Influence of the marine abundance of pink (Oncorhynchus gorbuscha) and sockeye salmon (O-nerka) on growth of Ozernaya River sockeye

The length and weight of Russian sockeye (Oncorhynchus nerka) returning to the Ozernaya River (Kamchatka) was substantially reduced in years when the ocean abundances of Kamchatkan pink (O. gorbuscha) and sockeye salmon were high. We found that the density-dependent reduction in sockeye growth on a per-capita basis was greater for sockeye than for pink salmon. However, the overall effect of pink salmon abundance on sockeye growth was greater beca use of the higher numerical abundance of pink salmon. The strongest statist ical relationships were found for sockeye from separate age groups; pooled data combining all age classes were statistically insignificant. We estimat e that, if pink salmon were absent, the most strongly affected age group of sockeye salmon (2.1 males) would weigh twice as much at maturity than if p ink salmon populations from eastern and western Kamchatka were both simulta neously at peak observed abundances. Trophic competition in the ocean betwe en pink and sockeye salmon can therefore have a significant influence on th e productivity of sockeye populations for the most strongly affected age gr oups. These effects are large enough that they should be explicitly conside red in the management of salmon populations.