White Sturgeon and Reservoir Water Quality


Water quality has been identified as a major factor affecting sturgeon survival in Brownlee Reservoir. Ralph Myers (Idaho Power Co.) and others have developed a water quality model using CE-Qual2 for Brownlee Reservoir to quantify the response of water quality variables to nutrient inflows and flow operations. The CE-Qual2 model shows considerable spatial heterogeneity in temperature and dissolved oxygen. In dry and normal years, an anoxic zone sets up during summer near the transition zone between the reservoir and free-flowing river.



Figure 1. Brownlee Reservoir at low pool.

At present, water quality is represented in a relatively simple manner in the Population Viability Analysis. We simply assume that sturgeon are uniformly distributed throughout the reach. The risk is summarized for the the worst day of the year for a representative year of each hydrologic type (dry, normal, and wet).


In order to evaluate the potential influence that spatial heterogeneity and movement of sturgeon may have on predictions about water quality effects, we are developing a spatial model that will allow us to evaluate two issues. First, does the ability of white sturgeon to move away from areas of poor water quality significantly improve their survival? Second, does the nutrient influx in the transition zone block this escape route? We are also investigating how avoidance behavior might affect the distribution of adult sturgeon in the reservoir as temperature and dissolved oxygen conditions change through the year.


When faced with degraded water quality conditions, fish will migrate away to areas with more favorable conditions. A number of lab and field studies have documented this fish avoidance behavior for both sublethal and lethal levels of metals, pesticides, dissolved oxygen and temperature (e.g. Sprague, 1964; Folmar, 1976; Magnuson et al., 1985; Claireux et al., 1995a, 1995b; Woodward et al., 1995, 1997; Schurmann et al., 1998; Goldstein et al., 1999). This movement benefits individual fish by allowing them to avoid areas with damaging or lethal water quality, but avoidance can also reduce available habitat and increase fish density (Coutant, 1985). Depending on the spatial location and extent of degraded water quality, avoidance behavior could act to slow or block fish access to spawning or feeding areas (e.g. Saunders and Sprague, 1967).


We calculate an index of sturgeon habitat quality for the locations along Brownlee Reservoir through the year. The index estimates sturgeon survival of two factors that are assumed to have independent effects. Literature estimates of lethal and sublethal effects of temperature and dissolved oxygen were compiled (Figure 2). An index of 1 indicates good conditions, an index of 0 indicates lethal conditions, and values between 0 and 1 are sublethal. We simulate sturgeon movement away from areas with poor water quality, and also include density-dependent movement in areas with good water quality.


Figure 2. Two components of reservoir water quality are temperature (left) and dissolved oxygen (right).


This simulation model will: