No abstract

General circulation models predict increases in air temperatures from 1 • C to 5 • C as atmospheric CO 2 continues to rise during the next 100 years. Thermal regimes in freshwater ecosystems will change as air temperatures increase regionally. As air temperatures increase, the distribution and intensity of precipitation will change which will in turn alter freshwater hydrology. Low elevation floodplains and wetlands will flood as continental ice sheets melt, increasing sea-levels. Although anadromous salmonids exist over a wide range of climatic conditions along the Pacific coast, individual stocks have adapted life history strategies-time of emergence, run timing, and residence time in freshwater-that are often unique to regions and watersheds. The response of anadromous salmonids will differ among species depending on their life cycle in freshwater. For pink and chum salmon that migrate to the ocean shortly after they emerge from the gravel, higher temperatures during spawning and incubation may result in earlier entry into the ocean when food resources are low. Shifts in thermal regimes in lakes will change trophic conditions that will affect juvenile sockeye salmon growth and survival. Decreased summer stream flows and higher water temperatures will affect growth and survival of juvenile coho salmon. Rising sea-levels will inundate low elevation spawning areas for pink salmon and floodplain rearing habitats for juvenile coho salmon. Rapid changes in climatic conditions may not extirpate anadromous salmonids in the region, but they will impose greater stress on many stocks that are adapted to present climatic conditions. Survival of sustainable populations will depend on the existing genetic diversity within and among stocks, conservative harvest management, and habitat conservation.

The movement of juvenile salmonids between small tributaries and main‐stem habitats in southeast Alaska watersheds is poorly understood. We observed movements of steelhead Oncorhynchus mykiss, coho salmon O. kisutch, and Dolly Varden Salvelinus malma between main‐stem and tributary habitats at weirs located on tributaries in the Staney Creek watershed in southeast Alaska. We used seasonal relative abundance (catch per unit effort) in eight main‐stem reaches and eight tributaries to corroborate observed movement in the two streams with weirs. We observed juvenile steelhead and coho salmon moving through the weirs into tributaries during the fall as flows increased and temperatures decreased. The relative abundance of steelhead was greater in main‐stem sites than in tributaries during the summer, whereas during spring and fall relative abundance in the tributaries was similar to that in the main stem. Juvenile coho salmon were abundant in tributaries during all seasons. The relative abundance of Dolly Varden was greater in the tributaries than in the main‐stem during all seasons. These results underscore the significance of links between main‐stem habitats and small tributaries for production of juvenile salmonids.

Populations of Pacific salmon (Oncorhynchus spp.) in southeast Alaska and adjacent areas of British Columbia and the Yukon Territory show great variation in biological characteristics. An introduction presents goals and methods common to the series of reviews of regional salmon diversity presented in the five subsequent chapters. Our primary goals were to (1) describe patterns of intraspecific variation and identify specific populations that were outliers from prevailing patterns, and (2) evaluate escapement trends and identify potential risk factors confronting salmon populations. We compiled stock-specific information primarily from management research conducted by the Alaska Department of Fish and Game. We used mainly exploratory and descriptive statistical procedures to examine patterns of intraspecific variation, and linear regression to evaluate escapement trends. We describe the most pervasive limitations of available data and recommend cautious evaluation of our results. These reviews nonetheless provide insight into the ecological and evolutionary ramifications of intraspecific variation for managing diversity and sustaining productivity of salmon resources.