Advice to Swimmers, Surfers, Kayakers & Divers Concerning Sharks in California Waters

by John E. McCosker, PhD


white shark
White shark patrolling in coastal waters. Photo by Al Giddings.

The danger of shark attack in California waters is miniscule, however should one have that experience it can be a very serious and most unforgettable event. Only 99 unprovoked attacks by sharks (all or nearly all have involved the white shark, Carcharodon carcharias), resulting in 9 fatalities, have occurred in California history. An average of 1.8 attacks/year have occurred in California during the last decade, which is much less than the numerous drownings, bee stings, and lightning strikes that cause fatalities each year.

 

At the California Academy of Sciences, my predecessors, colleagues, students and I have studied white shark behavior in order to better predict the risk to humans. Research accomplished and published by our scientists and others at the Point Reyes Bird Observatory, the University of California at Davis, and elsewhere have significantly increased our knowledge of White shark biology and thereby reduced the risk of attacks on humans as well as demonstrated the important role that sharks play within marine systems.

 

The following is a summary of some of our discoveries:

  • The white shark is the only species in California that presents a significant danger to humans.
  • White sharks live worldwide in cool, coastal waters. In the eastern Pacific, they live from Baja California, Mexico, to the Gulf of Alaska, and appear to be most abundant in California at the Channel Islands off southern California and locations north of Point Conception, California.
  • Adult white sharks feed primarily upon pinnipeds (seals and sea lions), and typically stalk their prey from behind and beneath before attacking -- in most cases, neither pinnipeds nor people see the shark before it bites them. The initial attack is so rapid and so forceful (adult white sharks weigh as much as 1-3 tons) that the victim is often lifted from the water, then released, after which the shark typically waits for the victim to bleed to death before attempting to consume it.
  • White shark attacks upon humans typically occur nearshore in water 10-30 feet deep.
  • The majority of attacks occur at the surface, placing swimmers, surfers, kayakers, and scuba divers (when at the surface) at greatest risk. The appearance of a surfer on a short surfboard, for example, might easily be mistaken by the shark for a basking sea lion (see photograph below).
  • White shark attacks are not random (see map below). The Farallon Islands, Año Nuevo Island (San Mateo County), and Tomales Point and Bird Rock (Marin County) are particularly dangerous locations and should be avoided.
  • White shark attacks have occurred during every month, but are most common in September and August.
  • White shark attacks have occurred between 7:00 (AM) and 6:00 (PM).
  • White sharks can see color, however they do not appear to discriminate in that they usually look skyward before an attack and only observe the surface silhouette of the victim.
  • One should never enter California waters alone in that the "buddy system" has saved the majority of attack victims.
  • Biologists now understand the importance of white sharks in coastal ecosystems through their role as top level predators within food webs. They are protected in California and elsewhere in the world and, like many other species of sharks, are endangered through overfishing and habitat destruction.

 

To learn more about sharks visit your local library, the web The International Shark Attack File (ISAF), and natural history museums and aquariums.

 

The following publications are useful for further information concerning white shark biology and attack behavior:

Ellis, R. and J. E. McCosker. 1991. Great White Shark. HarperCollins and Stanford University Press, New York. 270 pp.

McCosker, J. E. 1981. Great White Shark. Science 81, 2(6): 42-51.

McCosker, J. E. 1985. White shark attack behavior: observations of and speculations about predator and prey strategies. Memoirs of the Southern California Academy of Sciences, 9: 123-135.

McCosker, J. E. and R. N. Lea. 1996. White shark attacks in the eastern Pacific Ocean: an update and analysis. Pp. 419-434 In Great white sharks: The biology of Carcharodon carcharias. Academic Press, ed. by A. P. Klimley and D. G. Ainley. 517 pp.

McCosker, J. E. and R. N. Lea. 2006. White shark attacks upon humans in California and Oregon, 1993-2003. Proceedings of the California Academy of Sciences, 57(17): 479-501.

Tricas, T. C. and J. E. McCosker. 1984. Predatory behavior of the white shark (Carcharodon carcharias), with notes on its biology. Proceedings of the California Academy of Sciences, 43(14): 221-238.

 

I wish to thank Dr. Robert Lea of the California Department of Fish and Game and the Honorable Willie Brown, former Mayor of San Francisco, for advice and suggestions.

Surfer from the shark's point of view. Photo by Al Giddings.
Surfer from the shark's point of view. Photo by Al Giddings.

Locations of confirmed unprovoked attacks by white sharks in the eastern Pacific, 1926-2003. From McCosker and Lea, 1996.
Locations of confirmed unprovoked attacks by white sharks in the eastern Pacific, 1926-2003. From McCosker and Lea, 2006.