CARRYING-CAPACITY AND NORTH PACIFIC SALMON PRODUCTION - STOCK-ENHANCEMENT IMPLICATIONS

Ocean-ranching programs in Asia and North America are supplementing, o r have replaced, the natural production of some salmonid populations f eeding and maturing in the North Pacific Ocean. These activities, coup led with favorable survival conditions, have raised many stocks to his torical or near historical highs during the last decade and a half. St udies of ocean forage production and the response of nekton population s to changes in levels of forage demonstrate multi-year and interdecad al variability attributed to large-scale atmospheric cycles. The perio d since the most recent regime shift favored salmon production in Alas ka waters, but not off Washington and Oregon. We present modeled estim ates of the forage demand placed on coastal and oceanic feeding areas by wild and ocean-ranched pink salmon originating from Prince William Sound, Alaska, as a case history. Annual food consumption for these st ocks rose from less than 100,000 mt prior to 1976 to more than 300,000 mt after 1988, when hatchery production began dominating adult return s. Food demand was distributed nearly equally between survivors and no nsurvivors, and most of the food consumption occurred in the oceanic r ather than coastal environments. Because, for all species, adults that return at smaller than average size are less fecund and produce small er eggs and fry, increased competition for food resulting in smaller b ody size could influence the survival of progeny, with serious consequ ences for both wild and hatchery populations. Studies suggest that com petition can result from increased salmon production, diminished forag e production, and decreases in the size of ocean feeding domains.