Within the geographic range of salmonid fishes, many apparently suitable rivers and streams are used for reproduction by some species but not others. Scientists from the University of Washington and USGS investigated the effects of factors like temperature, elevation, and land use patterns on the spawning distribution of six native Pacific salmonids in the Skagit River basin, Washington: pink, chum, coho, and Chinook salmon, bull trout, and steelhead. Annual mean temperature and elevation had the strongest association with the variety of fish species spawning in a particular stream. In streams with warmer temperatures, all species except bull trout were more likely to be present. Bull trout were unique, in that they have a strong preference for cold water that is more likely to be found at higher elevations. These results highlight the importance of temperature in salmonid spawning and could help inform selection of conservation and restoration sites to improve conditions for the greatest variety of species.  

Austin, C.S., Torgersen, C.E., and Quinn, T.P., 2023, Who spawns where? Temperature, elevation, and discharge differentially affect the distribution of breeding by six Pacific salmonids within a large river basin: Canadian Journal of Fisheries and Aquatic Sciences, p. Online. https://doi.org/10.1139/cjfas-2022-0252