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Bibliographic Details
Main Author:	Greenland Institute of Natural Resources
Format:	Recurso digital
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Published:	Zenodo 2021
Online Access:	https://doi.org/10.5281/zenodo.17663657
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Table of Contents:

West Greenland (south of 69°N) has six caribou (Rangifer tarandus) regions  that contain several distinct populations. This report presents new  information, from a survey carried out in 2018, about the KangerlussuaqSisimiut (KS) population, which inhabits the North region.  The KS caribou were last surveyed in March 2010. Since then, there have been  long autumn hunting seasons of unlimited harvest, as well as a winter season.  A new estimate of abundance was overdue. Helicopter surveys in 2000, 2005  and 2010 used strip transect counts. In March 2018, helicopter was again used,  and for the first time Distance Sampling methods and analyses were applied.  Previous surveys have documented that Greenland caribou are  extraordinarily camouflaged against typical environmental conditions in  Greenland, and how this could reduce detection of caribou present within the  surveyed area. While almost anyone can detect running animals, stationary  animals can be difficult to detect. To investigate the proportion of non-moving caribou, the 2018 survey recorded caribou flight responses or lack thereof for  every group observed. Flight movement was absent in almost 32% of all  caribou groups observed during the survey. This underlines the importance  of skilled observers, as well as flying low and slow to make detection of  caribou easier. The 2018 survey’s Distance Sampling methods and analyses  corrected for undetected caribou and provided a robust estimate for caribou  abundance and density (below). It is reasonable to expect that any survey for  caribou would have some proportion of non-moving caribou present in the  surveyed area of the line transects. Additional results from two Greenland  caribou surveys completed in 2019, will confirm whether the observed  proportion in 2018, almost 1/3 non-moving caribou groups, is atypical or  typical. If typical, this suggests that a survey dataset including few  observations of stationary caribou groups would underestimate population  size correspondingly. In early March 2018, observed KS caribou were at relatively low elevations,  mean 361 m. A high proportion of polled KS cows was observed, 46%, which  is similar to earlier reports for this population. Polled cows are not likely due  to poor body condition, as is the common assumption for populations  elsewhere. For KS, polled cows may be the result of a reduced need for the  dominance conferred by antlers, given their small group sizes, and the xeric  8 climate reducing the need of competing for feeding craters dug down through  deep snow to obtain forage. The March 2018 demographics were improved relative to observed in 2005  and 2010. Specifically, late winter calf (age ≤ 10-months) percentage was ca.  21.8%, and calf recruitment was ca. 42 calves per 100 cows. However, 26-32%  of all calves were likely orphans without dams. This suggests that the true late  winter value for calf percentage was closer to 17% and recruitment ca. 31  calves per 100 cows. This level of recruitment is higher than the observed in  2005 and 2010. The March 2018 sex ratio was ca. 51 bulls per 100 cows. The  March 2018 demographics describe a caribou population that appears capable  of withstanding current harvests, while the calf recruitment is not high  enough to suggest the possibility of rapid population growth. Stochastic  catastrophic events excepted, there appears to be a low risk for future  population decline, while there is potential for slow growth. For March 2018, survey coverage was 10.6% of the study area, which is a  substantial improvement from the 1% coverage of the 2000-2010 strip transect  count surveys. The North region’s 2018 KS caribou population abundance  was estimated at ca. 60,469 caribou (95% CI: 51,932–70,410; CV = 0.074; SE =  4,501), with a density of ca. 2.59 caribou/km2 (95% CI: 2.23–3.02). This  Distance Sampling estimate was precise (CV = 7.4%). The population estimate  is ca. 38.5% lower than the estimated number of KS caribou in 2010. Before  concluding that a large decline has occurred, caution is needed because  several mitigating factors must be recognized. The 2010 survey had low  coverage and a high Coefficient of Variance (CV). Thus, it was likely not as  accurate or precise as the 2018 survey. Also, better GIS mapping in 2018  resulted in a smaller total area, which means that the 2010 estimate was  inflated. Furthermore, in 2018 survey methods changed to Distance Sampling.  This by itself precludes trend projections based on just the current and the  2010 strip transect count surveys. To predict a somewhat reliable population  trend, a time series of at least three estimates is needed and these must be  obtained with comparable methods. Albeit the 2018 Distance Sampling  estimate of ca. 60,469 caribou suggests decline in KS caribou abundance and  some decline could be expected, given both the poor calf recruitment of the  2005-2010 period and over a decade of harvest management aimed at  reducing KS caribou abundance. Regardless, this report’s good late winter calf  recruitment for 2018 does not support future decline. Instead, it suggests  possible stability or slow growth in future. It is also worth mentioning that an  9 alternate Model-based analysis of the 2018 dataset estimated a somewhat  higher 73,895 caribou (95% CI: 65,983-82,757, CV = 0.037) (Correia 2020).  Given there are two estimates begs the question, which is the most accurate  and precise? This is currently being investigated, requires additional results  from two other West Greenland caribou surveys completed in 2019, and  conclusions regarding Distance Sampling and Model-based estimates will be  published in a peer-reviewed journal. Whether 60,469 (95% CI: 51,932–70,410) or 73,895 (95% CI: 65,983-82,757), the  2018 KS caribou population size remains large relative to the area available,  23,303 km2. The KS caribou density from Distance Sampling was 2.6 caribou  per km2. Given good calf recruitment, population decline is not expected in  the immediate future. Like all estimates since 2000, the 2018 density exceeds  the recommended management target of 1.2 caribou per km2. Exceeding the  target density was assumed to raise risk of overgrazing and lead to  abundance decline. In Alaska and Canada, when overgrazing played a major  role, caribou declines took place over 15 to 20 years. Nevertheless, even after  almost two decades of high densities exceeding the target have passed, there  is no strong evidence of extensive overgrazing or decline in the KS caribou.  Since in 2018 recruitment improved to at least 31 calves per 100 cows, despite  an overall density of 2.6 caribou per km2, it appears that the North region can  support a higher density than expected. Pending additional results from two  other West Greenland caribou surveys completed in 2019, the target density  for caribou management will receive re-evaluation regarding what level is  compatible with demographics that facilitate sustainable populations and  harvests in Greenland.

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