Tailing Sharks in the Revillagigedo Archipelago
January 30, 2017
Shark Tagging and Conservation in the Revillagigedo Archipelago
by Courtney Mattison
In the radiant blue of the Revillagigedo Archipelago Biosphere Reserve, about 250 nautical miles south of Cabo San Lucas, sharks rule. From its depths, Galápagos, hammerhead and silvertip sharks find all they need to thrive. White tips and silkies abound. Even the elusive whale shark, its enormous body weightless and almost invisible in the deep blue, frequents these waters. Humans are merely guests, and earlier this month, the Mission Blue expedition team paid a visit.
Sharks and rays throughout the Mexican Pacific and Gulf of California are threatened by commercial fishing operations, some which catch tuna and trap sharks as bycatch while others target sharks outright. Last year, the Mission Blue expedition team discovered tons of dead sharks on the beach of Bahia Los Frailes in Cabo Pulmo Marine Park in the Gulf of California Hope Spot, only 250 nautical miles from the Revillagigedo Archipelago Biosphere Reserve. Luckily, this year’s expedition revealed more hopeful signs of health and resilience. Yet there is no doubt that sharks in Revillagigedo—Mexico’s “Little Galápagos”—are threatened.
“You shouldn’t notice such a big difference in shark abundance over a ten year period,” remarked Shane Taylor of Fins Attached after returning from a dive at Roca Partida, one of the four volcanic islands of the Revillagigedo Archipelago. “Ten years ago, you would have had to swim with your eyes closed to not see groups of Galápagos and silvertip sharks and even a wall of hammerheads on every dive” he said, recalling his first visits to the islands. “It’s hard to take the temperature of a place from one or two days of diving since things change every day,” said Mission Blue Board Director Shari Sant Plummer. “But compared to stories we’ve heard from even a few years ago, there seems to be a big difference.”
Data about where sharks feed, have their pups and migrate help researchers identify places of special importance to shark conservation. “It’s very important to collect these data because we want to know how much these animals are using the marine reserves,” says Dr. James Ketchum of Pelagios Kakunjá—the lead scientist sponsored by Fins Attached on our recent expedition. “This gives the park managers more data to support their existence.” Data collected by Dr. Ketchum and his team support the creation of networks of marine reserves, or better yet, no-take marine protected areas (MPAs) where all extractive uses, like fishing, are prohibited. “The key to protect these species is to make networks of marine protected areas,” says Dr. Ketchum.
New findings from acoustic tags placed on sharks in the Revillagigedo Archipelago reveal corridors of movement between the islands and the Gulf of California and broader Mexican Pacific, making these networks of protected areas more important now than ever thought before. Sharks outfitted with acoustic tags send signals to monitoring receivers planted underwater at around 30 meters (100 feet) deep throughout the region. When a shark comes within the 300-meter range of an acoustic receiver its tag sends a timestamp, allowing researchers to trace movements of individual sharks and recognize patterns in their behavior.
Protected species of sharks are sold on the black market to satisfy Chinese demand for shark fin soup, while unprotected ones are legally sold for their meat, with their fins also exported to Asia. Only whale sharks, great whites and basking sharks are protected under Mexican law, putting the sale of other more common (yet extremely threatened) species up for grabs. For example, the Eastern Pacific population of scalloped hammerhead (Sphyrna lewini) is listed as endangered by the IUCN Red List of Threatened Species and the U.S. Endangered Species Act, and is also listed on CITES (Convention on International Trade in Endangered Species) Appendix II, which prohibits international trade of shark products from this species without first verifying that these animals are being fished sustainably with legitimate certificates of origin. Yet in Mexican waters, the scalloped hammerhead is fair game.
Recording patterns in shark migration, feeding and reproduction behavior is more important now than ever before, as advances in tracking technology make it increasingly easy to understand how and where to protect key habitat. More robust research findings are also making it more compelling for policymakers to base regulations on science. Today in the Revillagigedo Archipelago, Dr. Ketchum says:
Fishermen can go in between the islands and fish whatever they want. But our proposal based on these studies is to make no-take zones of 40 nautical miles radius around each island, and in this way create a large no-take zone around the San Benedicto, Socorro, Roca Partida triangle of islands. We are also proposing a very large (400,000 square km) marine protected area around the whole archipelago, where fishing is limited.
By documenting the tagging process, Mission Blue aims to raise awareness about how tagging is valuable for protecting species under constant threat. “One of our long-range goals is to highlight the work of Dr. James Ketchum and Fins Attached so that the public understands the importance of studying sharks and protecting shark migration corridors and marine reserves,” says Kip Evans, Director of Expeditions and Photography for Mission Blue. He continues, “When these sharks leave the boundaries of the MPA, they get hammered. Essentially, there are no protections for them. So tracking data is essential to help us recognize the importance of these shark migratory corridors and help policymakers understand how to protect them.”
As Mission Blue embarks on its shark conservation program for 2017, we seek to support our partners and push the Revillagigedo Archipelago into full protection, including designation as a sanctuary for sharks with surveillance to enforce protection of these species. Join us by supporting our partners at Fins Attached and Pelagios Kakunjá.