Environmental Factors Related to the Distribution, Abundance, and Life History Characteristics of Mountain Whitefish in Idaho

Abstract

Mountain whitefish Prosopium williamsoni are a broadly distributed native salmonid in western North America, but comparatively little investigation has been made regarding their population characteristics. We surveyed 2,043 study sites to assess whether physiochemical stream conditions affected mountain whitefish distribution and abundance in southern Idaho, and at 20 of these sites life history characteristics were also estimated. A total of 581 sites were dry or contained too little water to support any fish species. Mountain whitefish were captured at 106 sites; for these sites only, mean abundance was 2.2/100 m². They were rarely present when mean wetted width was less than 10 m but were almost always present when wetted width was greater than 15 m. We estimated that within the study area there were approximately 4.7 ± 1.8 million mountain whitefish, mostly in fifth- to seventh-order streams, which comprised only 13% of the total stream kilometers but accounted for 93% of the total abundance of whitefish. Growth was positively related to mean annual water temperature and negatively related to site elevation. Mountain whitefish were long lived, most (90%) populations containing fish estimated to be at least 10 years old. This longevity produced total annual survival rates averaging 0.82 (range = 0.63–0.91). In general, the growth, fecundity, and survival of mountain whitefish were higher in the upper Snake River basin than in other areas for which data have been reported. Whitefish matured at about 250 mm and about age 2, with little variation in length and age at maturity between sites; males matured at a smaller size and younger age than females. The disproportionate use of larger (i.e., >15-m-wide) streams by mountain whitefish in southern Idaho differs from the situation in more northerly locations, where they apparently are more common in smaller streams.