Age, growth and reproduction of a common deep-water shark, shortspine spurdog (Squalus cf. mitsukurii), from Hawaiian watersPublished on 25 July 2011.
Charles F. Cotton, R. Dean Grubbs, Toby S. Daly-Engel, Patrick D. Lynch and John A. Musick.
About half of the extant shark species occur only in deep waters (defined as >200 m depth), yet few published studies on sharks include these taxa. As fisheries worldwide enter deeper waters, the provision of biological data for these little-known taxa is critical to management and conservation. The shortspine spurdog, Squalus cf. mitsukurii, is an abundant shark on the insular slopes of the Hawaiian Islands. We assigned ages by counting growth bands on the enamel caps of both dorsal fin spines. Age estimates ranged from 3 to 26 years for females and from 6 to 23 years for males. Growth was modelled with multiple length-at-age models, fitted using maximum likelihood estimation and nonlinear least-squares methods. For female data, the logistic model yielded the most biologically cogent parameter estimates (L∞ = 126 cm (total length, TL) and k = 0.080 year–1). The two-parameter von Bertalanffy Growth Model yielded optimal model fit and realistic parameter estimates for males (L∞ = 72 cm (TL) and k = 0.080 year–1). Maturity ogives suggested that females and males mature at 64-cm TL (15 years) and 47-cm TL (8.5 years), respectively. Fecundity ranged from 3 to 10 embryos; mating appeared to be aseasonal. We reveal a conservative life history, common among deep-water elasmobranchs, and provide further evidence of geographic variation in reproductive and growth parameters in this nominal species.
Marine and Freshwater Research 62(7) 811-822 http://dx.doi.org/10.1071/MF10307