Estimating unrecorded human-caused mortalities of grizzly bears in the Flathead Valley, British Columbia, Canada.

Bruce N Mclellan,Garth Mowat,Clayton T Lamb

doi:10.7717/peerj.5781

Bruce N Mclellan, Garth Mowat + Show 1 more

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https://doi.org/10.7717/peerj.5781

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Abstract

Managing the number of grizzly bear (Ursus arctos) mortalities to a sustainable level is fundamental to bear conservation. All known grizzly bear deaths are recorded by management agencies but the number of human-caused grizzly bear deaths that are not recorded is generally unknown, causing considerable uncertainty in the total number of mortalities. Here, we compare the number of bears killed legally by hunters to the number killed by people for all other reasons, for bears wearing functioning radiocollars and for uncollared bears recorded in the British Columbia (BC) government mortality database for the Flathead Valley in southeast BC. Between 1980 and 2016, permitted hunters killed 10 collared bears and 12 (9 known, 3 suspected) were killed by people for other reasons. This ratio differed (p < 0.0001) from the uncollared bears in the government database where 71 were killed by hunters while only 10 were killed for other reasons. We estimate that 88% (95% CI; 67–96%) of the human-caused mortalities that were not by permitted hunters were unreported. The study area may have low reporting rates because it is >40 km on a gravel road from a Conservation Officer office, so reporting is difficult and there are no human residences so there is little concern of a neighbor contacting an officer. Our results are likely indicative of other places that are road-accessed but far from settlements. We discuss the implications of sampling individuals for collaring and the possible implications of wearing a collar on the animal’s fate.

Highlights

Knowing how and why large mammals die is fundamental for effective management, conservation, and even developing land-use policies
Of the six unknown fates, four had collars outlast expected battery life, and one collar approaching the expected battery life failed while the bear was hibernating, leaving only one whose collar stopped transmitting with 1.8 years of theoretical battery life remaining so was a candidate for cryptic killing
By comparing the ratio of bears killed by permitted hunters to those killed by people for other reasons between the radiocollared bears and the uncollared bears in the Compulsory Inspection (CI) database, our estimates suggest that 84–88% of the bears killed by people for reasons other than permitted hunting were not reported in the Flathead study area

Summary

Introduction

Knowing how and why large mammals die is fundamental for effective management, conservation, and even developing land-use policies. Documenting illegal killing can be much more difficult even with radiocollared animals. Some people that illegally kill animals destroy radiocollars so animals being monitored seem to just disappear (McLellan et al, 1999; Goodrich et al, 2008). Various forms of unreported killing may be the dominant cause of death of animals in some areas (McLellan et al, 1999; Chapron et al, 2008; Liberg et al, 2012; Sönnichsen et al, 2017; Treves et al, 2017)

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