Flatfish discarding practices in bivalve dredge fishing off the south coast of Portugal (Algarve) J. Palma * , C. Reis, J.P. Andrade CCMar, Faculdade de Cie ˆncias do Mar e do Ambiente, Campus de Gambelas, Universidade do Algarve, 8000-810 Faro, Portugal Received 15 October 2002; accepted 28 April 2003 Abstract An evaluation of flatfish discards from bivalve dredge fishing on the south coast of Portugal (Algarve) was undertaken through fishing surveys carried out on board a professional dredge fleet. Data collection of the dredge fishery was carried out between November 2000 and February 2002. The data were compared with information gathered from abundance analysis surveys, and analysed independently of the target bivalve species (Chamelea gallina, Donnax trunculus, and Spisula solida). Flatfish and non-flatfish species accounted for 20.1% and 79.9%, respectively, of the by-catch species of the bivalve dredge fishery. Significant differences have been calculated between length composition of flatfish species in the by-catch and in the abundance surveys. This indicates an optimised performance of the bivalve dredge, which catches a small amount of undersized flatfish as by-catch. D 2003 Elsevier B.V. All rights reserved. Keywords: Bivalve fishery; Dredges; Flatfish; By-catch; Portugal 1. Introduction Fishing gear used to catch demersal fish and shell- fish often disturbs both the seabed and the organisms living within or on it (Collie et al., 2000), since the way in which trawling is conducted affects the survival of all the animals caught in the trawl (Wassenberg and Hill, 1989). The passage of a bivalve dredge, as with any other type of trawl across the seabed, leads to direct and/or indirect mortality of both commercial and non-commercial species. Indirect fishing mortality for beam, bottom and otter trawl has been extensively studied by some authors (Bergman and Hup, 1992; Fonds, 1994; De Groot and Lindeboom, 1994; Kaiser et al., 1994; Kaiser and Spencer, 1995; Engel and Kvitek, 1998; Piet et al., 2000; Bergmann and Moore, 2001a,b; Bergmann et al., 2001). Although bivalve dredging gear is specifically designed to catch bivalves, it also catches some (undersized) fish and benthic invertebrates. These animals are rapidly sorted on board and specimens that are undersized or of no commercial interest are returned to the sea. Thus, the main issue is to ascertain the chances of survival of the discarded fish, since some of them may be permanently damaged by the gear and will not survive after they had been returned to the sea (Bergman and Van Santbrink, 2000). Although some research has focussed on the effect 1385-1101/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1385-1101(03)00065-0 * Corresponding author. E-mail address: jpalma@ualg.pt (J. Palma). www.elsevier.com/locate/seares Journal of Sea Research 50 (2003) 129 – 137