep) P ro p o rtio n o fS e T u rtle In teractio n Figure 3 Proportion of Sea Turtle Interactions ( std. error) vs. Meters during the 2000 southern flounder gillnet fishery of Pamlico Sound, NC. -0.2 0 0.2 0.4 0.6 0.8 1 0 200 400 600 800 1000 1200 M eters Proportion of Sea Interactions Figure 4 Proportion of Sea Turtle Interactions ( std. error) vs. Height during the 2000 southern flounder gillnet fishery of Pamlico Sound, NC. 0 0.2 0.4 0.6 0.8 1 10 12 15 17 17.5 18 20 22 25 27.5 35 H eight(VerticalM esh C ount) Proportion of Sea Tur Interactions Conclusion The data gathered from this study seems to suggest that moving the starting date for the fishery or decreasing the amount of effort employed during the first half of the season will decrease the number of sea turtle takes. Even though the halves of the fishing season was not a significant factor, there were more than six times as many sea turtle interactions recorded in the first half than the second half. Sea turtles are still common in the area during the first two weeks of the season because water temperatures are still warm. During the 2000 season, water temperatures were unseasonably warm during both halves of the fishing season, which could have contributed to season being an insignificant factor because sea turtles were still present in the sound even in November (pers. observation). Moving the start date for the fishery back to October 1 (about 2 weeks) or reducing fishing effort by allowing fishermen to fish only 2 or 3 days a week during the first 2 weeks to reduce total fishery effort is suggested. Regulations are needed for the deep-water portion of the southern flounder fishery. Implementation of the low profile net did not result in a single sea turtle take. Also, these nets were approximately half as long (273 m) and half as tall (12 mesh vertical count) as the gillnets typically fished in the deep-water fishery. All sea turtle interactions occurred in gillnets with a vertical mesh count of 17 or more and the majority of sea turtle interactions occurred in nets with a length over 273 m (Figures 3 and 4). Also, these nets do not utilize a tie-down configuration, which is believed to increase sea turtle entanglement (J. Gearhart, pers. comm. 2001), however this analysis did not detect such an affect. Therefore, it is suggested that the deep-water fishery employ the low profile nets to help reduce the number of sea turtle takes. Works Cited Gearhart, J. 2001. Sea Turtle Bycatch Monitoring of the 2000 Fall Flounder Gillnet Fishery of Southeastern Pamlico Sound, North Carolina. NCDMF Completion Report for Incidental Take Permit 1259. NCDMF, Morehead City, North Carolina. 26 pp. North Carolina Division of Marine Fisheries. 2001. Application for an Individual Incidental Take Permit Under the Endangered Species Act of 1973. North Carolina Division of Marine Fisheries, Morehead City, NC. 29 pp. North Carolina Division of Marine Fisheries. 2000. Application for and Individual Incidental Take Permit Under the Endangered Species Act of 1973. North Carolina Division of Marine Fisheries, Morehead City, NC. 25 pp. Acknowledgements I would like to take this time to thank Dr. B. J. Copeland, Dr. Jim Rice, and Dr. Lundie Spence for their invaluable encouragement and support. I would also like to thank Jeff Gearhart and his crew at the North Carolina Division of Marine Fisheries for their cooperation and patience and Charles VanSalsbury for allowing me to be an observer on his fishing vessel. Special thanks go out to Larissa Bailey, Bob Barwick, Corey Oakley, Rob Aguilar and to the rest of the zoology graduate students at NCSU for their support and ideas. This study was supported by a grant received from the NOAA. Support was also received from NCDMF, NMFS, North Carolina Sea Grant Program and NCSU. Results •Total of 22 sea turtle interactions observed during the 2000 season o15 sea turtle interactions observed in the deep area of Pamlico Sound o19 sea turtle interactions observed in the first half of the fishing season •No significance between finding a sea turtle dead or alive, however it was suggestive (t = 1.92, p-value = 0.0562, Table 1) •Between species, only the CPUE of greens was significantly different than the CPUE of Kemp’s ridleys (t = 2.05, p- value = 0.0408, Table 2) •Area was the only significant variable in the fishing practices analysis (p- value = 0.0335, Figure 2) •Meters (length) of gillnet was the only significant variable in the gear parameter analysis (p-value = 0.002, Figure 3) •Height was not significant during backward elimination selection, however when analyzed separately it was significant (p-value = 0.0368, Figure 4) •Backward elimination selection analysis with area and length determined that length was the most significant factor (p-value = 0.0048) •4 sea turtle, all Kemp’s ridleys, interactions were observed during the 2002 gear testing, 3 in the control configuration and 1 in the double lead-line configuration
