Intra- and inter-specific competition and the reproductive success of sympatric Pacific salmon

Abstract

Individual female Pacific salmon fight for breeding space with conspecific and heterospecific females. We evaluated the consequences of this competition on the reproductive success of sockeye (Oncorhynchus nerka), chum (Oncorhynchus keta), and pink salmon (Oncorhynchus gorbuscha) in the Weaver Creek spawning channel, British Columbia. We hypothesized that differences in body size, relative abundance, and spawning date would influence the magnitude of interspecific interactions. Reproductive success (survival rate of eggs to emigrating fry) of the most abundant species, sockeye, was strongly and inversely correlated with conspecific abundance but not with the abundance of the other, less abundant species. Chum reproductive success was inversely correlated with sockeye abundance but not with the abundance of the scarce and smaller pink. Surprisingly, pink reproductive success was not correlated with sockeye abundance and only marginally correlated with chum abundance despite the fact that pink are smaller and spawn earlier than sockeye. Thus, intra- and inter-specific competition can substantially affect salmon reproductive success, but the magnitude of the competitive effects may depend on relative abundance, size, spawning date, and microhabitat preferences.