Effects of 17/0 circle hooks and bait on fish catches in a Southern Atlantic swordfish longline fishery

Amorim, Sérgio; Santos, Miguel N.; Coelho, Rui; Fernandez‐Carvalho, Joana

doi:10.1002/aqc.2443

Cited by 20 publications

(20 citation statements)

References 40 publications

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“…Crocodile and bigeye thresher sharks were the main caught shark species for only two studies each: crocodile shark was also the main caught shark in Amorim et al . () and bigeye thresher shark was also the main caught shark in Kim et al . ().…”

Section: Discussionmentioning

confidence: 96%

“…Bait type has been observed to affect size selectivity within some pelagic teleost and elasmobranch species (Amorim et al . ).…”

Section: Discussionmentioning

confidence: 97%

“…Pelagic shark species found in either just oceanic habitats or both oceanic and coastal habitats other than blue shark were the main caught shark species for 9 of the 30 studies. Crocodile and bigeye thresher sharks were the main caught shark species for only two studies each: crocodile shark was also the main caught shark in Amorim et al (2014) and bigeye thresher shark was also the main caught shark in Kim et al (2006). Blue shark was the main caught shark species in 17 of the 30 studies; catch composition affects catch and survival rates and hooking position (Gilman and Hall 2015).…”

Section: Hook Shapementioning

confidence: 99%

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A cross‐taxa assessment of pelagic longline by‐catch mitigation measures: conflicts and mutual benefits to elasmobranchs

et al. 2016

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Elasmobranch mortality in pelagic longline fisheries poses a risk to some populations, alters the distribution of abundance between sympatric competitors, changing ecosystem structure, processes and stability. Individual and synergistic effects on elasmobranch catch and survival from pelagic longline gear factors, including methods prescribed to mitigate bycatch of other vulnerable taxa, were determined. Overall relative risk of higher circle vs. J-shaped hook shark catch rates conditioned on potentially informative moderators, from 30 studies, was estimated using an inverse-precision weighted mixed-effects meta-regression modelling approach. Sharks had a 1.20 times (95% CI: 1.03-1.39) significantly higher pooled relative risk of capture on circle hooks, with two significant moderators. The pooled relative risk estimate of ray circle hook catch from 15 studies was not significant (RR = 1.22, 95% CI: 0.89-1.66) with no significant moderators. From a literature review, wire leaders had higher shark catch and haulback mortality than monofilament. Interacting effects of hook, bait and leader affect shark catch rates: hook shape and width and bait type determine hooking position and ability to sever monofilament leaders. Circle hooks increased elasmobranch catch, but reduced haulback mortality and deep hooking relative to J-shaped hooks of the same or narrower width. Using fish vs. squid for bait increased shark catch and deep hooking. Pelagic stingray (Pteroplatytrygon violacea) catch and mortality were lower on wider hooks. Using circle instead of J-shaped hooks and fish instead of squid for bait, while benefitting sea turtles, odontocetes and possibly seabirds, exacerbates elasmobranch catch and injury, therefore warranting fishery-specific assessments to determine relative risks.

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Section: Discussionmentioning

confidence: 96%

“…Bait type has been observed to affect size selectivity within some pelagic teleost and elasmobranch species (Amorim et al . ).…”

Section: Discussionmentioning

confidence: 97%

Section: Hook Shapementioning

confidence: 99%

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A cross‐taxa assessment of pelagic longline by‐catch mitigation measures: conflicts and mutual benefits to elasmobranchs

et al. 2016

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“…A range of prices would, perhaps, better reflect market fluctuations. On the other hand, current perceptions of fishermen are that changing the bait from the more expensive squid to cheaper mackerel, is worthwhile in areas or seasons of high shark abun dance (representing over 50% of the retained catch), as reported by Amorim et al (2015) in a similar fishery in the southern Atlantic Ocean. Therefore, a thorough as sessment (including the cost of replacing and repairing damaged gear) of the economic impact of banning wire leaders will be required if fisheries managers wish to consider such a measure to reduce unwanted bycatch in longline fisheries.…”

