No abstract

Regional habitat and fisheries management planning requires estimates of the capacity of watersheds to produce salmonids. To predict the average abundance of smolts of coho salmon Oncorhynchus kisutch produced by streams and rivers, we related estimates of smolt abundance to habitat features derived from maps and discharge records. We assembled a database of 474 annual estimates of smolt abundance from 86 streams in western North America for this analysis. We found that only stream length and to a lesser extent latitude were useful in predicting mean smolt abundance. The frequency distribution of annual estimates of smolt abundance from individual streams tended towards a normal rather than the more usual lognormal distribution; the median coefficient of variation in abundance was 37%. Our results are consistent with the view that, on average, smolt abundance is limited by spatial habitat, but that there is significant annual variation in abundance probably due to variation in habitat quality caused by climate, flow, or other factors. We conclude that forecasting smoll yield from stream length and latitude is feasible at the watershed or regional level, but that the precision of a prediction for a single stream is poor. A more detailed approach will be required for local forecasting.

Immediately after emergence from spawning gravels, fry of stream-type chinook salmon (Oncorhynchus tshawytscha) populations from tributaries of the upper Fraser River, British Columbia, distribute themselves downstream from the spawning areas, throughout the natal stream, and into the Fraser River. We tested the hypothesis that this range in dispersal distances is caused by innate differences in nocturnal migratory tendency among individuals. Using an experimental stream channel, we found repeatable differences in downstream movement behaviour among newly emerged chinook fry. Fish that moved downstream were larger than those that held position in the channel. However, the incidence of downstream movement behaviours decreased over the first 2 weeks after emergence. We propose that the variation among individuals in downstream movement behaviour we observed leads to the dispersal of newly emerged fry throughout all available rearing habitats. Thus, between- and within-population variation in the freshwater life history observed in these populations may be caused by small differences in the behaviour of individuals.

Objective: We describe juvenile migration tactics for spring/summer-run populations of Chinook Salmon Oncorhynchus tshawytscha that spawn in tributaries of the Fraser River, Canada. Methods:We trapped juveniles migrating from tributaries, and sampled juvenile Chinook salmon rearing in the Fraser River. Result:In four tributaries, we found two dominant life history types within each population: a natal-stream-rearing variant in which juveniles spend a year in their natal stream before migrating to the sea as yearling smolts; and a fry migrant variant in which juveniles disperse downstream from spawning areas to the Fraser River main stem soon after emergence. In a fifth tributary, where flows are regulated, juveniles migrated as parr later in the spring. Juveniles colonized the Fraser River main stem in spring and were distributed throughout the accessible length of the main stem. Their relative density in nearshore habitats was similar to that observed in other rivers. Migrants spend up to a year in the main stem before smolting as yearlings. Conclusion:The extensive year-round use of the Fraser River main stem appears to be unique among Chinook Salmon-producing watersheds, likely due to favorable environmental conditions in the main stem during the spring and summer months.The diversity of habitats used by these populations is an important consideration for the design of conservation programs that are intended to maintain or improve freshwater productivity.