Montana Fishery Project
Spawning Characteristics and Early Life History of Mountain Whitefish in the Madison River, Montana
January 2012 - June 2015
- Montana Fish, Wildlife & Parks
Despite the putative abundance of mountain whitefish in Montana water bodies (Brown 1952) and their availability as a sport fish (Brown 1971; Scott and Crossman 1973), relatively little is known about the ecology of mountain whitefish in Montana. Fish population monitoring programs in Montana are generally not designed to target mountain whitefish; therefore, available data are difficult to decipher and potentially unreliable for identifying long-term trends (Mountain Whitefish Summit 2009). However, at least some mountain whitefish populations in Montana are showing signs of decline (Mountain Whitefish Summit 2009). In the Madison River drainage, mountain whitefish numbers have declined in Hebgen Lake since the early 2000s (Mountain Whitefish Summit 2009), but trend data are not available for the Madison River. The Madison River Foundation has indicated concern over an apparent decrease in mountain whitefish in the Madison River. Thus, the Madison River Foundation, Trout Unlimited, PPL Montana, and Montana Fish, Wildlife and Parks have expressed interest in identifying life history characteristics, habitat requirements, and factors potentially limiting production of mountain whitefish in the Madison River (Mountain Whitefish Summit 2009; Lessner 2011). Factors limiting production of mountain whitefish may occur at various life-history stages; however, spawning success, the abundance of spawning individuals, and early life-history survival can have a strong influence on year-class strength and population abundance. Therefore, identifying spawning site habitat requirements, age at maturity, periodicity of spawning, and the distribution and habitat requirements of age-0 mountain whitefish will provide a strong foundation for understanding the population dynamics of mountain whitefish in the Madison River. Knowledge regarding the ecology of mountain whitefish in the Madison River is necessary before we can understand the mechanisms for population decline. It is generally accepted that mountain whitefish spawn in the autumn as water temperatures decrease (Scott and Crossman 1973); however, there is less consistency with regards to spawning site substrate use, depths used during spawning, use of tributaries for spawning, and the size of spawning congregations (Brown 1952; Scott and Crossman 1973; Pettit and Wallace 1975; Thompson and Davies 1976). Therefore, quantifying characteristics associated with mountain whitefish spawning sites in the Madison River will provide information that will likely assist in recovery of the species. Additionally, no data are available with respect to age at maturity for mountain whitefish in the Madison River or spawning periodicity for any population of mountain whitefish; these factors can greatly affect estimates of spawning population abundance (these data also greatly influence age-structured model outputs). Therefore, studies to identify age at maturity and spawning periodicity of mountain whitefish are warranted. Habitat use by, and the spatial and temporal distribution of age-0 mountain whitefish within streams is largely unknown. Recently hatched mountain whitefish may be easily sampled using dip nets in shallow areas along stream margins, but may move offshore in the summer (Brown 1952); therefore, different sampling methods may be effective at sampling during different seasons. For example, age-0 mountain whitefish may be effectively sampled using dip nets immediately post-hatch, drift nets during periods of higher discharge (e.g., May through June; Figure 2), and electrofishing during base-flow conditions. Therefore, evaluating appropriate methods for sampling mountain whitefish and seasonal effects on sampling efficiency are warranted, and application of appropriate sampling methods to characterize the distribution of age-0 mountain whitefish in the Madison River may help identify limiting factors for mountain whitefish recruitment.