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Coastal Commission approves mouse poison drop on Farallon Islands

San Francisco Chronicle logo San Francisco Chronicle 12/17/2021 By Tara Duggan

A controversial plan to kill invasive mice on the Farallon Islands National Wildlife Refuge by dropping poisoned bait from helicopters has moved one step closer to reality now that it gained approval from the California Coastal Commission on Thursday night.

At the end of a sometimes emotional seven-hour online meeting, the commission voted 5-3 to approve the proposal from U.S. Fish and Wildlife Service, which has been under consideration since 2004.

The issue has pitted environmental groups against each other, with supporters outlining the importance of removing mice to maintain biodiversity on the archipelago 27 miles west of the Golden Gate and opponents expressing concern, sometimes in tears, about the potential unintended consequences to other species.

The agency proposes dropping cereal pellets containing rodenticide to kill off the mouse population that has wreaked havoc on the ecosystem of the South Farallon Islands, which host 300,000 breeding seabirds. The poison drop would happen in fall, when the seabird nesting population is at its lowest and the invasive mouse population is at its highest.

“This project is necessary and is the right thing to do to stop the ecosystem carnage done by mice: a human-caused problem,” said Gerry McChesney, manager of the Farallon Islands National Wildlife Refuge, when introducing the latest proposal at the meeting. “Rare and unique species like the ashy storm-petrel are at risk from mice, from the impacts of rapidly accelerating climate change and from other human-induced threats.”

This was the second time U.S. Fish and Wildlife Service introduced the poison drop plan to the California Coastal Commission. The first was in 2019, when it was then removed from consideration after the commission asked for additional details.

The next step will be for the regional director of U.S. Fish and Wildlife Service to decide whether to approve it, or to make what’s called a record of decision. If that happens, the poison drop would likely be implemented in the fall of 2023 at the soonest, according to McChesney.

Brought to the islands in the 19th century, the mice attract burrowing owls that prey on the ashy storm-petrel, a dark-gray seabird about the size of a robin. Over half of the ashy storm-petrel’s global population of 10,000 nests on the islands and research indicates it will decline by 63% if no action is taken to remove the mice.

Commissioner Caryl Hart, who voted against the proposal, expressed concern in the meeting that the bait would end up in the ocean and be eaten by fish or crustaceans, including Dungeness crab or salmon that could end up in supermarkets. Wildlife officials said that the bait breaks down quickly in the surf, often within an hour, and the poison hasn’t been shown to linger in marine environments around other islands where it’s been used.

Other critics of Fish and Wildlife’s plan, including the Ocean Foundation and Sierra Club California, argue that the poison that would be used to kill the mice, brodifacoum, is unsafe for a wildlife refuge.

“This is one of the worst things this commission has ever been asked to approve. If I sound angry to you, that’s because I am,” said Sara Wan of Western Alliance for Nature, fighting tears as she described how the bait drop would happen in fall, when raptors fly over the island and could prey on poisoned mice. “This is not risk-free and could create a long-term disaster rather than a solution.”

Fish and Wildlife officials counter that the poison bait would only contain 0.0025% of the rodenticide and that it has been used in 63 successful mouse eradication projects at islands worldwide. Their plan also involves hazing Western gulls, the species most likely to eat any excess bait and be killed by it, to scare them away before the bait drop.

Supporters of the plan include Point Blue Conservation Science, which stations biologists on the islands year-round for wildlife research, along with many conservation groups like the National Audubon Society and the Nature Conservancy.

For many supporters, the issue is a local example of what’s at stake in the biodiversity crisis, in which 1 million species worldwide are threatened with extinction, according to the United Nations.

Islands in particular are found to have the highest rates of biodiversity, yet they’re also often threatened by invasive species, said Carolyn Kurle, professor of biological sciences at UC San Diego, at the meeting.

“One of the very best ways of protecting endangered species on islands is by eradicating invasive species on islands,” said Kurle.

Tara Duggan is a San Francisco Chronicle staff writer. Email: tduggan@sfchronicle.com Twitter: @taraduggan

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