Eamon Woolstenhulme
BIOL 1615
November 8, 2013
Research Paper Summary
Santa Catalina Island, part of the Channel Islands located approximately 25 miles west of
the southern California coast, is a unique biological community. While it is a Pacific island, it is
not tropical. The little rainfall it gets classifies it as a subdesert. Likewise, it is home to many
desert species (such as prickly pear cactus), invasive species (like fennel and eucalyptus), and
many unique endemic species, like the Catalina Island fox (urocyon littoralis catalinae) which
can only be found on the island and nowhere else in the world (Santa Catalina Island Fox). In
1998, a study was conducted to determine the population of foxes living on the island. It yielded
a health number. However, starting 1999, the number began to decline. Residents of the island’s
largest city and tourist destination (Avalon) reported sightings of disoriented and dead foxes in
and around the city. This caused concern for the Catalina Island Conservancy, the organization
that controls a majority of the island’s land, because the fox is considered an endangered species.
In October of 1999, the Conservancy teamed up with the Institute for Wildlife Studies and
launched an investigation “to further document the decline in the [Santa Catalina Island] fox
population and its possible cause” (Timm et al. 334).
Since the fox has no natural predators, it could be concluded that these deaths were not
predatorily caused. However, the disorientation of the foxes reported by island residents was
consistent with disease, specifically a neurological one. In order to confirm this, researchers
began by trapping as many foxes as possible along the island. The island is naturally bisected by
the isthmus and the town of Two Harbors located on it. The area of the island northwest to the
isthmus is commonly known as the “west end” and everything southeast as the “east end.” From
October 1999 to April 2000 (six months total), researchers set traps in areas foxes are commonly
seen. This included spots along major roads and game trails. Box traps were set up and baited
with dry dog food, cat food, and berry paste. Once a fox was caught, it underwent a physical
examination (including weight, age, gender, and reproductive status), and was examined for
signs of disease (ocular or nasal discharge, coughing, diarrhea, poor coat, and aberrant behavior.)
Once the exams were complete, a blood sample was drawn and the fox was tagged in order to
prevent it from being counted twice. After the trapping period, a total of 59 foxes were caught
and recorded (49 on the west end and 10 on the east end.) All but six were released back into the
wild; the six were retained for a captive breeding and vaccine study.
In addition to foxes, scientists trapped and recorded 14 feral cats in order to compare their
disease patterns to that of the foxes. The cats were given a physical examination and had a blood
sample drawn. Before the six month period began, researchers recovered the body of a deceased
fox found on the east end of the island.
After the trapping period, the fox and cat blood samples were sent to the New York State
Veterinary Diagnostic Laboratory at Cornell University to be tested for numerous diseases and
the fox carcass went to the University of California, Davis for an autopsy. The fox blood samples
underwent testing for multiple diseases including canine distemper virus (CDV), canine
adenovirus (CAV), canine parvovirus (CPV), canine corona virus (CCV), and toxoplasmosis.
These tests confirmed exposure to CDV in 87% of tested samples. Compared to 1998, this was a
rapid increase. Ten blood samples (eight of which were positive for CDV antibodies) were tested
for rabies. In addition, ten CDV-positive samples were tested for phocine distemper virus (PDV),
phocine morbillivirus (PMV), and dolphin morbillivirus (DMV). Feral cat samples were tested
for CDV, feline immunodeficiency virus (FIV), feline infectious peritonitis (FIP), feline
leukemia (FeLV), and toxoplasmosis.
In the results from the blood work, scientists were able to rule out CCV as the cause of
the epidemic because no fox had been exposed to it. Low exposure rates of CAV and CPV
allowed them to be dismissed as well. Rabies, which was only present in one fox, could have
been the pathogen. It was difficult to determine this since any fox that died from rabies was
never recovered. It was later determined that the one fox that tested positive for rabies got the
virus’ antibodies from a vaccine, rather than exposure. Since 87% of trapped foxes and 29% of
feral cats tested positive for CDV antibodies, it was becoming apparent that canine distemper
virus was the cause of the epidemic. This was supported by comparison of serum samples taken
in 1998 and samples in 1999-2000. The concentration of antibodies had substantially increased,
meaning the 1998 population was easily susceptible to CDV.
Further proof of a CDV outbreak was confirmed by an autopsy performed on the
deceased fox. Blood and tissue samples revealed a presence of the disease, as well as
Toxoplasma. Further testing determined the cause of death as bronchopneumonia caused by
CDV. While Toxoplasma is not fatal by itself, it could have been co-pathogen in the fox’s
demise.
