Stream Fish Community Stability and Our Ability to Detect Change

Researchers: Nick Jones and Ian Petreman

Project Description: Natural resources agencies are challenge with the task of monitoring fishes and their habitats to detect trends in environmental state. A significant change in state may indicate that management strategies and policy should change to meet management objectives (e.g., healthy fish populations, ecological integrity).  This monitoring assumes that we can accurately measure state and deal with inherent observer (sampling bias) and natural variability. We can design methods to reduce sampling variability and error; however, our ability to detect change commonly decreases as the natural variability of a system increases.  Disturbance plays a central role in the ecology of streams and maintains their dynamic spatial mosaic of environmental conditions (see Do extremes in flow and temperature influence stream fish communities?). This begs the question, what magnitude of change can we detect?

We summarize single-pass backpack electrofishing data by abundance, biomass, richness, diversity, evenness of the stream fish community and abundance, biomass, and growth of young-of-the-year (yoy) rainbow trout for 30 stream over ~10 years.  We then use this data to quantify the temporal variation using the coefficient of variation and examine our ability to detect changes in community measures.

 

Figure 1.  The temporal variation in fish abundance can be quite high.