Will Houston | Independent magazine Marine
California’s leading coastal regulators have approved the federal government’s plan to dump thousands of pounds of poisoned bait into the Farallon Islands to kill invasive mice that have infested the national wildlife sanctuary.
California’s fractured Coastal Commission voted 5-3 late Thursday to approve a plan that calls for dumping 2,880 pounds of rodenticide pellets by helicopter and by hand onto islands 27 miles off the coast of San Francisco and Marin County. Researchers at the US Fisheries and Wildlife Service say that the number of mice introduced by humans is in the tens of thousands and is causing damage to seabirds, unique species and ecosystems of the islands.
Five coastal commissioners who backed the plan said they are fighting the idea of throwing a rodenticide defense bait in one of the most protected habitats in North America. But after seven hours of testimony and debate, they were convinced by federal researchers and their staff, who said it was the only proven way to completely eradicate mice and restore the ecosystem.
“People have created this problem, and now I think we have an incredibly difficult decision to make to fix it,” said Commission Chair Donn Brownsea.
“I don’t want us to stop this island from healing and getting rid of these mice,” said Marine County Commissioner and Chief Katie Rice.
The hearings were the second review of the draft by the panel, which was first reviewed in mid-2019. The federal government temporarily withdrew the project after commissioners raised concerns about the lack of information on how the agency could have prevented impacts on the islands’ diverse wildlife. The agency came back this time with more, but the issue split environmental groups and some of the commissioners were still not convinced.
“I want this decision to be made beyond a reasonable doubt, and this is what I think is facing us all tonight,” said Commission Vice Chair Caryl Hart.
“This problem did not appear overnight, and now we want to get rid of it overnight,” said Commissioner Roberto Uranga.
Commissioners Carol Groom, Hart, and Uranga voted against the plan. Commissioner Daina Bochko was absent.
The Farallon Islands, with more than 200 acres, is home to the largest seabird colony in the lower 48 United States. The island is home to about 350,000 birds of 13 species, including puffins, gulls, guillemots and half of the world’s rare ash petrels. Thousands of sea lions come to the island to breed and also attract good whites in search of food. In addition, the island is home to unique species including the Farallon camel cricket and tree salamander.
But many of these creatures and habitats have suffered “significant suffering” after mice were introduced to the islands in the late 1800s, said National Wildlife Refuge manager Jerry McChesney. McChesney estimates that the house mouse population has reached at least 60,000, leading to a “serious imbalance” in the sensitive ecosystem.
The mice eat the seeds of sensitive plants, making room for invasive plants to grow. They also compete for food with the woody salamander and eat the local camel cricket. In addition, mice are attracted to non-native burrowing owls, which also prey on ash petrels.
Point Blue Conservation Science, which has been studying the islands since the 1960s, estimates that the ash petrel population could decline by 63% over the next 20 years.
The US Fisheries and Wildlife Service has been developing plans to control mice for 16 years. The agency studied other rodenticides, trapping and movement of contraceptives for owls and mice. Federal researchers have determined that the only proven solution to completely eradicate mice from islands around the world is to use the Brodifacoum-25D Conservation rodenticide.
Since 2005, 33 of 35 attempts to kill domestic mice on islands around the world using rodenticides have been successful, according to the US Fish and Wildlife Service.
“We have an urgent need to act to restore these rare and valuable species before the island’s ecosystem reaches a critical point beyond which it cannot recover,” McChesney told the Commission. “If we don’t act, we will fail.”
According to the plan, the service was to drop the poisoned bait from a helicopter and deliver it to South Farallon Island after two procedures with an interval of three weeks. The aerial drop will occur in November and December, when most of the seabird population has departed and the mouse population is declining due to lack of food.
Researchers froze western gulls for several weeks to keep them away from the island and prevent them from eating the poisoned bait. Salamanders, burrowing owls and predators such as peregrine falcons will be caught and held for several weeks to prevent collisions. Meanwhile, the agency will be monitoring the island and beaches from Sonoma to San Mateo for signs of poisoned wildlife.
Opponents said the plan risks killing other wildlife, polluting water and washing away dead birds on local beaches.
“Since when have we been converting our wildlife into toxic waste?” said Richard Charter, a senior fellow at the Ocean Foundation, who helped create the Greater Farallones National Marine Sanctuary.
They called for other options, including pending the development of contraceptives.
“With our great intentions and our intelligence, there should be more effective ways to deal with mice,” Goodall said in a pre-recorded message to the commission.
Federal researchers said that there is still a long way to go before murine contraceptives are available. Even so, they are only effective for controlling mouse populations, not eradicating them, McChesney said.
California recently banned the use of the rodenticide brodifacum on the mainland, but not to eradicate invasive species from the islands.
Point Blue Conservation Science spokesman Zachary Varnov said there is “a difference day and night between constant continuous use for population control on the mainland and one-time use by certified professionals on the island for total eradication.”
The plan was supported by several organizations that were the main proponents of the rodenticide ban, including the National Audubon Society and the Conservation Organization.