The following is an extract from Fader et al (2021)
If avoidance of depredators or minimizing contact with gear is not possible, modifying the terminal gear to release hooked animals or facilitating shedding of entangled gear may be the only option to mitigate bycatch impacts (Werner et al., 2015; Zollett and Swimmer, 2019; Swimmer et al., 2020). In longline fisheries, this strategy generally entails guidelines to encourage fishermen to remove gear from hooked or entangled animals, or the use of hooks with a targeted bending strength, such that hooks are weak enough to straighten and release toothed whales but sufficiently strong to retain target catch (Bayse and Kerstetter, 2010; Bigelow et al., 2012). This “weak-hook” strategy has been used successfully to reduce bycatch of large, non-target bluefin tuna (Thunnus thynnus) by 46% in the U.S. Gulf of Mexico pelagic longline fishery, with no statistically significant impact on catch rates of yellowfin tuna (Thunnus albacares) (Walter, 2017).
Controlled mechanical tests of bending strengths and behavior of hooks under strain in the lip tissue of dead odontocetes have helped identify candidate weak hooks for minimizing cetacean bycatch (McLellan et al., 2015). Field trials in the U.S. Atlantic large pelagics longline fishery and Hawai‘i deep-set longline fisheries have tested similar hook designs under controlled conditions (Bayse and Kerstetter, 2010; Bigelow et al., 2012). The bycatch of cetaceans was too rare to determine whether weaker hooks had a positive influence on the outcome of such events, but weaker hooks were returned straightened more often than strong hooks in each study and one pilot whale was observed released by a straightened hook in the Atlantic (Bayse and Kerstetter, 2010; Bigelow et al., 2012). Comparable rates of target catch were recorded in each study, although the Hawai‘i study was not carried out during the season when the largest tuna are caught (Bigelow et al., 2012) and the size of swordfish was slightly smaller on weak hooks in some Atlantic trials (Bayse and Kerstetter, 2010).
One obstacle to implementation of such measures is the understandable reluctance of fishermen to modify their terminal tackle, particularly if such changes might reduce the catch rates of large and valuable target species (e.g., Bigelow et al., 2012; Ayers and Leong, 2020). The post-release survival rates of animals hooked or entangled in pelagic longline gear are not well understood but have obvious and important implications for understanding population-level impacts (Garrison, 2007; Werner et al., 2015).
No difference in deployment compared with standard circle hooks.
Ayers AL, Leong K (2020) Stories of Conservation Success: Results of Interviews with Hawai‘i Longline Fishers. NOAA Adminsitrative Report H-20-11: https://doi.org/10.25923/6BNN-M598
- Bayse, S.M. and Kerstetter, D.W. 2010. Assessing bycatch reduction potential of variable strength hooks for pilot whales in a western North Atlantic pelagic longline fishery. Journal of North Carolina Academy of Science 126(1): 6-14.
- Bigelow, K.A., Kerstetter, D.W., Dancho, M.G., and Marchetti, J.A. 2012. Catch rates with variable strength circle hooks in the Hawaii-based tuna longline fishery. Bulletin of Marine Science 88: 425-447.
- Clarke, S., Sato, M., Small, C., Sullivan, B., Inoue, Y. and Ochi, D. 2014. Bycatch in longline fisheries for tuna and tuna-like species: a global review of status and mitigation measures. FAO Fisheries and Aquaculture Technical Paper No. 588. Rome, FAO. 199 pp. http://www.fao.org/3/a-i4017e.pdf
- Fader J.E., Elliott B.W., Read A.J. 2021. The Challenges of Managing Depredation and Bycatch of Toothed Whales in Pelagic Longline Fisheries: Two U.S. Case Studies. Front Mar Sci 8:. https://doi.org/10.3389/fmars.2021.618031
- Foster, F. and Bergmann C. 2012. Bluefin tuna bycatch mitigation research in the Gulf of Mexico pelagic longline yellowfin tuna fishery. In: International Symposium on circle hooks in research, management, and conservation - abstracts. Bulletin of Marine Science 88:791-815. http://dx.doi.org/10.5343/bms.2012.1031
- Garrison, L. P. 2007. Interactions between marine mammals and pelagic longline fishing gear in the US Atlantic Ocean between 1992 and 2004. Fish. Bull. 105, 408–417.
- McLellan WA, Arthur LH, Mallette SD, et al. 2015. Longline hook testing in the mouths of pelagic odontocetes. ICES J Mar Sci 72:1706–1713. https://doi.org/10.1093/icesjms/fsu181
- National Oceanic and Atmospheric Administration (NOAA). 2012. Taking of Marine Mammals Incidental to Commercial Fishing Operations; False Killer Whale Take Reduction Plan, Federal Register 29 November 2012. (available at https://www.federalregister.gov/ articles/2012/11/29/2012-28750/taking-of-marine-mammals-incidental-to-commercial- fishing-operations-false-killer-whale-take).
- Serafy, J. E., Cooke, S. J., Diaz, G. A., Graves, J. E., Hall, M., Shivji, M. and Swimmer, Y. 2012. Circle hooks in commercial, recreational, and artisanal fisheries: research status and needs for improved conservation and management. Bulletin of Marine Science 88:3 371-391. doi.org/10.5343/bms.2012.1038
- Swimmer Y, Zollett E, Gutierrez A (2020) Bycatch mitigation of protected and threatened species in tuna purse seine and longline fisheries. Endang Species Res 43:517–542. https://doi.org/10.3354/esr01069
Werner TB, Northridge S, Press KM, Young N. 2015. Mitigating bycatch and depredation of marine mammals in longline fisheries. ICES J Mar Sci 72:1576–1586. https://doi.org/10.1093/icesjms/fsv092
- Zollett EA, Swimmer Y (2019) Safe handling practices to increase post-capture survival of cetaceans, sea turtles, seabirds, sharks, and billfish in tuna fisheries. Endangered Species Research 38:115–125. https://doi.org/10.3354/esr00940