A tagged leopard shark.
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Kyle McBurnie
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Shark 'Highways' Crisscross the World: Photos
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Great whites and other sharks travel on "ocean highways," according to new research that is helping to define the routes. Mapping out the routes is enabling scientists to better understand the behavior of these apex ocean predators and to improve conservation tactics. Ongoing research also shows how busy both the sharks and these highways can be. "The sharks do show repeated travels along the same general paths, which is quite amazing since there are few 'road signs' in the open ocean," Mahmood Shivji, director of Nova Southeastern University's Guy Harvey Research Institute and the Save Our Seas Shark Research Center, told Discovery News. As for how the sharks know where to go, he added, "The main current hypothesis is that they use the earth's magnetic field to navigate, like some birds do." Great whites are among the most well-traveled sharks, swimming for thousands of miles with relative ease. In the winter, they migrate from the California and Baja coasts to a mid-Pacific open water area dubbed "The White Shark Café." Precisely why great sharks do this, however, remains a mystery. Photos: 5 Sharks, Rays Needing Urgent Protection
Neil Hammerschlag
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For the research projects, Shivji and his team are affixing satellite tags to multiple shark species. The tagging itself can be arduous, since the scientists are so close to the toothy predators. "This type of tracking research needs to be long-term to really reveal and understand patterns of shark migrations," he said. "Such long-term studies are difficult and expensive to conduct, in part because working on the ocean and with big animals poses considerable challenges." Great White Shark Explores Film Crew With Its Mouth
George Schellenger, Guy Harvey Ocean Foundation
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Once tagged with a satellite-tracking device, the sharks often need a bit of stimulation to get them back on their particular ocean route. This can be a dangerous hands-on process, as this researcher demonstrates. Sharks, Humans Living So Close; Why Not More Attacks?
George Schellenger, Guy Harvey Ocean Foundation
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Shortfin mako sharks continue to astound researchers, given the duration and miles involved in their migrations. "Our long-term satellite tracking data is showing that individuals can travel over 10,000 miles in a single year, and they also are starting to show indications of round-trip, repeated and predictable migration patterns," Shivji said. Shark GIF of the Day: Mako Shark
George Schellenger, Guy Harvey Ocean Foundation
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Along their highway-like migration routes, sharks seem to primarily stop for three things: food, sex and babies. Here, lemon sharks stop for their babies. Research conducted in Bimini in The Bahamas, spanning almost two decades, shows that female lemon sharks that were born there returned 15 years later to give birth to their own young. Some sharks never seem to forget home sweet home, even if it is a temporary safe-feeling spot before traveling begins again. Sharks With Friends: The Most Social Sharks
Matt Potenski
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Tiger sharks have been in the news lately because Shivji and his colleagues determined that these sharks undergo remarkable, bird-like migrations. The findings were published in the journal Scientific Reports. "The tiger shark migrations are bird-like in the sense that they seem to be following the same general round-trip, repeated migrations from warm over-wintering areas to temperate summer areas," he said. One tiger shark, named Harry Lindo, was tracked traveling more than 27,000 miles, possibly the longest-ever recorded distance traveled by any species of shark. "It is truly remarkable," Guy Harvey, a renowned marine artist, conservationist and fisheries ecologist said. Harvey has been working with Shivji on the shark tagging projects. Brad Wetherbee, another researcher on the team, noted that tiger sharks seem to have their own "café" as well, except they have given it a different name. "We joke that tiger sharks, not being media stars like great white sharks, wouldn't be comfortable in a 'café' and prefer to hang out in their 'truck stop' in the mid-Atlantic," Wetherbee, who is based at the University of Rhode Island, said. Three Deadliest Sharks Named
B. Watts/Guy Harvey Research Institute/NSU
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As they travel, sharks may go solo or with companions. Here, an oceanic whitetrip journeys on its own. This species has been in decline around the world due to overfishing, the researchers said. Oceanic whitetip sharks used to be one of the most common sharks seen close to the water's surface, but that's no longer the case. In terms of its journeys, Shivji said, "The initial data are suggesting that, although they are highly migratory, they don't travel as far out into the open ocean as the shortfin makos and tiger sharks do in the Atlantic -- an unexpected finding." How to Reduce Shark Attacks
George Schellenger, Guy Harvey Ocean Foundation
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This oceanic whitetip shark is definitely not traveling solo. Accompanying it are rainbow runners and pilot fish. The shark serves as a moving bodyguard for the much smaller, weaker fish. Oceanic whitetips, in turn, benefit from the fishes' presence, because pilot fish eat health-threatening parasites, dead skin and other undesirables off of the sharks. This kind of win-win arrangement is called "a mutualistic relationship." Shark Teeth Weapons Reveal Surprises
Lance Jordan, Microwave Telemetry, Inc.
