Migratory behaviour and survival of wild and hatchery coho salmon using acoustic telemetry

Climate is emerging as a primary determinant of marine survival and migratory behaviour for Pacific salmon. For example, a regime shift in the mid-1990s was correlated to a major change in the migratory behaviour of coho salmon (Oncorhynchus kisutch) in the Strait of Georgia, BC. The details of this new behaviour pattern remain relatively unknown. Furthermore, many coho stocks have been declining during the past three decades. Mitigative strategies –such as hatchery programs— have done little to reverse the trend, and little is known about how hatchery fish are affecting wild populations. The objective of this dissertation was to identify key mortality areas and provide the first look at the migratory behaviour of juvenile wild and hatchery coho in southwestern British Columbia using new telemetry technologies. As coho pre-smolts are relatively small compared with other salmonid species that are typically studied using acoustic telemetry, the identification of the appropriate sizes of fish and tags to use was critical. The first study tested the effects of surgically implanting the three smallest sizes of acoustic tags available on the growth, survival, performance and condition of coho pre-smolts. The first of three field studies to follow investigated the early migratory behaviour and survival of an endangered coho population. The second field study examined differences in physiology, survival and migratory behaviour between wild and hatchery-reared coho smolts. Finally, the third study analysed the altered marine migratory behaviour of juvenile coho in the Strait of Georgia. This dissertation provides the first evidence of high freshwater mortality rates in the endangered coho population, which has implications for the management and conservation of this and other at-risk stocks. I found differences in migratory behaviour and physiology between wild and hatchery-reared coho, suggesting that mitigative strategies need further evaluation. Finally, the timing of the anomalous coho migration out of the Strait of Georgia confirmed that population changes in the strait are a consequence of ecosystem-related impacts. These findings demonstrate how new technologies could be used to fill major information gaps and improve the management and conservation of Pacific salmon.Land and Food Systems, Faculty ofGraduat