Boulanger J., K. Poole, B. Fournier, J. Wierzchowski, T. Gaines, and A. Gunn. 2004. Assessment Of Bathurst Caribou Movements and Distribution In The Slave Geological Province. 107 pp

ABSTRACT 

Caribou (Rangifer tarandus groenlandicus) from the Bathurst herd come into contact with mineral developments during their annual movements within mainland Northwest Territories and Nunavut.  The influence of these developments on caribou movements and habitat use is poorly understood.  Here we examine Bathurst caribou distribution during the summer post-calving season relative to three diamond developments.  We used satellite collar and aerial survey data to analyze movement data of Bathurst caribou herd relative to vegetation type, phenology and productivity, local weather, insect activity, and proximity to the mine sites.  Our goal was to investigate caribou distribution relative to mine sites and explore how weather, vegetation and other factors affect caribou distribution relative to the mines. 

We used a number of data sources for our analyses.  Caribou location data included satellite data from 6–19 collared Bathurst caribou monitored annually from April 1996 to December 2003, and systematic aerial survey data collected within study areas surrounding the Ekati (1998–2003), Diavik (2002–2003) and Snap Lake (1999–2003) diamond developments.  Satellite collar location intervals ranged from weekly during the 1990s, to daily in 2002 and 2003.  Aerial surveys generally occurred on a weekly basis at all mines.  We examined caribou distribution using vegetation classification data, weather data, indices of insect abundance derived from weather data, a measure of plant productivity (Normalized Difference Vegetation Index; NDVI), and distance to development.  AICc model selection methods were generally used in most analyses to determine the models most supported by the data sets.

We used satellite collar data to examine the probability of caribou movements in and out of strata or areas surrounding the mine sites.  The mean and minimum distances of caribou from mine sites were relatively similar each year, and caribou were only close to the mine sites briefly for the pre-calving migration and for most of the post-calving through early fall period.  We detected a trend of increasing rates of movement of caribou from the vicinity of the Ekati and Diavik mine sites using the multi-strata analyses, but a weak trend of movement into Snap Lake mine buffer area.

We examined how comparable satellite collars and systematic aerial transects were in estimating the distribution of caribou herds relative to the mine sites by examining the relative proportion of collared caribou within the aerial survey study areas compared to the proportion of the entire herd within the survey study areas.  We found the estimated proportion of the population in mine areas as estimated by satellite collars was consistently higher than that estimated by aerial surveys on transects.  However, there was correspondence between each estimate even though the collar-derived estimate was often higher than transect-derived estimate for the Ekati and combined Ekati/Diavik areas.  No relationship was detected for Snap Lake mine site.  We suggest that the estimated proportion of the population as estimated by aerial surveys might be an underestimate of caribou occurring within the mine areas for Ekati and Diavik. 

We next modeled caribou habitat selection using vegetation data, NDVI, and insect activity indices as covariates, and examined the influence of distance from mine developments on caribou habitat selection using first satellite collar data, then data from the aerial surveys.  We used resource selection functions to assess habitat selection of caribou and the effects of mine sites on caribou distribution.  Results were evaluated using AICc model selection methods; we also assessed overall fit and the predictive ability of the most supported models.  Results demonstrated that caribou selection of habitat appeared to be affected by distance from mine site development.  The large-scale (weekly) analysis of caribou satellite collar locations suggested an influence of 50–65 km from mine sites, although this influence was not strong.  Although hampered by comparatively low sample sizes, analysis of fine-scale (daily) satellite data suggested a smaller influence distance, in the range of 20–25 km from mine development.  The aerial survey data suggested a measurable influence of mine sites on probability of caribou occurrence for the Ekati study area that increased with time out to about 20 km.  The combined Ekati/Diavik data yielded a slightly weaker model that also suggested an influence of distance from mine site.  The Snap Lake data set yielded the weakest model, which showed a weak and decreasing influence of mine site on probability of caribou occurrence. 

Our analyses suggest a trend of increasing rates of caribou movement from the vicinity of the Ekati and Diavik mine sites, and selection of habitat by caribou at further distances from these mine sites over time.  Trends in the influence of mine development on caribou distribution and habitat use in Snap Lake area were weaker.  Future analyses and monitoring of the influence of mine development on caribou distribution would be enhanced by larger sample sizes of collared caribou with frequent (daily) location intervals.  The aerial survey data provided a complimentary method to model caribou distribution.  Survey data would be made more robust by increasing location accuracy of observations, and by using line transect distance sampling to help estimate sightability of caribou within study areas.  We suggest that both satellite collar deployment and aerial surveys be continued for the near future to utilize two independent methods to monitor the influence of mineral developments on movements of the Bathurst caribou herd.