Development of a codend concept to improve size selectivity of Nephrops ( Nephrops norvegicus) in a multi-species fishery

• Published in: Fisheries research Vol. 111; no. 1; pp. 116 - 126
• Main Authors: Frandsen, R.P., Herrmann, B., Madsen, N., Krag, L.A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.09.2011; Elsevier
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Exploitation and management of natural biological resources (hunting, fishing and exploited populations survey, etc.); Fundamental and applied biological sciences. Psychology; Gadus morhua; Marine; Mixed species fishery; Nephrops norvegicus; Pleuronectes platessa; Sea water ecosystems; Selectivity; Square-mesh panel; Synecology; Trawl; ANE, North Sea, Skagerrak; ANE, Baltic Sea, Kattegat; Square-mesh panel; Mixed species fishery; Nephrops norvegicus; Selectivity; Trawl; Pleuronectes platessa; Gadus morhua; Concept; Mesh; Macrura; Crustacea; Marine environment; Vertebrata; Fishery; Arthropoda; Pisces; Scampi; Decapoda; Invertebrata
• ISSN: 0165-7836; 1872-6763
• DOI: 10.1016/j.fishres.2011.07.003

► A new concept combining square and diamond meshes in a 4-panel codend was developed and tested. ► It was found to increase L 50 of Nephrops without increasing discards of either plaice or cod. ► Expected numbers of Nephrops below MLS were reduced by ∼37%. ► Expected weight of marketable catch was also reduced by 21%. ► A 2nd experiment indicated that L 50 of Nephrops could be adjusted by changing the square-mesh panel. Species-specific differences in morphology and minimum landing size will often result in high discard rates in mixed-species fisheries. This is the case in the Danish Nephrops-directed fishery and the aim of this study was to improve the size selectivity of Nephrops without increasing catch below minimum landing size (MLS) of cod ( Gadus morhua) and plaice ( Pleuronectes platessa). A new codend concept combining square meshes and diamond meshes in a four-panel configuration was developed and tested in the Kattegat and Skagerrak. A 5 m long 70 mm square-mesh panel was inserted in the lower panel of the codend to increase size selectivity of Nephrops while the remaining three panels were made of standard 90 mm diamond-mesh netting to maintain selectivity of plaice and cod. The concept succeeded in significantly ( p < 0.0001) increasing L 50 of Nephrops without increasing discards of either plaice or cod. When using the new codend concept, expected numbers of Nephrops below MLS (carapace length = 40 mm) were reduced by approximately 37% but the expected weight of marketable catch was also reduced by 21%. The concept was adjusted and tested in a second experiment so that fishing using the new net configuration would remain commercially viable. This experiment indicated that size selectivity of Nephrops could be adjusted by changing the square-mesh panel but differences in mean selection between the gears were insignificant. We introduce a new analytical approach with increased statistical power to detect differences in selection parameters between different codends.