Coastal Commission approves plan to poison mice on Farallon Islands


the California Coast Commission signed the death warrant for tens of thousands of house mice living on the Southern Farallon Islands. The controversial plan, drawn up for years, was approved 5 to 3 on Thursday, December 16, after commissioners heard seven hours of compelling and passionate testimony from supporters and opponents.

While experts have agreed that non-native and invasive creatures are wreaking havoc on the island’s environmentally sensitive ecosystem, the means of execution – dropping 2,880 pounds of brodifacoum, a blood-thinning poison, on the islands from a helicopter – opposed a scientist to a scientist.

The rich and fragile biodiversity of the Southern Farallon Islands is at stake, whether because of the effects of house mice or the poison used to kill them. The islands are home to a variety of animal and plant species, as well as a breeding ground for seals and their relatives. The largest breeding colony of seabirds in the contiguous United States, and the world’s largest population of the rare Cinderella, a small seabird, inhabit the rocky islands. Migratory birds, bats and insects stop over on the archipelago during the migration. Rare and endemic species found on the islands include the Farallon tree salamander and the Farallon camel cricket.

Sailors brought the house mouse (Mus musculus) to the Farallons at the end of the 19th century. Since rabbits and cats were suppressed in the 1970s, mice have been the last remaining invasive species. With the small rodent population estimated at 500 mice per acre on the Southern Farallon Islands, the US Fish and Wildlife Service, which manages the islands, maintains that distributing bait pellets treated with the rodenticide brodifacoum is the only method of effective eradication.

November 2022, after the bird nesting and calving seasons for marine mammals have ended, is the target date to spill a ton and a half of poison in two drops. The pellets containing rodenticides will be dispersed by hand to all areas of the islands not reached by the helicopter drop. The goal is to eradicate all house mice from the Southern Farallon Islands.

Opponents of the plan have claimed the poison pellets have the potential to land in the ocean and move up the food chain to non-target species. While acknowledging that the mice have to go, they suggested using less destructive poisons or waiting until a highly effective mouse contraceptive is developed.

“There is no rush for the mouse,” said Sarah Wan, founder of the Western Alliance for Nature and former member of the California Coastal Commission, during her moving testimony. “Poison drop kills non-target species. And doing so in November, during the raptor migration, will affect raptors across the west coast. “

Eradicating the mice, which have a direct and indirect impact on the ecosystem of the Southern Farallon Islands, will help restore the natural balance, according to the US Fish and Wildlife Service. Mice feed on native sea insects, plants and birds and compete with salamanders for food. Migrating burrowing owls visit the islands during their fall migration, which coincides with the peak of the mouse population. Typically, owls, which prey on mice, left the islands to continue their migratory route; however, some remain due to the easy food source. When the mouse population declines, burrowing owls feed on Common Oceanite, Farallon’s cricket, and other native insects.

WildCare, a non-profit animal hospital in San Rafael, also testified at the commission hearing. The agency is concerned that the brodifacoum poison may remain on the island. Western gulls, abundant on the Farallons, travel between the mainland and the islands. San Francisco is 27 miles from the archipelago, and Marin is just 20 miles away.

“A letter from the Fish and Wildlife Service stated that 95% of the gulls in Fisherman’s Wharf are from the Farallons,” said Alison Hermance, spokesperson for WildCare, during her testimony.

The US Fish and Wildlife Service’s plan includes hazing gulls, using lights, statues and sounds, to keep them from staying on the islands while the poison is present and for weeks afterward. However, WildCare is not convinced that gull hazing will be effective, as the poison comes in “delicious cereal pellets,” according to Hermance.

WildCare is concerned that tens, hundreds or thousands of poisoned gulls may end up on area beaches, as has happened on Cape Cod, Hermance said in an interview with the Bohemian. If this is true, scavengers such as turkey vultures, red-tailed hawks, and coyotes could prey on the highly toxic carcasses, spreading the poison up the food chain. Already, 76% of predatory animals tested by WildCare have anticoagulant rodenticides, such as brodifacoum, in their bodies. The agency believes it will take care of a large number of animals affected by the decline in rodenticides next year.

Supporters of the plan, including Petaluma’s Point Blue Conservation Science and Island Conservation, an international organization based in Santa Cruz, have said the benefits of eradicating mice with poisoned pellets outweigh the potential risks, pointing to hundreds of ‘studies.

The eradication of the non-native black rat from Anacapa Island was one of the successes repeatedly mentioned during the hearings. The island, located 12 miles off the coast of Ventura, was once overrun by rats, which upended the delicate ecosystem. A method similar to that planned for the Farallon Islands was used to kill the rats, and scientists quickly reported positive results for Scripps murres, a rare seabird that breeds on the island. Twenty years later, there are still no black rats on the island and an astonishing recovery of rare birds and other species has taken place.

At the end of the hearing, members of the California Coastal Commission took turns interviewing Gerry McChesney, director of the Farallon Islands National Wildlife Refuge. McChesney answered a few tough questions from commission vice-chair Dr. Caryl Hart, who is also the acting director of the Sonoma County Agricultural Preservation and Open Space District.

Hart toasted McChesney over a photograph used during his presentation to the hearing, which showed a mouse eating a bird’s egg and had obtained information he had not previously disclosed – the photo did not not been taken on the Farallon Islands and there is no evidence that mice eat eggs on the Farallon Islands. Another concern for Hart was the likelihood of pellets entering the water. Hart ultimately voted against cutting rodenticides.

Commissioner Katie Rice, who also sits on the Marin County Board of Directors, asked McChesney a few questions. In an interview with the BohemianRice said she had already made up her mind to vote for the plan by then. “I really leaned on the scientists, environmentalists and people in the conservation movement and leaned on their experience and knowledge of restoring other islands,” Rice mentioned. “Overall, they all agreed on the importance of getting rid of the mice and allowing the species to recover. If we sit back and do nothing, we are causing much more harm. “


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