Tracking Coho Salmon on Humboldt Bay, California. Photograph by William Pinnix.

By Bill Pinnix
Arcata Fish and Wildlife Office

Biologists from the Arcata Fish and Wildlife Office (AFWO) employed acoustic transmitters to follow the movement of juvenile coho salmon as part of a cooperative study that gathered new knowledge about residence time and habitat use by the federally-listed salmon.

In the spring of 2007, coho salmon smolts were surgically implanted with acoustic transmitters and subsequent movements were monitored with a fixed receiver array and mobile tracking from a boat.  Of the 32 coho salmon smolts tagged, 28 migrated through the Freshwater Slough estuary and resided for an average of 12 days in the slough.  Of the 28 fish that entered Humboldt Bay, 24 successfully left Humboldt Bay for the open ocean and resided for an average of 15 days in the bay proper.  The data collected from this study have provided valuable evidence on what habitats juvenile coho salmon utilize in Humboldt Bay, as well as residence times in Humboldt Bay and Freshwater Slough.  In 2008, the AFWO will expand the acoustic telemetry project to include steelhead, as well as coho salmon from other drainages that enter Humboldt Bay.

Findings from the study will be used to formulate methods to minimize  the impacts of management activities on the salmon, as identified in the Humboldt Bay Management Plan. The Humboldt Bay Management Plan was developed by the Humboldt Bay Harbor, Recreation, and Conservation District, and completed in July 2007.

Data from the study will also be used to assess and prioritize estuary restoration actions within Humboldt Bay, as well as add to the body of scientific knowledge regarding juvenile salmonid use of estuarine environments.  

In the fall 2005, AFWO conducted a pilot study to determine the feasibility of using miniature acoustic transmitters to study movement and habitat use of salmonids in Humboldt Bay, California.  Results of the pilot study were positive and an investigation plan was developed and submitted to various federal, state, and local agencies for funding.  The AFWO was able to secure additional funding and support from the California Department of Fish and Game Marine Division, the Humboldt Bay Harbor Conservation and Recreation District, California Sea Grant, and Hilton’s Coast Seafoods Eureka Division for implementation of the project in 2007.  In addition, the project has gained the support of many local and state agencies, local environmental groups, local offices of federal agencies, as well as private businesses and stakeholders.