description
Species. Alive. Dead. Total. CPUE *. Green. 6. 4. 10. 2.65 -2. Tes t. t -value. p-value. Loggerhead. 6. 2. 8. 2.12 -2. Green-Kemp’s. 2.05. 0.0408. Kemp’s Ridley. 2. 2. 4. 1.06 -2. Green-Loggerhead. 1.75. 0.0814. Total. 14. 8. 22. 5.83 -2. Loggerhead-Kemp’s. 0.81. - PowerPoint PPT Presentation
Transcript of Sea Turtle Bycatch in a Demersal Gillnet Fishery in Pamlico Sound, North Carolina
Sea Turtle Bycatch in a Demersal Gillnet Fishery in Pamlico Sound, North Carolina Alan Bianchi, North Carolina State University, Department of Zoology, Campus Box 7617, Raleigh, NC 27695-7617
Introduction
The southern flounder (Paralichthys lethostigma) fishery is one of the most valuable finfish fisheries along the coast of North Carolina; landings of this fishery were valued at over $7 million in 1995 (NCDMF 1997). A large portion of this fishery is conducted in Pamlico Sound, North Carolina during the annual flounder fall migrations (September 15 to December 15). The increase in gillnet abundance utilized in this fishery over the past 10 years has begun to raise concerns among conservationists and fisheries managers. Not only has the concentration of gillnets increased, so has the number of sea turtle strandings in the southeastern portion of Pamlico Sound (NCDMF 2000; Gearhart 2001; NCDMF 2001a). The increase in sea turtle strandings prompted the North Carolina Division of Marine Fisheries (NCDMF) and the National Marine Fisheries Service (NMFS) to conduct observer trips on two gillnet fisheries, the spotted trout (Cynoscion nebulosus) and southern flounder fisheries, operating in the area in the fall of 1999 (NCDMF 2000; Gearhart 2001; NCDMF 2001). Observes implicated the southern flounder gillnets as a possible cause to the increase in strandings when two Kemp’s ridley (Lepidochelys kempii) sea turtles were observed taken on flounder trips and no sea turtle interactions were recorded during spotted trout trips (NCDMF 2000; Gearhart 2001; NCDMF 2001). The goal of this study was to determine the impact that southern flounder gillnets could be having on sea turtles in Pamlico Sound, NC. Examination of the catch-per-unit-effort of sea turtles were compared among the deep and shallow areas of Pamlico Sound, the first and second halves of the season, gear parameters, soak time, and gear configurations. The objectives of this study are: 1). To characterize the sea turtle bycatch composition and distribution, 2). To suggest reasonable and prudent regulations for the fishery and 3). To test experimental gillnet configurations in an effort to reduce sea turtle bycatch.
Study Area
The southern flounder gillnet fishery of Pamlico Sound, North Carolina is operated in two primary areas of the sound, which are separated by a sandbar (Figure 1). The shallow area is on the barrier island side of the sandbar while the deep area is located on the mainland side of the sandbar (Figure 1). Water depth in the shallow area rarely exceeds 3 m while the deep area ranges from 3-7 m.
Figure 1 Deep and shallow water southern flounder gillnet fisheries of Pamlico Sound, North Carolina (Map Generated by the NCDMF).
Methods •Data was collected from observer trips during the 2000 and 2001 seasons•Gear testing was conducted during the 2001 season and consisted of testing a control, double lead-line, and low profile configured gillnets in the deep water area•Catch-per-unit-effort = number of sea turtles / (100 meters * soak time)•Analysis divided into fishing practices (area, season, effort) and gear parameters (mesh size, length, twine size, etc.)•Logistical Regression analysis utilizing a backward model selection was employed to detect which variables weresignificant in the fishing practices and gear parameters analysis
Species Alive Dead Total CPUE*
Green 6 4 10 2.65-2
Loggerhead 6 2 8 2.12-2
Kemp’s Ridley
2 2 4 1.06-2
Total 14 8 22 5.83-2
Table 1 Total number of sea turtle interactions observed in the 2000 southern flounder gillnet fishery of Pamlico Sound, NC.
*CPUE = Total number of sea turtles / total number of nets employed
Table 2 Paired t-test analysis between sea turtle CPUE for 2000 southern flounder gillnet fishery of Pamlico Sound, NC.
