Ray bycatch in a tropical shrimp fishery: do bycatch reduction devices and turtle excluder devices effectively exclude rays?

Published source details Willems T., Depestele J., De B.A. & Hostens K. (2016) Ray bycatch in a tropical shrimp fishery: do bycatch reduction devices and turtle excluder devices effectively exclude rays?. Fisheries Research, 175, 35-42.
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This study is summarised as evidence for the following.

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	Fit mesh escape panels/windows and a size-sorting grid (rigid or flexible) to a trawl net Action Link

Fit mesh escape panels/windows and a size-sorting grid (rigid or flexible) to a trawl net

A replicated, paired, controlled study in 2012–2013 in a fished area of seabed in the Atlantic Ocean, off Suriname (Willems et al. 2016) found that a shrimp trawl net fitted with a square mesh escape panel in combination with a size-sorting escape grid reduced the overall catch of rays and individuals of three of five ray species, compared to a standard commercial trawl net, but larger rays had higher escape rates than smaller rays. Overall ray catch rate was reduced by 36% in nets with a panel and grid compared to without. By species, between 32–77% fewer individuals of sharpsnout stingray Dasyatis geijskesi (panel/grid: 38, without: 161 ind), longnose stingray Dasyatis guttata (panel/grid: 440, without: 741 ind) and smooth butterfly ray Gymnura micrura (panel/grid: 572, without: 858 ind) were caught, and catches were similar between trawl types for cownose ray Rhinoptera bonasus (panel/grid: 8, without: 11 ind) and smalleyed round stingray Urotrygon microphthalmum (panel/grid: 171, without: 181 ind). Rays caught in the panel/grid net were on average 21% smaller than rays caught in the standard net (panel/grid: 26 cm, without: 32 cm), significantly smaller for sharpsnout (38%) and longnose stingrays (23%), and catch rate of all species combined declined with increasing size in the panel/grid net (data reported graphically). Trials were done on Atlantic seabob shrimp Xiphopenaeus kroyeri fishing grounds during eight commercial trips from February 2012 to April 2013. A total of 65 simultaneous deployments of a standard diamond mesh trawl net (45 mm mesh size codend) fitted with a square mesh panel (150 mm mesh size) and a grid (aluminium ’Super Shooter’ turtle excluder device, 10 cm bar spacing), and a standard trawl net were completed (2.5–3.5 knots, 1 h). All rays caught were identified, counted and wing width recorded. See original paper for gear specifications.

(Summarised by: Rosslyn McIntyre)