Selectivity experiments in the NE Mediterranean: the effect of trawl codend mesh size on species diversity and discards
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Published source details
Stergiou K.I., Politou C.-., Christou E.D. & Petrakis G. (1997) Selectivity experiments in the NE Mediterranean: the effect of trawl codend mesh size on species diversity and discards. ICES Journal of Marine Science, 54, 774-786.
Published source details Stergiou K.I., Politou C.-., Christou E.D. & Petrakis G. (1997) Selectivity experiments in the NE Mediterranean: the effect of trawl codend mesh size on species diversity and discards. ICES Journal of Marine Science, 54, 774-786.
Actions
This study is summarised as evidence for the following.
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Use a square mesh instead of a diamond mesh codend in a trawl net Action Link |
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Use a larger mesh size Action Link |
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Use a square mesh instead of a diamond mesh codend in a trawl net
A replicated, randomized, controlled study in 1993–1994 in two seabed areas in the Aegean Sea, Greece (Stergiou et al. 1997, same experimental set-up as Petrakis & Stergiou 1997 and Stergiou 1999) found that a bottom trawl net with a square mesh codend did not allow more unwanted individuals and higher number of species (fish and invertebrates) to escape compared to a diamond mesh codend of the same mesh size. In two of two years, the average number of individuals (fish and invertebrates) and species escaping from the codend was similar between square and diamond mesh (individuals, square: 1,653–6,100/h, diamond: 1,486–8,167/h; species, square: 12–15/h, diamond: 12–16/h ). Experimental trawl deployments (using the same experimental set-up as Petrakis & Stergiou, 1997) were conducted in the Trikeri Channel in October 1993 (5 stations) and the North Euboikos Gulf in March 1994 (seven stations). A trawl net was randomly assigned either a 20 mm square mesh codend or 20 mm diamond mesh codend (12 hauls each codend), and towed for 45–60 min at depths between 73–210 m. Small mesh (10 mm) covers over the codend sampled the escaping fish catch. All individuals caught in the covers were identified and counted.
(Summarised by: Rosslyn McIntyre)
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Use a larger mesh size
A replicated, randomized, controlled study in 1993–1994 in two areas of coastal water in the Aegean Sea, Greece (Stergiou et al. 1997, same experimental set-up as Petrakis & Stergiou 1997) found that trawl codends of larger mesh size allowed the escape of more unwanted individuals and species (fish and invertebrates) compared to a conventional diamond mesh codend of smaller mesh size. For both sampling periods and for all species (fish and invertebrates combined), the average number of individuals (20 mm: 1,486–8,167 ind/h, 14 mm: 204–855 ind/h) and species (20 mm: 16 species, 14 mm: 9 species) that escaped was higher with the larger mesh compared to the standard. The ratios of commercial/non-commercial retained catch were higher in 20 mm diamond mesh codends (0.60–1.31) than in 14 mm diamond mesh codends (0.27–0.29). In October 1993 and March 1994, experimental trawl deployments were conducted in two areas (Trikeri Channel and North Euboikos Gulf, twelve stations in total) using a trawl fitted with either a 20 mm diamond mesh codend or a conventional 14 mm diamond mesh codend used by the fishery (12 hauls of each at each station). Codend type was randomly allocated and small mesh (10 mm) covers retained fish escaping through the meshes. For each deployment, the total number and weight caught by species in the codends and covers were recorded.
(Summarised by: Rosslyn McIntyre)
