Rainbow trout (Oncorhynchus mykiss) were introduced to the Laurentian Great Lakes from the Pacific Coast and make up an important part of the sport fishery. The potamodromous life history variant (migratory rainbows or steelhead) is most prevalent among wild populations in the Great Lakes, where they hatch in-stream, migrate to the lake as juveniles, and return to the stream as adults to spawn. Large inter-annual variability in survival of steelhead populations from the Bois Brule River, WI, and Knife River, MN, in western Lake Superior has been observed, but the underlying mechanisms have not been well explained. The focus of my study was to identify the underlying mechanisms that influence variability in survival of wild maiden spawning adults. Multiple linear regression analyses were used to identify in-stream and in-lake (western Lake Superior) sources of variability, and to indicate the environment (stream or lake) that was most limiting. Data for wild maiden spawning rainbow trout, including abundance, stream age and lake age, were provided by the WI and MN Departments of Natural Resources. The in-stream analyses included stream temperature, flow, precipitation, and winter minimum air temperature. The lake analyses included surface temperature, lake trout (Salvelinus namaycush) (predator) abundance and forage abundance. For in-stream influences, I found that total September precipitation was negatively correlated with survival during the first stream year for Brule River steelhead. Total winter precipitation was positively correlated with survival of Knife River juveniles in their first stream year. However, first year survival of juvenile steelhead in the Knife River was negatively correlated with high stream temperatures (degree days > 20°C). The number of Brule River first returning steelhead (maiden returns) was positively correlated with surface temperature in western Lake Superior in their first lake year. Maiden returns of Knife River steelhead were negatively correlated with cisco density (kg/ha) in their second lake year. Overall, my results suggest that variability in maiden returning steelhead for both populations is better explained by conditions in their river of origin than conditions in western Lake Superior, which have a secondary influence and may better explain variability in repeat spawning and stocked steelhead.
University of Minnesota M.S. thesis. July 2012. Major: Integrated biosciences. Advisor: Dr. Thomas R. Hrabik. 1 computer file (PDF); x, 60 pages.
Kaspar, Tyler Joseph.
The influence of lake and stream conditions on survival of migratory rainbow trout in the Bois Brule (Wisconsin) and Knife (Minnesota) rivers..
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