Salmonid Consumption by Nonindigenous Smallmouth Bass Determined by Bioenergetics Modeling

The Colville Confederated Tribe (CCT) is stocking kokanee salmon (Oncorhynchus nerka) in the Sanpoil River and restoring habitat for rainbow trout (Oncorhynchus mykiss). However, adfluvial migrations into Lake Roosevelt put them at risk of predation. The CCT wants to know what percentages of the 15,578 yearling and 23,738 2-3 year old rainbow and 589,580 fry and 10,080 yearling kokanee migrating out of the Sanpoil arm of Franklin D. Roosevelt Lake were consumed by smallmouth bass (Micropterus dolomieu).  We used mark-recapture data within Program Mark to estimate the smallmouth bass populations, and Wisconsin Fish Bioenergetics 3.0 to determine salmonid consumption. The smallmouth bass population (±95% CI) estimate was 41,291 (33,681 – 48,902) individuals based on 214 recaptures of 2,774 marked individuals. Kokanee fry and yearling made up 13.0% and 7.2% of the smallmouth bass diet by weight. Rainbow yearling and 2-3 year olds were 0.8% and 3.8% of the smallmouth bass diet by weight. A total of 88,474 kokanee fry, 271 kokanee yearlings, 811 rainbow yearlings, and 110 rainbow 203 year olds were consumed by smallmouth. Thus, approximately 15.0% of kokanee fry, 2.7% of kokanee yearlings, 5.6% of rainbow trout yearlings and 0.5% of rainbow trout 2-3 year olds were consumed.