Effects of eliminating shallow hooks from tuna longline sets on target and non-target species in the Hawaii-based pelagic tuna fishery

Published source details Beverly S., Curran D., Musyl M. & Molony B. (2009) Effects of eliminating shallow hooks from tuna longline sets on target and non-target species in the Hawaii-based pelagic tuna fishery. Fisheries Research, 96, 281-288.
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This study is summarised as evidence for the following.

	Action	Category
	Deploy fishing gear at selected depths to avoid unwanted species Action Link

Deploy fishing gear at selected depths to avoid unwanted species

A replicated, controlled study in 2006 of pelagic waters in the Pacific Ocean around Hawaii (Beverly et al. 2009) found that longlines deployed at selected depths (deeper) reduced catches of five out of 17 unwanted fish species compared to conventional, shallower-set longlines. Catch rates of five out of 17 unwanted species were lower on sets using deeper longlines compared to shallower longlines: wahoo Acanthocybium solandri (0.4 vs 1.2 fish/set), dolphinfish Coryphaena hippurus (1.3 vs 3.8 fish/set), blue marlin Makaira nigricans (0.1 vs 0.4 fish/set), striped marlin Kajikia audax (0.5 vs 1.5 fish/set) and shortbill spearfish Tetrapturus angustirostris (0.1 vs 0.6 fish/set). Catch rates of most other unwanted fish (11 out of 17 species – see paper for species individual data) were similar between longline depths, including the target commercial species bigeye tuna Thunnus obesus (5.7 vs 4.7 fish/set). One unwanted species, sickle pomfret Taractichthys steindachneri, was caught more frequently with deeper longlines (3.5 fish/set) than shallower longlines (2.0 fish/set). A total of 90 longline sets (2,000 hooks/set) were deployed from a vessel fishing out of Honolulu, Hawaii, in June-December 2006. Forty-five sets were modified using 3 kg weighted lines to keep all hooks at depths of 103 m at either end to 248 m in the middle. The other 45 were conventional sets with hooks at depths between 44–211 m. The vessel used deeper and shallower sets on alternate days.

(Summarised by: Leo Clarke)