Factors influencing the early marine ecology of juvenile sockeye salmon (O. nerka) in Rivers Inlet, British Columbia

The Rivers Inlet sockeye salmon (Oncorhynchus nerka) population was historically the third most numerous in British Columbia, with returns routinely exceeding one million adults. In recent years, the population has drastically declined, culminating in an utter failure of the adult spawning population in 1999, when returns were estimated at 3600 fish. Poor marine survival has been proposed as the primary cause of the decline. Existing evidence, including concurrent declines in sockeye salmon populations from nearby watersheds indicate the problem may lie in the early marine phase. We provide evidence suggesting that a crucial, population-limiting window may exist in the early marine phase, as the newly smolted juvenile sockeye salmon emerge into Rivers Inlet and nearby waters. Unless appropriate abiotic conditions exist in the lead-up to the juvenile migration, the brood year may suffer significant mortality. This, I propose, is a key contributor to reduced returns of Rivers Inlet sockeye salmon.