Sharks and sailors don't mix. Which is why, in the early 1960s, the U.S. Navy began sifting through data on shark attacks--to keep the two apart.

Back then, computers were big, relatively slow-witted machines. Programmers walked around with punch cards in their pockets and muttered to themselves in FORTRAN and ITRAN.

Consequently, it took several years for the Data Processing Department of the Naval Aerospace Medical Center in Pensacola, Florida, to log and review the pertinent details of all known encounters between people and sharks.

Now known as the International Shark Attack File, the Navy database by 1968 contained information on 1,652 separate encounters, some dating back to the 1500s. Here are a few of the file's highlights:

Case 1004: In 1590, while attempting to repair a ship's rudder in the Cochin River of India, an English sailor was attacked by an unidentified species of shark. Eyewitnesses reported, "the shark did bite off his hand and arme above the elbow, and also a peece of his buttocks."

Case 417: In about 1955, the body of a drowning victim was being towed ashore along the Marin Coast of California when a huge shark seized the body, causing the rowboat to come to a complete stop. A second shark was seen later, but no further attacks were made.

Case 869: In 1961, off the coast of New South Wales, Australia, a deckhand was bitten on the neck by a four-foot-long dog shark. Eyewitness accounts vary: Some say the deckhand was clowning with the shark aboard ship; others say he fell overboard and was immediately bitten. To release the victim, rescue workers were required to cut off the shark's head and open its jaws with a pair of pliers.

Case 1569: In 1967, while diving for abalone near Bird Rock in Bodega Bay, California, a scuba diver was seized by a shark that latched on to the left side of his body from the shoulder to below the waist. It took 200 stitches to close the multiple puncture wounds.

Lots of data, slim on trends
The best of the shark stories are summarized in Shark Attack, a 1974 book (now out-of-print) by H. David Baldridge, one of the original leaders of the International Shark Attack File project. While it makes for good reading, it does little to build confidence for those of us who enjoy spending time in the sea.

Furthermore, considering all the time and money the Navy spent gathering data, Baldridge's analysis of the attacks--in particular, his failure to report many meaningful trends among the 1,652 cases--is exceptionally weak.

For instance, Baldridge notes that 62 percent of all shark attacks in the Navy's file occurred in less than five feet of water. That's statistically significant, and might inspire some of us to spend the summer swimming in deeper channels, farther from shore. But Baldridge also points out that the vast majority of waders and bathers are found in shallow water. So, naturally, that's where most of the shark encounters would take place.

Baldridge also reports that the vast majority of attacks took place in the mid-afternoon. Does that mean we should limit our swim times to the morning or evening hours? Afraid not--later research has revealed these to be the most dangerous times off the day. Baldridge's midday statistic merely reflects the time when the majority of divers, beachgoers, and boaters are in the water.

While they run short on useful tips for regular folks seeking to avoid shark attacks, some of Baldridge's findings are outright amusing. He dismisses a San Francisco newspaper reporter's assertion that two-piece bikini bathing suits are especially attractive to marauding sharks, but does concur that sharks are drawn to what other researchers have dubbed Yum-Yum Yellow—the day-glo hue of most life rafts and emergency gear. (Note: More recent analysis of the International Shark Attack File contradicts this rather Edward Gorey-like assertion, since nearly a fourth of the divers attacked by great white sharks were wearing drab blue and black suits.)

Playing the numbers game
So what advice or guidance can we give people who spend their summer vacations on the shores of shark-inhabited seas?

Since Baldrige's days, the International Shark Attack File has nearly doubled in size. Now managed by George Burgess, a professor at the University of Florida in Gainesville, the file contains updates on more than 3,300 cases. No longer housed in a mainframe computer or managed by punch-card-wielding nerds, the file's data is accessible on the Florida Museum of Natural History's Web site, along with a series of summary pages, helpful charts, and graphs.

One of the most interesting pages of the site weighs the relative risk of being chomped by a shark with that of being bitten by dogs, cats, hamsters, horses, squirrels, and, yes, humans. In all cases, these other incidents far outweigh shark attacks. But of course, they get considerably less attention from the media.

In fact, more people die each year from falling coconuts than from shark bites, says Burgess, who likes to play the numbers game at least as much as Baldridge did.

Since 1876, there have been 254 confirmed unprovoked attacks on humans by great white sharks, 67 of which were fatal, Burgess says. Over the same time period, there have been 83 tiger shark attacks, resulting in 29 fatalities. Bull sharks have attacked 69 times with 17 fatalities.

That's not a lot, especially compared to the numbers of fatalities among people driving to and from the beach, adds Burgess. "We must realize whenever we enter the ocean, we're not in a bathtub or wading pool--it's never 100 percent safe."

As with any recreational activity, a participant must acknowledge that certain risks are part of the sport: Jogging might include shin splints, camping brings ticks and mosquitoes, tennis can result in sprained ankles, and so on, Burgess offers. Beach recreation has its inherent risks as well, and shark attack is simply one of many that must be considered before entering the water. Most people agree, however, that the extremely slim chance of even encountering a shark--much less being bitten--does not weigh heavily in their decision-making.

Good advice, seldom heeded
Ironically, what we do know about shark encounters and how to avoid them is often ignored.

It's common knowledge that you should leave the water if you see a shark or note the increased activity of diving birds--a clue that schools of shark-attracting fish are nearby, says Burgess. Still, several of the more recent cases in the International Shark Attack File include testimony by surfers who chose to catch the next wave or two even after seeing a shark's distinctive dorsal fin.

Similarly, we now know that the most dangerous times to be in the water are at sunrise or sunset, when many predatory fish species, including sharks, are most active. However, all four of last year's shark attacks on bathers in Florida took place at dawn or near dusk.

OK, so we're slow learners. But we've come a long way since 1890, when New York millionaire Hermann Oelrichs offered a reward of $500 for anyone who could prove that in temperate waters even one man, woman or child, while alive, had actually ever been attacked by a shark. (A macho outdoorsman like his contemporary, Teddy Roosevelt, Oelrichs frequently swam in shark-infested seas without adverse effects.)

Oelrichs's prize remained unclaimed for 25 years, prompting the New York Times to run an editorial titled "Let Us Do Justice to Sharks," which maintained that unlike their southern cousins, sharks in the Northern Hemisphere lacked the craving for human flesh.

A year later, in 1916, the Times was eating its words after a series of vicious shark attacks resulted in four deaths and one serious injury to bathers along the New Jersey coast.

The apparent culprit, an 8 1/2-foot-long great white shark, was eventually captured by fishermen in Raritan Bay, on the central New Jersey shoreline. Found in its stomach were 15 pounds of human flesh and bones--just one more statistic in the International Shark Attack File.

People say that to be a successful fisherman, one must learn to think like a fish. Perhaps to avoid being fish bait, we must start thinking like sharks. It's questionable whether the International Shark Attack File will help anyone do that. Still, it makes for the stuff of great conversations at the poolside lounge of your favorite seaside resort.