Size-Mediated Long Distance Emigration Patterns of Age-0 Coho Salmon in the Klamath River Corridor

The Klamath River is a large watershed, supporting salmonid populations with many life history variants. Coho Salmon in the basin demonstrate diverse life history tactics due to extreme variation in environmental conditions. Coho Salmon produced in the Shasta River, entering the Klamath River 190 miles from its mouth, are especially notable in their life history tactics. The Shasta River is one of the most unique rivers in North America that supports Coho Salmon, sourced primarily in large volcanic springs. As a result, some parts of the system produce exceptionally high growth rates for juveniles. In May and June 2011, 249 age-0 Coho Salmon emigrating from the Shasta River were PIT tagged as they left the river. The length frequency distribution of the fish was bimodal, reflecting spatially distinct patterns of growth. Subsequently, many of the fish were re-encountered in summer, fall, and winter in various refuge habitats along the mainstem Klamath River corridor over the distance to the mouth. All of these were from the smaller sized mode in length distribution. We hypothesize that the larger fish emigrated to the ocean as age-0 smolts. Monitoring work continues to understand the implications of these life history tactics.