Columbia River Bull Trout

Climate strongly influences regional and local bull trout distributions. Climate warming (predictions) of 1-5 degree C could result in losses of 18-92% of thermally suitable young producing habitat area and 27-99% of large habitat areas (>10,000 hectare).

A warming climate could profoundly affect the distribution and abundance of many fishes (Chu et al. 2005, Perry et al. 2005). Bull trout (Salvelinus confluentus) may be especially vulnerable to climate change (Rieman et al. 2007) given that spawning and early rearing are constrained by cold water temperatures creating a patchwork of natal headwater habitats across river networks. Because the size and connectivity of patches also appear to influence the persistence of local populations, climate warming could lead to increased fragmentation of remaining habitats and accelerated decline of this species.

Bruce Rieman and others (2007) modeled the relationships between 1) the lower elevation limits of small bull trout and mean annual air temperature and 2) latitude and longitude across the species’ potential range within the interior Columbia River basin of the USA to explore the implications of expected climate changes over the next 50+ years. Results indicate:

• A strong association between the lower elevation limits of bull trout distributions and longitude/latitude (consistent with patterns in mean annual air temperature); and
• Climate strongly influences both regional and local bull trout distributions.

Projected warming over the bull trout’s range could result in losses of 18-92% of thermally suitable natal habitat area and 27-99% of large (>10,000-ha) habitat patches suggesting that impacts on population size may be disproportionate to the simple loss of habitat area. Projected changes were not uniform across the species’ range, and some populations appear to face higher risks than others. The models and information generated in this study were not intended to be used at the level of individual patches but rather to gain some perspective of broad patterns and differences in vulnerability that may exist across the basin. Linking these spatial datasets to others developed for different reasons – with higher or lower resolution, or different underlying physical or ecological processes – could lead to inappropriate interpretations. Although more detailed information is needed to prioritize actions at local scales, results from this study could provide a foundation for regional prioritization in conservation management.

References:

• Chu, C., Mandrak, N., and C. Minns. 2005. Potential impacts of climate change on the distributions of several common and rare freshwater fishes in Canada. Diversity and Distributions 11(4):299-310. DOI: 10.1111/j.1366-9516.2005.00153.x.
• Perry, A., Low, P., Ellis, J. and J. Reynolds. 2005. Climate change and distribution shifts in marine fishes. Science 308(5730):1912-1915. DOI: 10.1126/science.1111322.
• Rieman, B., Isaak, D., Adams, S., Horan, D., Nagel, D., Luce, C. and D. Myers. Anticipated Climate Warming Effects on Bull Trout Habitats and Populations Across the Interior Columbia River Basin. Transactions of the American Fisheries Society 2007; 136: 1552-1565. DOI: 10.1577/T07-028.1.

Photo credits:

Spotlight photo: Metolius River bull trout photo: Image copyright by Jeremy Monroe, . Image used by permission. All rights reserved.

Photo above:  Bull trout angler hands: Copyright by Nathan Leavitt, Flickr user nate1031. Image used by permission. All rights reserved.