A new study in the Canadian Journal of Fisheries and Aquatic Sciences suggests that increased abundance of pink salmon in the North Pacific Ocean is linked to declining trends in sockeye salmon populations.
Their findings highlight the need for countries across the North Pacific Rim to recognize limitations of the North Pacific ecosystem and manage limited salmon resources at an oceanic scale, said Greg Ruggerone, of Natural Resources Consultants in Seattle, and Brendan Connors of ESSA Technologies, in Vancouver, British Columbia.
Ruggerone said he began his investigation when the Pacific Salmon Commission asked him, in the wake of the decline of Fraser River sockeye in 2010, to test whether competition at sea might explain the decline in the Fraser River salmon.
Ruggerone and Connors said their studies suggest that growing numbers of pink salmon in the North Pacific Ocean are leading to increased competition for food with sockeye salmon from Washington State through British Columbia to Southeast Alaska. This food competition results in slower sockeye salmon growth, delayed maturation and ultimately reductions in sockeye salmon survival and abundance, they said.
Pink salmon abundance exhibits a strong alternating year pattern related to their two-year life span, with pink salmon abundance greater in odd-numbered years.
The high abundance of humpies in the North Pacific, which reached 640 million adult fish in 2009 when many Fraser River sockeye populations collapsed, is linked to declining trends in most of the studied 36 sockeye populations over the past two decades, including sockeye salmon from the Fraser River.
Based on relationships found between sockeye survival and pink salmon abundance, for example, an increase in pink salmon abundance from 150 million to 600 million fish was predicted to result in the reduction of Fraser River red salmon abundance by 67 percent from some 16 million to 5.3 million sockeye salmon.
Ruggerone and Connors urged fishery managers to consider applying an ecosystem perspective when managing salmon, including a cap on industrial scale hatchery salmon production as one way to minimize the potential for increasing abundances of pink salmon adversely impacting wild sockeye salmon.