Today's Sharks: Smart, Tagged, and in Short Supply [Slide Show]
Research on sharks, and knowledge about them, is still just gaining speed as marine biologists race to learn about the cartilaginous predators before they are fished out of existence
WIRED WATERS The $168 million Ocean Tracking Network (OTN), headquartered at Dalhousie University in Nova Scotia, is "the next big thing" in shark tracking, Hueter says. The OTN combines archival and acoustic tags with a network of undersea receivers to create an "Internet of the ocean" that can collect data transmissions from passing great white sharks near Australia and Greenland as well as sharks in the Canadian Arctic and a dozen other pelagic regions all over the world. Shown here: Nick Jarvis of the Washington Department of Fish and Wildlife uses SCUBA to replace a receiver on a shallow water mooring.
Stéphane Kirchhoff, OTN Headquarters
LOOKING DOWN ON SHARKS Tags that can transmit data via satellite are the tool of choice for current shark field research. "Pop-up archival tags" (PATs) collect continuous information on depth, pressure and time, then "pop" off the shark up to the surface, where they transmit the archived data in bulk. "Smart position or temperature" (SPOT) tags transmit real-time data whenever the shark's tagged fin surfaces. This combined information gives shark researchers unprecedented detail into the fishes' behavior.
"Twenty-five years ago, we'd stick a tag on the shark and just hope that it would get recaptured or sighted somewhere else so we could infer what happened between point A and point B," says Robert Hueter, director of the Center for Shark Research at Mote Marine Laboratory in Florida, who has been tagging whale sharks since 2004. "But with satellite tracking tags, we get data from everything in between point A and point B. We can reconstruct locations, migratory patterns, even specific behaviors. It's made the sea transparent." Shown here: A great white shark with two tags: an acoustic one ( front) which transmits whenever the shark swims within 250 meteres of a listening station; and a pop-up tag ( rear) which releases itself from the shark at a pre-programmed time and transmits archived data via satellite once it reaches the surface. Scot Anderson/TOPP
SHARK DNA "It's been a slow process for genetics to find a place in shark research," says Jennifer Schmidt of the University of Illinois at Chicago, who studies population genetics of whale sharks (a whale shark is shown here) in collaboration with the nonprofit Shark Research Institute. Now it has become a powerful tool that allows researchers to gain new information about migratory and reproductive habits. After sampling the DNA of many different groups of feeding whale sharks from around the world, Schmidt found that they were all very genetically similar. "What this tells us is that the animals are migrating and interbreeding over long distances—hundreds or thousands of miles," she says.* And in a new study currently in press, Schmidt and her collaborators analyzed the paternity of 30 whale shark embryos that had been taken from a pregnant female caught in 1995. All were in different stages of development, yet all had the same father, which may mean, according to Schmidt, that female whale sharks can store sperm from one mate for months or years at a time and fertilize eggs at will during their long solitary travels in the open ocean.
* Correction (8/13/10): This sentence was edited after posting to correct a typo. It originally stated the distance as "hundreds of thousands" of miles. Flickr, jon hanson
SHARKS' AT THE ECOLOGICAL APEX As "apex predators" of their ocean habitats, sharks play a vital role in maintaining the health of coral reefs, estuaries and coastal fisheries. When sharks are overfished, "trophic (nutritional) cascades" can result as their absence ripples through the food web in ways that are only beginning to be observed and understood. In one particularly catastrophic example in 2004 collapsing populations of mako and hammerhead sharks (a school of hammerheads is shown here) off the southeastern Atlantic coast of the U.S. allowed swelling numbers of their natural prey, the cownose ray, to decimate the bay scallop fishery that had flourished there for over a century. "You can't have a healthy ecosystem when the top predators have been removed," Griffin says.
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FROM CONSTERNATION TO CONSERVATION "Because they are out of sight and much harder to study than land animals, shark conservation has only really gotten going within the last 10 years," says Elizabeth Griffin, a marine scientist at Oceana. As awareness of sharks' endangerment has grown, so have prohibitions on finning, which is the greatest current threat to sharks. Many regional fishery management organizations, however, allow loopholes in their regulations which hinder conservation efforts. "They have finning bans, but they don't include catch limits—so you can't fin sharks, but you can catch as many as you want," Griffin says. Whereas instituting a complete ban on all shark fishing is unlikely, fostering sustainability is ambitious enough. "There should be management for sharks just like we have for tuna," Griffin says, "and that just doesn't happen on an international level."
CUTTING-EDGE CAMS "High-tech cameras are a shark filmmaker's bread and butter, but in many cases they are equally important to the shark researcher," says Shark Week producer Jeff Kurr, who has been collaborating with marine biologists on documentaries for 20 years. "We've used new technology like night vision, thermal imaging and high-speed HD to capture shark behavior in amazing detail. We used a towed underwater camera to learn how great white sharks stalk seals from below, and our footage may reveal how seals escape these ambush attacks roughly 50 percent of the time due to the pressure wave of water that precedes the shark." Shown here: a great white shark breaching in South Africa.
Chris Fallows/Apex Images/Discovery Channel
SHARK COGNITION Samuel Gruber from the University of Miami and other researchers have been combating the image of sharks as "mindless death fish from hell," as he puts it, for decades. "Very little research [on shark cognitive behavior] has been done since the 1970s," Gruber says, "but these things go in cycles, and there is a lot of renewed interest in individual variation in sharks regarding their capacities for learning, remembering and behaving." Gruber cites sharks' high brain-to–body weight ratio as a clue that they might be more intelligent than we give them credit for. "There's a clear line between the higher and lower vertebrates in terms of brain-to–body weight," Gruber explains. "Birds and mammals have a higher ratio; fish, amphibians and reptiles are lower. But sharks land above the line associated with these lower vertebrates. They've been independently evolving for half a billion years, and they have brains that are comparable to [those of] mammals in some ways." His research showed that lemon sharks were able to remember a visual discrimination task for at least a year without retraining, and Gruber says they also showed spatial preferences akin to "handedness" in mammals.
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