Section: Leader Materialsmentioning

confidence: 99%

“…With regard to shark bycatch, particular attention has been given to the use of different hook styles (Watson et al, 2005;Yokota et al, 2006;Coel ho et al, 2012a;Amorim et al, 2015) and bait types (Watson et al, 2005;Coelho et al, 2012a;. However, there are few published studies on the effects of wire leaders on longline catches, despite the general concern regarding increasing catches of sharks.…”

mentioning

confidence: 99%

Effects of leader material on catches of shallow pelagic longline fisheries in the southwest Indian Ocean

Santos¹,

Lino²,

Coelho³

2017

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Abstract-Catches from a commer cial longline fishery targeting sword fish (Xiphias gladius) on monofila ment nylon leaders were compared with catches on wire leaders in the Indian Ocean. More taxa were caught on wire leaders, which also showed higher catch rates (13% and 56%, in number and weight, re spectively) of blue shark (Prionace glauca). In contrast, catch rates of swordfish were not significantly af fected by leader material. Nylon leaders showed lower athaulback mortality for most bony fishes, ex cept swordfish. Higher biteoff rates were observed on nylon monofila ment, likely owing to the escape of species with sharp teeth, such as sharks. Both leader types caught most species within similar size ranges, but larger mean sizes of blue shark were recorded on wire leaders.

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Standardized catch and survival rates, and effect of a ban on shark retention, Palau pelagic longline fishery

Gilman

Chaloupka

Merrifield³

et al. 2015

Aquatic Conservation

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1. Pelagic longline fisheries affect both market and vulnerable bycatch species and can have broad effects on community structure and processes.2. Observer data from the Palau longline fishery were analysed to identify opportunities to mitigate vulnerable species bycatch, determine temporal trends in local abundance, and assess changes following a ban on shark retention and wire leaders. Catch and haulback condition data for bigeye and yellowfin tunas, blue and silky sharks and pelagic stingrays were fitted to standardized catch and survival rate models.3. The fishery caught silky and blue sharks, olive ridley sea turtles and other species of conservation concern. 4. Changing from shallow sets to deep daytime sets might reduce shark and sea turtle catch rates but increase turtle haulback mortality rates, maintain economically viable tuna catch rates, but increase catch rates of pelagic stingrays, a lower conservation concern than main caught species of sharks and turtles. 5. Focusing fishing effort during the middle of the calendar year would maximize yellowfin tuna and minimize silky shark standardized catch rates, but maximize blue shark catch rates. 6. A large decline in shark fishing mortality rate very likely occurred following a ban on shark retention and wire leaders. This was due to large reductions in the nominal shark catch rate and shark retention, partially offset by decreases in the shark haulback survival rate and pre-catch survival rate. Significantly higher blue shark and lower pelagic stingray nominal catch rates occurred on wire vs. monofilament leaders. Significantly higher blue shark and lower yellowfin tuna nominal catch rates occurred on sets using shallow 'shark lines'. It is a research priority to compare the probability of shark pre-catch survival after escaping from monofilament leaders with an ingested hook and trailing line to the survival probability when captured on wire leaders.

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Effects of 17/0 circle hooks and bait on fish catches in a Southern Atlantic swordfish longline fishery

Cited by 20 publications

References 40 publications

A cross‐taxa assessment of pelagic longline by‐catch mitigation measures: conflicts and mutual benefits to elasmobranchs

A cross‐taxa assessment of pelagic longline by‐catch mitigation measures: conflicts and mutual benefits to elasmobranchs

Effects of leader material on catches of shallow pelagic longline fisheries in the southwest Indian Ocean

Standardized catch and survival rates, and effect of a ban on shark retention, Palau pelagic longline fishery

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