Tropical prawn trawl bycatch of fish and seasnakes reduced by Yarrow Fisheye Bycatch Reduction Device

Published source details Heales D.S., Gregor R., Wakeford J., Wang Y.-., Yarrow J. & Milton D.A. (2008) Tropical prawn trawl bycatch of fish and seasnakes reduced by Yarrow Fisheye Bycatch Reduction Device. Fisheries Research, 89, 76-83.
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This study is summarised as evidence for the following.

	Action	Category
	Install escape devices on fishing gear: Snakes & lizards Action Link
	Fit large, supported escape openings (such as Fisheyes, Bigeyes and radial escape sections) to trawl nets Action Link

Install escape devices on fishing gear: Snakes & lizards

A replicated, paired, controlled study in 2002–2005 on the sea bottom in the Gulf of Carpentaria, Australia (Heales et al. 2008) found that adding a metal-barred escape hatch (‘Yarrow Fisheye’) to a prawn trawl net reduced unwanted catch of sea snakes. Overall, trawl nets modified with a metal-barred escape hatch caught 44% fewer sea snakes (76 snakes caught in 113 trawls) than unmodified trawl nets (134 snakes in 113 trawls). In separate trawls, catch rates of commercially-targeted tiger prawns Penaeus spp. were similar when modified (13–18 kg/net) and unmodified (13–19 kg/net) nets were used. Unwanted catch of sea snakes was assessed on a single commercial prawn trawler in September–November 2004 (41 trawls) and August–November 2005 (72 trawls). On each trawl, the vessel was fitted with a pair of nets (one starboard, one portside) both fitted with a metal-barred escape hatch in the codend (see original paper for design details) behind a downward-facing grid with escape zone (‘Super Shooter’ turtle excluder device). On each trawl, the escape hatch on one net was sewn shut (classed as unmodified) and the other was left open (classed as modified). The modified net was swapped between the starboard and port-side every two weeks by opening and sewing shut the escape holes on the nets in rotation. Prawn catch rates were assessed during 42 trawls over 13 nights in November 2002.

(Summarised by: Katie Sainsbury)
Fit large, supported escape openings (such as Fisheyes, Bigeyes and radial escape sections) to trawl nets

A replicated, paired, controlled study in 2002 of a fished area of seabed in the Gulf of Carpentaria, off Australia (Heales et al. 2008) found that using a large, supported escape opening (new design of Fisheye) in a prawn trawl net reduced the amount of unwanted small catch (fish and invertebrates combined) compared to a standard prawn trawl net with no large escape opening. The average catch weight of small unwanted fish and invertebrates was lower with the Fisheye escape opening compared to without (with: 136–219 kg, without: 183–254 kg). In addition, there was no difference in the average catch weights of the commercial target species of tiger prawns, Penaeus esculentus and Penaeus semisulcatus, between trawl nets (with: 13–18 kg, without: 13–19 kg). Data were collected in November 2002 from 29 comparative trawl deployments by a commercial trawler on prawn fishing grounds in the south-western area of the Gulf. The vessel towed a pair of identical prawn trawl nets, both fitted with a compulsory downward-excluding size-sorting grid (Super-shooter type). One of the trawl nets also had a new design of large escape opening (Yarrow Fisheye): a rigid frame on the upper trawl section, creating a semi-round escape opening (see paper for specifications). The combined use of size-sorting excluder grids with other catch reduction devices was made compulsory in Australia’s Northern prawn fishery in 2000. Catches were separated into small unwanted catch (fish and invertebrates combined) and target prawn species and weighed.

(Summarised by: Natasha Taylor)