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Assessing narrow and composite Nordmøre-grid bar spaces in southeastern Australian penaeid trawls
Journal article   Peer reviewed

Assessing narrow and composite Nordmøre-grid bar spaces in southeastern Australian penaeid trawls

Matt K. Broadhurst
Fisheries research, Vol.288, pp.1-9
08/2025
DOI: https://doi.org/10.1016/j.fishres.2025.107451
Appears in  Recent Faculty of Science and Engineering Publications

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Abstract

Bycatch reduction Grids Penaeid trawl Selectivity
Owing to concerns over unwanted mortalities of fish in a southeastern Australian trawl fishery targeting school prawns, Metapenaeus macleayi (~13–25mm carapace length; CL), three experiments were done to quantify the effects on species- and size-selectivity due to reducing bar spaces throughout Nordmøre-grids (405 × 848mm), and in the upper section only (405 × 424mm; ‘composite grids’). In all experiments, a conventional grid comprising 20-mm bar spaces was the control. During experiment 1, trawls with treatment grids comprising either 18- or 16-mm spaces (i.e. close to the maximum heights of the largest school prawns) caught similar quantities of school prawns as the control, and while there were no significant catch or size effects, mean incidental catches of fish were incrementally lower in trawls with the 18- (by 12%) and 16-mm grids (by 46%). In the second experiment, two composite grids comprising 20-mm spaces in the lower section and either 16 or 14mm in the top (16/20- and 14/20-mm grids) were fished against the control. Only the 14/20-mm grid significantly reduced the catches of school prawns (by 17% across all sizes) and the weight of incidental catch (by 46%). The 16/20- and 16-mm grids were then compared in trawls against the control during experiment 3 to inform likely species-specific vertical orientations anterior to the grid. There were no significant effects on school prawn catches or sizes (although mean weights were lower for the 16- than 16/20-mm grid), but the weights of incidental fish catches were similarly and significantly lower for both narrower-spaced grids (by 50 and 57%). The data imply bar spaces in regional Nordmøre-grids can be reduced to widths ~1mm larger than the maximum carapace dimensions (height) of the largest school prawns, and in the top section to maximise species selectivity. Similar configurations may apply to other trawl fisheries targeting penaeids.

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