Trawl gear selectivity and the effect of mesh size on the deep-water rose shrimp (Parapenaeus longirostris, Lucas, 1846) fishery off the gulf of Cadiz (SW Spain)

The deep-water rose shrimp (Parapenaeus longirostris, Lucas, 1846) is a typ ical shrimp which is one of the main target species in the demersal fishery in the Spanish south Atlantic region. In this paper, the selectivity param eters of this species have been studied in two different selectivity survey designs (research vessels and in commercial fishing vessels). We have foun d 2 mm difference between both methods in the 50% retention length (L-50) T he selection factors obtained from the oceanographic vessels range from 0.3 7 to 0.49, while those from the commercial vessels are lower, from 0.32 to 0.39. The effects of mesh size changes in the present exploitation pattern are also considered. The present exploitation pattern is far from to optima l due to an overexploitation of the smaller sizes. The different simulation s of changes in mesh size do not show great differences in maximum sustaina ble yields, but important market variations occur above 30% and 50% over th e present obtained values. In reference to the immediate effects which coul d produce an increase of the mesh size, losses of 36%, 51% and 62% for the referred mesh sizes (50, 55 and 60) using the selectivity parameters obtain ed from the surveys of research vessels are estimated. If obtained from the surveys of the commercial vessels, these values correspond, respectively, to 27%, 42% and 73%. (C) 2000 Elsevier Science B.V. All rights reserved.