Recent Study Shows Moose Are Declining on Michigan’s Isle Royale

A 2024 survey shows the wolves are holding steady, but the moose are declining on Isle Royale.

Isle Royale is known for its moose and wolves. Michigan’s isolated National Park in northwest Lake Superior has been the location for the longest-running predator-prey study, which began in 1958. This research is one of the longest-running ecological studies in the world. It focuses on understanding the dynamics between the wolf predator population and the moose prey population, along with their broader ecological impacts on the island’s environment.

Each year, Michigan Technological University in Houghton provides a comprehensive overview of the wolf and moose populations on Isle Royale and assesses their interactions and impacts on the ecosystem. This report also examines the island’s weather patterns and their influence on field research alongside other wildlife and vegetation studies.

This year’s study was recently released and reports the following:

Wolf Population

In January 2024, the estimated wolf population on Isle Royale was 30, with four distinct packs identified and one solitary wolf. The packs included the West Pack (four wolves), Middle Pack (seven wolves), East Pack (13 wolves), and the newly identified Northeast Pack (five wolves). A lone wolf resided near the island’s eastern end. While no evidence indicated pup births in the West Pack in 2023, litters were observed among the Middle, East, and Northeast Packs. However, the study notes limitations due to an unusually short two-week survey window caused by warm temperatures affecting ice landing conditions. Genetic analyses are underway to understand wolf pack compositions better.

Moose Population

The estimated moose population for January 2024 was 840, a 14% decrease from the previous year. This decline continued a longer-term trend that began after 2019, with an overall 60% drop in population since then. The recruitment rate of nine-month-old calves was 5.5%, significantly below the historical average of 13.3%. This low recruitment and wolf predation appear to be a critical factor in the population decline. Additionally, necropsies reveal a rising proportion of moose dying from wolf predation, shifting away from malnutrition as a primary cause of death. The study further notes that moose density is higher in the eastern portion of the island.

In an ecological context, “recruitment rate” refers to the proportion of new individuals entering a population over a specific period. Precisely, it measures the addition of younger individuals (often calves, juveniles, or offspring) to a population.

Weather and Ice Conditions

El Niño weather patterns resulted in unseasonably warm conditions, impacting the research. Average temperatures during the study were –2.8°C, considerably warmer than previous years, while ice concentrations on Lake Superior were near record lows. These conditions severely constrained aerial surveys, leading to a truncated two-week research period instead of the usual seven weeks.

Vegetation Analysis

Balsam firs, a primary winter forage species for moose, have shown significant impacts from moose browsing. Approximately 31% of tagged saplings had their terminal leaders browsed, and overall survival rates are declining, with sapling mortality now over 9% annually. The cumulative effect of moose browsing, alongside spruce budworm infestations, has led to a significant decline in the recruitment of mature balsam fir trees. Only 5.6% of mature balsam firs tagged since 1988 remain alive.

Other Wildlife

Observations of other wildlife were limited due to the short survey period. However, there was a noted decline in the snowshoe hare population, and scavenging behaviors of red foxes were observed. Bald eagles were seen feeding on moose carcasses, and some exhibited glaucomatous eye conditions. Raven scavenging was also documented.

Research Highlights

A significant highlight is a study on the relationship between periodontitis, osteoporosis, and osteoarthritis in moose and its implications for humans. The research found strong links among these diseases, demonstrating that moose with periodontitis were significantly more likely to suffer from severe osteoporosis and osteoarthritis. The findings support the growing understanding that oral diseases may have broader health impacts across species.

For more information, visit https://digitalcommons.mtu.edu/wolf-annualreports/

Source: “Ecological Studies of Wolves on Isle Royale: Annual Report 2023-2024,” authored by Sarah R. Hoy, Rolf O. Peterson, and John A. Vucetich from Michigan Technological University.