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SOWLS AL, DEGANGE AR, NELSON JW, LESTER GS. com (PJC); Carter Biological Consulting, 1015 1980. Catalog of California seabird colonies. Hampshire Road, Victoria, British Columbia V8S Washington, DC: US Fish and Wildlife Service, 4S8 Canada (HRC); US Fish and Wildlife Service, Biological Services Program, FWS/OBS-78/78. San Francisco Bay National Wildlife Refuge Com- 253 p. plex, PO Box 524, Newark, California 94560 USA TAKEKAWA JE, CARTER HR, HARVEY TE. 1990. De- cline of the common murre in central California, (GJM, MWP); Present Address (MWP): US Fish 1980–1986. In: SG Sealy, editor. Auks at sea. Stud- and Wildlife Service, Red Rock Lakes National ies in Avian Biology 14:149–163. Wildlife Refuge, 27820 South Centennial Road, Lima, Montana 59739 USA. Submitted 9 March Department of Wildlife, Humboldt State University, 2005, accepted 27 July 2005. Corresponding Editor: Arcata, California 95521 USA; phil࿞capitolo@hotmail. CJ Ralph.

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SUSPECTED SURPLUS KILLING OF HARBOR SEAL PUPS (PHOCA VITULINA) BY KILLER WHALES (ORCINUS ORCA)

JOSEPH KGAYDOS,STEPHEN RAVERTY,ROBIN WBAIRD, AND RICHARD WOSBORNE

Key words: harbor seal, killer whale, Orci- novel mortality pattern in harbor seals (Phoca nus orca, Phoca vitulina, surplus killing, preda- vitulina) that strongly suggests 1 or more in- tion, disease, San Juan Islands, Washington dividuals from 1 of these ecotypes killed seal pups for reasons other than consumption. Within the inland waters of Washington State As part of an ongoing disease-screening pro- and southern British Columbia Province, 3 dis- ject, complete postmortem examinations were tinct ecotypes of killer whales (Orcinus orca) oc- performed on dead marine mammals in suit- cur. The better known ‘‘resident’’ and ‘‘tran- able condition from San Juan County, Washing- sient’’ populations each display unique genetic ton (48.6ЊN, 123.0ЊW). Necropsies were orient- (Hoelzel and others 2002), dietary (Baird and ed toward determining the cause of morbidity Dill 1995; Ford and others 1998), behavioral or mortality and to survey for specific patho- (Baird 2000), vocal (Ford 1990) and morpholog- gens. Routinely complete examinations were ical differences (Baird and Stacey 1988). The performed and gross observations were record- resident pods, also known as the ‘‘southern res- ed. Tissue samples were preserved in 10% neu- ident’’ population, eat primarily fish and occur tral buffered formalin, processed, and evalu- in large stable groups (Bigg and others 1990). ated microscopically. Kidney and liver were Transients feed primarily on other marine screened for heavy metals, and other ancillary mammals and occur in smaller and less stable tests such as aerobic bacterial culture, poly- groups (Baird and Dill 1995, 1996; Baird and merase chain reaction, and attempted virus iso- Whitehead 2000; Baird 2000). The 3rd popula- lation were performed as indicated. tion, which is seen occasionally in the area, is Since 1977, The Whale Museum (Friday Har- called the ‘‘offshore’’ ecotype (Wiles 2004). bor, Washington) has maintained a database of These killer whales are believed to be primarily public and scientific sightings of killer whales fish eaters (Hoelzel and others 2002) that are and other cetaceans in Washington and south- smaller in size than other ectotypes and genet- ern British Columbia inland waters. In 1981, ically distinct from both residents and tran- the marine mammal sighting network was ex- sients, although more closely related to the res- panded to include stranding data for San Juan ident killer whales. We recently identified a County. These databases provided stranding WINTER 2005 GENERAL NOTES 151

TABLE 1. Characteristics and gross lesions of harbor seal pup carcasses found in San Juan County, WA, September and November, 2002. Seal pups were killed but were largely uneaten.

