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Fishery Bulletin 102(4) 



probability of bycatch can motivate bycatch mitigation 

 research. Finally, the ability to predict bycatch on the 

 basis of explanatory variables allows one to examine the 

 relative effectiveness of different management measures 

 designed to reduce bycatch (Kobayashi and Polovina 2 ). 

 Ultimately this framework can improve the assessment 

 of threats to turtles and broaden conservation options. 



Magnitude of bycatch 



During May-December in 2001 and 2002, an estimated 

 169 animals were captured incidentally by commercial 

 sea scallop dredge vessels in two areas of the Mid- Atlan- 

 tic Bight. Throughout the entire Mid-Atlantic Bight, the 

 magnitude of bycatch was probably larger, particularly 

 because the factors associated with the high bycatch 

 rates were not specific to the controlled access areas. Of 

 the 11 observed turtles measured for size, 9 (82%) were 

 between 70-80 cm straight carapace length (the large 

 juvenile stage). Stage class models indicate that the long- 

 term survivability of loggerhead sea turtles is sensitive 

 to mortality at this life stage (Crouse et al., 1987). 



Factors influencing bycatch 



The incidental capture of turtles occurs where there 

 is overlap between fishing effort and turtle habitat. 

 The elevated probability of turtle bycatch occurring 

 in warm waters, during summer, at depths between 

 50 and 60 m is consistent with the habitat regime of 

 loggerhead sea turtles in the Mid-Atlantic (Shoop and 

 Kenney, 1992; Epperly et al., 1995; Coles and Musick, 

 2000). During the oceanic phase of their life cycle, sea 

 turtles occupy habitats at specific temperatures or with 



bathymetric features that concentrate prey and other 

 areas of enhanced productivity (Polovina et al.. 2000). 

 In Mid-Atlantic waters, high aggregations of loggerhead 

 sea turtes have been observed in the summer, in waters 

 22-49 m deep, at temperatures from 20° to 24°C (Shoop 

 and Kenney, 1992). In the Hudson Canyon and Virginia 

 Beach controlled access creas, the bycatch of sea turtles 

 was associated with habitat conditions rather than gear 

 characteristics. From these findings, it may be possible 

 to predict future hotspots for sea turtle bycatch in the 

 controlled access areas where fishing effort and sea 

 turtles overlap in time and space. These hotspots may 

 be centered over the portion of the Hudson Canyon 

 where depths are between 50 and 60 m. after waters 

 warm to 19 C. 



Because of the low amount of observer data in the 

 Virginia Beach area, predicted bycatch rates for this 

 area were based largely on conditions within the Hud- 

 son Canyon area. Sea scallop fishing effort occurs year- 

 round both north and south of the Hudson Canyon, 

 and high concentrations of loggerhead sea turtles (de- 

 termined from migratory patterns) exist in spring and 

 fall from North Carolina to northern Maryland ( Shoop 

 and Kenney, 1992). It is probable that the distribution 

 of turtles and scallop fishing effort co-occur in other 

 regions of the Mid-Atlantic, particularly south of the 

 Hudson Canyon. The scallop dredge fishery in the Mid- 

 Atlantic is a complex, dynamic system; there may be 

 other factors influencing the bycatch of sea turtles in 

 the fishery south of the Hudson Canyon that were not 

 observed. However, without additional data on turtle 

 interactions in these areas, it is unwise to extrapolate 

 bycatch estimates beyond the scope of the data in this 

 analysis. 



2 Kobayashi. D. R., and J. J. Polovina. 2000. Time/area 

 closure analysis for turtle take reductions. Appendix C, 

 Environmental Impact Statement, FMP for Pelagic Fisher- 

 ies of the Western Pacific, 44 p. NMFS Honolulu, Hawaii, 

 96822. 



Conservation management options 



Time and area closures Models of turtle migrations can 

 be used to predict interactions with fisheries in time 

 and space to maximize the efficiency of time and area 



