U. FLORIDA (US) — Sharks know what they want and how to get it, swimming to a target in a direct path from as far as four miles away and reaching specific resource areas as far as 30 miles away.
“There’s been several studies that have shown that marine predators, like sharks, penguins, turtles, and tunas, move using particular types of random walks, but there’s going to be times when these animals don’t move randomly,” says Yannis Papastamatiou, marine biologist at the University of Florida.
“This study shows that at times sharks are able to orient to specific features, and in the case of tiger sharks, the distance over which they’re performing those directed walks is likely larger than the distance of the immediate range of their sensory systems.”
“Directed walk” describes when a shark is moving toward a known goal rather than randomly swimming.
The research is reported in the Journal of Animal Ecology.
Researchers tracked data from acoustic transmitters on nine tiger sharks off the south shore of Oahu, Hawaii in 1999, nine blacktip reef sharks in the lagoons of Palmyra Atoll in the Central Pacific Ocean in 2009, and 15 thresher sharks off the southern California coast in 2010.
The animals were followed for at least seven hours and the statistical analysis determined whether the sharks were moving randomly or toward a known goal.
While tiger sharks have acute senses of sight, hearing and smell, their home range covers hundreds of square miles, including resource spots outside their sensory range. As bounce divers, they also almost continuously swim between the surface and about 250 to 330 feet below.
“At times these tiger sharks were swimming across a deep channel, open ocean, often at night,” Papastamatiou says. “So the question is, ‘What are they orienting to in such a seemingly featureless environment?’ It really just highlights how impressive their navigation can be.”
Adult thresher sharks could orient at greater distances than juveniles, most likely because of their advanced development. Blacktip reef sharks only traveled randomly, which has to do with their small home range compared to larger areas covered by thresher and tiger sharks.
Sharks’ “mental map” may have to do with their ability to sense magnetic fields.
“Probably the most interesting sense and still the most misunderstood is magnetic reception,” Papastamatiou says.
“There is an increasing amount of evidence that lots of, if not all animals, can to a certain degree detect magnetic fields. That is something that could potentially be used over very large distances because there are gradients in the earth’s magnetic field and they could use those as landmarks—so even swimming through open ocean, which seems featureless to us, may not be featureless to sharks if they could detect these magnetic fields.”
The research would potentially be useful for obtaining accurate population dispersal models for the sharks so that movement patterns can be predicted after changes caused by fishing or the relocation of prey.
“This study is important because it uses quantitative methods to try to understand the underlying ecological reasons for animal movement,” says Kevin Weng, a marine biologist at the University of Hawaii at Manoa.
“Studies such as this one are stepping stones to achieving predictive skill for animal movement, and better understanding of navigation, population dynamics and ecology.”
Researchers from the University of California San Diego, California State University Long Beach, and the University of Rhode Island contributed to the study.
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