Identifying Temperature Thresholds Associated with Fish Community Changes in British Columbia, Canada, to Support Identification of Temperature Sensitive Streams

Abstract

We collected fish samples and measured physical habitat characteristics, including summer stream temperatures, at 156 sites in 50 tributary streams in two sampling areas (Upper Fraser and Thompson Rivers) in British Columbia, Canada. Additional watershed characteristics were derived from GIS coverages of watershed, hydrological and climatic variables. Maximum weekly average temperature (MWAT), computed as an index of summer thermal regime, ranged from 10 to 23°C. High values of MWAT were associated with large, warm, low relief watersheds with a high lake influence. Measures of community similarity suggested that the fish community changed most rapidly through a lower transition zone at an MWAT of about 12°C and an upper transition zone at an MWAT of about 19°C. These results were confirmed using existing fisheries inventory data combined with predictions of MWAT from a landscape-scale regression model for the Thompson River watershed. For headwater sites in the Chilcotin River watershed (which drains into the middle Fraser River), the relative dominance of bull trout versus rainbow trout (based on inventory data) decreased with increasing predicted MWAT although the distinction was not as clear as for the Thompson River sites. The fish communities in these watersheds can be characterized in terms of very cold water (bull trout and some cold water species), cold water (salmonids and sculpins) and cool water (minnows and some cold water salmonids). The two transition zones (ca 12 and 19°C) can be used to identify thresholds where small changes in stream temperature can be expected to lead to large changes in fish communities. Such clear, quantifiable thresholds are critical components of a management strategy designed to identify and protect vulnerable fish communities in streams where poor land use practices, alone or in combination with climatic change, can lead to changes in stream temperatures.

Physico-chemical thresholds in the distribution of fish species among French lakes

“…Minnow and stone loach are cold water species inhabiting similar zones than brown trout and having upper values of their temperature ranges near 18°C (20 and 18°C for minnow and loach, respectively, FishBase, 2016). The value of 18°C is close to the community threshold of 19°C identified by Parkinson et al (2016) from fish communities of Canadian streams, separating cold from cool water assemblages. It is also comparable to the maximal temperature threshold of 15.7°C found by Brucet et al (2013) as a major split value to explain fish diversity in European lakes by a regression tree analysis.…”

“…The existence of community thresholds assumes that several species share similar thresholds because they have the same ecological preferences or they replace each other in environmental gradients. In British Columbia (Canada), community temperature thresholds were derived from the analysis of river fish samples at 156 sites, marking large changes from very cold to cold and eventually cool water species (Parkinson et al, 2016). Another Canadian study showed that lake water acidity reduced fish diversity with a pH threshold between 5 and 5.5 (Tremblay and Richard, 1993).…”

Slow climate velocities of mountain streams portend their role as refugia for cold-water biodiversity

“…Life in mountain streams (where mean annual temperatures <5°C are common) requires special physiological adaptations (13), so aquatic communities typically have low species richness (14,15). However, those extreme conditions also make mountain streams resistant to nonnative species invasions such that many indigenous communities remain intact even after a century of climate change and the global pandemic of anthropogenic species introductions (16).…”

Integrating Fish Assemblage Data, Modeled Stream Temperatures, and Thermal Tolerance Metrics to Develop Thermal Guilds for Water Temperature Regulation: Wyoming Case Study

“…The Wyoming coolwater range identified in this study is warmer than a transitional zone identified in another headwaters region in British Columbia, which ranged from 12–13°C to 19–20°C in terms of summer MWAT (Parkinson et al. ).…”

“…; Parkinson et al. ). Threshold detection approaches include multivariate methods, such as ordination, cluster, and similarity index analyses, or threshold indicator methods (Wehrly et al.…”