Age, growth, longevity, mortality and reproductive biology of Dipturus oxyrinchus , (Chondrichthyes: Rajidae) off the Gulf of Gabès (Southern Tunisia, central Mediterranean)

The age, growth, longevity, mortality and reproductive parameters were estimated for Dipturus oxyrinchus from the Gulf of Gabes (Southern Tunisia, central Mediterranean Sea), collected monthly during 2007 from commercial fisheries. The present study provides the first data on age and growth of this species in Tunisian waters, as well as additional data on its reproduction. A total of 240 females (16.5-105 cm total length (T-L)) and 280 males (15.5-95 cm T-L) were examined to study the reproductive cycle. A subsample of 285 specimens (175 females and 110 males, ranging from 15.5 to 105 cm T-L) were analysed to study the age and growth. The oldest female in this study was 25 yr and 105 cm T-L, whereas the oldest male was 22 yr and 95 cm. The annual deposition of growth bands was verified by marginal increment and edge analysis. The von Bertalanffy growth parameters were L-infinity = 123.9 +/- 2.56 cm, K = 0.08 +/- 0.004 yr(-1) and t(0) = -1.26 +/- 0.04 10(-1) yr for females and L-infinity = 102.1 +/- 3.23 cm, K = 0.12 +/- 0.007 10(-3) yr(-1) and t(0) = -1.18 +/- 0.03 10(-1) yr for males. Growth was not significantly different between sexes. The maturity size was 72.05 cm for males and 82.1 cm for females. The maturity age was estimated to be 11.95 and 13.96 years, respectively, for males and females. Size and age at maturity were not significantly different between sexes. The estimated longevity was 26.18 and 38.84 yr for males and females, respectively. Based on life history parameters, natural mortality was estimated at 0.53 yr(-1) for females and 0.41 yr(-1) for males.