Hydrobiologia 449: 279–291, 2001. J.P.M. Paula, A.A.V.Flores & C.H.J.M. Fransen (eds), Advances in Decapod Crustacean Research. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 279 Effect of codend mesh size on the performance of the deep-water bottom trawl used in the red shrimp ﬁshery in the Strait of Sicily (Mediterranean Sea) S. Ragonese 1 , M. Zagra 2 , L. Di Stefano 2 & M.L. Bianchini 3 1 Ist. Ricerche Risorse Marine e Ambiente, IRMA/CNR, Via Vaccara 61, 91026 Mazara (TP), Italy 2 Ist. Istologia Embriologia, Universit` a, Palermo, Italy 3 CNR, Rome and Soc. Porto Romano, S. Marinella (RM), Italy Key words: bottom trawl, codend retention, deep-water shrimp, Aristaeomorpha foliacea, Mediterranean Sea Abstract The inﬂuence of different codend nets mounting diamond-shaped (16, 20, 24, 28 and 45 mm, mesh side) in the performance of the commercial bottom trawl presently in use in the Strait of Sicily (Central Mediterranean Sea) to catch deep-water red shrimps, Aristaeomorpha foliacea and Aristeus antennatus, is analyzed. In two surveys carried out in ﬁshing grounds in spring and summer 1993, 93 daylight hauls (of 3 hours each) based on the covered codend (cover of 14 mm mesh side) method were carried out. The composition and quantity of the combined, retained and escaped catch for the most relevant species and mixed categories of the different gear conﬁgurations (codends + cover) were analyzed and compared by applying both univariate (ANOVA) and multivariate (clustering and multidimensional scaling) techniques. The reduction of by-catch, the economic loss and the economic efﬁciency were used as indexes of the retention performance of the different codends. The overall catch was 6398 t (23 kg/h); Aristaeomorpha foliacea accounts for most of the catch in number, weight (48% of the total) and value (87% of the total value). Bony ﬁshes, cartilaginous ﬁshes and other crustaceans are the by-catch, representing, respectively, 26%, 16% and 9% of the catch in weight, the rest belonging to cephalopods. The use of the different codends does not inﬂuence the overall performance of the gear. No saturation was detected, with the escapement ratio uninﬂuenced by the amount retained. Considering the retention characteristics, results indicate that the 16 mm and 20 mm mesh codends are not selective, whereas the 24/14 and 28/14 conﬁgurations produce increased escaping ability. The 45 mm mesh sieves out 79% of specimens, indicating that no masking effect was induced by the cover. Regarding economic efﬁciency, the 20/14 conﬁguration provides values comparable to those obtained with the 24/14, whereas the 16/14 conﬁguration is as efﬁcient as the 28/14. The lowest efﬁciency was obtained using the 45/14 conﬁguration. Multidimensional scaling and clustering techniques (performed on 20, 24 and 28 mm codends) allow to discriminate the escapement ability of the 28/14 gear conﬁguration only. Present results support the introduction of the 28 mm mesh codend in the deep-water red shrimp ﬁsheries in the view of a precautionary management of the resources. Introduction The Mediterranean bottom trawl ﬁsheries are tra- ditionally characterized by the use of very small diamond-shape mesh sizes in the codends (about 14– 16 mm side), which practically tend to retain almost all the animals encountered by the gear (Ragonese et al., 1994; Stergiou et al., 1997). Fishery scientists and regulatory agencies have demanded an increase in the mesh size as a management tool to reduce the ﬁshing pressure on juveniles and to improve the state of the resources (Caddy, 1990). At the moment, both Italian and European legislation require a minimum of 20 mm mesh side (European Union, 1994), but ﬁshermen are reluctant to adopt such new mesh, given the neces- sity to exploit a mixture of species which show higher growth rates, and shorter life span than the Atlantic counterpart on one hand and the aim to catch some