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INTRODUCED ARCTIC FOX ERADICATION EFFORT AT KASATOCHI ISLAND, ALEUTIAN ISLANDS, ALASKA,

SUMMER ---. 1984

by FREDRIC G. DEINES

and BOB WILLGING

Key Words: Arctic Fox. Introduced predator control Seabird management Aleutian Islands Western Andreanof Island Group Kasatochi Island

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Restrictions: Internal Document - Not for Publication

U. S. FISH AND WILDLIFE SERVICE ALEUTIAN ISLANDS UNIT

ALASKA MARITIME NATIONAL WILDLIFE REFUGE P. O. BOX 5251 NAS ADAK

FPO SEATTLE, WA 98791-0009 (Adak, Alaska)

January 20, 1985

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ARLIS Alaska Resources

Library & Information Services Anchorage, Alaska

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. DEPAR'IXEm dF l'RE L'ITERIOR - Refereed publication

Non-refereed publication u.s. FISH AND W'Il.DLIFE SERVICE - Unpublished presenta~ion ~0 I I

conference or workshop I

.t • .'C::C'lJl'IVE suMMARY OF PUBLICATION OR REPORT x Internal administ=a t ive re?or: · ~

Other (see remarks)

! I'!U DATE Introduced Arctic Fox ETadication Ef f ort At January 20, 1985 I

Kasatochi Island, Aleutian Islands, Alaska, I.D . NO. I Summer -- 1984

A.U11iOR(S) Fredric G. Deines and CITATION I

Bob Wil l ging

OBJECTIVE Eradicate as many introduced arc tic f o x as t h e limited available time would permit from Kasatochi Island to benefi t migratory seabir~s.

" ME'l'BOD OF S'l'UDY When field work was completed early on another island, an attempt'Tfox · r r

eradication on the small significant seabird is land of Kasatochi was scheduled. The program was imple mented 14 to 16 June and 14 t o 15 August, 1984. A combination of calls~ firearms, traps, snares, and denning c ar t r idges were used.

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MA..I.N FINDINGS . A t otal of 59 arctic fox we r e k illed on Kasatochi during the 1984 summer f ield season. Of this number, 55 were a d ults (18 male, 29 female and 8 unknown) • Three female fox examined for placental scars s howed an average of eight scars. The stomach con-tents o f three fo x visually examined showed the remains of one, three and six auklets. The most successful eradication method was c al ling and shooting, accounting for 81 percent of the fo x taken followed bv trappinq with 19%

CONCLUSIONS That the majority of the fox were eradicated from Kasatochi in 1984. The 'few I

remaining fox will be taken the next field season during a follow-up operation.

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MANAG~ n!PLICAT!ONS Total eradication of the introduced arctic fox will allow the mi-gratory bird resources of this significant bird i sland to return to its pre-fox population . Free of fox ·, the island will also provide a migrational stopover spot ann potential nesting habitat for the endangered Aleutian Canada goos e .

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.. ADDITIONAL REMARKS Fox eradication should continue both for migratory birds (seabirds pri-

marily ) and the endangered Aleutian Canada goose . Aut horization to use chemical toxicants for this purpose should be sought. . .. - - .

U?DArES OR ~uPERsEDES I.D • NO. I ... T"lll T I Cl I

:PROGRAM ..l"1·'-l.~·~ I .. ·· - . . Alaska Resources

FOR COPI.;:S OF PUBLICATION OR REFORT CONTACT . L.lU.la.ty ex mrormat:ton ~ervtces Anchorage, Alaska . I

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LIST OF EXPEDITION MEMBERS June Crew:

Chris Ambroz - Biotechnician, AIU-AMNWR, Adak, AK Jon Andrew - Biologist, Realty Division, Anchorage, AK Fred Deines·- Refuge Biologist, AIU-AMNWR, Adak, AK Scott Hatch - Biologist, Research Division, Anchorage, AK Rich Johnson - Volunteer Biologist, AIU-AMNWR, Adak, AK Bob Willging - Volunteer Biologist, AIU-AMNWR, Adak, AK

August Crew: .,,. ___ _ Chris Ambroz - Biotechnician, AIU-AMNWR, Adak, AK ~'fi ·

Tony Degange - Biologist, Research Division, Anchorage, AK Fred Deines - Refuge Biologist, AIU-AMNWR, Adak, AK Van. Klett - Assistant Refuge Manager, AIU-AMNWR, Adak, 'AK Mark Koepsel - Biotechnician, AIU-AMNWR, Adak, AK Bob Willging - Volunteer Biologist, AIU-AMNWR, Adak, AK Fred Zeillemaker -Refuge Manager, AIU-AMNWR, Adak, AK

