Life histories and vulnerability to exploitation of elasmobranchs: Inferences from elasticity, perturbation and phylogenetic analyses

Abstract

We used life history traits to categorize vulnerability of elasmobranchs to exploitation. However, the utility of this approach required that the links between life histories and population dynamics be explored. We constructed standardized three-stage matrix models for 55 species of sharks and rays. Using these models we (1) conducted elasticity analyses to determine how the vital rates of mortality (M) and fertility (f) influence elasmobranch population growth rate r, (2) determined the response of elasticity to changes in the levels of exploitation, (3) estimated sensitivity of elasticity to perturbation in vital rates, and (4) examined the taxonomic distribution of model inputs and species vital rates, such as size at maturity (Lmat), and total length (Lmax), We found positive relationships between the elasticity of λ (population growth rate) to changes in juvenile and adult stages to longevity and age of maturity; however, the age of maturity and the elasticity of λ to changes in the adult stage relationship appeared to be invariant. There was a negative relationship between both longevity and age of maturity and the elasticity of λ to changes in inter-stage transitions of the models. Under varying fishing levels, estimates of elasticity were robust to changes in survival. Elasticity and perturbation analyses suggested that compensatory responses to exploitation in elasmobranchs were less likely to be expressed as changes in fertility than as changes in juvenile and adult mortality and stage durations (i.e. changes in age of maturity). Combining vital rates and elasticities, we found similar suites of life histories and demographics within groups at various taxonomic levels.