Influence of hydrological processes on the spatial and temporal variation in spawning habitat quality for two chum salmon stocks in interior Alaska

Abstract

I investigated the hydrological mechanisms that influence spatial and temporal variability in incubation habitat quality for summer- and fall-run chum salmon. The intragravel habitat was characterized by measuring water velocity, temperature, and dissolved oxygen (DO). Habitat quality was characterized by determining the survival of eggs in gravel filled baskets. Summer-run egg survival was greatest in a zone of upwelling produced by hydraulic gradients between the main Chena River and a slough. Water took approximately one month to make this trip and microbial activity likely reduced the concentration of DO considerably. As a consequence of these processes, there was considerable spatial and temporal variability in upwelling velocity, DO, and temperature. Most variability in egg-to-fry survival was explained by DO, and, to a lesser extent, by water velocity. Fall-run fish used an area of groundwater upwelling on the south side of the Tanana River. Here physical habitat characteristics were spatially and temporally uniform compared to the summer-run site, a consequence of the larger spatial scale of processes generating the upwelling. Egg-to-fry survival was low despite high DO and favorable temperature. This was probably the consequence of glacial silt invading egg baskets and reducing intragravel flow related to falling groundwater tables.