Evaluation of the Morrison soft turtle excluder device: prawn and bycatch variation in Moreton Bay, Queensland

Published source details Robins-Troeger J.B. (1994) Evaluation of the Morrison soft turtle excluder device: prawn and bycatch variation in Moreton Bay, Queensland. Fisheries Research, 19, 205-217.
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This study is summarised as evidence for the following.

	Action	Category
	Install exclusion and escape devices on fishing gear Action Link
	Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net Action Link

Install exclusion and escape devices on fishing gear

A replicated, controlled study in 1991–1992 in oceanic and estuarine waters off the coast of Queensland, Australia (Robins-Troeger et al. 1994) found that when a soft mesh panel with escape hole (‘Morrison soft TED’) was added to a trawl net no loggerhead turtles Caretta caretta were caught accidentally. No loggerhead turtles were caught in the modified net but were occasionally caught in the unmodified net (no data on turtles are provided). Catch rates of target prawns Penaeus spp. and Metapenaeus bennettae varied between no significant reduction and a 29% reduction in modified compared to unmodified nets, depending on location and season (data reported as a cross-site analysis of fishing power, see original paper for details). Trawl nets modified by adding a polypropylene mesh panel with an escape hole in front of the codend were tested in two trials (May 1991 and January 1992) on a 15 m research trawler in an oceanic site with sandy substrate and an estuarine site with a muddy bottom. Unmodified nets were towed first (number of trawls not specified) and then the modified net was used. Between 17 and 23 tows were completed in each trial, each lasting 45–100 minutes.

(Summarised by: Katie Sainsbury)
Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

A replicated, paired, controlled study in 1991–1992 at one coastal seabed and one estuarine site in the Coral Sea, Australia (Robins-Troeger 1994) found that using a flexible (mesh) size-sorting escape grid (a Morrison soft turtle excluder device) inside a prawn trawl net resulted in variable reductions of unwanted non-commercial catch (fish and crustaceans) compared to nets without a grid. The reductions in weight (21–32%) of unwanted catch (fish and crustaceans) in nets with a flexible escape grid were significant at both sites in 1991, but not in 1992 (2–18%). In addition, larger unwanted non-commercial catch including stingrays Amphotistius kuhlii and shovelnose rays Rhinobatus batillum were not caught in nets with a flexible escape grid, but they were occasionally caught in nets without an escape grid (numbers not reported). Prawn catch (Metapenaeus bennettae, Penaeus plebejus, Penaeus esculentus) was significantly reduced (17–30%) in nets with a grid at one site in 1991 and both sites in 1992. Paired fishing deployments were done on a research vessel towing two prawn trawl nets at two sites in Moreton Bay off Queensland in May 1991 (low prawn catches) and January 1992 (high prawn catches). A flexible grid made of 150 mm monofilament mesh was installed inside one trawl net and the other net was unmodified. In each year, 17 to 23 deployments of 45–100 min were completed at each site. Codend catches were landed and processed separately.

(Summarised by: Khatija Alliji)