Continued aggressiveness by one or more black bears at Apostle Islands National Lakeshore in Wisconsin have forced park officials to close Sand Island to all visitors until further notice.

Park officials initially closed the nearly 3,000-acre island to overnight use because a bear (or bears) had been raiding campsites. But efforts to persuade the bruins not to look to humans for meals failed.

After several bear incidents where one or more bears entered campsites at Lighthouse Bay and East Bay, damaged property, and successfully found human food, park staff closed Sand Island to overnight use on July 1. Rangers successfully rerouted all camping parties to campsites on other islands, of which the lakeshore counts 21.

Day use was still permitted, however. Nonetheless, on July 3 a bear climbed at least twice onto a boat that was beached at Lighthouse Bay and successfully removed sausages and other food from a cooler. While the bear has not acted aggressively toward humans, and does run away when frightened, he or she keeps coming back.

“The late spring means that bears probably can’t find much to eat right now on the islands, making human food really tempting,” said Apostle Islands Superintendent Bob Krumenaker. “It’s absolutely critical that visitors to the islands be diligent about making sure that no food is left unattended – even on boats. We don’t want to have to close any more islands, but this is a safety issue. It’s a good reminder that we are guests in the bears’ home – not the other way around.”

Bears might be driven to investigate human food because the berrie production on the islands has been late this year due to a long winter and a cool spring, park officials say.

Park staff will monitor bear activity on Sand Island, and will step up deterrence action in hopes of teaching the bear(s) to stay away from areas frequented by people. The closure will be re-evaluated at least weekly.

According to the Park Service, the bear population on Sand Island nearly doubled between 2002 and 2010 (from 6 to 10 bears) and the population of 18 bears on 5,078-acre Oak Island is exceptionally high. For many years Stockton Island was thought to have the highest population density in Wisconsin and among the highest in North America, the agency notes. That title has been passed to 10,054-acre Oak Island, with Sand Island a close second.