Significance of Early Emergence, Environmental Rearing Capacity, and Behavioral Ecology of Juvenile Coho Salmon in Stream Channels

Abstract

Coho behavior was examined in two glass-walled stream channels containing riffle-pool series. The apparatus permitted volitional residence. Experimental groups of coho in each channel were permitted to emerge from a simulated redd environment and subsequently studied for 5 months.Aggressive behavior in these coho fry was initiated within 1 week of emergence from the gravel. Within 10 days of emergence, coho occupied and defended feeding territories well-distributed in riffles. Initial aggression was nipping and chasing but within 2 weeks of emergence, aggression also involved threat.Pools appear to constitute principal security features of coho environment. A behavioral pattern termed "fright huddle" was observed and described. Individual fish developed habitual living patterns in the channels, and smaller fish tended to occupy downstream areas.Earliest-emerging coho enjoyed ecological advantages over later-emerging fish. The former were larger at a given time and had a greater tendency to remain in stream channels, suggesting that they have "settler's rights" to available environment and/or better feeding opportunity. The results are discussed with reference to environmental rearing capacity and volitional residence.