A Case for Cumulative Effects Assessments in Protecting Caribou Populations

Despite being an unassailable cultural icon in Canada and enjoying a broad geographic spread, the North American caribou (Rangifer tarandus) faces many challenges to its long-term survival. Indeed, as of November, 2014, the majority of caribou subspecies have been listed as endangered, threatened, or of special concern under the Species at Risk Act[1] and continue to exhibit declining population trends outside of natural fluctuations[2]. As can be seen in the following illustration, every subspecies aside from barren-ground caribou and certain ecotypes of woodland caribou have been given special status, yet all herds suffer from a receding historical range[2]:

Distribution and Status of Caribou Subspecies in Canada

One major factor contributing to this decline is the large-scale disturbance to high-quality caribou habitats from development projects[3][4]. Although the environmental impact assessment (EIA) process is intended to minimize or avoid a project’s potential environmental impacts prior to implementation, it has not proven to be exceedingly effective in predicting or mitigating impacts on caribou populations due to its narrow, project-based approach[5]. Instead, more comprehensive practices such as cumulative effects assessments (CEAs) must be employed so the interactions between proposed activities and specialized, migratory species like caribou can be adequately understood.

Typically, a zone of influence around a project is demarcated in order to assess the spatiotemporal extent of its disturbances on caribou populations[4]. This approach, however, implicitly assumes that disturbances are isolated to a single project and neglects the interaction of effects from multiple projects and stressors in the region which combine to inflate the initial zone of influence and magnify its impacts. Properly assessing a project’s true zone of influence is essential for accurate impact predictions as caribou will often exhibit an avoidance response when encountering a zone of influence, whereby they alter their behaviour, distribution, or selection of suitable habitats[4]. Some observed avoidance responses have been so severe that caribou populations like the woodland caribou in northern Alberta have avoided high-quality habitats 1 km near oil and gas wells, equivalent to a 22-48% loss in available habitat[4]. Pictured below is an example of a suitable boreal habitat that could be abandoned by caribou if cumulative disturbances in the region are too great[6].

Caribou Entering Boreal Forest Habitat

Negative impacts on caribou populations are not always so linear either. A study by Beauchesne et al. (2014) showed that woodland caribou responded to an increase in cumulative anthropogenic disturbances by expanding their home ranges, a behaviour shift which resulted in greater energy expenditures and risk of exposure to predators[3]. These kinds of indirect effects generally occur outside the scope of an individual project yet they still interact to endanger caribou population persistence. Similarly, Frid and Dill (2002) provide a simple model that depicts how effects like disturbances and predation encounters displace caribou from preferred habitats and create a cascading response that indirectly affects population size[7].

Model of Indirect Effects on Caribou Population Size

Given the complexity of population dynamics then, the simpler project-based approach to impact prediction and evaluation should be relegated to smaller projects that do not infringe upon caribou habitats. CEA is currently the most viable tool to address the myriad of spatiotemporal factors at the landscape level, and, while often criticized for being ineffective[4], it has great potential for improvement. One suggestion to render CEAs more effective is to establish cumulative effect thresholds that are incorporated into the approval process for industrial activity occurring within caribou ranges[5]. As of yet though, no such thresholds exist within any jurisdiction in Canada[5].

References

[1]Environment Canada. (2014). Species at Risk Act (S.C. 2002, c.29). Ottawa, ON: Minister of Justice.

[2]Gunn, A., Russell, D., and J. Eamer. (2011). Northern caribou population trends in Canada. Canadian Biodiversity: Ecosystem Status and Trends 2010, Technical Thematic Report No. 10. Ottawa, ON: Canadian Councils of Resource Ministers.

[3]Beauchesne, D., Jaeger, J.A.G., and M. St-Laurent. (2014). Thresholds in the capacity of boreal caribou to cope with cumulative disturbances: Evidence from space use patterns. Biological Conservation, 172, 190-199. http://dx.doi.org/10.1016/j.biocon.2014.03.002

[4]Johnson, C.J., and M. St-Laurent. (2011). Unifying Framework for Understanding Impacts of Human Developments on Wildlife. In D.E. Naugle (Ed.), Energy Development and Wildlife Conservation in Western North America (pp. 27-54). Washington, DC: Island Press.

[5]Anderson, R.B., Dyer, S.J., Francis, S.R., and E.M. Anderson. (2002). Development of a Threshold Approach for Assessing Industrial Impacts on Woodland Caribou in the Yukon. Whitehorse, YT: Applied Ecosystem Management Ltd.

[6]Youds, M. (December 26, 2013). Mountain Caribou Face Uncertain Future [Article]. Retrieved from http://www.vancouversun.com/technology/Mountain+caribou+face+uncertain+future/9325826/story.html

[7]Frid, A., and L. Dill. (2002). Human-caused Disturbance Stimuli as a Form of Predation Risk. Conservation Ecology, 6(1): 11.