Tuesday, July 29, 2014

Considering Epidemic Disease Threats to Island Foxes

courtesy of Paul Bronstein
What saved the Catalina Island fox from rapid extinction when canine distemper virus was introduced between 1998-1999? 

An isthmus and human action

Epidemic disease poses a major threat to naive island species like the Channel Island fox. When distemper was introduced via a raccoon transported unknowingly to the island, the disease spread rapidly throughout the island fox population. Nearly all of the 103 surviving Catalina Island foxes lived north of the isthmus, a narrow neck of land connecting the western and eastern parts of the island.

photo from NOAA of Santa Catalina Island
Fox traffic across this exposed area is minimal.

At the recent Island Fox Conservation Working Group Meeting, Brian Hudgens from the Institute for Wildlife Studies (IWS) reported on his findings “Mapping Epidemic Risk in Island Foxes.”

Working with Julie King from the Catalina Island Conservancy, they considered the map of Catalina Island and the areas where epidemic disease is most likely to be introduced via human visitors–the towns of Avalon and Two Harbors, beaches and harbors, and youth camps. They combined this with fox related factors:

  1. island fox population density on Catalina
  2. typical home range size of individual island foxes
  3. range overlap with neighboring island foxes
  4. number of interactions with neighboring foxes
It quickly became apparent that island fox density on Catalina Island is highest in the areas near human habitation; the areas which also pose the greatest risk for disease introduction.

Next, Hudgens created a computer model calculating how introduced canine distemper virus would travel across the island and through the island fox population. What they didn’t expect was that in most cases it didn’t matter where the disease was introduced, in 3 - 4 months an epidemic would cause 100% mortality island-wide. The only deviation was a reduction to 90-100% mortality, if the disease was introduced at the far western end of the island, with the isthmus to hinder the infection spread.

Adding vaccination into the modeling dramatically changed the modeling outcome and the most significant protection was provided by island-wide vaccination of individual island foxes. When a significant number of island foxes across the island were vaccinated in the model, animals that were not vaccinated had a four-times better chance of surviving as well.

Friends of the Island Fox funded 400 island fox distemper vaccinations in 2012.

Each vaccination for rabies or distemper costs $10.

Vaccination provides vital protection for these rare island foxes. Successful recovery can only be maintained through vigilant proactive protection.