Slowly but surely, as Lake Superior rises and the constant flow of the St. Louis River pummels its shores, Interstate Island is disappearing into the Twin Ports harbor.
The little island that straddles the Minnesota-Wisconsin border is about half the size it was a decade ago, and that’s bad news for a small colony of common terns that nests on the island each spring, one of only two tern colonies remaining on all of Lake Superior.
About 150 nesting pairs of the endangered terns are crammed onto the island with more than 30,000 adult and young ring-billed gulls each summer, and the terns have been losing the battle for the ever-shrinking real estate.
But a $1.4 million effort to raise the tiny island is underway this week, a project to bring sand and gravel and rock out by barge to raise the island and keep it high and dry enough for the terns to keep nesting there.
Lake Superior has been rising since 2015 and is now more than a foot above normal, pushing into the harbor while continued erosion, especially during high-wind events, takes its toll. Big floods like the 2012 deluge that struck Duluth have washed away even more.
Despite efforts to erect “exclosures,’’ or fencing, to keep the hungry gulls away from the tern chicks, the shrinking island has forced the two species closer together. The gulls have been eating both tern eggs and newly hatched tern chicks.
Only 113 nests were counted last year, down from the 20-year average of 185, reports Fred Strand, a retired Wisconsin DNR wildlife manager who has been working for years to restore the island's terns. He listed “chronic egg predation by gulls” as the problem. And without human intervention, the terns won't be able to hang on.
“We call terns a ‘high-maintenance’ species,’’ he said. “Without annual management of gulls and vegetation (cutting brush and trees on the island to keep it open) there would be no suitable nesting habitat for them'' in the Twin Ports.
As first reported last July in the News Tribune, money for the project comes from Minnesota conservation sales tax funds and from federal wildlife and Great Lakes restoration grants. The Minnesota Land Trust, Minnesota Department of Natural Resources and Wisconsin DNR are heading the effort. They now have permits and a contractor — J.F. Brennan Co. — bringing material to the island in coming weeks, scrambling to complete their work and get off the island before the terns show up to nest in early May.
Gini Breidenbach, St. Louis River program coordinator for the Minnesota Land Trust, said work this month will focus on the middle of the island, where the terns nest. After the terns migrate south, the U.S. Army Corps of Engineers will expand the island on the Wisconsin side to double its current size using material dredged from shipping channels. Meanwhile, wildlife crews will build new tern nesting areas, with better fencing to keep gulls away from their little island neighbors.
In all, about 70,000 yards of material will be brought in to beef up the island, the equivalent of more than 4,000 dump-truck loads. The dredged sand will be tested to make sure it's not contaminated. Sand from shipping channels, dredged to allow big boats to navigate the harbor, usually is clean because it fills in quickly, swept downstream by the river. (Material dredged from boat slips and bays that aren't flushed by currents often is contaminated with legacy pollutants.)
The project is part of the massive Great Lakes Restoration Initiative to dredge or cap pollution, restore fish and wildlife habitat and thwart invasive species across all the Great Lakes. Interstate Island — which sits along the main shipping channels in the Duluth-Superior harbor just upstream of the Blatnik Bridge — is a protected bird sanctuary and is closed to the public from March 1 to Aug. 30 each year, not that you'd want to go there considering the shower of gull guano you'd get.