Behavioral interactions between coho (Oncorhynchus kisutch) and chinook salmon (Oncorhynchus shawytscha) and prey fish species

The predator-prey behavioral interactions between two salmon species, coho salmon (Oncorhynchus kisutch) and chinook salmon (Oncorhynchus tshawytscha), and their prey species were examined under laboratory conditions. These behaviors were studied to determine the bases for prey selection by salmon in Lake Michigan and ultimately facilitate predictions on shifts or changes in salmon diets. Chinook and coho salmon captured all prey items in the open water portion of the aquarium, and they had similar attack behaviors. Average attack swimming speeds varied from 2.6 to 3.6 m/s, and average escape swimming speeds varied from 2.6 to 2.9 m/s. There were no significant differences in attack swimming speeds and escape swimming speeds. There was a significant difference in median reactive distances between the prey captured and those that escaped. There was no reactive distance (0.00 m) for 96% and 98% of the successfully captured prey by chinook and coho salmon, respectively. Only 4% and 10% of the unsuccessful attacks by chinook and coho salmon, respectively. had no reactive distance (0.00 Ln). Salmon would repeatedly attack a school and capture individuals separated from the school, Alewives. bloaters and fathead minnows were easy prey because they remained in the open water portion of the aquarium and stayed in schools until only a few individuals remained. The schooling behavior of spottail shiners and emerald shiners was an effective anti-predation lactic against salmon attacks, After some experience with yellow perch, salmon were reluctant to attack them and would often break off attacks on them, When coho salmon were presented with different proportions of bloaters and yellow perch, they significantly attacked and captured bloaters in preference to yellow perch.