Fisheries Sustainability via Protection of Age Structure and Spatial Distribution of Fish Populations

The objective of U.S. fisheries management, as mandated by National Standard 1 of the Sustainable Fisheries Act of 1996, is to maintain fish stocks at levels sufficient to produce maximum sustainable yields (MSY). Mandated levels of fishing may be less than MSY but are not to exceed these levels. MSY, of course, has been a highly elusive goal (Larkin 1977). Operationally, National Standard 1 has been interpreted by most fisheries management plans to mean that fishing should maintain some minimum spawning biomass deemed adequate to ensure that recruitment is not limited by insufficient egg or larval production. In the Pacific groundfish fishery and elsewhere, management is based on maintaining egg or larval output per recruit at or above 40% of the unfished level, referred to as B40 (while the unfished level is B0). Functionally this means maintaining the spawning biomass at 40% of the estimated virgin stock level, with adjustment for age-specific fecundity. Other biological reference points used in managing this fishery are B25 (25% of the unfished level), which is the overfishing threshold, and B10 (10% of the unfished level), which is the threshold at which the fishery is closed (even though bycatch mortality may continue). Despite these guidelines, periodic population assessments, and attempts at careful regulation of fisheries, many rockfish and other groundfish stocks declined, some severely, and consequently were declared “overfished” (Table 1). These declines have resulted in very restrictive rebuilding plans that include large-scale fishery closures. Estimated rebuilding times, even with no further fishing, are quite long and in some cases may not be achieved within our lifetimes (Table 1). How did such widespread stock declines occur? Was this challengFisheries Sustainability via Protection of Age Structure and Spatial Distribution of Fish Populations