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1984. Sampling commercial rockfish landings in California. 

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 Shaw, W., and C. P. Archibald. 



1981. Length and age data of rockfishes collected from B.C. 

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1977. Analysis of age determination methods for yellowtail 

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1981. Retrieval of otoliths and statoliths from gastrointes- 

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 Westrheim, S. J., and W. R. Harling. 



1975. Age-length relationships for 26 scorpaenids in the 

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1980. Size composition, age composition, and growth of chili- 

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W'VXLIE Echeverria, T. 



1986. Sexual dimorphism in four species of rockfish genus 

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Tina Wyllie Echeverria 



Southwest Fisheries Center Tiburon Laboratory 

 National Marine Fisheries Service, NOAA 

 3150 Paradise, Drive, Tiburon. CA 9U920 



CRATER WOUNDS ON 



NORTHERN ELEPHANT SEALS: 



THE COOKIECUTTER SHARK STRIKES AGAIN 



A variety of wounds are observed on northern ele- 

 phant seals, Mirounga angustirostris. We report a 

 new type of wound observed on juveniles, primarily 

 from the Mexican islands west of Baja California and 

 rarely from off California. The form and shape of 

 these wounds, and their similarity to wounds re- 

 ported from other marine mammals, fishes, and 

 squids, suggest that they were caused by a small, 

 squaloid shark of the genus Isistius, commonly 

 known as the cookiecutter or cigar shark. 

 The shape of wounds, their location on the victim's 



body, the time of the year that the wounds are 

 received, and the age of the seal provide a good in- 

 dication of the cause. During the breeding season, 

 for example, suckling seal pups bear bite marks on 

 the snout, head, and rump, these having been in- 

 flicted by adult females (Le Boeuf and Briggs 1977). 

 Weaned pups and adult females bear fresh bite 

 marks of varying severity caused by adult males 

 biting their necks while attempting to mate with 

 them, and breeding-age males inflict a variety of bite 

 wounds on each other during fights to establish 

 dominance (Le Boeuf and Reiter in press). During 

 winter and spring, Mirounga angustirostris of both 

 sexes and all ages exhibit fresh wounds inflicted by 

 white sharks. Car char odon carcharias. The shape 

 and serrated edges of those wounds are easily 

 distinguished from the smooth-edged and halfmoon- 

 shaped wounds caused by boat propellers (Le Boeuf 

 et al. 1982; Tricas and McCosker 1984). 



The wounds that we discovered were round, 

 hollowed-out craters, smooth edged at the margin, 

 about the size of a tennis ball, and unlike any of the 

 wounds described above. The similarity in appear- 

 ance of these wounds to scars inflicted by Isistius 

 upon cetaceans (Van Utrecht 1959) and fishes (Jones 

 1971) implicate the cookiecutter shark as the prob- 

 able cause. The only reported eastern Pacific occur- 

 rence of an Isistius is that of an /. hrasiliensis from 

 off the Galapagos (Compagno 1984). However, we 

 have examined additional eastern Pacific specimens 

 of/, hrasiliensis, including a specimen from off Isla 

 de Guadalupe. 



Background information. Northern elephant seals 

 inhabit traditional island and mainland sites from 

 mid-Baja California, Mexico, to central California. 

 Their range at sea along the Pacific coast is from 

 Isla Cedros, Mexico, to the southern Aleutians. 

 Feeding occurs beyond the continental shelf in deep 

 water (Le Boeuf et al. 1986). It is not known how 

 far from shore they go to feed, but some animals 

 have been seen as far as 3,000 miles away on Mid- 

 way Island in the mid-Pacific (Condit and Le Boeuf 

 1984). Several islands are used regularly throughout 

 the year (Guadalupe, San Benito, Cedros, and Co- 

 ronoados in Mexico and San Miguel, San Nicolas, 

 Ano Nuevo, and the Farallones); the sex and age 

 composition of each colony varies with time of year 

 (Le Boeuf and Bonnell 1980). Late August or early 

 September, when most of the observations reported 

 in this paper were made, is the end of the molt 

 period for adult and subadult males and the begin- 

 ning of the fall haul-out for juveniles, 1-4 years old. 

 Breeding-age males, observed on land at this time, 

 are completing the annual molt, a process that takes 



FISHERY BULLETIN: VOL. 85, NO. 2, 1987. 



387 



