Age, growth, and reproductive biology, of the winter skate, Leucoraja ocellata, in the western Gulf of Maine

Abstract

This study describes the age, growth and reproductive biology of the winter skate, Leucoraja ocellata, in the Western Gulf of Maine. Age was estimated by enumerating annular bands within the vertebral centra. Precision of the age estimates was evaluated using the Index of Average Percent Error and the annual nature of growth band formation was documented using marginal increment analyses. Growth was assessed with the use of the von Bertalanffy growth equation. Age and size at maturity was estimated by measuring morphological and histological changes in the reproductive tract and circulating steroid hormone concentrations. Maturity ogives for males predict that 50% maturity occurs at a total length of 730 mm and at 11 years. For females, maturity ogives predict that 50% maturity occurs at a total length of 760 mm and between 11 and 12 years of age. To elucidate the reproductive cycle of the winter skate, plasma concentrations of the sex steroids testosterone (T), 17beta-estradiol (E2), and progesterone (P4) were determined by radio immunoassay and compared to morphological and histological changes occurring in the reproductive tract over a complete reproductive cycle for mature individuals. Overall, when the results of my dissertation are combined, they indicate that the winter skate is a late maturing, slow growing, long lived species, with an apparent succinct reproductive cycle. Like many other elasmobranchs, these characteristics make L. ocellata \u27s populations highly susceptible to exploitation by commercial fisheries