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Behavioural ecology of chum salmon (O.keta) and coho salmon (O. kisutch) alevins in the gravel Dill, Lawrence Michael

Abstract

An integrated laboratory and field approach was used to study the behaviour and ecology of Pacific salmon (genus Oncorhynchus) alevins in the gravel. The hypothesis tested was that these yolk sac fry move throughout the gravel prior to emergence, that this movement has both lateral and vertical components, and that changes in the physical or biological environment will alter certain parameters of subgravel behaviour. Eyed chum salmon (0. keta) eggs were buried in incubation channels at Robertson Creek, B. C. Eight experimental treatments were chosen, utilizing two gravel sizes, two burial depths and two planting densities. The fry were captured at emergence by means of specially designed traps that allowed determination of degree of lateral movement, pattern of emergence and survival to emergence. The fry were also sampled for condition (weight-length ratio) at the time of emergence. In the larger gravel, survival was greater, lateral movement was increased, and initial emergence was earlier. At the greater burial depth the emergence period was longer. At the greater burial density initial emergence was earlier. Condition at emergence was the same in all treatments. The behaviour of coho salmon (0. kisutch) alevins was examined in specially constructed aquaria, where light and flow conditions were as natural as possible. The same environmental factors were varied as in the field. In addition to a general description of alevin behaviour, detailed analyses were carried out on: vertical and lateral movement, orientation, spatial distribution, condition, survival and pattern of emergence. In the larger gravel vertical and lateral movements were increased, survival was higher, area utilization was greater and condition at emergence was poorer. At the greater burial depth lateral movement towards the outlet was increased and initial emergence was earlier. Vertical movement was decreased because more fry were trapped within the gravel. At the higher density the alevins moved farther towards the inlet. The mean area occupied per alevin was unchanged by density and suggests competition within the gravel. The orientation of the alevins is discussed in relation to light and current. The results indicate that larger gravel is better than smaller gravel for the incubation of Pacific salmon. Burial depth seems unimportant, but should be great enough to prevent predation. The question of optimum density requires further study. Emergence patterns may apparently be modified through environmental control.

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