Researchers praise Monterey Bay Aquarium efforts to reveal threats facing sharks
29th March 2004
For many, the word "shark" conjures up a picture of the tooth-filled mouth of the giant from "Jaws". Yet few sharks fit this man-eating model. The great white shark featured in the book and film is just one of nearly 400 species of sharks, with the vast majority more threatened by human activities than the other way around.
In fact, said one leading shark researcher, sharks could go the way of the dinosaurs unless there’s a dramatic change in fishing practices and a concerted effort to protect global shark populations.
"We have to understand, after 400 million years of survival, how close to extinction some of these shark populations really are," said Ransom Myers, a noted fisheries biologist based at Dalhousie University in Halifax, Nova Scotia. "The time to act is now, before they have reached the point of no return. I want there to be real hammerhead sharks when my five-year-old son grows up, not just models like we have today of dinosaurs."
Myers will attend the April 2 opening of "Sharks: Myth and Mystery", a new exhibit at the Monterey Bay Aquarium that features sharks of the world and the way they’re celebrated in human cultures around the globe.
The exhibit will feature nearly two dozen species of sharks and rays including Galapagos sharks, scalloped hammerheads, blacktip and whitetip reef sharks, zebra sharks and African catsharks. With habitat displays ranging from tropical coral reefs to river systems, and Australia to Africa, visitors will have an unprecedented opportunity to view and experience the beauty and diversity of sharks and rays.
The exhibit will also show how sharks are featured in folklore, dance, and artwork from cultures across the globe. From Aboriginal creation myths to the totem carvings of the Haida people in the Pacific Northwest, sharks have captured the imagination and won the respect of people around the world.
For Web visitors, there's also a streaming Web cam that offers an opportunity to see scalloped hammerhead and Galapagos sharks, along with pelagic stingrays.
Despite this far-flung fascination, little is known about the status and behaviour patterns of most sharks and rays. What is known provides both inspiration to learn more about these mysterious animals -- and a warning that many may become extinct in our lifetime if we don’t change current fishing practices.
"By developing this extraordinary exhibit, the Monterey Bay Aquarium is helping to raise one of the most urgent conservation issues of our time," said Myers. "Sharks are in trouble worldwide but their plight is largely out of sight and mind. This exhibit brings these great fish into view."
Sharks evolved over 400 million years ago and have remained relatively unchanged through time. They range in size from the dwarf shark that, at 8 inches (20 centimetres), is the length of a windshield wiper, to the gentle, boat-sized whale shark that can reach 39 feet (12 metres) in length. Sharks inhabit a wide array of habitats, from the tropics to icy polar seas to fresh water lakes, and from the ocean’s surface to 3,300-foot (1,000-metre) depths.
Or at least they used to!
"The data aren’t available to assess all sharks, but wherever we have data we see large, rapid declines," said biologist Julia Baum, also of Dalhousie University and the author of two recent studies on the status of sharks. "Shark diversity is incredible. It’s important for people to see the smaller sharks that are different from the stereotypical ‘man-eating’ image, because the vast majority of sharks are not a threat to humans."
Baum and Myer’s 2003 publication in the international journal "Science" showed that in the past 15 years, many shark populations in the Northwest Atlantic Ocean -- an area stretching from Canada to Brazil -- have declined by over 75 percent. Sharks have been hit hard both by fishing directed at them, and as accidental catch in longline fisheries that target other species.
Scalloped hammerheads, one of the species in "Sharks: Myth and Mystery", suffered the largest declines, with an 89 percent drop in population from 1986 to 2001. Similarly, the researchers’ just-published cover study in the February 2004 issue of "Ecology Letters", indicates that oceanic whitetip sharks -- thought to have been the most common warm-water oceanic shark in the world -- have plummeted to less than one percent of their mid-1950s population numbers in the Gulf of Mexico.
"Researchers in the 1960s suggested that oceanic whitetip sharks were the most common large species on Earth," said Myers. "What we have shown is akin to the herds of buffalo disappearing from the Great Plains -- and no one noticing."
Myers also published a high-profile study in "Nature" last May demonstrating 90 percent declines in populations of the world’s big fishes, including sharks.
Each year approximately 100 million sharks and rays are killed by commercial fishing fleets -- half in fisheries targeting sharks, half as accidental catch in gear intended for other commercial species.
Because sharks grow slowly, mature at a late age and give birth to only a few "pups" following a long gestation period, these top predators are particularly vulnerable to overfishing. They are also targeted for shark finning, still practiced by over 100 countries and in international waters. Because shark fins fetch a high price for traditional medicine and soup, sharks are caught, their fins hacked off, and their sometimes still-living bodies thrown overboard as waste.
While most species in "Sharks: Myth and Mystery" are coastal sharks that may not face longline fisheries, some like the blacktip reef shark have been targeted for finning. For coastal sharks the main threat is targeted fisheries. Some countries use bottom longlines to catch sharks, and in many developing countries they are targeted in traditional fisheries using gillnets -- a significant source of fishing mortality globally for coastal species.
Commercial fishing pressures, coupled with a low reproductive rate compared to that of most other fishes, make sharks among the most vulnerable of large ocean predators. The Monterey Bay Aquarium’s "Seafood Watch" program distributes pocket guides to help consumers, retailers and restaurateurs select seafood from fisheries managed in ways that preserve healthy populations of ocean wildlife -- including sharks.
Through recent advances in electronic tagging technology, more is known about what sharks are doing in the ocean. Stanford University and Monterey Bay Aquarium researcher Barbara Block is spearheading an international collaboration to tag top ocean predators in the Pacific including white sharks, salmon sharks, mako sharks, blue sharks and thresher sharks.
"By better understanding how large predators such as sharks use the ocean, we can better understand how humans can develop sustainable fisheries without as much bycatch," said Block. "Our objective is to garner the knowledge that will lay the foundation for future management."
For example, in a study published in "Nature" in 2002, Block and her colleagues reported that tagged white sharks from the coast of California travel as far as Hawaii and the eastern tropical Pacific, and can dive to almost half a mile below the surface.
Tagging of coastal sharks in Florida found they have internal "storm warning alarms" and head to deeper waters before the arrival of hurricanes -- likely in response to dropping barometric pressures.
Myers is now leading a global effort to assess the state of sharks around the world. He said he hopes that a shift in public perception will help to preserve these mysterious and ancient predators.
"If we don’t change fishing practices and make concerted efforts to help them, these incredible fish will go the way of the dinosaurs," he said.