The influence of habitat characteristics on abundance and growth of juvenile Coho Salmon Oncorhynchus kisutch in constructed habitats in the middle Klamath River basin

Substantial investment has been directed toward construction of off-channel ponds in the middle Klamath River basin to benefit Coho Salmon populations. Previous research showed that abundance, retention, and growth of juvenile Coho Salmon varied across sites but were not consistently different between constructed ponds and natural habitats; instead, variation was attributed to individual site characteristics. However, the characteristics responsible for these differences are not clear. In this exploratory study, I investigated the effect of accessibility on juvenile Coho Salmon abundance within nine constructed ponds. I also assessed whether habitat conditions, Coho Salmon density, and food availability within the ponds could predict abundance, retention, and growth of Coho Salmon. Few strong relationships were found between characteristics of ponds and the response variables. Despite potentially stressful conditions at some sites, Coho Salmon occupied most ponds through the summer, suggesting that they provide suitable rearing habitats. Lack of accessibility throughout the year had potentially important effects on the survival and life history of individuals trapped in constructed ponds. Retention rates were strongly correlated with zooplankton availability, while Coho Salmon density and available benthic prey displayed little correlation with retention. While growth rate differed among ponds; while measures of prey availability did not explain variation in growth rate, growth rate was negatively correlated with Coho Salmon density in the ponds. Constructed off-channel ponds serve as important rearing habitat for Coho Salmon and an increased understanding of their role in Coho Salmon rearing and production is necessary.