Determination of causes for recent declines in marine survival rates of many Pacific
salmon populations has been hindered by lack of information on where and when mortality
predominantly occurs. Acoustic telemetry was used to monitor movements of tagged
outmigrating juvenile salmon, and mark-recapture models were used to estimate survival.
Several methods were developed for estimating detection probabilities (p) of tagged fish: models
for combining multiple populations with partially-overlapping migration routes allowed for
sharing of information among populations to compensate for small sample sizes; models for
estimating p using only local information at detection stations reliably predicted mark-recapture
p at large sample sizes; estimated p during mobile transect surveys attenuated from transect lines
and depended on boat speed; variation among tags in acoustic strength resulted in minor
heterogeneity in p; and p estimates derived from test tag passes were used to estimate freshwater
residualization rates.
Migration patterns varied among species, with steelhead and sockeye salmon quickly
leaving Georgia Strait, and coho and Chinook salmon instead likely residing in the inshore Strait
during summer months, thereby confounding interpretation of early ocean mortality. High
mortality often occurred before ocean entry. Variation in survival during the downstream and
inshore coastal migration was largely attributed to size-selective mortality against smaller fish
and variation in migration distance or travel time. Some components of mortality during the
downstream and inshore migration were independent of distance travelled, suggesting high
mortality periods soon after release in freshwater and soon after ocean entry. Compared to wild
conspecifics, hatchery-reared steelhead suffered high mortality immediately after release, and
this survival difference was maintained through the inshore migration. In an experiment to test
the effect of solar ultraviolet radiation during freshwater rearing on smolt mortality, no survival
differences were observed between UV-shaded and UV-exposed treatment groups of coho or
sockeye salmon. Overall, instantaneous mortality rates (time-based or distance-based) were
highest soon after release, declined during the inshore migration, and were lowest for the
remainder of smolt-to-adult ocean life, supporting hypotheses of high mortality early in the
migration but not ruling out hypotheses of high mortality during the first marine winter.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/16642 |
| Date | 05 1900 |
| Creators | Melnychuk, Michael Colin |
| Publisher | University of British Columbia |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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