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Influence of deer harvest regulations on antlerless harvest...

Influence of deer harvest regulations on antlerless harvest, abundance and sex and age composition: Implications for managing deer in the face of Chronic Wasting Disease

Summary

  • An antler point restriction (APR) harvest regulation was enacted in three counties in southwestern Michigan, and the effects of this regulation on deer harvest and relative abundance were evaluated.
  • Relative abundance of female and male deer remained unchanged in the APR area, while sublegal male deer abundance increased in two of four townships in the non-APR area.
  • Antlerless deer harvest did not change in the APR area, and this pattern matched that of the non-APR area.

Background

In 2018, the Natural Resources Commission (NRC) instructed the Department of Natural Resources (DNR) to establish a Chronic Wasting Disease (CWD) assessment area within the five-county CWD core area. This area was used to experimentally evaluate the effectiveness of regulations, such as antler point restrictions (APR), on the prevalence and spread of CWD, increasing antlerless deer harvest and decreasing deer populations. The DNR informed the NRC that assessing the influence of harvest regulations on the prevalence and spread of CWD was not feasible because collecting sufficient samples from deer to test for and detect a change in low prevalence rates was not possible and, given all possible variables that potentially influence the prevalence and spread of CWD, even if a change was detectable it could not be assumed that the regulation change was the cause. To address questions regarding deer harvest and abundance, the DNR recommended a harvest regulation change that included applying an APR (four antler points on at least one antler) in Ionia, Mecosta and Montcalm counties (APR area) while leaving regulations unchanged in Kent and Newaygo counties (non-APR area) to serve as a control (Fig. 1). A survey conducted by the DNR indicated that 63% of deer hunters in the five counties supported the APR and 68% supported conducting a study to investigate the effects of the APR. The NRC enacted the recommended APR regulation change from 2019 through 2021.

Approach

To estimate potential changes in relative abundance of deer, researchers from the DNR and Michigan State University (MSU) conducted camera trapping in eight townships within the five-county area over four consecutive summers, 2019 to 2022 (Fig. 1). In this context, summer 2019 served as a pre-regulation year, and results from the following three years (post-regulation) were compared to results from 2019 to assess any potential change in deer relative abundance. Researchers collected over 2.6 million photos from 144 different camera locations over the four summers. After using artificial intelligence to screen about 44% of photos, multiple observers documented that 906,792 remaining photos recorded at least one deer. Sex and age of photographed deer were verified by two independent observers, and statistical models developed from results were used to assess any potential change in relative abundance compared to the baseline estimated in 2019. Statistical comparisons were assessed at the 95% credible interval level, and non-overlapping credible intervals indicated a significant difference.

Findings

Across APR and non-APR townships, there was a lack of evidence supporting a reduction in female deer relative abundance, although abundance did increase in 2021 in one non-APR township (Fig. 2). No significant trends in legal antlered deer abundance were observed in APR and non-APR townships (Figs. 3 and 4). However, a significant increase in sublegal antlered male abundance was observed in Townships A and D in the non-APR area (Fig. 4). The DNR estimated deer harvest in the five counties using annual harvest surveys of hunters. In APR and non-APR area counties, no difference in antlerless deer harvest was observed (based on overlapping 95% confidence levels; Fig. 5). Also, antlered deer harvest did not differ significantly in the APR and non-APR area counties (Fig. 6). However, the antlered deer harvest in the APR area declined from 2018 to 2019 before increasing in 2020, likely a result of protecting sublegal (yearling) bucks in 2019 that were recruited into the 2020 population as bucks with legal antlers (adults).

Conclusions

We applied an APR regulation in a portion of Michigan’s core CWD-infected area in an attempt to change the harvest of specific sex and age classes of deer and decrease deer abundance. We detected no decrease in female deer relative abundance in the APR area. We detected a slight increase in sublegal male deer abundance in the non-APR area. Furthermore, we failed to detect a significant change in the harvest of different sex and age classes of deer resulting from the APR.