Weak Hooks

'Weak hooks' refers to weak circle hooks, constructed of thinner gauge stock wire than standard circle hooks of the same size, and designed to straighten at a lower strain (pull) level than standard hooks, thereby allowing large hooked animals to escape while retaining the target catch [6].
 
Use of weak hooks is in an early experimental phase, as described in this excerpt from Clarke et al. (2014):
"Spurred by a desire to develop better mitigation techniques for interactions between the Hawaii-based deep-set pelagic longline fishery and false killer whales Pseudorca crassidens, a study was conducted in 2010 to test 'weak' hooks. These hooks are designed to straighten more easily than other hooks and, thus, were hypothesized to effectively release large non-target species while maintaining catch rates of target species. It should be noted, however, that weak hooks would not be expected to have any effect on depredation rates.
 
Weak hooks have been previously tested in the Atlantic to minimize pelagic longline interactions with pilot whales Globicephala macrorhynchus [1]. In that study, there was no difference between the catch rates for the target yellowfin tuna and swordfish species on weak or strong hooks, which indicates that target species catch rates can be maintained. However, interactions with marine mammals were too few to evaluate whether they were successfully released by the weak hooks.
 
In the Gulf of Mexico, weak hooks were trialled as a means of decreasing the selectivity of gear for larger Atlantic Bluefin tuna when targeting yellowfin tuna [4]. That study found that catches of bluefin tuna were statistically significantly reduced by 56 percent when using the weak hooks while yellowfin catch rates were maintained [2].
 
Prior to the false killer whale interaction issue, the deep-set Hawaii longline fishery had already voluntarily transitioned from primarily using Japanese tuna hooks in the early 2000s to using circle hooks, or a combination of circle hooks and other hooks, by the late 2000s (i.e. it is only the shallow-set Hawaii longline fishery for which circle hooks are mandated). As circle hooks are weaker than the traditional hooks, this voluntary change to circle hooks in the deep-set fishery was estimated to result in a weakening of hooks by at least 30 percent (i.e. comparison based on the strongest circle hook).
 
In weak hook trials conducted in Hawaii, the 15/0 circle hooks used represented a weakening of 46 percent (for the 4.5 mm gauge) and 64 percent (for the 4.0 mm gauge) as compared with a Japanese tuna hook. Of more than 300 000 hooks deployed, 76 were found to have been straightened and 70 of these were weak hooks. Tuna catch rates were maintained on the weak hooks, although it was noted that in seasons other than the trial season larger bigeye tuna are caught, and whether these sizes of bigeye tuna would have been retained on the weak hooks is unknown. It is probable that the main factors in determining whether hooks are straightened are the direction and force of the pull, which is in turn determined by whether the hook is attached to the branch line with a ring or non-ring, the location of hooking and the force applied to the mainline and branch line during haulback [2].
 
Under new regulations designed to minimize interactions with false killer whales as of December 2012, the deep-set Hawaii longline fishery is now required to use circle hooks with a maximum wire diameter of 4.5 mm and an offset of 10 degrees or less. In addition, monofilament leaders and branch lines in this fishery must have a minimum diameter of 2 mm, and leaders or branch lines made from any other materials must have (an equivalent) minimum breaking strength of 181.4 kg. The purpose of the latter requirement is to ensure that the hook is the weakest component of the terminal tackle and thus straightens before any other element of the branch line fails (leaving the terminal tackle attached and risking post-release mortality [5]."
Further Research
Unaddressed in weak hook studies conducted to date is that the identities and fates of species that escape capture by straightening hooks are essentially unknown [6]. While weak hooks reduce the catch rates of certain species, their conservation value cannot be fully assessed until the extent of injury and post-escape survival are determined [6].
 
Suggestions for future research include determining the species identity, weight, and survival of weak-hook escapees [6].
References
  1. 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.
  2. 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.
  3. 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
  4. 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
  5. 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).  
  6. 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