Thirteen years ago, an outbreak of canine distemper virus nearly destroyed the Catalina Island fox population. (The virus may have been introduced by a raccoon that stowed away on a boat from the mainland.)
Now the threatened population has stabilized at 1,500 individuals, said Julie King, director of conservation and wildlife management for the Catalina Island Conservancy. King announced the good news last week after completing the Island-wide annual trapping survey for 2012.
Thirteen years ago, an outbreak of canine distemper virus nearly destroyed the Catalina Island fox population. (The virus may have been introduced by a raccoon that stowed away on a boat from the mainland.)
Now the threatened population has stabilized at 1,500 individuals, said Julie King, director of conservation and wildlife management for the Catalina Island Conservancy. King announced the good news last week after completing the Island-wide annual trapping survey for 2012.
Even so, the Catalina Island fox will probably remain on state and federal endangered species lists.
The official Island fox population estimate is down from the 2011 estimate of 1,542. “It is a slight decrease from last year, but still within the same range,” King said.
Biologists use a population-modeling program called density to analyze capture and recapture data for animals such as the fox, and calculate a population estimate for the entire Island.
“This year, we reduced the number of traps included in the survey from 400 to 243, and utilized six of the 10 trap-lines that we had completed last year,” King said. “We expected to catch fewer individuals in total, but the number of foxes captured within these six lines was almost identical to that captured within these same trap-lines last year.”
Foxes are captured in a wire box cage that is lined with grass and baited with a sweet berry lure mixed with cat food.
Upon capture each fox is given a health assessment, weighed, micro-chipped and vaccinated against canine distemper and rabies.
Ear mites, believed to be associated with a high prevalence of ear tumors, are treated, a blood sample is collected in support of ongoing research initiatives and radio collars on select foxes are inspected and replaced if necessary before each fox is released at their site of capture.
King said that the fox population on the West End of the Island has been fairly stable for the last 10 years because canine distemper virus didn’t extend west of the Isthmus.
“The East End population has been increasing annually up until this point,” she said. “This is the first year it has reached a plateau.” She said that the current number of 1,502 individuals is a good general number given the current habitat for foxes on the Island.”
“Moving forward the fox population will continue to fluctuate slightly from year to year,” King said, “these fluctuations will be linked closely to available resources, and rainfall.”
Conservancy biologists will continue to vaccinate at least 300 foxes annually against both canine distemper virus and rabies in their effort to protect the population against a future disease outbreak.
“We have conducted research investigating the persistence of protective level antibodies produced in response to our vaccination strategy,” King said. “A single vaccination only provides approximately four months of protection. For that reason, annual boosters are necessary to ensure that foxes are adequately protected.”
Weekly aerial monitoring of 50 to 60 radio-collared foxes will also continue courtesy of contract pilot Mike Sheehan.
Most of the radio-collared foxes remain unvaccinated and serve as disease sentinels. In the instance when fox mortality is detected, the carcass is immediately collected and shipped to the California Animal Health and Food Safety Laboratory in order to identify the exact cause of death.
“Being able to identify the threats greatly improves our ability to understand and protect this unique species,” said King.
Island foxes exist on six of the largest California Channel Islands with genetic evidence supporting separation of the species into six distinct subspecies. Four of the six subspecies have suffered marked population declines due to disease, on Catalina Island, and predation by golden eagles on San Miguel, Santa Cruz, and Santa Rosa Islands.
“Despite the fact that Catalina is now home to the largest Island fox population,” King said. “Many of the other Islands are further ahead in their protection efforts.” “All of the other Channel Islands have instituted policies where there are no dogs or cats allowed, and all non-native or feral animals have been removed.” King said. “This is not possible on Catalina due to our large resident human population and annual visitors numbering about one million, but we do ask that people on Catalina be responsible pet owners by vaccinating their pets, keeping cats indoors, and dogs on a leash.”
The Catalina Island fox remains listed as “threatened” by the California Department of Fish and Wildlife and “endangered” by the U.S. Fish and Wildlife Service.
Currently, the federal agency is finishing up its five-year status review of four listed Island fox subspecies, and once completed a decision may be made to down-list or delist one or more of those populations, or their protected status may remain unchanged.
“Although nothing has been formally approved yet, the indication I’ve received is that our fox may be down-listed to federally threatened, but delisting is fairly doubtful for our population,” King said. “We would need to show that all threats associated with the original listing have been adequately addressed.”
“Until we can reduce or eliminate the threat of a future disease introduction, the Catalina Island fox may not ever be delisted,” King said.
King said that “human activities contributed to more than half of the 24 fox mortalities documented in 2012. Although vehicle trauma remains the highest cause of documented fox mortality, several foxes were killed by off-leash dogs, drowning in water containers, or becoming trapped in trash containers without adequate lids.”
“If you are on the road, you will be seeing a lot more foxes, especially during dawn and dusk,” she said. “Please keep your speed down to 25 miles per hour and watch out for them.”
