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Effects of a hook ring on catch and bycatch in a Mediterranean swordfish longline fishery: small addition with potentially large consequences
Author(s) -
Piovano Susanna,
Swimmer Yonat
Publication year - 2017
Publication title -
aquatic conservation: marine and freshwater ecosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.95
H-Index - 77
eISSN - 1099-0755
pISSN - 1052-7613
DOI - 10.1002/aqc.2689
Subject(s) - swordfish , bycatch , hook , fishery , mediterranean climate , fishing , mediterranean sea , oceanography , fish <actinopterygii> , biology , ecology , tuna , engineering , geology , structural engineering
The purpose of this study was to investigate the effects of a circle hook ring on catch rates of target fish species and bycatch rates of sea turtles, elasmobranchs, and non‐commercial fish in a shallow‐set Italian swordfish longline fishery. Results were compared from 65 sets from six commercial fishing vessels totalling 50 800 hooks in which ringed and non‐ringed 16/0 circle hooks with a 10° offset were alternated along the length of the longline. In total, 464 individuals were caught in the 4 years of experiment, with swordfish ( Xiphias gladius ) comprising 83% of the total number of animals captured. Catch rates of targeted swordfish were significantly higher on ringed hooks (CPUE ringed hooks = 8.465, CPUE non‐ringed hooks = 6.654). Results indicate that ringed circle hooks captured significantly more small‐sized swordfish than non‐ringed circle hooks (27.7% vs. 19.5%, respectively). For species with sufficient sample sizes, the odds ratio (OR) of a capture was in favour of ringed hooks; significantly for swordfish (OR = 1.27 95%CI 1.04–1.57), and not significantly for bluefin tuna ( Thunnus thynnus ) (OR = 1.50, 95%CI 0.68–3.42) nor for pelagic stingray ( Pteroplatytrigon violacea ) (OR = 1.13, 95%CI 0.54–2.36). All six loggerhead turtles ( Caretta caretta ) and three of the four blue sharks ( Prionace glauca ) were captured on ringed hooks, however, the small sample sizes prevented meaningful statistical analysis. In summary, results from this study suggest that the addition of a ring to 16/0 circle hooks confers higher catchability for small‐sized commercial swordfish, and does not significantly reduce catch rate of bycatch species and protected species in a Mediterranean shallow pelagic longline fishery. These findings should motivate fisheries managers to consider factors in addition to hook shape when aiming to promote sustainable fishing practices. The presence of a ring has the potential to negate some conservation benefits. Copyright © 2016 John Wiley & Sons, Ltd.