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Abstract

This paper reports on the maturity pattern and the estimation of length at sexual maturity for Aristaeomorpha foliacea females, based on two years of seasonal research trawl surveys. Two approaches were used: gonadic condition (empirical scale) and presence/absence of spermatophores. Ready-to-spawn females (IV stage) occurred almost exclusively in summer throughout the area surveyed. Distribution of the proportion of "mature" (III + IV stages) females showed the classic "sigmoid" shape but with a general failure to attain 100% maturity, even though in the largest size classes there is substantial inter-year variability. The presence of spermatophorcs, however, being a sign of adulthood, with almost all the medium/large specimens positive, showed a better approximation to the sigmoid curve. An attempt to combine the two curves, in order to more precisely identify the length at maturity, is illustrated and discussed. The logistic model has been chosen in a form that allows the asymptote to be < 1. The maximum reproductive potential is defined as the point of intersection of the two curves (spermatophores and maturity). This maximum is reached after about 18 months, at a carapace length of 40 mm.

In: Crustaceana

The spatial representation of decapod crustaceans (Crustacea, Malacostraca) of the Strait of Sicily (Central Mediterranean Sea) is presented for the first time, together with comments on their vertical and horizontal distributions. The most relevant trawlable species were analysed using quantitative data gathered in 260 daylight lasting hauls, which covered a large portion (about 100 000 km2) of the investigated area. The index of local abundance, standardized to 1 km2, both in weight (Biomass Index), number (Density Index) and mean body weight were obtained for each species and for all species combined. A spatial representation of the Density Index was produced for all decapod crustaceans combined and for the most frequent species. In particular, the indices were transferred under a GIS system and spatial maps produced by applying the program ArcView™ 9.0. Different interpolators were tested and the most exact interpolator (IDW Inverse Distance Weighting) was chosen. Both historical (i.e., doubts about the presence or identification of the species) and spatial (i.e., differential distribution among different fishing areas) heterogeneity were detected and commented upon. Concerning the trawlable bottoms, very few species (such as Parapenaeus longirostris (Lucas, 1846), Aristaeomorpha foliacea (Risso, 1827), Aristeus antennatus (Risso, 1816), Nephrops norvegicus (Linnaeus, 1758) and Plesionika martia (A. Milne-Edwards, 1883)) are consistently and largely represented in the catches. A high spatial heterogeneity, likely reflecting the complex interaction between fishing pattern, hydrological features and bottom typology, was made evident.

In: Crustaceana