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Validating a narrow codend cover and improving selectivity in south-eastern Australian fish trawls targeting eastern school whiting, Sillago flindersi
Journal article   Peer reviewed

Validating a narrow codend cover and improving selectivity in south-eastern Australian fish trawls targeting eastern school whiting, Sillago flindersi

Matt K Broadhurst and Russell B Millar
Fisheries Research, Vol.251, pp.1-8
07/2022
DOI: https://doi.org/10.1016/j.fishres.2022.106302
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Validating a narrow codend coverView
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Abstract

Covered codend Selectivity Square-mesh panel Trawl
As part of attempts to improve selection among south-eastern Australian benthic fish trawls, an experiment was done to assess: (1) for confounding effects of a narrower-than-recommended hooped cover over a conventional trawl codend; and then (2) the associated size selection of eastern school whiting, Sillago flindersi; and (3) if this could be improved by inserting a large panel of smaller square-shaped mesh. The narrow cover was required to avoid contacting the seabed and did not affect trawl wing-end spread or catching efficiency. Despite a stretched mesh opening (SMO) of 96 mm and much larger than all S. flindersi (11–26 cm total length; TL), the conventional codend had a low 50% size at retention (L50) of 16.8 cm TL (selection range of 5.9 cm), which was close to the minimum marketable length. The capture of small S. flindersi by the large-meshed codend was attributed to an excessive increase in circumference (from 100 to 200 meshes) and a legally permitted ‘catch-separating’ rope to restrict fractional mesh openings to <~21%. Replacing ~1/4 of the 96-mm SMO netting in the codend and anterior extension with a panel of square-shaped mesh (~42-mm SMO hung on the bar) marginally (p = 0.065) improved size selection for S. flindersi (by allowing some fish <~15 cm TL to escape). Increasing the size of mesh in the panel to ~47 mm hung on the bar might allow more smaller S. flindersi to escape. But using a smaller mesh size throughout the entire codend, concurrent with other gear or spatio-temporal controls when targeting S. flindersi might be a more coherent management option than retroactively handicapping the existing large-mesh codends.

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