FWP seeks to bolster Wild Horse Island's declining bighorn sheep population

Wildlife officials are seeking public input on a proposal to increase the bighorn sheep population on Flathead Lake's Wild Horse Island after the Montana Fish and Wildlife Commission gave initial approval for the project to move forward during a public meeting Aug. 20.

Montana Fish, Wildlife and Parks says the island's sheep population has declined in recent years and that issues such as inbreeding may impact the group's genetic diversity.

The population was started in 1939 with the release of six bighorn sheep from the Sun River, and was later augmented with two rams from a separate herd in 1987. The 2,160-acre island is a state park managed by FWP, which aims to keep the sheep population between 100 and 120.

However, a recent survey found only 75 or so sheep roaming the island, which is only accessible by water vessel.

That herd count came as a surprise to wildlife officials, who recently relocated 26 sheep from the island to the Tendoy Mountains in Beaverhead County after 2018 and 2019 surveys revealed the population was between 130 and 140 sheep. No survey was completed in 2020 before the relocation effort, but officials moved ahead with the project based on results from the previous studies.

"Reasons for the apparent decline are unknown," the agency said in its new relocation proposal.

Hunting is not permitted on Wild Horse Island, which lies within the boundaries of the Flathead Reservation. And wildlife officials found no concerning pathogens while screening sheep for disease during the 2020 relocation effort.

FWP officials have, however, discovered evidence of mountain lion activity on the island in recent years, which may be contributing to the decline. It's unclear how a mountain lion would have arrived on the island, though researchers believe the cat might have walked across Flathead Lake during a recent winter season when the water body froze over and created an icy bridge.

FWP Wildlife Division Administrator Ken McDonald told the commission that inbreeding and other problems are now of concern, given the herd's declining population. While those problems don't require immediate attention, he said, "we wanted to get ahead of the curve on this one."

The agency is proposing to relocate disease-free bighorn sheep to the island from a population in the Eureka area. Due to the smaller size of the identified herd, McDonald said the effort likely would take at least a year.

Montana law requires the commission approve the transportation of bighorn sheep and other species from one part of the state to another.

The five-member commission is expected to make a final decision in October. The public will be able to submit comments at fwp.mt.gov.