Is It Safe to Go Back in the Water?

In the waters off Fletcher Cove Park, a popular Southern California beach area in the town of Solana Beach just north of San Diego, David Martin, 66, a retired veterinarian and triathlete, was killed by a shark as he swam with a group of nine others. Martin died from blood loss as a result of deep, violent shark bites to both legs.

In the frenzied aftermath of the April 25 attack, San Diego County officials posted an unprecedented warning for the public to stay out of the water along 13 miles of coastline; U.S. Coast Guard and San Diego County sheriff's helicopters patrolled 17 miles of beach for two days looking for more sharks so they could warn beachgoers. No other sharks were spotted.

During its investigation of the attack, the San Diego County medical examiner's office sought the assistance of shark attack expert Ralph Collier, founder of the Shark Research Committee and author of "Shark Attacks of the Twentieth Century: From the Pacific Coast of North America." Collier, who pioneered the technique of measuring tooth impressions to determine shark species and size following an attack, concluded during the autopsy that Martin was killed by a 15-to-16-foot great white.

Collier talked to NEWSWEEK's Jamie Reno about the rarity of shark attacks off the Pacific Coast, this latest attack, and whether it's really safe to go back into Southern California waters. Excerpts:

Is there any way to determine why this shark attacked at this particular time and place?
Ralph Collier: There are three behaviors when it comes to sharks biting objects: predatory, investigative and displacement. In a predatory attack a shark bites because it is feeding. With investigation, the shark isn't quite sure what the object is and will circle it, use all its sensory systems to figure it out and then take a sample bite, hold it for a few seconds and then release it and swim off. With displacement the shark perceives the object as a potential threat and chases it away. In this particular case I was able to determine during my examination that there were at least four bites and as many as six. The initial bite obviously informed the shark that this was not a seal. However, for whatever reason it continued to attack. It is not entirely clear which of these three things motivated the shark in this case. Dr. Martin was swimming with others and was wearing a wet suit. It was a violent attack, but there was no tissue loss. The most important thing now is interviewing witnesses. Their observations will be very important as far as attempting to understand the shark's motivation, but we may never know.

How were you able to determine the size of the shark?
When we started examining the lacerations, we recovered two small tooth fragments that I determined were from lower teeth in the shark's jaw. We measured the distances between the individual tooth punctures. Taking those measurements and looking at not only measurements taken previously from other sharks of known length but also using my formula, we were able to come up with size of the shark. In this case the tooth dimensions we obtained confirm that it was a great white not less than 15 feet and no more than 16 feet.