Estimation and analysis of biological parameters in elasmobranch fishes: a comparative life history study

Published life-history parameters for sharks, skates, and rays over a wide geographic range were used to develop predictive models to estimate parameters that are difficult to measure or have not been previously estimated in elasmobranch species. We determined empirical relationships between body size (total length) and length at maturity (L-m) and age at maturity (T-m). The data used in determining these empirical relationships, the von Bertalanffy parameters asymptotic length (L-infinity) and growth rate (k), and natural mortality (M) and maximum age (T-max) were used to describe the life-history strategies of elasmobranch fishes. M/k and Beverton's growth-maturity-longevity plots were used to make comparisons between teleost fishes, reptiles, and elasmobranchs. We found that the M/k ratio in elasmobranchs is significantly different from those for other fish and reptile taxa. We linked elasmobranch species fecundity (f) and T-m to potential vulnerability to population decline under exploitation. We found that larger species of elasmobranchs have lower growth rates (k) and potential population increases (r'). Elasmobranchs can be categorized by species maximum length to determine susceptibility of decline under exploitation. Generally, species greater than 100 cm are characterized by life-history and population traits that place them at greater risk of population decline.