Trophic and fishery interactions between Pacific hake and rockfish: Effect on rockfish population rebuilding times

Abstract

Several species of overfished Pacific rockfish (genus Sebastes) are incidentally caught in the fishery targeting Pacific hake Merluccius productus. Juvenile rockfish also comprise a small amount of Pacific hake diets. We used 2-species, age-structured models to estimate how prey selectivity by Pacific hake, life history and population structure of rockfish, spatiotemporal overlap, and fishery closures might affect the time required to rebuild overfished rockfish populations to 40 % of unfished spawning stock biomass. As prey selectivity increased, rebuilding time increased moderately for widow rockfish S. entomelas and darkblotched rockfish S. crameri, and more sharply for canary rockfish S. pinniger. Darkblotched rockfish were the least sensitive to Pacific hake predatory selectivity, which was likely related to their rarity in Pacific hake diets, not their stochastic reproductive success. Spatiotemporal overlap between rockfish and Pacific hake also increased rebuilding times, primarily because of higher rockfish bycatch, not predation. Early fishery closures and Pacific hake predation had an interactive effect that prolonged widow and canary rockfish rebuilding times, partly as a function of model assumptions and partly because fishery closures led to increased predation on juvenile rockfish. Because an ecosystem-based approach to fisheries management involves considering the influence of ecological factors on fish populations, models that examine interactions between depleted species and predatory species are essential. In this case, it appears that overfished rockfish rebuilding times can be significantly affected by the dynamics of a key predator, but also that the predatory effect can be mitigated by effective bycatch control. © Inter-Research 2008.