To Study Rare Sharks, Scientists Are Heading to Fish Markets

Science
جمعه 21 دی 1397 ساعت 1:27
813
Smith sonian mag
Most people try to avoid encounters with unknown sharks, but last year, David Ebert was on a mission to find a potentially new species he’d only seen in a picture. The photo was taken in 2017 by a colleague in a small village on the east coast of Sri Lanka.
Ebert, a shark biologist and director of the Pacific Shark Research Center at Moss Landing Marine Laboratories in California, could rightly be called a shark sleuth. He is one of the foremost authorities in the world for finding and identifying new species of sharks, rays and chimaeras, or ghost sharks. The photo from Sri Lanka, however, seemed to Ebert to contain a species unlike any other genus of shark, and he was eager to try to find a specimen of the shark to examine.
Ebert traveled to the village of Mutur in March 2018, where the picture was taken, and approached fishing boats as they pulled into various points up and down the beach. The fishermen sell deep sea sharks to a liver oil processing plant in the area. Ebert showed the photo around and was told that one fisherman had caught a pair of the mysterious sharks the day before, but had thrown them back into the sea, as this particular species doesn’t have as oily a liver as other deep water species.
“This is an example of the types of ‘lost sharks’ that I look for, species that no one is paying any attention to,” Ebert says in an email.
The shark sleuth thought he had narrowly missed his chance. The ocean is a big place, and the chances are fairly slim of catching a specific species of shark that has never been characterized by scientists and has an unknown habitat range. The odds become even less likely when searching for a species that likes to spend its time in deep waters.
“Unfortunately, it’s only through these things being caught that you become aware of them,” Ebert says.
An eastern pygmy dwarf false catshark ( Planonasus indicus ) collected by David Ebert last March in Sri Lanka. (Marsha Englebrecht)
But fortunately Ebert had some help in his search. The next day, he had an entire market full of fishermen keeping a close watch to see what turned up in their nets. Sure enough, when the fishermen brought their catch in around midday, they had a two-foot specimen of what would be named the eastern pygmy dwarf false catshark, ( Planonasus indicus), one of only two species in a relatively new genus, found in water about 2,300 feet deep.
“Needless to see I was pretty happy, doing a couple cartwheels on the beach that day,” Ebert says. He went on to find an additional five to ten new species in Sri Lanka as part of a biodiversity survey that he is still conducting on sharks, rays and chimaeras of the Indian Ocean.
Compared to marine biologists, scientists on land have significantly more tools to discover new species, track population numbers, and generally gain an understanding of how ecosystems operate and change over time. These landlubberly tools include satellite images, analysis of hair snags, camera traps, the study of scat, and the ability, in some cases, to follow individual animals and document their behavior. The oceans present many additional challenges, but the watery places of the world also hold a wealth of secrets for scientists who know how to look for them.
While the work can be a little gruesome, combing through the bycatch of fish markets like the one in Mutur is one of the best ways for marine biologists to track obscure species that spend most of their time in perpetual darkness, largely unknown and unseen by humans. Surveying fish markets is a cost effective way for scientists to study what types of sharks are in a given area without ever having to get their feet wet, especially in regions like the Indian Ocean where knowledge of the ecology is relatively sparse.
Shark researchers like Ebert, who first started digging up new shark, ray and chimaera species in “scrap shark piles” in a fish market in northern Taiwan in 1988, use these markets to find new species and track population changes. Other researchers have found species that were known but hidden from scientists for years, like the Ganges river shark found in a market near Mumbai after a decade-long absence.
“A fleet of fishermen is always more efficient at finding sharks,” says Julia Spaet , a postdoctoral shark researcher at Cambridge University. She adds that this is particularly true where shark numbers may be dropping in an area.
As part of an effort to study populations of sharks, rays and chimaeras in the Red Sea , which are in dire straits in many situations, Spaet conducted surveys in fish markets around Jeddah in Saudi Arabia, measuring specimens, documenting species, counting populations and taking tissue samples. To survey the day’s catch, she would head to the fish markets well before dawn. The sharks were often dumped right onto the ground between trucks, and without cooling facilities, temperatures could reach nearly 120 degrees Fahrenheit. “It’s still dark, you’re wading through blood and engine oil and have this terrible smell,” Spaet says.
