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Marine Ecology and Stock Assessment Program

Stock-Structured Distribution of Western Alaska Juvenile Chinook Salmon From United States BASIS Surveys, 2002-07

Stock distribution information from coded-wire tag recoveries and single nucleotide polymorphism (SNP) genetic markers of western Alaska juvenile Chinook salmon (Oncorhynchus tshawytscha) captured during U. S. Bering-Aleutian Salmon International Surveys (BASIS) are used to provide insight into Chinook salmon migratory patterns during their first summer at sea.

Juvenile Chinook salmon were primarily distributed within the coastal domain (bottom depths < 50 m) during mid-August to early October, 2002-07 (the time period sampled by the BASIS survey), and peak densities were observed adjacent to primary Chinook salmon-producing rivers in western Alaska.

These distribution patterns reflect a lower apparent dispersal rate from ocean entry locations than other stream-type Chinook populations in the Gulf of Alaska. Chinook salmon stock mixtures did not support significant mixing of juveniles originating from the southern and northern Bering Sea shelf regions (south and north of 60°N) during their first summer at sea.

Limited marine dispersal rates and limited mixing of stocks from different production region both support the assertion that regional abundance indices reflect regional production of juvenile Chinook salmon and are not confounded by significant stock mixing of juveniles from different production regions typically observed in the Gulf of Alaska.

Coded-wire tagged juvenile Chinook salmon from the Whitehorse Rapids Hatchery in the Yukon River were captured near the Bering Strait during 2007 and provide evidence for the existence of a northern migratory corridor for juvenile Yukon River Chinook salmon. Northward migration of Yukon River Chinook salmon has not been observed in previous surveys; therefore, the anomalously warm conditions and extensive loss of sea ice during 2007 are believed to be the primary factors contributing to the occurrence of the northern migratory corridor.

By James Murphy

BASIS Symposium Held in Seattle

Dramatic fluctuations in the ocean growth and survival of many Asian and North American Pacific salmon populations over the past decade have been attributed to changes in the Bering Sea and other marine ecosystems. The absence of scientific observations for salmon, ecologically related species, and environmental conditions in the North Pacific Ocean has limited our understanding of these changes and how they affect salmon populations and economies around the Pacific Rim.

International research efforts to address these issues were developed by the North Pacific Anadromous Fish Commission (NPAFC) as part of its science plan. The research plan, called BASIS (the Bering-Aleutian Salmon International Survey), began in 2002 as a coordinated program of cooperative research on Pacific salmon in the Bering Sea. The goal of BASIS research was to clarify the mechanisms of biological response by salmon to the conditions caused by climate change in the Bering Sea.

A symposium to discuss recent BASIS research was held 2325 November 2008 in the Sheraton Hotel in Seattle, Washington. Ed Farley (ABL) chaired a steering committee consisting of Tomonori Azumaya, Richard Beamish, Ki Baik Seong, Vladimir Sviridov, and Shigehiko Urawa. During the symposium, the NPAFC commemorated the efforts from the research and contract vessels Kaiyo maru and Wakatake maru (Japan), TINRO (Russia), and Sea Storm and Northwest Explorer (USA) for their expertise and support in conducting BASIS research surveys.

The symposium focused on three main topics: 1) overviews of climate change, Bering Sea ecosystems, and salmon production; 2) biological responses by salmon to climate and ecosystem dynamics; and 3) discussion and summary on BASIS 200206: where do we go from here? There were 42 oral and 30 poster presentations. All presentations were in English.

It was evident from the symposium presentations that the Arctic is warming and that sea ice extent is declining.

By Jamal Moss

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