Interactions for food and space between sympatric populations of juvenile coho salmon and coastal cutthroat trout in a stream simulator during winter and spring / by G.J. Glova and J.C. Mason. : Fs97-4/1429E-PDF

"Interactions for food and space between sympatric populations of underyearling coho salmon and coastal cutthroat trout were investigated in a stream simulator during winter and spring. Temperature was the main determinant of coho and trout microhabitat use in winter. At 3 C, both species almost exclusively occupied pools, whether in allopatry or in sympatry. At 5 C, minor segregation was evident, with species relative abundance in riffles being higher for trout and in pools for coho. Factorial analyses of variance indicated temperature, size of fish, water velocity and simulated food supply were ranked (high to low) as affecting microdistribution. Coho and cutthroat trout fry communicated using the same signal set as in summer with chases, nips and lateral displays comprising more than 80% of their total aggressive activity. Non-contact behaviors were more frequently used by coho; nipping was more frequently used by trout. Both salmonids were most aggressive when food was present, irrespective of temperature. However, levels of aggressiveness differed with temperature and space: at 3 C, aggression was low and neither species defended riffles; at 5 C, aggression was higher and both species actively defended riffles during feeding. Patterns of species microhabitat use and behavioral interactions in spring were similar to, but more pronounced than those in winter at 5 C. Stream management strategy should take into account the importance of providing adequate winter cover appropriate to the different age-classes in sympatric populations of coho salmon and coastal cutthroat trout"--Abstract, page ii.

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