Publication Abstract

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

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

M.G. Frisk, N.K. Dulvy and T.J. Millar

Simple approaches to assessing vulnerability to population decline are required to determine the conservation or management requirements of less economically important fishes. One approach is to use life history traits to categorize vulnerability to exploitation. However, the utility of this approach requires that the links between life histories and population dynamics be explored. We constructed standard three-stage matrix models for 45 species of sharks and rays. We (1) conducted elasticity analyses and stage-based population models 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 the effects on elasticity of perturbing model vital rates by estimating the sensitivity of elasticity, 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 l to changes in juvenile and adult stages to longevity and age of maturation; however, the age of maturation and the elasticity of l to changes in the adult stage relationship appeared to be invariant. There was a negative relationship between both longevity and age of maturation and the elasticity of l to changes in inter-stage transitions of the models. Under varying fishing levels, "snap shot" 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 taxonomic groups at various levels. We discuss the implication of these findings in a management context.

Reference:

M. G. Frisk, N. K. Dulvy and T. J. Millar (2004) Life histories and vulnerability to exploitation of elasmobranchs: Inferences from elasticity, perturbation and phylogenetic analyses. Journal of the North Atlantic Fisheries Organisation 35: article 4

M. G. Frisk, N. K. Dulvy*, T. J. Millar

Journal of the North Atlantic Fisheries Organisation 35: article 4