Lacerated Puncture Date found Gender Decapitation flippers wounds Whale ecotypes sighted 3 Sep male partial unilateral none residents, transients, offshores 13 Sep female complete no yes residents, transients, offshores 1Nov female partial bilateral yes residents, transients 10 Nov female complete bilateral yes residents, transients 10 Nov male partial no yes residents, transients

data as well as information on the presence of (Table 1). Aside from the nutritional status of 1 killer whale ecotypes within the region. All animal, gross and microscopic examination, sighting and stranding data are recorded by trace mineral analysis of liver and kidney, and species, date, location, and by quadrants of ap- aerobic bacterial culture of multiple organs did proximately 2 km2 (Heimlich-Boran 1986, 1988; not reveal underlying disease, suggesting that Felleman and others 1991; Olson 1998). The ob- seals were healthy at the time of predation. servers contributing to the killer whale data- Serrated lacerations consistent with shark base include the untrained general public, long bites were not seen on any of the carcasses. time shoreline residents, trained marine natu- Margins of the partially to completely truncat- ralists, and marine mammalogists with exten- ed torsos or heads were sharply delineated and sive photo-identification experience. Observa- variably hemorrhagic. Based on wound mea- tions submitted by the untrained general pub- surements and comparison with archived killer lic are only included in the database when they whale skulls (The Whale Museum, unpubl. are verified through an interview or have a con- data), the dimensions and spacing of the semi- vincing description of the species that can be elliptical pattern of puncture wounds seen on 4 corroborated with at least 1 other sighting. of the 5 carcasses were consistent with the Stranding data are collected by a group of mandibular span and dentition of killer trained volunteers. whales. Sighting records confirm the presence Between 3 September and 10 November 2002, of resident (all 3 pods; J, K. and L) and transient 13 harbor seal pups were found dead on beach- killer whales in the region during both periods es in San Juan County during 2 distinct time and the presence of offshores only during the spans: from September 3 to September 13 and 1st time period (Table 1). Consequently, we hy- November 1 to November 10 (Table 1). Five car- pothesize that 1 or more killer whales were casses (3 females and 2 males) had similar likely responsible for all 5 killings. gross lesions indicating predation without con- Between 1982 and 2002, 281 dead harbor sumption (Table 1). Specifically, carcasses had seals were reported in San Juan County (The various combinations of the following gross le- Whale Museum, unpubl. data), with no injuries sions: partial or complete decapitation, lacera- of this type found. We hypothesize these events tions to the hind flippers, and 1- to 3-cm-di- represent a novel pattern of killing without in- ameter, semi-elliptical abrasions and occasion- tent to eat and that 1 or more transient killer al punctures on the thorax and/or abdomen whales were most likely responsible. In this re- (Fig. 1 and Table 1). In 1 animal, abdominal vis- gion transient killer whales are the main pred- cera herniated from an abdominal puncture, ator of harbor seals and seals are the whales’ and 2 additional animals had large amounts of most important prey (Baird and Dill 1996). Ad- blood in their chest cavities (hemothorax). The ditionally, the pattern of these seals being acute hemorrhage noted in several animals killed in 2 short and distinct periods matches suggested that trauma was antemortem and the travel patterns of transient whales that of- the proximate cause of death. Four carcasses ten make relatively brief appearances in the in- were in good nutritional condition as evi- land waters of Washington and British Colum- denced by adequate subcutaneous and visceral bia and then are not seen for sometimes years adipose stores and only the seal pup found on at a time (Baird and Dill 1995). If 1 or more 1 November, 2002 was moderately emaciated transients were responsible for these mortality 152 NORTHWESTERN NATURALIST 86(3)

FIGURE 1. Photograph of a harbor seal pup (2002- SJ036) with lesions suggestive of killer whale predation without consumption. Note the missing head, arrows pointing to the puncture wounds arranged in a semi- elliptical pattern, and the lacerated hind flippers. Photo courtesy of KC Balcomb III, Center for Whale Re- search, Friday Harbor, Washington.

