Confounding effects of knot orientation in penaeid trawls

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• 作者：Matt K. Broadhurst^a ; ^b ; ^{matt.broadhurst@dpi.nsw.gov.au" class="auth_mail" title="E-mail the corresponding author} ; David J. Sterling^c ; Russell B. Millar^d
• 关键词：Knots ; Penaeids ; Selectivity ; Trawl efficiency ; Trawl surveys
• 刊名：Fisheries Research
• 出版年：2016
• 出版时间：July 2016
• 年：2016
• 卷：179
• 期：Complete
• 页码：124-130
• 全文大小：568 K

文摘

This study assessed the potential for confounding engineering and/or catching effects due to different knot (‘sheet bend’) orientations (and therefore positive or negative hydrodynamic lift) in the principal horizontal panels of a penaeid trawl. During 24 paired comparisons, orientating all meshes in the top and bottom belly panels of a trawl to produce a negative angle of attack (AOA) for all knots resulted in greater wing-end spread, and lower catches of school prawns, Metapenaeus macleayi per hectre trawled (means reduced by up to 26%) and three key species of schooling fish (by up to 67%), but more debris (4×) than when the meshes were orientated to produce a positive AOA. By comparison, catches of two other benthic fish remained unaffected by knot orientation. These catch differences were attributed to the negative-AOA trawl potentially assuming a considerably lower position in the water column (and species-specific orientations). The results demonstrate that it is essential to maintain consistency in knot orientation in penaeid trawls when testing gear modifications and/or during fishery-dependent or -independent surveys.