ACKNOWLEDGEMENTS

Thanks are extended to the captain and crew of the charter vessel "Vestfjord" for providing excellent support during the two seg­ments of the Kasatochi fox eradication program. Special appre­ciation must also be given to our volunteer biologists, biologi­cal technicians and to personnel from the Anchorage Research and Realty Divisions for their enthusiastic and professional support of this project. This is especially noteworthy because of the change in the schedule which allowed this work to be accom­plished. Thanks are extended to Van Klett and Fred Zeillemaker for editing this report.

INTRODUCTION

Kasatochi Island is 287 hectares (717 acres) in size, is located in the central Aleutians 19.2 kilometers (12 miles) off the west­ern tip of Atka Island and about 88 km (53 mi) east of Adak. The island is roughly circular with a diameter of about 2.4 km (1.4 mi). A crater with a summit of 316 meters (1,038 feet) descends inward to a .8 km (.5 mi) wide caldera lake near sea level.

The outer slopes of the island are steep and sheer cliffs inter­spersed with rock slides dominate the north side. Narrow, fine sand beaches are found on the south, east and west sides. All of the slopes are heavily vegetated. The vegetation of Kasatochi is described by Bailey and Trapp (1983).

It is well documented that arctic fox can greatly reduce and limit nesting bird populations in the Aleutian Islands. Murie (1936) ·st~ted that "there is no question that foxes are living on the birds' of Kasatochi Island". Murie recommended that fox iarming be terminated on Kasatochi· and the island reserved for its bird life. Auklets (hctb~g sp.) presently nest on Kasatochi in numbers exceeding 30,000 birds (Bailey and Trapp 1983).

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Additional auklet colony areas were observed thfs year so this number is .suspected to be considerably low, perhaps as much as half. Murie (1936) reported large numbers of nesting tufted puffins (fL~teLgYl~ giLLb~t~) • Puffins are currently greatly reduced in number (Sowls, Hatch and Lensink 1978).

Bald eagles (H~li~eetyg leYgQgepb~lyg) and peregrine falcons (f~lgQ peLe9LinY~) are common at Kasatochi. A breeding colony of 1,450 Steller's sea lions (~YID~tQP.i~~ iYb~t~) was reported by Bailey and Trapp (1~6l). Over 1,000 sea lions were observed during the eradication effort. Numerous sea otters (~nby.Q.L-'J'i'';;·;c" lYt.r.i~) utilize the extensive offshore kelp beds.

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Because of the significant past and present wildlife values, \·,· small size, close proximity to Adak and general workability, a high priority was assigned to Kasatochi for fox eradication when other scheduled tasks allowed. Unfortunately the opportunity did not occur until 1984 because of fox elimination efforts elsewhere to benefit the endangered Aleutian Canada goose (~Lant~ g~n~9en= ~ig l~ygQp~.rei~) • When goose work on Chagulak Island was com­pleted five days ahead of schedule in 1984, it was decided to' seize the opportunity to initiate fox eradication on Kasatochi. This marked the first effort to primarily benefit migratory birds through fox eradication. All previous fox elimination efforts have been primarily for the Aleutian Canada goose. The goal was to eliminate as many fox as possible from Kasatochi in the limit­ed time available, hopefully even rendering the island fox free.

METHODS

Using the 125 foot charter vessel "Vestjford" as a base, up to four crews of two to three personnel each worked various parts of the island killing fox. The crews were systematically placed around the island using 13 foot inflatable boats. fox removal efforts covered two periods: 16 to 19 June and 14 to 15 August 1984. The first effort was the longest and most intensive, producing the greatest number of fox.

Fox were killed using a combination of firearms, leghold traps and denning cartridges (Table 1). The island was subdivided into thirds with a major trapping effort conducted in each segment. Traps were set along traveled beaches and upland trails. Set types used have been described.previously by Arnbroz, Deines and Dragoo (1983).

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Table 1. Equipment Used for 1984 Fox Eradication Effort, Kasatochi Island

1 Inflatable Zodiak boat 2 25 HP Johnson outboard 1 9 HP Evinrude outboard 6 Mustang flotation work suits . \ 6 Survival suits

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Table 1 continued.