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Sand tiger sharks live very deep in the ocean, unlike more surface dwelling, or "pelagic," tiger sharks, shortfin makos and oceanic whitetips. In fact, sand tiger sharks prefer to stay close to the bottom of ocean floors. "Migrations are seasonal in the western Atlantic, with migrations along the coast into cooler waters in the summer and warmer waters in the winter," Shivji said. Sand Tiger Sharks Are Curious About People
Erik Rebeck
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Caribbean reef sharks also undergo migrations, with females traveling to "nursery" waters northwest of the Brazilian coast. These sharks, dubbed "the silent sea predators," are formidable hunters, but thankfully pose little threat to humans because they tend to avoid interactions with us. In this case, a bait ball containing fish and other edibles was intentionally dropped into the Caribbean reef shark's territory, leading to a feeding frenzy. Shivji said that tracking all migratory sharks poses major challenges, especially because sharks cover so much territory. This further poses conservation challenges, since waters off the coasts of multiple countries are involved, all linking up into the shark highways. "The shark long-term tracking will show where and when they spend the most time during their travels on a predictable basis," Shivji said. "Once we know this, fishery regulation and protection become more tractable since they provide geographic areas to focus management and conservation efforts on." Shark GIF of the Day: Whitetip Reef Shark
Greg Grimes, Wikimedia Commons
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Marine scientists now believe that sharks – just like migrating birds, wildebeest and salmon – are using their noses to find their way home after long trips away.
It’s long been known that sharks have a keen sense of smell to detect prey, but two new experiments are the first to prove that sharks also smell tiny amounts of chemicals in the water as a homing device.
In a paper published today in PLOS One, Andrew Nosal, a post-doctoral researcher at the Scripps Institution of Oceanography and the Birch Aquarium in La Jolla, Calif., found that the leopard sharks who were taken several miles off the San Diego coast were twice as likely to find their way home if they were able to smell.
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Those with their noses blocked – by harmless cotton balls and petroleum jelly – sort of wondered around, according to Nosal.
“What was amazing is that sharks that could smell find found their way back to shore no problem,” Nosal said.
The experiment is fascinating in itself, using 15 leopard sharks that could smell, and 11 with blocked nostrils.
“We kidnapped them from their home, put them in a small holding tank, on the way out in the boat,” he said. “We wanted to make sure the sharks couldn’t retrace their steps. We covered the tank with opaque tarp so couldn’t see sun, we aereated from a scuba tank, so there were no chemical cues. And we hung a strong magnet so no chance they could use geomagnetic cues. Yet upon release they could come straight back.”
Every summer, thousands of leopard sharks congregate in the shallow waters off La Jolla Shores Beach, a popular place for children and families and who can watch the sharks with a mask and fins.
These pregnant female sharks have found a sweet spot of sorts where currents arising from an underwater canyon cancel each other out, giving the sharks a less turbulent, quiet, and slightly warmer spot to incubate their babies.
Nosal has been studying the leopard shark for several years. He says that coastal sharks that migrate, such as the leopard sharks, have larger olfactory bulbs than those who do not. The olfactory bulb is a sense organ in the brain that processes chemical signals through the nose.
“Sharks with coastal migration those tend to have larger olfactory bulbs than expected for their size,” Nosal said. “All these things pointed to smell as a way to navigate and it hadn’t been demonstrated until now.”
So what are they smelling? Nosal said they could be following gradients of plankton or amino acids that make up prey in the water. The sharks’ home area likely smells different than the open ocean several miles out to sea.
We are hypothesizing that these sharks are following chemical gradients,” Nosal said. “These gradients are correlated with coastal productivity, we have upwellings that fuel a lot of growth and that sustains a lot of organisms. There could be chemicals associated with increased productivity.”
Researchers in Florida’s Tampa Bay found similar results in tracking young blacktip sharks.
Jayne M. Gardiner, assistant biology professor at the New College of Florida, published a paper in 2015 in Integrative and Comparative Biology that found sharks with blocked noses also had trouble finding their way back to their home territory.
Gardiner said that more evidence is coming in that smell is just as important as other environmental clues to help sharks migrate from places where they feed to places where they raise theier young.
“We have bits and pieces from various animals, but we don’t have the whole story yet,” Gardiner said. “Most of us are in agreement is that it’s a fairly similar story across different animals.”