A comparison of aggressive and foraging behaviour between juvenile cutthroat trout, rainbow trout and F1 hybrids

‘Successful’ introduced species are often thought to cause declines or extinctions of native species through competitive superiority. In western North America, introduced rainbow trout, Oncorhynchus mykiss, have completely replaced many native cutthroat trout, Oncorhynchus clarkii, populations; however, few studies have identified the mechanisms that may allow rainbow trout to outcompete cutthroat trout. We raised Yellowstone cutthroat trout, Oncorhynchus clarkii bouvieri, rainbow trout, and their first generation hybrids in a common environment and conducted pairwise contests to test for differences in aggression, ability to defend a feeding station, and amount of food captured between these species and their hybrids. We did not detect a difference in number of aggressive acts conducted between cutthroat, rainbow and hybrid trout; however, cutthroat trout had the lowest success in occupying the feeding station and captured a lower proportion of food than rainbow and hybrid trout. Furthermore, hybrid crosses and rainbow trout had highest success at holding the feeding station and capturing food items when competing against cutthroat trout. Our study suggests that juvenile Yellowstone cutthroat trout are less successful at maintaining profitable feeding territories and capturing food items when competing against rainbow trout and first generation hybrids.