The population dynamics of little skate Leucoraja erinacea, winter skate Leucoraja ocellata, and barndoor skate Dipturus laevis: predicting exploitation limits using matrix analyses

Abstract

Over the past thirty years catches of skates have increased in the western Atlantic as a result of targeted fisheries and as by-catch. Presently, sustainable harvest levels for skates in the western Atlantic are unknown. Available life history information was used to model three western Atlantic skate species, little skate Leucoraja erinacea, winter skate Leucoraja ocellata, and barndooor skate Dipturus laevis, to determine their population growth rate and susceptibility to population decline under exploitation. Population characteristics were estimated using age-based matrix analyses for little and winter skate and a stage-based matrix approach for barndoor skate. The intrinsic rate of population increase (r) for little, winter and barndoor skates were 0.21, 0.13 and 0.20, respectively. Fishing mortality resulting in equilibrium conditions, where the intrinsic rate of increase is zero, were 0.35 for little skate, 0.16 for winter skate and 0.20 for barndoor skate. Elasticity analyses indicated that juvenile survival contributed most to population growth in little skate and winter skate, and adult survival contributed the most in barndoor skate. Thus, conservation measures should focus on juvenile and adult stages of these species. In the absence of fishing mortality, elasticity of fecundity was low for all species, however; at high exploitation levels the contribution of fecundity to population growth rate increased. Stochastic analyses were performed by varying first year mortality (egg stage to the completion of one year of life), and model parameters for each species to generate estimates of the distributions of biological reference points. Our study supports the finding that long-lived, slower growing, late maturing species are highly vulnerable to exploitation. Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.