Long-Term Monitoring of the Columbia River in British Columbia, Canada: What We Have Learned after 10 Years of Systematic Sampling

In Canada, flow regulation of the lower Columbia River became a reality in the late 1960s with the development of multiple hydroelectric dams and storage reservoirs constructed as part of the Columbia River Treaty, an international agreement between the US and Canada detailing the water rights and benefits of several large water storage projects in both Canada and the US. In 2001, BC Hydro established a monitoring program for the Columbia River downstream of Hugh L. Keenleyside Dam (located approximately 56.5 km upstream of the Canada-US border) to detect temporal changes in fish population dynamics and to determine if any changes observed could be related to dam operations. As part of the program, mountain whitefish, rainbow trout, and walleye were repetitively captured in September and October by night-time boat electroshocking and implanted with Passive Integrated Transponder (PIT) tags. Analysis of these data showed significant annual trends in population abundance and structure, recruitment, and survival. As an example, rainbow trout population abundance nearly doubled between the early 1990s and the present study and growth rates of younger rainbow trout and mountain whitefish significantly increased over the same time period. Ten years of observational data on other fish species and habitat characteristics also showed strong temporal trends, including a decreased abundance of redside shiner, an increased abundance of sculpins, and increased densities of invasive aquatic vegetation, and documented the invasion of several non-native fish species (e.g., northern pike and smallmouth bass). Relating specific changes in the aquatic community to specific system influences has proved difficult. In many instances, the observed changes to the aquatic community were likely the result of more than one environmental change, as over the same time period, major changes to the system have included modifications to the flow and temperature regimes, decreased levels of industrial pollutants from both pulp and smelter operations, upstream reservoir fertilization projects, a decreased adult white sturgeon population, and an intensive juvenile white sturgeon stocking program. This study illustrates the utility of a long-term time-series of fish population data in identifying changes to fish populations, but also illustrates the difficulties of assessing the causes of change because of the multitude of natural and anthropogenic factors that may contribute to these changes.