Test t-value p-value
Green-Kemp’s 2.05 0.0408
Green-Loggerhead 1.75 0.0814
Loggerhead-Kemp’s
0.81 0.4205
Figure 2 Proportion of Sea Turtle Interactions ( std. error) vs. Area during the 2000 southern flounder gillnet fishery of Pamlico Sound, NC.
Area
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Figure 3 Proportion of Sea Turtle Interactions ( std. error) vs. Meters during the 2000 southern flounder gillnet fishery of Pamlico Sound, NC.
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Figure 4 Proportion of Sea Turtle Interactions ( std. error) vs. Height during the 2000 southern flounder gillnet fishery of Pamlico Sound, NC.
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Conclusion
The data gathered from this study seems to suggest that moving the starting date for the fishery or decreasing the amount of effort employed during the first half of the season will decrease the number of sea turtle takes. Even though the halves of the fishing season was not a significant factor, there were more than six times as many sea turtle interactions recorded in the first half than the second half. Sea turtles are still common in the area during the first two weeks of the season because water temperatures are still warm. During the 2000 season, water temperatures were unseasonably warm during both halves of the fishing season, which could have contributed to season being an insignificant factor because sea turtles were still present in the sound even in November (pers. observation). Moving the start date for the fishery back to October 1 (about 2 weeks) or reducing fishing effort by allowing fishermen to fish only 2 or 3 days a week during the first 2 weeks to reduce total fishery effort is suggested.
Regulations are needed for the deep-water portion of the southern flounder fishery. Implementation of the low profile net did not result in a single sea turtle take. Also, these nets were approximately half as long (273 m) and half as tall (12 mesh vertical count) as the gillnets typically fished in the deep-water fishery. All sea turtle interactions occurred in gillnets with a vertical mesh count of 17 or more and the majority of sea turtle interactions occurred in nets with a length over 273 m (Figures 3 and 4). Also, these nets do not utilize a tie-down configuration, which is believed to increase sea turtle entanglement (J. Gearhart, pers. comm. 2001), however this analysis did not detect such an affect. Therefore, it is suggested that the deep-water fishery employ the low profile nets to help reduce the number of sea turtle takes.
Works Cited
Gearhart, J. 2001. Sea Turtle Bycatch Monitoring of the 2000 Fall Flounder Gillnet Fishery of Southeastern Pamlico Sound, North Carolina. NCDMF Completion Report for Incidental Take Permit 1259. NCDMF, Morehead City, North Carolina. 26 pp.
North Carolina Division of Marine Fisheries. 2001. Application for an Individual Incidental Take PermitUnder the Endangered Species Act of 1973. North Carolina Division of Marine Fisheries, Morehead City, NC. 29 pp.
North Carolina Division of Marine Fisheries. 2000. Application for and Individual Incidental Take Permit Under the Endangered Species Act of 1973. North Carolina Division of Marine Fisheries, Morehead City, NC. 25 pp.
Acknowledgements
I would like to take this time to thank Dr. B. J. Copeland, Dr. Jim Rice, and Dr. Lundie Spence for their invaluable encouragement and support. I would also like to thank Jeff Gearhart and his crew at the North Carolina Division of Marine Fisheries for their cooperation and patience and Charles VanSalsbury for allowing me to be an observer on his fishing vessel. Special thanks go out to Larissa Bailey, Bob Barwick, Corey Oakley, Rob Aguilar and to the rest of the zoology graduate students at NCSU for their support and ideas.
This study was supported by a grant received from the NOAA. Support was also received from NCDMF, NMFS, North Carolina Sea Grant Program and NCSU.
Results •Total of 22 sea turtle interactions observed during the 2000 season
o15 sea turtle interactions observed in the deep area of Pamlico Soundo19 sea turtle interactions observed in the first half of the fishing season
•No significance between finding a sea turtle dead or alive, however it was suggestive (t = 1.92, p-value = 0.0562,Table 1)•Between species, only the CPUE of greens was significantly different than the CPUE of Kemp’s ridleys (t = 2.05,
p-value = 0.0408, Table 2)•Area was the only significant variable in the fishing practices analysis (p-value = 0.0335, Figure 2)•Meters (length) of gillnet was the only significant variable in the gear parameter analysis (p-value = 0.002, Figure
3)•Height was not significant during backward elimination selection, however when analyzed separately it wassignificant (p-value = 0.0368, Figure 4)•Backward elimination selection analysis with area and length determined that length was the most significant factor(p-value = 0.0048)•4 sea turtle, all Kemp’s ridleys, interactions were observed during the 2002 gear testing, 3 in the control configuration and 1 in the double lead-line configuration