events, this marks a distinct pattern variation whales in the region. The killing of these har- from prior observations. Previous observations bor seal pups appears to be for reasons other by Baird and Dill (1996) detected only 4 in- than consumption. Evidence of bite wounds to stances when Ͼ1% of a pinneped carcass was the head and flippers of all animals and to the apparently abandoned by transient killer thorax and abdomen of 4 of the 5 animals in- whales. In the 5 cases we identified, the entire dicates that whales had ample opportunity to carcasses, excluding all or part of the head, consume these seals, but did not do so. Simi- were abandoned. The cases observed by Baird larly, Stacey and others (1990) observed tran- and Dill (1996) were found in August and Sep- sients killing or wounding seabirds in the same tember, the period when harbor seal pups in study area without consuming them. the area are being weaned, are foraging on Because they were sighted during only 1 of their own, and are most vulnerable to preda- the 2 time periods in which these seal carcasses tion. Food intake rates for transients are more were found and because they are believed to be than double during this period compared to fish eaters (Hoelzel and others 2002), it is un- the remainder of the year, and prey handling likely that offshore ecotype killer whales were times are also approximately double during responsible for these killings. Although resi- this period, presumably because the whales are dent killer whales feed primarily on fish (Ford more than meeting their energetic needs and and others 1998), they have been reported to extended prey handling is serving some other harass, but not kill harbor seals and porpoises purpose (Baird and Dill 1995). The 5 killings (Phocoena phocoena and Phocoenoides dalli)(Jef- from 2002 described here occurred in Septem- ferson and others 1991; Ford and others 1998; ber and November, just after the time when Richard Osborne, The Whale Museum, Friday food intake rates are highest for transient killer Harbor, WA, pers. obs.). Also, all 3 resident WINTER 2005 GENERAL NOTES 153 pods were sighted in the region during both of San Juan County Marine Mammal Stranding Net- the time periods in which these seal carcasses work, including E McConnell, P Moran-Hodge, D were found. Consequently a potentially valid Schermerhorn, C Soos, R Tallmon, and others who hypothesis for these 5 cases is killing by 1 or helped collect carcasses and conduct necropsies. A Kent provided technical support with image prepa- more resident killer whales. ‘‘Aberrant’’ behav- ration. T Jefferson, P Olesiuk, and G Wiles provided ior by a single resident whale could explain all comments that improved the quality of this manu- of these moralities. If true or if an offshore kill- script. This work was performed with the help of er whale was responsible for these mortalities, funding from the John H Prescott Marine Mammal then there is concern this behavior could result Rescue Assistance Grant, The Whale Museum, and in the transmission of pathogens from harbor the SeaDoc Society, a marine ecosystem health pro- seals to these killer whale ecotypes. While tran- gram of the UC Davis Wildlife Health Center. sient whales are probably regularly exposed to such pathogens through routine handling and LITERATURE CITED consumption of harbor seals, this would rep- BAIRD RW, 2000. The killer whale-foraging speciali- resent a novel route for disease transmission in zations and group hunting. In: Mann J, Connor R, resident killer whales. Disease is an important Tyack P, Whitehead H, editors. Cetacean socie- ecological force and exposure to potential nov- ties: field studies in behavior. Chicago, IL: Uni- versity of Chicago Press. p 125–153. el pathogens such as a morbillivirus or herpes BAIRD RW, 2001. Status of killer whales, Orcinus orca, virus could impact the health status of the in Canada. Canadian Field-Naturalist 115:676– southern resident killer whale population 701. (Gaydos and others 2004), which is considered BAIRD RW, DILL LM. 1995. Occurrence and behavior endangered in Canada (Baird 2001) and Wash- of transient killer whales: seasonal and pod-spe- ington (Wiles 2004). cific variability, foraging behavior and prey han- Regardless of the ecotype responsible it is dling. Canadian Journal of Zoology 73:1300– apparent that these harbor seals were killed for 1311. a purpose other than consumption. These BAIRD RW, DILL LM. 1996. Ecological and social de- deaths could represent examples of surplus terminants of group size in transient killer whales. Behavioral Ecology 7:408–416. killing, which is defined as predators killing BAIRD RW, STACEY PJ. 1988. Variation in saddle patch prey in numbers exceeding that which can be pigmentation in populations of killer whales (Or- consumed at 1 time (Wobeser 2000). It is char- cinus orca) from British Columbia, Alaska, and acterized by an absence of, or a low level of, uti- Washington State. Canadian Journal of Zoology lization of the carcass by the predator (Short 66:2582–2585. and others 2002). This behavior has been de- BAIRD RW, WHITEHEAD H. 2000. Social organization scribed in red foxes (Vulpes vulpes) (Short and of mammal-eating killer whales: group stability others 2002), spotted hyenas (Crocuta crocuta) and dispersal patterns. Canadian Journal of Zo- (Kruuk 1972), mink (Mustela vison) (Wobeser ology 78:2096–2105. 2000), and other mammalian predators (Short BIGG MA, OLESIUK PF, ELLIS GM, FORD JKB, BAL- COMB KC. 1990. Social organization and geneal- and others 2002) and has been previously pro- ogy of resident killer whales (Orcinus orca)inthe posed in transient killer whales (Stacey and coastal waters of British Columbia and Washing- others 1990; Jefferson and others 1991). The ton State. Report of the International Whaling mortality pattern involving harbor seal pups in Commission Special Issue No. 12:383–405. 2002 resembles surplus killing. Alternate ex- FELLEMAN FL, HEIMLICH-BORAN JR, OSBORNE RW. planations are that such predation could rep- 1991. Feeding ecology of the killer whale, (Orci- resent a form of play behavior or result from nus orca) in the Pacific Northwest. In: Pryor KW, adults training younger whales to hunt. This Norris KS, editors. Dolphin societies: discoveries mortality pattern has not been observed in har- and puzzles. Berkeley, CA: University of Califor- bor seal carcasses found since 2002. This is not nia Press. p 113–147. FORD JKB. 1990.Vocal traditions among resident kill- likely to be due to a reduced abundance of har- er whales (Orcinus orca) in coastal waters of Brit- bor seal pups as seal abundance has not varied ish Columbia. Canadian Journal of Zoology 69: greatly since 2002. Continued surveillance 1454–1483. should reveal whether this pattern of predation FORD JKB, ELLIS GM, BARRETT-LENNARD LG, MOR- resumes in the future or was a single event. TON AB, PALM RS, BALCOMB KC. 1998. Dietary Acknowledgments.—We thank the volunteers of the specialization in two sympatric populations of 154 NORTHWESTERN NATURALIST 86(3)

