SIMPLE SIZE-STRUCTURED MODELS OF RECRUITMENT AND HARVEST IN PACIFIC SALMON (ONCORHYNCHUS SPP)

Growing evidence suggests that in Pacific salmon (Oncorhynchus spp.), components of reproductive success besides fecundity are size dependen t. However, managers setting escapement goals usually estimate reprodu ctive potential of a stock in terms of total number of spawners, numbe r of female spawners, or potential egg deposition given a mean size of spawners. Interannual variation in size composition of spawners may t hus result in errors in assessing reproductive potential. Here, we dev elop models of recruitment and harvest and determine optimal size-sele ctive harvesting strategies. These optimal strategies range from the c urrent large-fish harvests (larger-than-average fish are caught, leavi ng smaller fish to spawn) to small-fish harvests, where the reverse is true. If the body mass (M) of individual spawners increases more rapi dly than reproductive success (RS) with respect to increasing length o f adult females (e.g., if number of eggs alone best measures RS), then sustainable biomass yield is maximized by the current large-fish harv est. However, if RS/M increases with increasing length of females (e.g ., if total biomass of eggs best measures RS), then small-fish harvest maximizes sustainable yield. Evidence suggests that some salmon popul ations show this latter pattern; thus, large-fish harvests may generat e suboptimal yields.