A broken beaver dam and a draining lake contributed to an area of deep mud being exposed on Isle Royale, which has led to the entrapment and death of at least four moose, researchers discovered.
The issue was brought to light when a researcher from the island’s long-running wolf and moose study led by Michigan Technological University spied a bull moose stuck in the mud on the shore of Lake Ojibway.
The researcher took some pictures of the animal to document its position and its plight.
“Unfortunately, that moose was not able to free itself and it died shortly after these photographs were taken (it had probably been stuck in the mud for several days),” project staff said Sunday in a Facebook post.
“When we sent a team back to check on the animal, they discovered that this moose was not the only victim of the lake.”
The leg bones of three other moose were found stuck in the mud, and researchers surmised those animals died in the last year after becoming stuck in the deep mud pit on the shoreline and not being able to get out.
Lake Ojibway is on the eastern end of Isle Royale.
The island for decades as been home to the world’s lengthiest predator-prey study by researchers tracking Isle Royale’s wolf and moose populations. With about 1,600 moose on the remote island wilderness — which is also a national park — there have been concerns in recent years that the growing population of moose will overbrowse the island’s vegetation. Recent field studies show trees being heavily denuded in some areas.
Last year, the National Park Service began a multi-year experiment to trap wolves in Minnesota and Canada and release them on Isle Royale, to bolster its wolf population which had dwindled to just two.
A dozen new wolves are now living on the island this year, along with the original island-born pair. Evidence of moose killed by wolves already have been documented by researchers on the island this spring.
But the moose trapped in the mud pit succumbed to a different fate, researchers said.
Lake Ojibway is a frequent gathering spot for moose in the spring and summer because they can feed on aquatic plants there — a staple of their warm-weather diet.
“However, the beaver dam that had been holding back Lake Ojibway since the 1950s blew out in November 2017, and it was not repaired by the beavers,” researchers said.
“Since then, the lake has continued to drain, and as the water level dropped, it has exposed an increasingly large area of deep mud along the lake’s former shoreline.”