EXECUTIVE SUMMARY 

Decline of the Island Fox

 The island fox is distributed as six subspecies, one on each of the six largest California Channel Islands. Surveys of foxes on Santa Catalina Island in 1999 and 2000 indicated a severe decline of more than 90%– due to an outbreak of canine distemper virus (CDV). Similarly, fox populations have declined for other reasons on three of the northern Channel Islands. As a consequence, all four subspecies were listed as endangered under the federal Endangered Species Act on 5 March 2004, and all six subspecies are listed as threatened by the California Department of Fish and Game.  

Results of a population viability analysis conducted by Kohlmann et al. (2003, 2005) suggested that the Santa Catalina subspecies was at a critically low level, where risk of extinction is significant, especially when recurrent catastrophic events, such as CDV, are included in the model. They concluded that the population cannot sustain repeated catastrophes (i.e., more than once every five years) when the survival of foxes is reduced by >50%. They also concluded that to maintain a high degree of genetic heterozygosity and to prevent demographic stochasticity, a goal of at least 150 animals on each side of the island should be adopted, prior to stopping population augmentation via captive breeding.

 Island Fox Recovery Efforts

 In 2000, a multi-faceted plan was implemented to conserve the Santa Catalina Island subspecies by:

• Monitoring foxes across the entire island using trap/mark/recapture to compare the relative abundance and distribution of island foxes east of the Isthmus (the “EAST END”) affected by the 1999 CDV outbreak, with that of foxes in the unaffected area west of the Isthmus (the “WEST END”).

• Capturing and radio collaring juvenile foxes from the WEST END for translocation to the EAST END as a means to quickly augment that subpopulation. Tracking these foxes over time would provide valuable site-specific information on juvenile dispersal, pair-bond formation, coarse-scale habitat use, and survival.

• Inoculating wild foxes against CDV. All translocated and captive-bred foxes released to the wild were also vaccinated against CDV prior to release.

• Implementing a captive-breeding program to protect a subset of the population against another catastrophic CDV outbreak and to produce offspring to augment the natural repopulation of the EAST END of the island.

Results

 Fox Abundance

During the main mark-recapture period (19 July–25 September 2004) we captured 209 individual foxes (103 on EAST END; 106 on WEST END) a total of 349 times. An additional 53 individuals (31 males, 21 females) were captured outside the main trapping period, bringing the total number of individual foxes captured since the previous annual report to 262.  

For comparison, during the main trapping period in 2003, 130 individual foxes (65 on EAST END; 65 on WEST END) were captured a total of 191 times; in 2002, 117 individual foxes (50 on EAST END; 67 on WEST END) were captured a total of 183 times, and during the main trapping period in 2001, 125 individual foxes (24 on EAST END; 101 on WEST END) were captured a total of 248 times. The distribution of traps and number of trap-nights were similar between years 

We estimate the current island-wide fox population at 360 (141 WEST END: 219 EAST END). This estimate includes 262 (106 WEST END: 156 EAST END) foxes captured since the previous report; six monitored foxes that were not captured but are known to be alive; three captive foxes; and 89 (35 WEST END: 54 EAST END) foxes estimated for areas unsampled (untrapped) during systematic trapping conducted in the summer of 2004. The eight captive-reared pups and the 20 captive adults released to the wild in late 2004 were included in the island-wide estimate, but the 5 known mortalities during the reporting period were excluded.

The EAST END, which comprises 84% of the entire island, now harbors approximately 61% of all known live foxes. Mean estimated densities were 5.3 foxes/km² and 1.2 foxes/km² on the WEST END and EAST END, respectively. The frequency distribution of densities derived from a grid-based estimation showed that most grid cells on Santa Catalina Island had low fox densities (mean =1.92 foxes/km², SD = 2.518).

