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Locomotor responses of juvenile and adult sockeye salmon (Oncorhynchus nerka) to acute changes in temperature and salinity Tolson, Graeme M.


The locomotor responses of juvenile and adult sockeye salmon (Oncorhynchus nerka) to concurrent changes in temperature and salinity were examined in a controlled laboratory setting. I hoped to better understand how these environmental factors influence the coastal movements of migrating salmon. Juvenile sockeye were captured during the downstream migration from Great Central Lake on Vancouver Island, British Columbia, Canada. The fish were acclimated for 1 wk at 10°C, 20 ppt, and then tested in annular activity tanks. Spontaneous locomotor movements were recorded during concomitant changes in temperature and salinity using infra-red photometry. Raising the water temperature by 4°C in 1 h caused a dramatic increase in locomotor activity. Decreasing temperature by 4°C or varying salinity by 10 ppt from the control levels did not influence routine swimming speed and there was no interaction between factors. Adult sockeye homing to the Fraser River, British Columbia, Canada were captured along the nearshore migration route in two oceanographically distinct regions. Three groups of fish were collected from the cold, saline waters of Queen Charlotte Strait, near the northern end of Vancouver Island. Two groups of sockeye were captured within 60 km of the Fraser River in the warmer, less saline waters of the Strait of Georgia. The adults were acclimated 2-5 days at 12°C, 30 ppt and locomotor activity was tested in annular activity tanks. Routine swimming speed and turning rate rose when the water temperature was raised by 4°C in 2 h, however, locomotor activity was not influenced by decreasing temperature. In addition, decreasing salinity by 10 ppt in 2 h had no effect on swimming activity of adult sockeye and there was no interaction between the two factors. Fish taken from the Strait of Georgia generally showed a less dramatic response to increasing temperature than adults captured in Queen Charlotte Strait. Results indicate that warm coastal temperatures may influence the nearshore migration of both juvenile and adult sockeye salmon.

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