By Bryan Maitland, Ph.D. Candidate, University of Wyoming
In the boreal forest – Canada’s largest biome that in conjunction with its circumpolar counterparts in Russia and Alaska contain the largest collection of lakes, rivers, and wetlands in the world – industrial activities related to the exploration and development of natural resources have created large networks of roads and in turn the construction of hundreds-of-thousands of stream-crossing structures. Due to the highly dynamic and stressful environment in which boreal fishes live (e.g. long cold winter and short growing seasons), they are extremely sensitive to additional anthropogenic stressors. Watersheds in west-central Alberta are an ideal example of this, particularly as they contain valuable habitat for two species of special concern (i.e. Bull Trout and Arctic Grayling), and have experienced high levels of land-use disturbance from intensive forest harvesting and oil and gas exploration/extraction activities (e.g. roads, forest cutblocks, oil and gas well sites, pipelines). Accordingly, the authors asked the question: are stream crossings a primary driver of fish communities in the boreal forest?
To answer this, they turned to a watershed in the Upper Peace River basin where they examined instream habitat and fish communities in 33 streams that were crossed by either 1) culverts, 2) bridges, or 3) lacked a crossing structure (reference streams). Using mixed models and multivariate ordination techniques, they found that culverted streams were characterized by high percentages of fine-grained, silty substrates, reduced water velocity, higher water temperatures, decreased dissolved oxygen concentration, and increased water depth. Overall fish density and richness were impacted by stream crossings indicating fish habitat fragmentation. Species-specific responses were observed, with those adapted to slower moving, deeper and more sediment-laden streams more prevalent on culverted streams. In general, their results suggest that alterations to stream ecosystems associated with stream crossings, both in terms of habitat fragmentation and degradation, may be driving large-scale changes in stream fish communities in the boreal forest.
As the cumulative effects of natural resource development and additional stressors such as natural abiotic stressors, climate change and forest pests remain largely unknown for the boreal region, this research sheds light on serious concerns for the long-term persistence and biodiversity maintenance of freshwater ﬁsh in boreal forest watersheds. In particular, these results suggest problems for many species of fish found in the Peace River basin, particularly species of concern such as Arctic Grayling and Bull Trout as they may be cut off from important spawning and over-wintering habitats, or loose suitable habitat through sedimentation processes. With expanding industrial development expected in much of North America’s boreal forest, the research team highlights the pressing need for mitigation measures which limit impacts from stream crossings to ensure proper ecosystem function in freshwater systems, and further hopes this project will aid in the management of resource road development through out the boreal forests.
Maitland, M.B., Poesch, M., Anderson, A.E., Pandit, S.N. 2015. Industrial road crossings drive changes in community structure and instream habitat for freshwater fishes in the boreal forest. Freshwater Biology: DOI: 10.1111/fwb.12671