Spring black bear harvest and predation pressure on moose calves in a multi-predator system

The moose (Alces alces; mooz in Anishinaabemowin, Ojibwe language will follow scientific names) is a vital subsistence food source to Anishinabe people of the midwestern United States and has recently declined in Minnesota, USA, with poor calf survival as a contributing factor. Predation is the primary cause of moose calf mortality and we explored whether calf predation rates could be reduced through management of a single predator in a multi-predator system. Thus, we examined predation rates and causes of calf mortality before (2013-2015) and during (2016-2018) implementation of a spring black bear (Ursus americanus; makwa) harvest season, using baits to attract black bears, on the Grand Portage Indian Reservation, Minnesota, where black bears and gray wolves (Canis lupus; ma'iinganag) are the primary predators of moose calves. We validated our early study findings for the 5 years following the initial study with intermittent spring bear hunting seasons, from 2019-2023. The spring bear hunt was canceled because of a pandemic lockdown in 2020, resumed 2021, and was closed in 2022 and 2023. Black bear harvest prior to adding a spring bear hunting season was 0.038 bears harvested/km(2) from 2012-2015, whereas after initiating a spring hunting season (2016-2018) it was 17% higher at 0.046 bears/km(2). We observed significantly lower bear predation (by 68%) in association with spring bear management and no compensatory change in the level of wolf predation. The validation years strengthened our findings that spring bear hunting seasons reduce moose calf predation rates, with an overall 68% lower proportion of bear predation on moose calves in the years when spring bear hunts were held. Mean proportion of calf predation attributed to bears was 4.9 times higher (30% vs. 6%) in the years when a spring bear hunt was not held. Despite an increasing wolf density during the study period, we did not observe a compensatory increase in wolf predation during spring bear hunt years. The results of this work suggest that the addition of a spring bear hunt, during a time when moose calves are most vulnerable to bear predation, has the potential to increase moose calf survival even in the presence of wolves.