50 Victor #2 double coil spring leg hold traps 50 Iron trap stakes

2 Over/under 20 gauge .223 combination rifle/shotgun 1 Ithaca 12 gauge shotgun

25 Denning car.u.idges Commercial fox bait and/or commercially canned tuna

Each fox team cat: r ied a firearm and whenever a fox was obserV4:!d within range it was shot. If a fox was observed at a distance an attempt was made to stalk closer and/or to call it into rang~ by using a variety of whistles and barks. The majority of the shooting took place within the auklet colonies since the fox were concentrated in these areas preying on nesting seabirds.

Although slightly later in the foxes' reproductive sea~on than desired, denning ~artridges were still used whenever an active den was found. Prior to using the cartridges, all entrances except one were plugged using tundra. The cartridge was placed deep in the den, using the unplugged entrance, and lit. Then the den entrance was closed. The burning cartridge produced CO gas which killed any fox present in the den. Plugging all the den entrances within the boulder strewn auklet colonies proved to be challenging and in some cases impossible.

Gross analysis of the stomach contents was made of three of the fox which were shot. This was not possible in the other cases because of bullet damage to the carcass and in some instances having the carcass fall out of reach within the rock crevices. The fox caught in traps were also initially checked and all had empty stomachs. It was decided that overnight digestion while in the traps probably removed all identifying evidence, so no fur­ther attempts at stomach contents analysis were made on trapped fox.

Placental scars were checked on three of the female fox. This was not done on all females again because of damage to the car­cass caused by shooting and varying technical skills among crew members.

RESULTS AND DISCUSSION

A total of 59 fox were destroyed on Kasatochi during the two efforts in the 1984 summer field season (Table 2). Of this tot:al 48 were shot and 11 were trapped. The sex ratio of the animals killed was: 18 males, 29 females and 12 unknown.

As shown in Table 2, the early eradication effort accounted for the majority of the fox taken, 88 percent. The low number (12 percent) taken in August is in its~lf an indication of the suc­cess of the early June work. Thirteen of the 27 animals killed in June were found to be lactating. Eradication of these animals

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Table 2. Information From Fox Eradicated on Kasatochi Island in June and August During the 1984 Field Season

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IJYD~-~L~Qjg~tiQD-~!!QLt ___ l_bY9Y§t_~L~Qjg~1iQD_~ffQLt_l_1Qt~l-~L~Qig~tiQD_~ffQLt Means of l _____ s~~-gf_fg~-----1 ~-~---B~~-gf_fQ~-----1 l ____ s~~-Qf_fQ~ ____ I ~~~gigatiQDLl_lMal~l_f~IDal~l_Unk~L211gt~ll_Mal~-lf~IDal~-1Dnk~_l1Qtal_l_Mal~lf~m~l~_lUnk~l_1Qtal

I I I I I I I I I I I I Shot I 15 I 21 I 5 I 41 I o I 2 ·1 5 I 7 I 15 I 23 I 10 I 48

I I I I I I I I I I I I Trapped I 3 I 6 I 2 I 11 I o I o I o I o I 3 I 6 I 2 I 11

I I I I I I I I I I I I Total I 18 I 27 I 1 I 52 I o I 2 I 5 I 7 I 18 I 29 I 12 I 59

/1 Denning cartridges are not listed as a means of·eradication. They were used on Kasatochi and undoubtably accounted for an unknown number of additional fox. The majority of these fox were probably adult females and pups.

/2 Unknown sex is shown for animals whose carcasses were damaged by shooting to the extent -that the sex could not be determined and for those which fell into rock crevices among the auklet co~ony after being shot and-were lost.

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undoubtably impacte4_feproductidn. Only adults were killed dur­ing the June effort. Of the seven fox taken in August, four were pups. Three o{ these were killed near a den site in an auklet colony along with an adult female. The low number of pups taken· in August shows the impact that the June eradication effort had on reproduction."

Shooting the fox was the most successful means of eradication, accounting for 81 percent while trapping accounted for 19 per­cent. Denning cartridges were used and.undoubtedly were effe.c-­tive especially during the June work but the exact·numbers o:f\:fox killed is unknown. Denning cartridges were not used in some\dens found in the auklet colony as the numerous holes and entrances in the talus rendered them ineffective.

Ninety trap nights were expended in June yielding one fox per 8.18. trap night. Nineteen device nights (14 trap and five snares) yeilded no fox in August. A total of approximately 216 man hours of effort produced an average of one fox taken per 4.15 man hours in June as compared to one fox per 18 hours (126 hours total) expended in August. Averaging the two together shows 5.8 hours of effort was required for each fox killed on Kasatochi in 1984. No fox were trapped during the August effort and the trails showed some signs of revegetation. This, too, is an indicator of the success of the June eradication work.