Fox Physical Condition

We conducted 330 physical examinations on 258 foxes between 1 January 2004 and 30 April 2005. The most common physical abnormalities noted were ear mite infestations (45% of all occurrences), notched or torn ears (17%), old, healed wounds (15%), and cuts or abrasions (14%). Fewer than 28% of foxes suffered from any discernible parasite loads. Twenty foxes broke or loosened one or more teeth while in a trap. The remainder of trap-related injuries consisted of minor cuts and abrasions. Three captured foxes had fresh fractures, none of which were considered life threatening; two with broken tails and the third with a broken toe. These fractures did not appear to have resulted from being captured.

Of greatest concern was that a relatively large proportion of older foxes captured on the WEST END had proliferative tissue masses in one or both ears. Those individuals with serious ear conditions were brought to the clinic, sedated with Isoflourane gas anesthesia, and the ears treated. If tissue proliferations appeared to be potential tumors, biopsies or resection of the tissue masses were performed. The majority of foxes whose ear tissues were biopsied were diagnosed as suffering from ceruminous gland carcinoma, a highly aggressive but normally rare cancerous tumor. Four captive foxes were also diagnosed with this form of cancer. The prevalence of this tumor type in this population of foxes is considered to be highly unusual, and investigation of the disease and potential risk factors within the population is ongoing.

Monitoring of Released Captive-bred Pups and Adults 

Between 1 April 2004 and 30 April 2005 we monitored a total of 71 radio-collared foxes to estimate survival rates, determine the cause of mortalities, and to map use areas. As of 30 April 2005, 27 foxes were being monitored: 12 adults and 8 pups released in late 2004 and 7 captive-born pups from 2003. During the same period we successfully received signals on the 71 monitored foxes a total of 1567 times. In addition, we obtained 800 locations on the 71 monitored foxes during the same period. Since January 2001 we have radio monitored a total of 79 foxes for survival. Sixty-eight (86%) of these foxes were still alive during the reporting period.

This high survival rate was expected because the Santa Catalina subspecies lacks predators and these foxes were released into low [fox] density areas, minimizing competition with resident foxes.

During our effort in June 2004 to determine the reproductive status of radio collared foxes, we successfully located and observed 22 foxes (13 females, 9 males) during walk-ins. Of the 13 females observed, we feel confident that 8 had offspring; two females were observed with pups and six others exhibited aggressive behaviors when approached. No males were observed with pups.

 Canine Distemper Virus Vaccination

Since the last reporting period (through December 2003), 145 wild or captive foxes have been vaccinated. These include 76 foxes on the EAST END (34 males, 42 females), and 69 foxes on the WEST END (34 males, 35 females). Since the vaccination program began in 2000 we have administered CDV vaccine inoculations to 274 individual foxes when captured.  

Captive Breeding Program

Island-wide trapping results in 2004 indicated that both subpopulations on Santa Catalina Island had either reached or where approaching the recovery goal set by Kohlmann et al. (2003, 2005) of at least 150 individuals in each subpopulation. Based on the trapping results, a decision was made to close the captive breeding facility and release all captives to the wild. All captive adults (with exceptions noted below) and all 2004 pups were released from the facility in late 2004.  

In 2004, six female foxes in the Captive Breeding Facility produced 12 pups, of which 8 survived, and 1 escaped and its survival status is unknown. As of 31 May 2005, there were 4 foxes in captivity, all adults. Two of these foxes were not released in the fall of 2004 due to serious health problems: metastatic ear cancer in one case, and ear cancer and severe arthritis in the other. Two adult males who were released in the fall of 2004 from the captive facility are in captivity for medical care that was necessary due to injury or illness observed in the wild by the monitoring biologists. It is expected that both will be released in June of 2005.  

Mortalities 

Between 1 August 2004 and 30 April 2005, 5 mortalities were confirmed by carcass recovery. Four of the foxes were adults that were born in the wild, brought into the captive breeding facility, and then released back to the wild in late 2004. Three of the four died from vehicular trauma (roadkill) soon after their release to the wild, but the cause of death of the fourth was undetermined due to poor carcass condition. The remaining fox was a wild-born (in 2004) pup that was not radio collared, the cause of death of which is pending the results of a necropsy.

PROPOSED RECOVERY ACTIVITIES 

We propose the following activities to aid in the recovery of island foxes on Santa Catalina Island: