The movements and distribution of bull trout (Salvelinus confluentus) in response to sockeye salmon (Oncorhynchus nerka) migrations in the Chilko Lake system, British Columbia

The migrations of animals between discrete locations frequently generate a range of ecological side effects. While many of the consequences of migrations are well understood, migratory coupling – the movements of predators over large spatial scales in response to migrant prey – has received little attention. I sought to describe a potential occurrence of migratory coupling in the Chilko Lake system, British Columbia, where bull trout (Salvelinus confluentus) aggregate near the lake outlet during the annual migration of anadromous sockeye salmon smolts (Oncorhynchus nerka), presumably to consume migrant smolts. To characterize the influence of the smolt migration on the spatial distribution of bull trout, I surgically implanted acoustic transmitters into 20 bull trout and tracked their movements throughout the Chilko system for one year. Because bull trout generally become increasingly piscivorous with size and age, I also combined acoustic telemetry with age estimates and length measurements to determine whether bull trout size, age, or growth influences their behavioural response to the smolt migration. Bull trout travelled substantial distances and 47% returned to the lake outlet during the smolt migration in consecutive years, suggesting that a portion of the population may be responding to the migrant smolts. However, bull trout returned to the outlet up to three months prior to the arrival of smolts at the outlet, thus their spatial distribution may also be influenced by other factors such as site fidelity. Furthermore, if bull trout are responding to the smolt migration, it remains unclear whether they are anticipating the arrival of smolts at the lake outlet or are following the diffusion of smolts from the lake. There was no detectable difference in age, size, or growth ratio among bull trout that returned to the outlet in consecutive years and those that did not; however, my inability to detect a difference may be a result of my small sample size and narrow range of ages and sizes. Through collecting these data, I also provided the estimates of size-structure, age-structure, and spatial distribution for Chilko bull trout, which has been identified as critical information for the management of bull trout in BC.Forestry, Faculty ofGraduat