The majority of the arctic fox killed were taken in and around the major auklet colonies on the island. This is to be expected since the fox prey heavily on the auklets during their summer nesting season. A gross stomach contents analysis was conducted on three of the fox shot. The remains of an entire crested auklet was found in one, the bills of three auklets in another and the bills of six auklets in another. The impact of such predation on the auklet colonies of Kasatochi is significant. If you estimate 50 adult fox on the island and take an average of three auklets per day during the approximately 90 day breeding season of the bi~ds, a total of 13,500 birds a season could be lost to this introduced predator. This does not take into ac-

. count the caching of some additional birds which is the charac­teristic of arctic fox.

Placental scars of three females examined showed seven, eight and nine scars respectively, an average of eight scars per female, indicating a high reproductive rate. This number compares favor­ably with the average number of 7.4 placental scars per female found during the Rat Island fox eradication effort (Hanson, Goos, and Deines, 1984).

All of the fox taken were blue phase except for one white phase female. All appeared to be in good condition except an old female taken in August which was blind in one eye and had no tail. Th~ fox were not wary of man and in most cases easy to qall and shoot. This is what you would expect on a remote Aleu­tian island, but much unlike what was found on Amukta Island. On

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Amukta, the fox were wary of man from the beginning of the. eradi­cation effort.

One last interesting comparison between Kasatochi and other fox eradication islands, such as Amukta and Rat islands, is the number of fox killed per hectare or acre. Kasatochi is a small island (287 ha or 717 ac) with a large number of birds (estimated 30,000 crested and least auklets) and had 59 fox killed on it in 1984 or about one fox per 5 ha (12 ac). Amukta has few birds and little fox habitat, is 4,970 ha (12,425 ac) in size and had.~9 fox on it or about one fox per every 102 ha ( 254 ac) • Rat :11sland also has few birds but does have good scavenging beaches for fox, is 2,752 ha (6,881 ac) and had 163 fox or aboQt one fox perd7 ha (42 ac). Small Kasatochi Island supported the highest fox densi­ty (1 fox/12 acres) because of the large auklet colonies on the island.

It should be noted that although migratory birds (auklets spe­cies) will be the primary benefactor from fox eradication, Aleu­tian Canada geese will also benefit. One goose was observed flying over the west side of the island and goose droppings were also found on the vegetated slopes.

RECOMMENDATIONS

Although the results. of the 1984 eradication effort on Kasatochi Island were extremely successful and promising, it is doubtful that all the fox on the island/were killed. To insure complete eradication of the introduced arctic fox from this significant bird island and Qther migratory bird islands in general, the following recommendations are made:

1. Continue Kasatochi eradication effort during the 1985 field season with a follow-up in 1986.

2. Start all eradication efforts earlier in the season, pref~r­ably in May, but no later than June to eliminate reproduction.

3. Document the bird resources of the island for pre- and post­fox eradication comparisons.

4. Eradicate fox on o.ther islands where migratory birds would be the primary benefactor.

5. Seek authorization to use chemical tci~icants for fox eradica-tion to benefit migratory birds. ·

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LITERATURE CITED

Ambroz, C. A., F. G. Deines and D. Dragoo. 1983. Initial Arctic Fox Eradication Program on Amukta Island, Aleutian Islands, Alaska, 1983. U. s. Fish and Wildlife Service, unpublished report. 32 pp.

Bailey E. P. and J. L. Trapp. 1983. A Reconnaissance of Breed­ing Marine Birds and Mammals in the East-Central Aleutian Islands - Kasatochi to the Island of Four Mountains - Summer of 1982, With Notes on Other Species. u. s. Fish and Wild­life Service, unpublished draft report. 70 pp.

Hanson, K., M. Goos and F. G. Deines. 1984. Introduced Arctic Fox Eradication at Rat Island, Aleutian Islands, Alaska, Summer 1984. u. s. Fish and Wildlife Service, unpublished report. 10 pp.

Murie, o. J. 1959. Fauna of the Aleutian Islands and Alaska Peni~sula, North American Fauna 61:1-364.

Sowls, A. L., s. A. Hatch and c. J. Lensink. 1978. Catalog of Alaskan Seabird Colonies. u. s. Fish and Wildlife Service. FWS/OBS-78/78. 32 pp .

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