Saturday, February 26, 2011

Historic Steelhead Abundance in Puget Sound

A new paper out this week takes a good, empirical look at historical abundance of steelhead in Puget Sound. The research done by Nick Gayeski, Bill McMillan and Pat Trotter uses commercial fishery records from the late 1800s and concludes that current steelhead populations in Puget Sound range from approximately 1-4% of their historic levels. The authors had river specific catch data for the Nooksack, Skagit, Snohomish and Stillaguamish and had aggregate data for the rest of the sound. Then using estimated catch rates and an assumed average steelhead size from 7-9.5 pounds they were able to model a range of likely historical run sizes.

They estimate that historically the rivers of Puget Sound supported 485 to 930 thousand winter steelhead. River specific estimates for the Nooksack, Skagit, Snohomish and Stilly were 101-169 thousand, 70-149 thousand, 114-224 thousand and 52-100 thousand respectively. The authors then compared steelhead declines to estimates of habtiat loss and conclude that while steelhead populations have declined approximately 98% in the Puget Sound, roughly 66% of the historically available habitat remains accessible. These estimates do not account for changes in the quality or capacity of the freshwater habitat, but highlight the degree to which population densities of steelhead have declined. The paper is also a stark reminder of the inadequacy of current escapement goals which are typically well below 10% of historic abundance levels as recovery targets.

Read the paper here:
Gayeski et al. 2011 - Historic abundance of Puget Sound steelhead

No comments: