Abundance and biological traits of the spottail mantis shrimp, Squilla mantis (L., 1758) (Crustacea: Stomatopoda), off the southern coast of Sicily

In order to establish "historical" benchmark values, length-based methods were used to analyze size structure, growth and mortality of the spottail mantis shrimp, Squilla mantis (L., 1758), off the southern coasts of Sicily (Mediterranean Sea). Data were gathered with bottom trawl surveys carried out during autumn in the period 1994-2008. The species occurred almost exclusively in the shelf (10-200 m), showing irregular abundances (20-885 ind.km(-2) and 0.7-16.6 kg.km(-2)) and a marked preference for the shallower depths (10-50 m). The sex ratio was significantly different from 1.0 [F/M = 1.33], whereas no significant sex-related differences resulted in the total length-body weight relationship (In W-g = -11.405 + 3 x In TLmm) or the length frequency distributions (LFD). Three modal groups were identified in both sexes; the von Bertalanffy growth function (vBGF) was estimated, on sex combined, using TL infinity = 190 mm resulting from the Powell-Wetherall method; thus, the other parameters were K-yr = 0.41 year(-1) and t(0) = -0.52 year. The total annual mortality coefficients was also derived (Z(yr) = 0.98), indicating a mortality off southern Sicily - during the investigated period - lower than in other Mediterranean stocks of S. mantis.