Our presence in the water, migration patterns, and "chumming" help to explain multiple close encounters between humans and sharks
Reports of great white shark encounters with humans have been abundant this summer, with a few harrowing incidents of sharks circling tourist and fishing boats yielding dramatic images. These events suggest the toothy predators are becoming more brazen but experts believe several, more innocent, factors are at work.
One of the most unusual incidents happened last month. Field specialist Dorien Schroder of Oceans Research, a marine organization based in South Africa, was working in Mossel Bay with six crewmembers. They were documenting the dorsal fins of sharks, as part of an identification program, when a 10-foot-long great white shark suddenly landed on their vessel.
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"Next thing I know I hear a splash, and see a white shark breach out of the water from the side of the boat hovering, literally, over the crewmember who was chumming (with fish oils) on the boat's portside," Schroder recalled.
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Schroder and colleagues managed to pull the crewmember to safety as the 1,102-pound shark thrashed over fuel and bait storage containers, working its way into the boat and cutting fuel lines in the process. Schroder radioed for help. The shark and all of the people on board survived the incident.
Cassie Heil, an Oceans Research spokesperson, told Discovery News, "The great white shark involved in the boat incident would have had to breach 3 meters (nearly 10 feet) out of the water to land on the boat in the way it did. The shark wound up half in and half out of the boat, but panicked and went further into the vessel."
Enrico Gennari, director of oceans for the South African company, suspects that one shark may have wound up on top of another.
"A white shark's most vulnerable area is its stomach because under the dermis and muscle layer, the vital organs are exposed," explained Heil. "Therefore, swimming above another shark, which may be focusing its attention upwards looking for prey, leaves the shark above it in a very vulnerable position causing it to leave the area quickly sometimes by breaching."
George Burgess is coordinator of museum operations for the Florida Museum of Natural History and is director of the Florida Program for Shark Research and the International Shark Attack File.
"Animals land on boats with some regularity," Burgess told Discovery News. "When a great white shark jumps, it can cover some distance. When coming up with great speed, it's not going to worry where it lands."
He was reminded of leopard stingrays that land on boats in Florida, sometimes with deadly consequences. A few years ago, a 75-pound stingray leapt out of the Atlantic Ocean at Vaca Key and slammed into a woman, killing her in the process. Burgess himself has seen billfish "bounce off the side of boats" he's been in.
Great white sharks, however, are more often spotted circling boats. For example, a few days ago, one of the apex predators circled a charter boat off the Fraser Coast in Australia for over 30 minutes. It later consumed a large snapper that was being reeled in. The boat's operator, Mark Bargenquast, told the Fraser Coast Chronicle, "He came up then swam around and around us for about half an hour, eyeballing us each time he went past."
Bargenquast added, "He showed no fear, no fear at all."
Shark experts suspect at least four factors are driving these close encounters. First, as Juliet Eilperin, author of the new book Demon Fish: Travels Through the Hidden World of Sharks (Pantheon, 2011) points out, "Sharks aren't coming after us; we're coming to them." Our population continues to grow, even as the shark population declines, so there are more chances of us encountering marine predators.
Second, the summer months always increase participation in boating, recreational water sports and other outdoor activities, putting more people at possible risk. Third, Heil mentioned that great white shark migration patterns take the sharks down the U.S. East Coast during the summer, putting them closer to populated areas.
Finally, and of most concern, Burgess said some tour operators, such as in South Africa, are repeatedly using fish oils or other bait to attract great white sharks. Like humans lined up at a fast food joint, Burgess said sharks congregate "expecting something to put in their mouth."
Certain great white sharks may therefore learn to associate humans with food.
"We could be changing the behavior of these animals and affecting abundances," he said. "That 'eco-friendly dive' to see sharks should, in some cases, be looked at as manipulated."
Image: Ocean's Research.