Longevity overfishing

摘要

Overfishing is generally considered to be a reduction in biomass below some critical level such that the remaining fish are not able to replenish the population. We propose that the removal of large numbers of older age groups by fishing is also a form of overfishing, which we identify as longevity overfishing. Longevity overfishing is a potentially important consideration for the commercial fisheries off Canada's Pacific coast that are dominated by species that have maximum ages of 30 years or longer. Sablefish is one of the key long-lived species that is managed for biomass and not longevity. An age structured model showed that if younger fish do not have the same productivity per unit biomass as older fish, the population depleted of older fishes would not recover after a shift of carrying capacity from a prolonged period of poor productivity to a more productive ocean ecosystem. Current management of long-lived species implicitly assumes that young fish will have the same productivity as older fishes, an assumption that is not supported by a sparse literature, and is thus not precautionary. We propose that the evolved age structure is an indication that long-lived species must be managed for longevity as well as biomass, which requires a management time frame that is decades and not annual.