Influence of sexual maturity and age on the bathymetric distribution of Dipturus oxyrinchus in the Sardinian seas (Central Western Mediterranean)

BELLODI, ANDREA;MULAS, ANTONELLO;FOLLESA, MARIA CRISTINA;CANNAS, RITA;Cannas S.;MARONGIU, MARTINA FRANCESCA;PORCU, CRISTINA;Cau A.

2013-01-01

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Abstract

The influence of maturity stage and age on the bathymetric distribution of longnosed skate Dipturus oxyrinchus (Linnaeus, 1758) in the Sardinian seas was investigated. Since 2005 to 2012, a total of 494 (266 females and 228 males) individuals, from 15.7 and 115.5 cm TL, were caught during experimental and commercial trawl surveys at depths between 129 and 650m. Each individual was measured and weighted. Maturity stages were attributed following the MEDITS scales for the elasmobranchs. The age was evaluated through the count of vertebral centra’s annuli from a subsample of 75 females and 53 males. The VBGF parameters were determined (L∞ = 149.2, s.e.=15.72; k = 0.08, s.e. = 0.02; t0 = -0.8, s.e. = 0.29 and L∞ = 118.97, s.e. = 10.82; k = 0.11, s.e. = 0.02; t0 = -1.08, s.e. = 0.32 for females and males, respectively). ANOSIM (global R = 0.136, p<0.001) showed differences among the six considered strata (A to F with intervals of 100m). Upper than 300m (A and B strata) were mostly found immature individuals from 3+ to 6+ and specimens ≥12+ at maturity stage 2 and 3 for females and males, respectively. Between 300-500m, the population was composed almost exclusively by immature skates <5+. Over 500m were mainly present younger immatures (<3+) of both sexes and older females (>12+, stage 3 and 4). D. oxyrinchus seems to mate in shallower waters. After that females migrate to deeper strata to spawn, while younger individuals carry out a reverse migration during growth.