killer whales (Orcinus orca) in coastal British Co- ton and British Columbia [thesis]. Bellingham, lumbia and adjacent waters. Canadian Journal of WA: Western Washington University. 90 p. Zoology 76:1456–1471. SHORT J, KINNEAR JE, ROBLEY A. 2002. Surplus killing GAYDOS JK, BALCOMB KC, OSBORNE RW, DIERAUF L. by introduced predators in Australia—evidence 2004. Evaluating potential infectious disease for ineffective anti-predator adaptations in native threats for southern resident killer whales (Orci- prey species? Biological Conservation 103: 283– nus orca): a model for endangered species. Biolog- 301. ical Conservation 117:253–262. STACEY PJ, BAIRD RW, HUBBARD-MORTON AB. 1990. HEIMLICH-BORAN JR. 1986. Fishery correlations with Transient killer whale (Orcinus orca) harassment, the occurrence of killer whales in greater Puget predation, and ‘‘surplus killing’’ of marine birds Sound. In: Kirkevold BC, Lockard JS, editors. Be- in British Columbia. Pacific Seabird Group Bul- havioral biology of killer whales, New York, NY: letin 17:38. AR Liss. p 113–131. WILES GJ. 2004. Washington State status report for HEIMLICH-BORAN JR. 1988. Behavioral ecology of the killer whale. Olympia, WA: Washington De- killer whales (Orcinus orca) in the Pacific North- partment of Fish and Wildlife. 106 p. west. Canadian Journal of Zoology 66:565–578. WOBESER G. 2000. Suspected surplus killing of HOELZEL AR, NATAOLI A, DAHLHEIM ME, OLAVAR- grebes by mink. Blue Jay 58:137–139. RIA C, BAIRD RW, BLACK NA. 2002. Low world- wide genetic diversity in the killer whale (Orcinus The SeaDoc Society, UC Davis Wildlife Health Cen- orca): implications for demographic history. Pro- ter-Orcas Island Office, 1016 Deer Harbor Road, ceedings of the Royal Society, London 269:1467– Eastsound, WA 98245 USA, [email protected] 1473. (JKG); British Columbia Ministry of Agriculture JEFFERSON TA, STACEY PJ, BAIRD RW. 1991. A review and Food, Animal Health Center, 1767 Angus of killer whale interactions with other marine Campbell Road, Abbotsford, BC V3G2M3 Canada mammals: predation to co-existence. Mammal (SR); Cascadia Research Collective, 218 ½ W 4th Review 21:151–180. Avenue, Olympia, WA 98501 USA (RWB); The KRUUK H. 1972. Surplus killing by carnivores. Jour- nal of Zoology 166: 233–244. Whale Museum, 62 First Street North, Friday Har- OLSON JM. 1998. Temporal and spatial distribution bor, WA 98250 USA (RWO). Submitted 17 Decem- patterns of sightings of southern community and ber 2004, accepted 16 June 2005. Corresponding transient orcas in the inland waters of Washing- Editor: JC Lewis.

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