Do by-catch reduction devices in longline fisheries reduce capture of sharks and rays? A global meta-analysis

Published source details Favaro B. & Côté I.M. (2015) Do by-catch reduction devices in longline fisheries reduce capture of sharks and rays? A global meta-analysis. Fish and Fisheries, 16, 300-309.
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This study is summarised as evidence for the following.

	Action	Category
	Modify longline configuration Action Link
	Attach an electropositive deterrent to fishing gear Action Link
	Use a different bait type Action Link
	Use a different hook type Action Link

Modify longline configuration

A review in 2013 of two studies in a meta-analysis of 27 studies to assess methods to reduce unwanted shark and ray (Elasmobranchii) catches in longline fisheries worldwide (Favaro & Côté 2015) found that modifying the configuration of longlines by using nylon lines instead of wire lines to attach the hooks to the main longline reduced the overall amount of unwanted sharks and rays caught in one of two cases. Numbers of sharks and rays caught on breakable monofilament lines were 58% lower than on wire lines. However, tarred multifilament nylon lines (designed to make them easier for fish of all species to see and avoid) caught similar numbers of sharks and rays to traditional wire branch lines (data reported as graphical analysis). The systematic review summarized 44 datasets from 27 studies of the effects of various actions to reduce unwanted shark and ray catch, and identified one study comparing breakable monofilament nylon lines with wire lines and one comparing tarred multifilament lines instead of wire lines. Full literature search methods are reported in the original paper.

(Summarised by: Leo Clarke)
Attach an electropositive deterrent to fishing gear

A systematic review in 2015 of 17 relevant studies of 44 in global pelagic waters (Favaro & Côté 2015) of devices to reduce unwanted catch, found that using electropositive and magnetic materials, or a combination of both, on hooks in longline fisheries did not reduce the amount of unwanted sharks and rays (Elasmobranchii) caught overall, compared to traditional J hooks alone. Data were reported as percentage catch reductions relative to the standard. Numbers of sharks and rays caught on hooks with electropositive and/or magnetic materials were not significantly different overall than those caught on J hooks alone (electropositive: 18% less, magnets: 32% less, combined: 29% less). One study found a reduction in catches of juvenile scalloped hammerhead Sphyrna lewini of 57% on hooks with electropositive materials, but authors note the result was inconsistent with that for adults. The systematic review summarized the effects of various actions to reduce unwanted catch, including using electropositive materials, magnetic materials, or a combination of both in longline fisheries from 10, five and one global studies respectively.

(Summarised by: Leo Clarke)
Use a different bait type

A systematic review in 2015 of two relevant studies from 44 that assessed a range of ways to reduce unwanted catch in longline fisheries in global pelagic waters (Favaro & Côté 2015) found that changing bait colour (dyeing it blue) did not reduce the unwanted catches of sharks and rays (Chondrichthyes) compared to traditional bait. Numbers of sharks and rays caught on bait that had been dyed blue were similar to those caught on traditional, non-dyed bait (data reported as graphical analysis). Three global databases were searched, and publications identified that reported the numbers of sharks and rays caught in fishing gears with and without devices to reduce unwanted catch (‘bycatch reduction devices). A meta-analysis was carried out on 44 studies, two of which two contained data on the effects of using different bait types.

(Summarised by: Leo Clarke)
Use a different hook type

A systematic review in 2015 of 44 studies assessing the reduction of unwanted catch of sharks and rays (Elasmobranchii) in longline fisheries worldwide (Favaro & Côté 2015) found that using circle hooks or appendage hooks (circle hooks with an additional wire arm to increase its width) did not reduce the overall amount of unwanted sharks and rays caught compared to traditional J hooks, but did catch fewer of one of three individual species. Overall, the catch percentages of sharks and rays caught on circle and appendage hooks were similar to J hooks but catches of pelagic stingray Pteroplatytrygon violacea were reduced by almost 75% on circle hooks. Blue shark Prionace glauca and Galapagos shark Carcharinus galapagensis catches were similar between all hook types (data reported as graphical analysis). The systematic review summarized the effects of various actions to reduce unwanted catch (see original paper for search methods) from 27 publications yielding 44 studies reporting shark and ray catch data. A total of 23 and 17 studies reported effects of using circle hooks and appendage hooks, respectively, relative to control hooks.

(Summarised by: Leo Clarke)