The effects of metal contamination on larval white sturgeon in the upper Columbia River
Sturgeon populations are imperiled worldwide. Declines are attributed to many factors including habitat degradation and alteration, overexploitation, and contamination. In North America, white sturgeon (Acipenser transmontanus) populations in the upper Columbia River (UCR) face many of the same factors. White sturgeon in this system have been declining for decades due to a lack of recruitment to the population, despite evidence of spawning and early larval survival in the wild. Early life stage white sturgeon are among the most sensitive of aquatic species to copper. The UCR has been contaminated with metal laden slag and liquid effluents from smelter and mining activities, resulting in UCR sediment metal concentrations, including copper, being elevated. The goal of my dissertation was to understand the potential role of metal contamination in the decline of white sturgeon in the UCR. This effort included toxicity tests with copper contaminated water as well as sediments collected from the URC, with a focus on the behavioral responses of exposed fish as a consequence of sublethal exposures. In chapter 1, I exposed early life stage white sturgeon to sublethal concentrations of copper, one of the contaminants of concern in the UCR, to characterize and quantify the effects of copper on swimming and feeding behavior. I found that changes in larval sturgeon swimming behavior were apparent up to seven days earlier than mortality and that copper exposure reduced food consumption in juvenile sturgeon. Critical swimming performance, however, was not affected by copper exposure. While not directly lethal, these alterations in behavior would impair a sturgeon's ability to locate, capture, and consume prey, thus impacting survival. In chapter 2, I evaluated the toxicity of metal contaminated sediments from the UCR to larval white sturgeon. Sediment was collected from six sites in the transboundary reach of the UCR. All six sites had elevated metal concentrations above equilibrium partitioning sediment benchmarks, which would suggest the metals could pose a risk to benthic invertebrates. The overlying water metal concentrations were also above water quality criteria levels in three of the six sites. I found sediment at one site reduced survival and affected swimming behavior of larval sturgeon.In chapter 3, I provide a synthesis evaluation of white sturgeon life history with what has been reported about metal contamination in the UCR, including documented concentrations from the river, and what we know about how metals affect larval sturgeon behavior and survival. Of particular concern are reported field observations of large numbers of sturgeon larvae with empty guts at a critical point in their life cycle. By putting all these pieces together, I found that metal contamination in the UCR could be reducing the prey base of larval sturgeon, altering swimming behavior to increase likelihood of starvation or predation, and evidence of an additional exposure route when larval sturgeon ingest sediment. Thus, the most important findings from my dissertation include 1) low, environmentally relevant concentrations of copper alter swimming behavior of larval sturgeon indicative of sublethal injury, 2) sediments collected from the UCR can affect larval sturgeon survival and swimming behavior, and 3) metal concentrations measured at some sites in the UCR are above effect concentrations from laboratory studies. These findings suggest that metal contamination could be a factor in the decline of the upper Columbia River white sturgeon, and should be considered in recovery efforts for the population.