A bio-economic analysis of experimental selective devices in the Norway lobster (Nephrops norvegicus) fishery in the Bay of Biscay

¹ Université de Brest, UMR AMURE, IUEM, 12 rue du Kergoat, CS 93837, 29238 Brest Cedex 3, France
² IFREMER, UMR AMURE, Dép. RBE, Unité d’Economie maritime, BP 70, 29280 Plouzané Cedex, France
³ IFREMER, Dép. RBE, Unité de Sciences et Technologies halieutiques, Station de Lorient, 8 rue François Toullec, 56100 Lorient, France
⁴ Oceanic Developpement, Consulting Office, 28 quai de la Douane, 29200 Brest, France
⁵ IFREMER, Dép. RBE, Unité Sciences et Technologies halieutiques, BP 70, 29280 Plouzané Cedex, France

^a Corresponding author: claire.macher@ifremer.fr

Received: 8 June 2012
Accepted: 15 October 2012

Abstract

Several fleets with various fishing strategies operate as a mixed fishery in the Bay of Biscay. Among the main fleets, bottom trawlers target Norway lobster (Nephrops norvegicus) and, together with gillnetters, they also catch hake (Merluccius merluccius). Trawling leads to average-size catches that are below the minimum landing size (MLS); such catches are discarded since they cannot be sold. These discards result in negative impacts on stock renewal, as most of them do not survive. This also results in an economic loss for both bottom trawlers and gillnetters since these discards represent a future loss of rent. This study, based on the 2009 and 2010 selectivity experiments at sea, assesses the short- and long-term bio-economic impacts of four experimental selective devices aimed at reducing N. norvegicus and M. merluccius discards over a 20-year simulation period. Tests were conducted at sea on a research trawler. Using the impact assessment model for fisheries management (IAM model), selectivity scenarios for trawlers in the Bay of Biscay were compared to a theoretical selective scenario of adopting an optimal device that catches only N. norvegicus and M. merluccius above MLS (9 cm and 27 cm total length, respectively). Costs and benefits were analyzed with the objective of finding the best compromise between a reduction in discards of undersized fish and a loss of valuable catches among the experimental devices. Selectivity scenarios show positive impacts on stocks but different economic impacts between fleets. The combination of a square mesh cylinder with a grid and square mesh panels gives the closest results to the theoretical scenario tested in terms of stock recovery and economic benefits. This experimental device leads to low economic losses in the short term and eventually to higher N. norvegicus yields, which would be favourable for fleets that greatly contribute to N. norvegicus fishing efforts.