Sunday, May 22, 2011

Research Tracks Movement and Survival of Juvenile Salmon through the Georiga Strait


Ocean survival has long been thought to exert a strong influence on salmon population dynamics with early marine survival considered the most critical phase in a salmons migration. Despite its known importance, difficulties in tracking the movement and survival of juvenile salmon once they hit the marine environment have long limited our ability to understand the processes that affect survival in the ocean. However constantly improving tag technology and a new network of acoustic telemetry receivers called the Pacific Ocean Shelf Tracking array (POST) are shedding light into the movement and mortality of smolts as they enter the Pacific. Now a group of Canadian researchers have published findings from a four year study of early marine smolt migration in the Georgia Strait. Lead author David Welch and a group of collaborators tagged coho, Chinook, sockeye and steelhead in 14 locations throughout the Georiga Basin and tracked movement and survival from their natal watersheds to the continental shelf. Their findings shed new light on the movement and timing of mortality for juvenile salmon in the ocean.

Like previous they found that coho and Chinook spent a protracted period in the Georgia strait, with most spending the summer months feeding and making much more gradual progress towards the high seas. Steelhead and sockeye however moved much more directly towards the open ocean. Smolts from most of the study populations migrated through the Northern Strait of Georgia and Queen Charlotte Sound while a few migrated south through the Strait of Juan de Fuca. Populations showed consistency between years and individuals in their route of migration. Steelhead and Sockeye showed a median survival of 16.5% from tagging to their exit of the Salish Sea, however as the authors point out that leaves a large proportion of the total mortality unexplained by early marine survival. Some have suggested that mortality once fish exit the Georgia Strait may be due to the delayed effects of parasitism or disease from salmon farms however more research is needed and should shed important light into the timing and nature of high seas mortality during the lifecycle of ocean migrating salmon and steelhead.
Read an article in the Globe and Mail

read the paper Welch et al. 2011

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