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 ts hawytscha), and their prey species were examined under laboratory cond itions. These behaviors were studied to determine the bases for prey s election by salmon in Lake Michigan and ultimately facilitate predicti ons on shifts or changes in salmon diets. Chinook and coho salmon capt ured all prey items in the open water portion of the aquarium, and the y 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 t he successfully captured prey by chinook and coho salmon, respectively . Only 4% and 10% of the unsuccessful attacks by chinook and coho salm on, respectively. had no reactive distance (0.00 Ln). Salmon would rep eatedly attack a school and capture individuals separated from the sch ool, Alewives. bloaters and fathead minnows were easy prey because the y remained in the open water portion of the aquarium and stayed in sch ools until only a few individuals remained. The schooling behavior of spottail shiners and emerald shiners was an effective anti-predation l actic against salmon attacks, After some experience with yellow perch, salmon were reluctant to attack them and would often break off attack s 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.