Inter-relationships between the spawning migration of Eagle Lake rainbow trout, streamflow, snowpack, and air temperature

Pine Creek has historically provided critical spawning and rearing habitat for Eagle Lake rainbow trout (ELRT, Oncorhynchus mykiss aquilarum). Over the past 100+ years modifications of Pine Creek watershed (e.g., overgrazing, timber harvest, passage barriers, culverts) decoupled the ELRT from its stream habitat. Introduced brook trout (Salvelinus fontinalis) now dominate historic rearing areas in the upper watershed. Passage barriers were constructed on Eagle Lake tributaries to prevent ELRT from spawning in degraded habitat, denying the ELRT access beyond the first kilometer of stream. Since 1950 the lake fishery has been maintained by artificial spawning. Offspring are reared in hatcheries and released into Eagle Lake. Since 1987 changes in grazing management, reconstruction of culverts, and other conservation projects have resulted in marked improvement of habitat, although ELRT have been not allowed to attempt their natural spawning migration. Their ability to migrate has been questioned, and concerns led to a petition for listing under the federal Endangered Species Act. We report on a long term study to track the spring migration of ELRT spawners in Pine Creek. We tracked the upstream migration of ELRT spawners from the mouth of Pine Creek. We then related ELRT spawner migration to stream flow and snowpack, and related flows to snowpack and air temperature. It is possible to predict ELRT migration distance from flow, duration of flow, or from snowpack. The relationships between migration distance and flow, and migration distance and snowpack in the upper watershed were weak. However, sample sizes were small, due to the limited number of years in which fish have been tracked, and the cessation of operation of the flow gages. The positive relationships between migration distance and seasonal average daily mean streamflow, and between streamflow and snowpack are particularly interesting in light of climate predictions for California. By the end of this century snowpack is likely to be reduced 65-97% in the elevation range of Pine Creek. The creek is likely to flow more during the winter, due to winter rain events, and to have lower summer baseflows. It is possible that ELRT spawners might shift to a strategy of earlier migration, moving upstream to areas of perennial summer flow during winter rain events. However, the fish currently lack the opportunity to experience and adapt to flow changes that are likely to occur with climate change