Effects of the circumference of codends and a new design of square-mesh panel in reducing unwanted by-catch in the New South Wales oceanic prawn-trawl fishery, Australia

Published source details Broadhurst M.K. & Kennelly S.J. (1996) Effects of the circumference of codends and a new design of square-mesh panel in reducing unwanted by-catch in the New South Wales oceanic prawn-trawl fishery, Australia. Fisheries Research, 27, 203-214.
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This study is summarised as evidence for the following.

	Action	Category
	Fit mesh escape panels/windows to a trawl net Action Link
	Decrease the circumference or diameter of the codend of a trawl net Action Link

Fit mesh escape panels/windows to a trawl net

A replicated, paired, controlled study in 1995 of a seabed area in the Tasman Sea, Australia (Broadhurst & Kennelly 1996) found that fitting square mesh escape windows to the codend of a prawn trawl reduced the amount of overall unwanted catch (fish and invertebrates) and stout whiting Sillago robusta and long-spined flathead Platycephalus longispinis, compared to codends without square mesh windows, for two codend circumferences. The average weight of discarded catch (fish and invertebrates) was reduced by 35% (100 mesh) and 40% (200 mesh) in codends with square mesh windows (with: 20–40 kg, without: 32–70 kg). For two individual fish species caught in sufficient amounts, stout whiting and long-spined flathead, average numbers and weights of discards were reduced by 33–64% and 33–56% respectively. In addition, the average weight of the target king prawn Penaeus plebejus catch remained similar between trawl nets (with and without: 5–9 kg). Data were collected in March 1995 on a commercial trawler equipped with three trawl nets. The two outer nets were used to test four codends: a 40 mm diamond mesh codend, 100 or 200 mesh circumference, fitted with two square mesh windows, one inside the other of 40 mm (outer) and 50 mm (inner) mesh; and a control 40 mm diamond mesh codend, 100 or 200 mesh circumference and no square mesh windows (see paper for specifications). A total of 10 deployments for each of the four paired comparisons were done.

(Summarised by: Khatija Alliji)
Decrease the circumference or diameter of the codend of a trawl net

A replicated, paired, controlled study in 1995 of an area of seabed in the Tasman Sea off New South Wales, Australia (Broadhurst & Kennelly 1996) found that decreasing the codend circumference in prawn trawl nets reduced the discarded catch of commercial and non-commercial small fish in three of five cases compared to a larger standard circumference codend. In codends of standard diamond mesh, average catch numbers of discarded fish were lower in small circumference codends compared to larger for two of two species: stout whiting Sillago robusta (small: 600 fish/haul, large: 1,800 fish/haul) and long-spined flathead Platycephalus longispinis (small: 500 fish/haul, large: 1,800 fish/haul). In diamond mesh codends fitted with square mesh panels, average number of discarded fish was lower with the smaller circumference for one of three species, stout whiting (small: 300 fish/haul, large: 800 fish/haul), and similar for long-spined flathead (small: 400 fish/haul, large: 700 fish/haul) and red spot whiting (small: 70 fish/haul, large: 60 fish/haul). In addition, commercial target king prawn Penaeus plebejus average catch weights were similar between codend circumferences (both 5–7 kg/haul). Data were collected in March 1995 on commercial prawn-trawl grounds using a commercial trawler fishing with a triple rigged net. Four codends were tested in pairs using the outer two nets (number of deployments not reported): 100 mesh and 200 mesh (standard) circumference, each set with without square mesh panels (see original paper for gear specifications). After each tow codend catches were sorted separately and the numbers and weights of commercial and non-commercial retained and discarded species recorded.

(Summarised by: Khatija Alliji)