Growth, mortality and yield-per-recruit of the deep-water shrimp Aristeus antennatus (Crustacea-Aristeidae) of the Strait of Sicily (Mediterranean Sea)

Abstract

The MIX and Compleat ELEFAN methods were used to analyse length-frequency distributions of females of the deep- water shrimp Aristeus antennatus in order to estimate growth, mortality and yield-per-recruit. Length data were gathered in four seasonal experimental trawl surveys made in the Strait of Sicily (Mediterranean Sea). Up to four annual cohorts were distinguishable. Modal lengths were integrated and the parameters of the von Bertalanffy growth function estimated by a weighted non-linear regression, yielding an asymptotic carapace length of 69.1 mm and 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 applying ELEFAN-I and producing a confidence interval by bootstrap resampling; this last procedure revealed the presence of two possible solutions corresponding to a ‘slow’ and a ‘fast’ growth hypothesis. The growth estimates derived from the modal progression analysis in any case fall inside the confidence ellipse of the bivariate plot of the asymptotic lengths and growth coefficients derived from the bootstrapped data sets. The total annual mortality was estimated as Z = 1.1, following Heincke's approximation; two values of annual natural mortality, M l = 0.5 and M h = 0.8, were used afterwards. As a negative allometric length-weight relationship ( b < 3) does exist, the incomplete beta function was 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 increase, from 1 to 1.5 years, in the age of first capture; this could be 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.