Diel Shifts in Microhabitat Selection of Steelhead and Coho Salmon Fry

Diel shifts in habitat selection of newly emerged steelhead Oncorhynchus mykiss and Coho Salmon O. kisutch fry were investigated in three northern California coastal watersheds. Steelhead and Coho Salmon fry occupied shallow water near stream margins during both day and night; however, the proportion of fry within 0.5 m of the stream margin increased from 6% during the day to 44% at night. Similarly, the proportion of fry in 10 cm of water or less increased from 26% during the day to 76% at night. Reductions in depth and distance to stream margins were significant at all sites, suggesting that these behaviors are common attributes for steelhead and Coho Salmon fry in this region. These results also suggest that newly emerged fry are potentially vulnerable to becoming stranded due to reductions in stream stage and water surface area, particularly at night. Although our observations were undertaken to better understand the risks to salmonids from vineyard water use for frost protection, the results have implications for any anthropogenic streamflow changes during the spring season. Received September 6, 2016; accepted June 3, 2017Published online August 9, 2017