Effects of codend circumference and twine diameter on selection in south-eastern Australian fish trawls

Published source details Graham K.J., Broadhurst M.K. & Millar R.B. (2009) Effects of codend circumference and twine diameter on selection in south-eastern Australian fish trawls. Fisheries Research, 95, 341-349.
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This study is summarised as evidence for the following.

	Action	Category
	Decrease the circumference or diameter of the codend of a trawl net Action Link

Decrease the circumference or diameter of the codend of a trawl net

A replicated, paired, controlled study in 2005 of an area of seabed in the Tasman Sea, Australia (Graham et al. 2009) found that a smaller codend circumference in fish trawl nets did not reduce the discarded catch of five of five non-target fish species, or total discarded catch (fish and invertebrates). For five of five fish species (see original paper for species individual data), average catch numbers discarded were similar between small and large codend circumferences (small: 2–284 fish/haul, large: 54–502 fish/haul). The numbers (small: 753 fish/haul, large: 1,224–1,257 fish/haul) and weight (small: 104 kg/haul, large: 112–128 kg/haul) of total discarded catch (all fish and invertebrates) were also similar between codend circumferences. In addition, the number (small: 305 fish/haul, large: 685–1,468 fish/haul), but not weight (small: 94 kg/haul, large: 156–158 kg/haul) of commercial retained catch (fish and invertebrates) was lower in the smaller codend compared to the larger. Between March and November 2005, gears trials were done in a south-eastern Australian trawl fishery targeting school whiting Sillago flindersi. Three test codends, one 100 mesh and two 200 mesh circumferences, were tested in pairs during alternate deployments (16 paired deployments each) with a small mesh (40 mm) codend of 450 mesh circumference (see original paper for full specifications). Catches were counted and weighed by species and the lengths of the most abundant fish measured. Commercial species were divided into retained and discarded categories.

(Summarised by: Khatija Alliji/Natasha Taylor)