Researchers noted a more successful trapping rate on the west end of the island. Even
though there were fewer trap nights on the west end (one west end night for every seven east
end), there were nearly five times as many foxes trapped than on the east end. It is important to
note that the west end of the island makes up less than 15% of the island’s mass. These trapping
patterns led scientists to determine that the disease was “spatially explicit and not an island-wide
phenomenon” (Timm et al. 337); although the results of the blood tests made it hard to prove.
Nine out of ten east end foxes tested positive for CDV antibodies, indicating exposure. These
results initially supported the claim that this was a spatial incident. However, twenty-seven out of
thirty-one foxes captured on the west end tested positive for the antibodies. This puzzled
researchers since very few foxes ever came near the isthmus (four of the ten east end foxes were
trapped within 2.3 km of the isthmus.)
The deceased fox which had died due to CDV had tissue and blood samples removed.
The strain of CDV found in this fox was a 98% match to CDV found in North American
raccoons. This led researchers to believe one or more raccoons had made their way to the island
from the mainland. Foxes are more susceptible to raccoon diseases (or any disease of an invasive
species) since they are newly introduced to the foxes’ evolutionary history. While
Toxoplasmosis (a feline disease) was found in 43% of the feral cats, it was only considered a copathogen since feral cats have been present on the island longer than raccoons. This allowed
foxes to gain a defense against feline diseases.
Once the trapping period concluded in April, 2000, researchers learned that the “density
of the fox population on the east of [Santa Catalina Island] in 1999 dramatically reduced” (Timm
et al. 340). When compared to population numbers in previous years, it was estimated that only
5% of the 1998 east end population survived the epidemic. The west end data revealed a healthy
population comparable to that of previous years. The island’s total population, however, was
severely less than those of endemic fox species of some neighboring Channel Islands (i.e. Santa
Cruz, San Clemente, San Nicholas.)
The presence of CDV in the deceased fox was the first concrete indicator of a CDV
outbreak. Supporting evidence came from classic signs of an epidemic. For instance, no juvenile
(less than one year old) foxes were recorded, which is consistent with patterns of other
outbreaks, where juveniles are very susceptible to disease. Researchers then had to determine
how CDV came to the island. It was hypothesized that one or more raccoons had stowed away
on a commercial boat or private yacht and managed to disembark on to the island. This was
supported in multiple capacities. Avalon is a popular tourist destination. Yacht owners are able to
moor in Avalon Bay. In addition, a ferry makes multiple runs to and from Avalon. It is very
possible that a stowaway raccoon managed to get on the island. In the foxes that tested positive
for CDV antibodies, the ones with the highest concentrations were found in or very close to
Avalon. Multiple disoriented and dead foxes were reported by Avalon residents and the dead fox
retrieved by researchers was found close to the city. Scientists also observed that foxes able to
survive the epidemic lived on the west end, which is the farthest part of the island from Avalon.
The challenging part was determining how west end foxes got the antibodies. The natural
and man-made barriers of the isthmus and Two Harbors make it very unlikely that a fox crossed
from one side of the island to the other. Physical characteristics of foxes, such as monogamy,
low reproduction rates, and short life spans also made it difficult to determine. It is possible that
a private yacht or commercial boat moored in Two Harbors might have unknowingly stowed a
raccoon. Also, the west end is home to many summer camps and yacht clubs which temporarily
moor commercial and private boats. Any number of these could have housed a raccoon, though it
is unlikely.
Studies conducted as early as 1988 revealed that CDV antibodies had been present in low
concentrations in foxes. There is a chance that a raccoon made its way to the island but died
before it could infect a large number of the fox population. However, domestic pets such as dogs
as the feral cats were able to host the virus before it became an epidemic. After 2000, CDV is no
longer considered a threat to the fox population, since most individuals have antibodies to it. In
order to prevent this from happening again, researchers have advised and carried out the
following:
1) vaccination of the remaining [Santa Catalina Island] foxes...; 2) translocation of
juvenile foxes from the west end to the east end of the island; 3) development of a captive
breeding and release program as a safeguard against extinction and to enhance the
population recovery; 4) long-term population monitoring using radio-collared animals to
identify mortality factors; 5) encouraging vaccination of all domestic dogs on Santa
Catalina Island and ; 6) establishment of a feral cat and introduced wildlife program.
(Timm et al. 342)
These have had profound effects on the foxes’ population, which had risen to a steady number.
In 2009, the Catalina Island Conservancy “estimated that the fox population had grown to over
900 individuals” (…Island Fox).
Works Cited
Santa Catalina Island Fox. Institute for Wildlife Studies. 2012. Web. 9 October 2013.
Timm, Steven F. et al. “A Suspected Canine Distemper Epidemic as the Cause of a Catastrophic
Decline in Santa Catalina Island Foxes (Urocyon littoralis catalinae).” Journal of
Wildlife Diseases 45.2 (2009) : 333-343. Print.