(Newser) – Those suffering from musophobia would be wise to steer clear of the South Farallon Islands. The archipelago, which sits just 27 miles off San Francisco, is the most rodent-dense island in the world, with an average of 500 Eurasian house mice occupying each of its 120 acres (that's 60,000 total). The only humans who have to deal with them are the scientists studying the otherwise uninhabited island's unique ecosystem—and things have gotten so bad that they say the ground often seems to be moving, and other species are being threatened. On Friday, the Fish & Wildlife Service released a 650-page report that sums up its review of the 49 methods suggested for getting rid of the creatures, which are believed to have made their way to the islands via 19th-century seal-hunting vessels. It determined there are only two options: One, douse the island with rodenticides. Two, do nothing.

Though other ideas included carting in feral cats, trapping, and sterilization, the Fish & Wildlife Service say that any method other than poison—which would entail food pellets treated with one of two anticoagulants being dropped on the island, ultimately causing the mice to bleed to death—would have too great an effect on the ecosystem. But the effort wouldn't be as simple as just dropping and waiting, explains the SF Chronicle: peregrine falcons and burrowing owls would have to be captured and held elsewhere; methods would have to be put in place to deter sea gulls. And while mice have been wiped from more than 50 islands around the globe using rodenticides, animal rights groups are staunchly opposed, and note that in the aforementioned cases, other species also perished; KTVU also notes that products made with one of the poisons under consideration were banned from sale this year by the EPA because they are so toxic to animals. But biologists say that even with those casualties, the ecosystems have bounced back. A decision is expected by year-end. (Click for a more disturbing story involving tens of thousands of rodents.)

