Homing patterns of steelhead trout in Lake Erie: Evidence for within-stream stock partitioning

With limited natural reproduction, the Lake Erie steelhead trout (Oncorhynchus mykiss) fishery relies on smolt stocking (~2 million/yr) into MI, OH, PA, and NY streams. There is question about where to release the hatchery fish in a tributary and how well they imprint on the location within a tributary. Conneaut Creek flows from PA and empties into Lake Erie in OH. Thus, both PA and OH stock steelhead smolts (~75,000/yr each), but in different locations. PA fish are stocked about 40 km from the river mouth, while OH fish are released about 3 km from Lake Erie. We determined the distribution of spawning steelhead in Conneaut Creek (i.e., who travels the 40 km through OH to PA?) using otolith chemistry because the OH stock has a unique chemical signature (high Sr) from the hatchery water that we can detect with 100% certainty using LA-ICPMS. There was no significant difference in population proportions from the expected 1 OH: 1 PA ratio (n=53, χ², p>0.5) in the Ohio sample, but none of the spawning steelhead collected in PA were from the OH stock (n=41, χ², p<0.0005).  Thus, there appears to be strong homing for the stream location where they were released.