Introduction & Objectives

Chinook salmon (Oncorhynchus tshawytscha) are an iconic species found throughout the North Pacific Ocean and support invaluable subsistence, commercial and recreational fisheries. In addition to its importance to fisheries, Chinook salmon are an important food source for many apex marine predators, including the endangered Southern Resident Killer Whale (SRKW; Orcinus orca). Currently, coast-wide changes in Chinook salmon population demographics and production have been documented from western Alaska to California, including several Evolutionarily Significant Units (ESUs) from the U.S. Pacific Northwest that are protected under the U.S. Endangered Species Act (ESA).

The U.S. Navy conducts at-sea training in the Gulf of Alaska (GOA), including the Temporary Maritime Activities Area (TMAA). As part of the Marine Species Monitoring Program, the Navy is interested in understanding the overlap of occurrence between populations of Chinook salmon, particularly the ESUs that are listed under the ESA, and specific Navy activities. This is challenging, as relatively little is known about the at-sea distribution and behavior of Chinook salmon, despite the fact that most individuals reside in the ocean for the majority of their lives. Therefore, an improved understanding of the distribution and behavior of Chinook salmon in the marine environment is important when addressing potential interactions between this species and specific Navy exercises within GOA. The goal of this study is to provide critical information on the spatial and temporal distribution of Chinook salmon and to utilize genetic analysis techniques to inform salmon management.  

Technical Approach

Tagging is occurring at several sites within the GOA. PSATs will be attached to healthy fish of sufficient size to track their movements.  After a pre-determined time, the tag will detach, float to the surface, and transmit recorded movement data via satellite to the researchers.  Tissue samples will also be collected for laboratory genetic analysis in order to determine fish origin.

Progress & Results

To qualitatively describe the spatial distribution, movement, vertical distribution, occupied habitat, and natural mortality of Chinook salmon in the GOA, PSATs were attached to individuals near Chignik, AK (n = 20), Kodiak, AK (n = 20), and Yakutat, AK (n = 20) in 2020 – 2021, and tissue samples were collected for genetically determining stock-of-origin of each tagged fish. Additional tagging efforts are planned for the spring and summer of 2022 in Craig, AK and Sitka, AK.

Of the 60 PSATs deployed, data were transmitted by 57 tags, providing >3,720 days of data. Reporting locations of tags were widespread across the eastern North Pacific Ocean, ranging as far west as the Bering Sea to as far east as the U.S. Pacific Northwest. Movement models suggested that the majority of tagged fish remained over the continent shelf within relatively close proximity (

Fifteen tagged Chinook salmon were inferred to have occupied the GOA TMAA (~252 aggregated days) while at liberty (i.e., tag deployment to pop-up date). While occupying waters of the TMAA, Chinook salmon spent the majority of their time (58%) in waters over the continental shelf, and spent a minority of their time over the continental slope (22%) and basin (20%). In addition to providing information on the horizontal and vertical distribution of Chinook salmon, PSATs provided evidence of mortality of tagged fish caused by endothermic fish(s) (n = 17), an ectothermic fish (n = 1), marine mammals (n = 3), and unknown (n = 6) causes. Genetic analyses suggested that all tagged Chinook salmon were from populations originating in southern Southeast Alaska, British Columbia, Washington, and Oregon.

While this study contained a small sample size, the tagged Chinook salmon were comprised of individuals from many populations extending from Southeast Alaska to the U.S. Pacific Northwest, making results pertinent for many populations throughout North America, including stocks of concern and those listed under the ESA. The information about Chinook salmon gained in this study may be used to provide insights into important management issues in the North Pacific Ocean, including overlap between Chinook salmon and Navy exercises in the GOA and Northwest Training and Testing (NWTT) ranges.