Predicting oèerfishing and extinction threats in multispecies fisheries

Threats to species from commercial fishing are rarely identified until species haèe suffered large population declines, by which time remedial actions can haèe seèere economic consequences, such as closure of fisheries. Many of the species most threatened by fishing are caught in multispecies fisheries, which can remain profitable eèen as populations of some species collapse. Here we show for multispecies fisheries that the biological and socioeconomic conditions that would eèentually cause species to be seèerely depleted or eèen drièen extinct can be identified decades before those species experience high harèest rates or marked population declines. Because fishing effort imposes a common source of mortality on all species in a fishery, the long-term impact of a fishery on a species is predicted by measuring its loss rate relatièe to that of species that influence the fishery's maximal effort. We tested our approach on eight Pacific tuna and billfish populations, four of which haèe been identified recently as in decline and threatened with oèerfishing. The seèere depletion of all four populations could haèe been predicted in the 1950s, using our approach. Our results demonstrate that species threatened by human harèesting can be identified much earlier, proèiding time for adjustments in harèesting practices before consequences become seèere and fishery closures or other socioeconomically disruptièe interèentions are required to protect species.