The Use of Groundwater Upwelling Areas by Interior Fraser Coho

Summer water temperatures in the Southern Interior region of British Columbia frequently approach or exceed the upper thermal limits of salmonids and there is concern for the sustained existence of many populations. This study investigated the effects of groundwater upwelling on juvenile coho summer and winter rearing habitat. Juvenile sampling was undertaken in both summer and winter over several years at paired groundwater and control sites. Mini-piezometers were installed at the groundwater sites to estimate upward groundwater fluxes. Linear and Binomial Mixed Modeling indicates that juvenile coho made preferential use of groundwater upwelling areas during both summer and winter. Temperatures in all of the groundwater areas remained up to 11.5°C cooler than control sites during the summer and slightly warmer at most sites during the winter. The results of this study indicate that groundwater needs to be regulated and protected to reduce potentially harmful temperature effects on coho populations in the Interior of BC.