Researchers searching for specific species at fish landings often need to sift through much of the day's catch. (Julia Spaet)
An even greater challenge for Spaet was that women don’t traditionally enter fish markets in that part of the world, let alone a blonde German foreigner. The locals didn’t know how to react at first, but after a while they began to open up, telling her critical information about where they found certain species and how things have changed over time in terms of abundance and distribution.chimaeras
Spaet says speaking with the fishermen is as critical as documenting the sharks themselves, especially because the fishing communities work with ancestral knowledge acquired over decades. She found a specimen of pigeye shark that was previously unknown to occur in the area, and it was only through talking to fishermen that she determined quite a few of them are brought up in the nets—it wasn’t just a lost individual.
Ebert says that building a relationship with fishermen is just as important as visiting fish markets to see what turns up. Fishermen still recognize him whenever he turns up in the Daxi market in Taiwan, and some will occasionally send him photos of odd things that turn up in their nets. Since his initial success, Ebert has gone on to name 42 new species of shark, ray and chimaera, and he has roughly as many specimens on hand which he hasn’t gotten around to naming yet . Many of these animals aren’t the massive, charismatic shark species you may imagine, but small blackish gray sharks about a foot long, often in the lanternshark genus.
Hollie Booth, a sharks and rays advisor for the Wildlife Conservation Society, says that building relationships with local fishing villages is critical to the conservation work they do. She monitors shark fishing in Southeast Asia, though much of her work is spent in the markets of Indonesia, which has one of the world’s biggest shark fisheries.
Most of these sharks are bycatch that are snagged unintentionally while pursuing other fish, but the sharks are kept because the fins can be valuable to foreign markets in China, Hong Kong and Singapore. The meat and other parts of the sharks can often be sold locally for food, as well.
One exception to this rule is in Tanjung Luar on the island of Lombok, a famous shark fishing village due to the number of large, pelagic sharks brought in, like hammerheads and silky sharks. Booth says that the beach is pretty dirty here and the smell of the place is rank. But when colleagues make faces due to the stench or the grisly view of locals hacking up sharks with machetes, it makes it more difficult to gain fishermen’s help in monitoring the ecological realities out at sea.
Booth works with a huge number of Indonesian scientists who watch local shark markets, collecting data on species, catch numbers and fishing practices. “We probably have what’s Indonesia best fishing data set,” Booth says.
The researchers provide this data to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). They also share their findings with the Indonesian government, which lacks the resources to keep tabs on the vast fishing industry in the country, as part of an ongoing collaborative effort to develop the nation’s first fisheries management plan.
“It’s a huge issue because it’s almost certainly unsustainable,” Booth says, but adds that it isn’t always easy to stop or regulate shark fishing because the practice can be an important source of income for many poor coastal communities.
A hammerhead and other species of shark on a cart a the fish landing in Jeddah, Saudi Arabia. (Julia Spaet)
Rima Jabado , founder and lead scientist at Gulf Elasmo Project , a United Arabic Emirates-based nonprofit organization focused on advancing research, education and conservation of sharks, rays and chimaeras, says that the monitoring of shark markets is also important for fisheries management.
In addition to the Ganges river shark that had not been seen for a decade, Jabado has been involved with work that identified the first sand tiger shark in UAE waters in over 15 years. Her work at fish landing sites also led to the rediscovery of the smoothtooth blacktip shark after more than 100 years. She says that while tracking sharks at markets has limitations—researchers can’t learn much about migratory behavior this way, or how sharks interact with different habitats—the practice can help define the range, and in some cases the existence, of certain shark species.
Long-term monitoring can also reveal the effects of fishing itself. Ebert says that sometimes, changing species at the markets can reflect changing trends in fishing techniques. In some markets he's seen a shift to focus on deep sea fishing, as many of the coastal fishing stocks have been exhausted due to a lack of regulation.
Jabado points out that it’s important to balance data from landing sites with research on actual living sharks in the wild whenever possible. But the markets still provide an invaluable resource for researchers.
“You would need thousands of staff members to go out every day and use different survey methods in the ocean in hundreds of different locations just to cover the area that fishing usually covers,” Spaet says. “And you need to do this over many centuries, basically, to get the same information that these fishermen have. It’s just not possible to do that as a researcher.”
لینک اصل محتوا در Smith sonian mag
برچسب ها