Estimates of Breeding Females & Adult Herd Size and Analyses of Demographics for the Bluenose-East Herd of Barren-Ground Caribou: 2018 Calving Ground Photographic Survey

John Boulanger
Jan Adamczewski
John Nishi
Dean Cluff
Judy Williams
Heather Sayine-Crawford
Lisa Marie LeClerc
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This report describes the results of a calving ground photo survey of the Bluenose-East caribou herd conducted in June of 2018 west of Kugluktuk, Nunavut (NU). The survey objective was to estimate abundance of breeding females and overall herd size that could be compared to results of previous calving ground surveys done in 2010, 2013 and 2015.

We used collared caribou locations and flew systematic reconnaissance survey transects at 10 kilometer (km) intervals over the calving ground and adjacent areas to delineate the annual concentrated calving area, assess calving status, allocate survey effort to geographic strata of similar caribou density, and time the aerial photography to coincide with the peak of calving. Based on collar movements and observed proportions of calves, it appeared that the peak of calving would occur soon after June 8 and the photo plane survey was flown with excellent field conditions (blue skies) on June 8. We delineated two relatively large photographic strata in the higher density areas, in part because we were concerned that patchy snow would reduce sightability of caribou and we thought that aerial photography would provide better accuracy and precision compared to visual counts under these conditions. On June 8 we also conducted visual surveys of two other strata with lower densities of breeding caribou. For the visual surveys, we used a double observer method to estimate and correct for sightability of caribou. A double observer method was also used to estimate sightability of caribou on the aerial photographs as some caribou (on or on the edges of snow patches) required extra effort to identify. The estimate of 1+year old caribou on the core calving ground was 19,161 (95 percent Confidence Interval (CI) =16,512-22,233) caribou. Combining these numbers with the results of the composition survey, the estimate of breeding females was 11,675 (CI=9,971-13,670). This estimate was precise with a coefficient of variation (CV) of 7.7 percent. The estimate of adult females in the survey area was 13,988 (CI=12,042-16,249). The proportion of adult females classified as breeding was higher in 2018 (83 percent) than in 2015 (63 percent). Herd size was estimated as the number of adult females on the survey area divided by the proportion of females in the herd from a 2018 fall composition survey. The resulting estimate of Bluenose-East herd size in 2018 was 19,294 caribou at least two years old (CI=16,527-22,524). Comparison of 2015 and 2018 adult female numbers and overall trend 2010-2018 indicated an annual rate of decline of 20 percent (CI=13-27 percent) and a herd reduction of 50 percent between 2015 and 2018. This decline could not be attributed to issues with survey methods. Assessment of movement of collared females between the Bluenose-East and neighbouring Bluenose-West and Bathurst calving grounds from 2010-2018 showed minimal movement of cows to or from neighbouring herds. Demographic modeling that used composition, collared caribou, and survey data estimated that the cow survival rate was low in 2018 (0.72, CI=0.60-0.83) and calf survival has declined iv since 2010. We suggest population surveys every two years, and annual monitoring of cow survival, calf productivity and calf survival for this herd in the future.