PIFSC Sea Turtle Longline Research EA June 1, 2009
3.2.3 Potential Impacts to Shark Populations
A significant bycatch issue in the Pacific Island Region as well as in many other regions of the world is the bycatch of sharks on longline and other fishing gear. In some fisheries, such as the Hawaii-based longline fisheries, shark species such as blue sharks (Prionace glauca) make up 33% of the total catch (Walsh et al. 2002), some of which are released alive, some of which are landed and sometimes finned, and some of which are discarded dead. Data suggest that blue sharks are being captured at levels close to or possibly exceeding maximum sustained yield (Clarke et al. 2006). Reports suggest that some shark populations such as scalloped hammerhead sharks (Sphyrna lewini), oceanic whitetip sharks (Carcharhinus longimanus), and tiger sharks (Galeocerdo cuvier) have decreased between 60% and 99% in certain areas (Baum et al. 2003, Baum et al. 2004). A lack of both fundamental biological information and fishery-dependent data for most shark species means that there is a high degree of uncertainty in the status of these species.
Use of circle hooks baited with squid resulted in a significant but small increase in capture of blue sharks, but when either circle hooks or J hooks are baited with fish, blue shark capture was significantly decreased (Read 2007). After the regulations requiring the use of circle hooks baited with fish were instituted in the Hawaii-based longline fishery, the CPUE of all sharks caught as bycatch declined significantly by 36%. Switching from squid to fish bait appeared to make the highest contribution to reducing the incidental catch of sharks on longline gear. Switching from squid to fish on circle hooks in the Hawaii-based longline fishery resulted in a significant and large reduction in shark capture rates without compromising target CPUE (Gilman et al. 2007).
Conclusion regarding potential impacts on shark populations from interaction with research-related longline fishing gear
Therefore, use of hooks baited with fish rather than squid in research conducted in domestic and foreign longline fleets and transferring this technology to foreign fleets to reduce sea turtle bycatch should decrease the incidental take of sharks as well, especially blue sharks, while maintaining the catch rate of target species. The use of circle hooks in the Hawaii-based shallow-set fisheries does not appear to appreciably reduce blue shark catch rates, but does appear to increase survivorship of those that are caught, based on observer records (in: SWFSC 2007). Therefore, no adverse impacts should occur to shark populations from the existing and proposed research activities, and it is expected that incidental take of sharks should decrease with the transfer of technology and use of fish bait in foreign fleets.
A cumulative impact analysis will not be conducted, as shark populations would not be impacted by the proposed action.
3.2.4 Summary of Cumulative Impacts and Climate Change Contributions
Although assessing the cumulative effects of field research projects is difficult, the past, present, and future research activities are not likely to have had or have any significant adverse effects on the environment, and have shown to be effective on reducing sea turtle bycatch without increasing bycatch of other nontarget species and while maintaining or improving CPUE of target fish. The current and proposed research and technology transfer programs are consistent