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

Abstract

The age, growth, longevity, mortality and reproductive parameters were estimated for Dipturus oxyrinchus from the Gulf of Gabès (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 (TL)) and 280 males (15.5–95 cm TL) were examined to study the reproductive cycle. A subsample of 285 specimens (175 females and 110 males, ranging from 15.5 to 105 cm TL) were analysed to study the age and growth. The oldest female in this study was 25 yr and 105 cm TL, 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∞ = 123.9 ± 2.56 cm, K = 0.08 ± 0.004 yr−1 and t0 = −1.26 ± 0.04 10−1 yr for females and L∞ = 102.1 ± 3.23 cm, K = 0.12 ± 0.007 10−3 yr−1 and t0 = −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.

Life‐history traits of the long‐nosed skate Dipturus oxyrinchus

“…Both sexes were equally distributed confirming the pattern proposed by Yigin & Ismen () and Kadri et al . (), but a dominance of females was observed in the deepest strata (501–800 m) as also reported for other elasmobranchs such as Etmopterus spinax (L. 1758) (Porcu et al ., ).…”

“…Yigin & Ismen () in the north Aegean Sea and Kadri et al . () in southern Tunisia. Such dimorphism appears to be a common feature in elasmobranchs and, in general, the Rajidae [ e.g .…”

“…Only a few studies have fully explored alternative models to analyse elasmobranch growth patterns (Fisher et al ., ) showing, however, that the classical von Bertalanffy function does not always offer the best fit to the data, especially in batoids (Neer & Thompson, ). According to available literature, growth models other than the classical von Bertalanffy were not available for the present species (Yigin & Ismen, ; Kadri et al ., ). The present results emphasize that among the four investigated growth models, the Gompertz function provided the best fit, despite being based on a relatively small sample size and indicates the need to test multiple models in elasmobranch age and growth studies.…”

“…Late age at maturity, with females maturing later than males, was previously observed in other Mediterranean areas such as the north Aegean Sea (Yigin & Ismen, ) and southern Tunisia (Kadri et al ., ). However, these studies reported smaller sizes of L 50 , although a study using MEDITS data of all Mediterranean geographic sub‐areas (Serena et al ., ) showed a similar L 50 .…”

“…Hitherto, age, growth and reproduction of D . oxyrinchus have been studied in Turkish (Yigin & Ismen, ) and Tunisian waters (Kadri et al ., ). In addition, a few other papers have been published on other biological aspect of this species, such as feeding behaviour (Kadri et al ., ; Yigin & Ismen, ; Mulas et al ., ) and oviducal gland morphology (Marongiu et al ., ).…”