Effects of a hook ring on catch and bycatch in a Mediterranean swordfish longline fishery: small addition with otentially large consequences

Piovano, Susanna and Swimmer, Yonat (2017) Effects of a hook ring on catch and bycatch in a Mediterranean swordfish longline fishery: small addition with otentially large consequences. Aquatic Conservation: Marine and Freshwater Ecosystems, 27 (2). pp. 372-380. ISSN 1052-7613

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Abstract

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.
2. 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
(CPUEringed hooks = 8.465, CPUEnon-ringed hooks = 6.654).
3. Results indicate that ringed circle hooks captured significantly more small-sized swordfish than non-ringed
circle hooks (27.7% vs. 19.5%, respectively).
4. 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.
5. 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.
6. 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.

Item Type:	Journal Article
Subjects:	G Geography. Anthropology. Recreation > GE Environmental Sciences S Agriculture > SH Aquaculture. Fisheries. Angling
Divisions:	Faculty of Science, Technology and Environment (FSTE) > School of Marine Studies
Depositing User:	Fulori Nainoca - Waqairagata
Date Deposited:	16 Jun 2017 03:59
Last Modified:	16 Jun 2017 03:59
URI:	https://repository.usp.ac.fj/id/eprint/9971

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