GROWTH, MORTALITY AND YIELD-PER-RECRUIT OF THE DEEP-WATER SHRIMP ARISTEUS-ANTENNATUS (CRUSTACEA-ARISTEIDAE) OF THE STRAIT OF SICILY (MEDITERRANEAN-SEA)

The MIX and Compleat ELEFAN methods were used to analyse length-freque ncy distributions of females of the deep-water shrimp Aristeus antenna tus in order to estimate growth, mortality and yield-per-recruit. Leng th data were gathered in four seasonal experimental trawl surveys made in the Strait of Sicily (Mediterranean Sea). Up to four annual cohort s were distinguishable. Modal lengths were integrated and the paramete rs of the von Bertalanffy growth function estimated by a weighted nonl inear regression, yielding an asymptotic carapace length of 69.1 mm an d an annual Brody's coefficient K=0.532, with a location parameter t(0 )=0 (line through the origin). The consistency of these estimates was evaluated by comparison with the corresponding parameters obtained app lying ELEFAN-I and producing a confidence interval by bootstrap resamp ling; this Last procedure revealed the presence of two possible soluti ons corresponding to a 'slow' and a 'fast' growth hypothesis. The grow th estimates derived from the modal progression analysis in any case: fall inside the confidence ellipse of the bivariate plot of the asympt otic lengths and growth coefficients derived from the bootstrapped dat a sets. The total annual mortality was estimated as Z=1.1, following H eincke's approximation; two values of annual natural mortality, M(1)=0 .5 and M(b)=0.8, were used afterwards, As a negative allometric length -weight relationship (b<3) does exist, the incomplete beta function wa s applied to compute the yield-per-recruit values. Analysis of the Y/R curves suggests that the current Y/R can be improved by a moderate in crease, from 1 to 1.5 years, in the age of first capture; this could b e obtained by increasing the mesh size of the cod-end from the present 18 mm to 28 mm, without any economic loss, even short term.