Aspects of the reproductive biology of skates (Chondrichthyes: Rajiformes: Rajoidei) from southern Africa

Abstract

AbstractEbert, D. A., Compagno, L. J. V., and Cowley, P. D. 2008. Aspects of the reproductive biology of skates (Chondrichthyes: Rajiformes: Rajoidei) from southern Africa. – ICES Journal of Marine Science, 65: 81–102. New information is presented on the reproductive biology of 22 southern African skate species. Sex ratios for most species were relatively even. Sexual dimorphic differences in disc shape were evident in all species, but the total length (LT) to disc width (D) relationship was significantly different in only three species, and the LT to weight (W) relationship significant in just five species. Sexual dimorphism relative to maximum total length (LTmax) was absent in all but the two largest species. Males and females of the same species grow to a similar LTmax except those whose LTmax is >1.5 m LT. Size at first and 50% (LT50) sexual maturity was approximately the same for both sexes in all but the two largest species. First maturity occurred at >60% of LTmax for all species for which sufficient data were available, and most (n = 18) matured at >75% LTmax. The large size at maturity relative to LTmax suggests that growth slows or is partially suspended following sexual maturity. The egg cases of 15 species are described, and a key to their identification is presented. Egg cases in utero were observed throughout the year suggesting that most species reproduce year-round.