Effects of hydrologic change and variability on upstream limits of stream fish distribution
Coldwater stream fishes are widely predicted to move upstream in response to warming downstream river temperatures. However, in the process they may encounter upstream limits, which are likely to be exacerbated by increased hydrologic variability if upstream locations draining small basins switch from perennial to ephemeral flow, with important but currently unknown implications for coldwater habitat and stream fish populations. In this project, we will look at the current determinants of upstream limitation for Eastern Brook Trout in several (8-10 large watersheds) throughout their native range, and use hydrologic models and GIS analysis to predict future upstream limits and consequent habitat distributions under climate change scenarios.
We have identified key climate-associated drivers of brook trout occupancy, abundance and population dynamics. High summer temperatures appear to decrease brook trout growth and survival across a wide range of environmental contexts, and factors associated with relatively low summer water temperatures (including high levels of forest cover) increase probability of occupancy. In contrast, the relationship between streamflow, population dynamics, and occupancy was more context-dependent requiring additional research to establish robust relationships and forecasts. Across five watersheds in the northeast, we have so far found little evidence of reduced occupancy or abundance in small (< 1 km2) watersheds, suggesting that these very small headwaters could serve as vital refugia in a changing climate.
This project provides a framework for managers to predict status of coldwater fisheries resources and differences in relative resilience among streams, watersheds and regions.