The Farallon Islands have a mouse problem. The solution is raising eyebrows.

July 8, 2019, 1:59 p.m.
Waves crash on rocks off the coast of the Farallon Islands.
Photo: Pete Niesen/Shutterstock

The Farallon Islands, which lie about 27 miles off the coast of San Francisco, are known for their sea stacks, or vertical columns of rocks. They're also known as the residence of some of the world's largest populations of seabirds, five marine mammals and several rare species, such as the Farallon arboreal salamander and the Farallon camel cricket.

In the 19th century, invasive species were introduced to the Farallons, so now the islands are also home to mice. At their peak each year, there are about 450 of these tiny rodents per acre, which is among the most recorded for any island in the world. According to a report presented by the U.S. Fish and Wildlife Service to the California Coastal Commission, the mice have "led to long-term ecological damage," as they wreak havoc on breeding seabird populations, native plants and amphibians.

The proposed solution is to toss about 2,900 pounds of pellets containing a total of 1.16 ounces (or 33 grams) of rodent bait Brodifacoum-25D Conservation from the sky with the goal of eradicating the mice and restoring the balance of the ecosystem. The report says scientists considered 49 potential mechanical, biological and chemical removal methods before settling on this plan.

There's the possibility that the poison will affect species other than their intended target, according to the report, but this "would not be significant in the context of species populations in the region."

In addition, the poison could affect water quality and marine life if it drifts into the ocean. But the report states that because the rodenticide isn't very soluble in water, it "would lead to only very temporary and localized reductions in water quality with no adverse long-term effects."

Scientists behind the report argue that the ends justify the means.

"The proposed restoration efforts would result in significant long-term benefits to native seabirds, amphibians, terrestrial invertebrates, and plants and will help to restore natural ecosystem processes on the islands."

Not everyone thinks it's a good idea

The Farallon Islands are home to the Farallon Arboreal salamander. The Farallon Islands are home to the Farallon Arboreal salamander. (Photo: Adam Searcy/Flickr)

More than 400 species of birds have been spotted in the Farallon National Wildlife Refuge with more than 25% of breeding seabird populations in California found on the islands. In addition, the islands are home to northern fur seals, stellar sea lions, California sea lions, harbor seals and northern elephant seals, as well as an array of other wildlife including white sharks, arboreal salamanders and hoary bats.

With so much wildlife, the islands have a lot of fans.

Four dozen people wrote to the commission about the proposed plan. Most were outspoken in their displeasure.

"It remains incumbent on the Wildlife Service to find a more targeted and environmentally benign single-species approach at the Farallones, one less dependent on persistent food-chain poisons that have a known record of killing animals that are not part of the problem," wrote Erica Felsenthal of Beverly Hills, California. "Responsible stewardship of America’s public trust living resources, particularly within our National Marine Sanctuaries and elsewhere on the California coast, deserves a more precautionary approach."

Kim Fitts, who identified herself as a wildlife biologist, wrote, "Undoubtedly the poison will travel up the food chain; not only killing the intended mice, but also the entire predator/carnivore community living with the coastal zone. This is exactly how the food web is destroyed for generations."

And Kim Sandholdt of San Rafael, California, wrote, "While the mice are a problem, there needs to be a better solution to the situation. Rat poison is the easy way out. It will take a lot of time and labor to get out there and trap and eradicate the mice. Figure it out, please!"