Using life history and persistence criteria to prioritize habitats for management and conservation

In many marine and terrestrial systems, individuals of a focal species may be found in habitats that are neither essential nor of particular concern for conservation. For example, finding fish in a location does not make that location essential. This recognition begs the question of how one identifies the most important habitats for a particular species. We introduce new tools for use when prioritizing habitats for conservation and management, with application to Essential Fish Habitat (EFH). If density-dependent effects can be ignored, then elasticities of population growth rate with respect to adult survival, fecundity, and juvenile survival provide a means of identifying how susceptible the growth rate of the population is to perturbations in vital rates of particular life stages. We develop such a theory and apply it to 16 species of commercially harvested Sebastes rockfishes. We also show that the conclusions may differ significantly depending upon the estimate of mortality rate that is used. This suggests that although estimating mortality rates of fish in the field is difficult, it is crucial to do so. When density-dependent effects are important, we use a stochastic life history model to compute the moderate-term persistence of the stock, an important metric of population biology, as a function of the demographic parameters determined by the habitat. Although developed with fish in mind, the ideas here also apply to other taxa and systems.