A Comparison of Calving and Post-calving Photo-surveys of the Bluenose-East Herd of Barren-ground Caribou in Northern Canada in 2010

Posted on May 8, 2017

Author

Jan ADAMCZEWSKI, John BOULANGER, Bruno CROFT, Tracy DAVISON, Heather SAYINE-CRAWFORD, and Boyan TRACZ

CWBM 6 (1): 4–30.

Correspondence: J. Adamczewski, GNWT ENR, Box 1320, Yellowknife, Northwest Territories, X1A 2L9, Canada.

Email: jan_adamczewski@gov.nt.ca


Abstract

Two photographic survey methods have long been used in Canada’s Northwest Territories and Nunavut to estimate herd size in migratory barren-ground caribou herds (Rangifer tarandus groenlandicus). The calving photo-survey provides an estimate of the abundance of breeding females on the calving grounds in June and can be extrapolated to an estimate of herd size to account for caribou not on the calving grounds. The post-calving photo-survey is carried out in July when large dense groups of caribou formed in response to insects can be photographed and counted. We carried out both surveys for the Bluenose-East caribou herd in 2010 in Nunavut to provide a side-by-side comparison.

ADAMCZEWSKI et al.

The calving photo survey in early June produced an estimate of 51,757 ± 11,092 (95% Confidence Interval) breeding females on the calving grounds. We estimated 114,472 ± 15,845 ≥1-year-old caribou from the photographed and visually counted June survey strata. The estimate of breeding females was extrapolated to a herd size of 105,326 ± 40,984 ≥2-year-old caribou using estimates of sex ratio and pregnancy rate; an alternate extrapolation of 120,880 ± 13,398 ≥2-year-old caribou was derived from strata-based estimates of cows and an estimate of sex ratio. Counts of photographed caribou aggregations in July resulted in a total of 92,481 ≥1-year-old caribou in 39 groups. An estimate of herd size using a Lincoln-Petersen formula was 98,646 ± 13,965 ≥1-year-old caribou and an estimate using the Rivest estimator was 122,697 ± 31,756 ≥1-year-old caribou. The Rivest-derived estimate was likely closest to true herd size (all ≥1-year-old caribou). We compared strengths and limitations of the 2 survey methods, and their applicability for management.

Key Words: Barren-ground Caribou, Calving, Photo-survey, Population Estimate, Post-calving.

 

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