Wolves and the Isle Royale Environment

A collaborative effort to restore ecological functions of wolves on the island ecosystem.


Background

Wolves play a critical role on the main island of Isle Royale National Park by affecting the abundance and spatial distribution of moose and beaver, and by extension, the abundance, distribution, and type of vegetation on the island. Wolf-moose relationships have been studied on Isle Royale for over 50 years, providing one of the longest ecological studies of predator-prey dynamics in the world. By 2015 wolf abundance on Isle Royale declined and extirpation seemed likely; consequently the National Park Service (NPS) began to assess management alternatives documented in an environmental analysis. The selected alternative included one or more introductions of wolves to Isle Royale within 5 years, with the goal of restoring the ecological role of predation in the Isle Royale ecosystem.

In June 2018, the NPS and partners began implementation planning considering the panel’s recommendations to achieve restoration objectives. Objectives included introduction of wolves from a broad geographic area within the Great Lakes region that was genetically diverse with characteristics (e.g., experience hunting moose) considered important to their persistence. State, provincial, and tribal partners have authority to capture wolves within their respective jurisdictions and coordinated these efforts. Nineteen wolves captured in Michigan, Minnesota, and Ontario during September 2018–2019 were translocated to Isle Royale. We estimated 14 wolves present on Isle Royale on 14 April 2020. Eight wolves died with the most common cause of mortality intraspecific aggression.

©Jacob W. Frank/NPS

Summary 2018-2020

Reproduction: GPS location data suggested female wolf 014F denned in spring 2019 and established several rendezvous sites. Images from a remote camera in September 2019 support at least two pups were reared. Location data from GPS collars also demonstrated denning activity for wolf 001F in early April 2020. Genetic analysis of scat samples will provide additional support for reproduction of these wolves. Limited data suggested potential for denning activity for wolves 012M and 015F during spring 2020; however, collar failure precluded confirmation.

Cluster investigations: We investigated clusters of wolf GPS locations during May–September 2019 to estimate predation or scavenging events. Of 381 location clusters investigated, we identified 50 predation events of which 24 were moose (Alces alces), 19 were beaver (Castor canadensis), 3 were snowshoe hare (Lepus americanus), and 4 were other species. We documented 117 instances of concurrent space use by wolves at these clusters. Thirty-one instances (26.5%) were associated with prey remains, 62.4% were associated with bed sites, and 11.1% were unknown.

Moose: We estimated abundance of moose during 14–15 March 2020 using a double-count distance sampling framework from a helicopter. We surveyed about 95% of Isle Royale and observed 236 moose in 136 groups.

Trail cameras: During summer 2019 we installed 156 remote cameras about 1 km apart on and off trails to document wolf distribution in relation to prey species and determine how wolves and other mammals respond to visitor abundance and distribution. We will continue monitoring wolf and moose populations with our partners to characterize their effects on this ecosystem and the success of the wolf introduction program.

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