That only juvenile northern elephant seals exhibit 

 fresh crater wounds may be explained in several 

 ways. It suggests that this age category is the only 

 one exposed by depth or location to feeding Isistius; 

 or, it may suggest that older age classes are able 

 to avoid attack. Another interesting hypothesis con- 

 cerns the common prey of both Isistius and 

 Mirounga, midwater squid. It has been speculated 

 that the bioluminescent pattern of Isistius might 

 simulate the pattern of a large midwater squid and 

 thereby attract squidophagus predators (Jones 1971) 

 upon which it could prey. It seems unlikely that an 

 Isistius could outswim a Mirounga; attacks by the 

 shark would thus be accomplished either by attract- 

 ing the seal, perhaps for a closer inspection of the 

 shark, or by attacking the seal by stealth and sur- 

 prise. The location of attack scars on the head region 

 of Mirounga would indicate a frontal approach, 

 whereas the scars on the back and flanks might in- 

 dicate that the seal was unaware of the impending 

 attack. Both scenarios are likely. It is also possible 

 that juveniles seals are more readily attracted to the 

 display of Isistius, not having learned yet to 

 distinguish them from squid. Further insight into 

 these hypotheses will be provided as more data con- 

 cerning the spatial and temporal distribution of 

 Isistius are collected. 



Acknowledgments 



We thank Al Giddings of Ocean Images and the 

 National Geographic Society for financing this ex- 

 pedition; Doc White of the Whitewater Enterprises; 

 the crew of the MV Mirage for the logistics, 

 camaraderie, and good food; R. H. Rosenblatt of the 

 Scripps Institution of Oceanography for making 

 available the specimens of Isistius; and an anony- 

 mous reviewer for advice and comments. This pro- 

 gram was supported in part by the National Science 

 Foundation grant BSR-8605000 to B. J. Le Boeuf. 



Literature Cited 



BONNELL, M. L., B. J. Le Boeuf, M. 0. Peirson, D. H. Dett- 



MAN, AND G. D. FARRENS. 



1979. Summary report 1975-1978. Marine Mammal and 



Seabird Surveys of the Southern Cahfornia Bight Area. Vol. 



III. Pinnipeds. Bur. Land Manage., Dep. Inter., Contract 



AA.550-CT7-36, 535 p. 

 Compagno, L. J. V. 



1984. Sharks of the world. An annotated and illustrated 



catalogue of shark species known to date. Part 1. Hexan- 



chiformes to Lamniformes. FAO Fish. Synop. 4(1):1- 



249. 

 CoNDiT, R. AND B. J. Le Boeuf. 



1984. Feeding habits and feeding grounds of the northern 



elephant seal. J. Mammal. 65:281-290. 



Johnson, C. S. 



1978. Sea creatures and the problem of equipment 

 damage. U.S. Naval Inst. Proc, p. 106-107. 

 Jones, E. C. 



1971. Isistius brasiliensis, a squaliod shark, the probable 

 cause of crater wounds on fishes and cetaceans. Fish. Bull., 

 U.S. 69:791-798. 

 Le Boeuf, B. J., and M. L. Bonnell. 



1980. Pinnipeds of the California islands: abundance and 

 distribution. In D. M. Power (editor). The California islands: 

 Proceedings of a Multidisciplinary Symposium, p. 475-493. 

 Santa Barbara Museum of Natural History, Santa Barbara, 

 CA. 

 Le Boeuf, B. J., and K. T. Briggs. 



1977. The cost of living in a seal harem. Mammalia 41: 167- 

 195. 

 Le Boeuf, B. J., and J. Reiter. 



In press. Lifetime reproductive success in northern elephant 

 seals. In T. H. Clutton-Brock (editor). Reproductive Suc- 

 cess. Univ. Chicago Press, Chicago. 

 Le Boeuf, B. J., M. Reidman, and R. S. Keyes. 



1982. White shark predation on pinnipeds in California 

 coastal waters. Fish. Bull., U.S. 80:891-895. 

 Le Boeuf, B. J., D. P. Costa, and A. C. Huntley. 



1985. Diving behavior of northern elephant seals. 6th Bien- 

 nial Conference on Marine Mammals, 22-26 November 1985, 

 Vancouver, British Columbia. 



Le Boeuf, B. J., D. P. Costa. A. C. Huntley, G. L. Kooyman, 

 and R. W. Davis. 



1986. Pattern and depth of dives in northern elephant seals, 

 Mirounga angustirostris. J. Zool. Lond. 208:1-7. 



Mackintosh, N. A., and J. F. G. Wheeler. 



1929. Southern blue and fin whales. Discovery Rep. 

 1:257-540. 

 Tricas, T. C, and J. E. McCosker. 



1984. Predatory behavior of the white shark (Carcharodon 

 carcharias), with notes on its biology. Proc. Calif. Acad. 

 Sci., 43(14):221-238. 

 Van Utrecht, W. L. 



1959. Wounds and scars on the skin of the common porpoise, 

 Phocaena phocaena (L.). Mammalia 23:100-122. 



BuRNEY J. Le Boeuf 



Institute of Marine Sciences and 



Department of Biology, 

 University of California, 

 Santa Cruz. CA 95061^ 



California Academy of Sciences, 



Golden Gate Park, 



San Francisco, CA 9Itll8 



John E. McCosker 

 John Hev^^itt 



392 



