Non-commercial invertebrate discards in an experimental trammel net fishery J. M. S. GONC ¸ ALVES, L. BENTES, R. COELHO, P. MONTEIRO, J. RIBEIRO, C. CORREIA, P. G. LINO & K. ERZINI Centro de Cie ˆncias do Mar – CCMAR/CIMAR, Universidade do Algarve, Faro, Portugal Abstract Non-commercial invertebrate discards in an experimental trammel net fishery were studied in relation to selectivity of the gear, depth, soak time and season. Forty experimental fishing trials were carried out over a 1-year period with six combinations of small mesh (100, 120 and 140 mm) inner and large mesh (600 and 800 mm) outer panels. On average, 43.8 ± 12.2 (SD) (individuals 1000 m )1 of net) of non-commercial invertebrates were discarded, accounting for 48% and 65% of the total catch and total discards by numbers, respectively. Within non-commercial invertebrates discards, the six most abundant species by number were Phallusia mammillata (Cuvier) (27.5%), Cymbium olla (L.) (13.0%), Sphaerechinus granularis (Lamarck) (11.3%), Paracentrotus lividus (Lamarck) (10.9%), Astropartus mediterraneus (Risso) (8.2%) and Astropecten aranciacus (L.) (8.1%); Echino- derms (43.1%) particularly important. The highest and lowest discard ratios were found in autumn and winter, respectively. Discards generally decreased with depth, varied considerably in relation to soak time and were not related to mesh size combinations. Trammel nets seem to be the most important gear in terms of ecological impacts on benthic invertebrates compared with other coastal fishing gears and at the depths studied (15–60 m). KEYWORDS: biodiversity, by-catch, discards, fisheries, gear selectivity, invertebrates. Introduction The maintenance of marine biodiversity is an impor- tant priority for conservation, and fishing is one of the activities that most impacts on marine communities, removing rare and abundant species, changing species composition, modifying and even destroying habitats (e.g. Hall 1999). Discarding is a common practice in fisheries worldwide, accounting for an estimated 8% of the annual commercial fish catches or 7.3 million ton of fish returned to the sea (Kelleher 2005). As discarded organisms are often dead or in a poor state, their discarding represents a loss of diversity of marine communities (e.g. Hall 1996; Hall, Alverson & Metu- zals 2000). With the growing consciousness of the importance of ecosystem functioning for sustainability of fisheries resources (e.g. Gislason, Sinclair, Sainsbury & OÕBoyle 2000), a number of studies on the evaluation of the effects of fishing on the environment have been undertaken (e.g. Jennings & Kaiser 1998; Collie, Hall, Kaiser & Poiner 2000). As trammel nets are one of the most widely used gears in coastal waters worldwide, there have been some studies on discards (e.g. Purbayanto, Tsunoda, Akiyama, Arimoto & Tokai 2001; Coelho, Erzini, Bentes, Correia, Lino, Monteiro, Ribeiro & Gonc¸alves 2005; Gonc¸alves, Stergiou, Hernando, Puente, Mou- topoulos, Arregi, Soriguer, Vilas, Coelho & Erzini 2007) but, as with discard studies for most gears, the emphasis was on vertebrates or commercially valuable or protected species. In the Algarve (southern Portugal), 130 coastal fishing vessels were licensed to fish with trammel nets in 2002, accounting for 14.8% of all the licenses, with only longline licenses more important (DGPA 2007). Given that the coastal vessels are allowed to fish up to 9.0 km of trammel nets, the quantity of trammel nets used in Algarve waters (coastline of 160 km) could easily exceed 1000 km. Trammel netting takes place at depths from 10 to 90 m, mostly within 6 nautical miles of the shore. The target species of this fishery are demersal and benthic species, such as cuttlefish, sea breams, soles, red mullet, skates and spiny lobster and Correspondence: Jorge M. S. Gonc¸alves, Centro de Cieˆncias do Mar – CCMAR, Universidade do Algarve. FCMA Campus de Gambelas, 8005-139 Faro, Portugal (e-mail: jgoncal@ualg.pt) Fisheries Management and Ecology, 2008, 15, 199–210 Ó 2008 The Authors. Journal compilation Ó 2008 Blackwell Publishing Ltd. doi: 10.1111/j.1365-2400.2008.00607.x Fisheries Management and Ecology