Sharks and turtles migrate using this underwater highway
3:48 AM EDT, Tue July 13, 2021
Cocos Island lies 340 miles off the coast of Costa Rica in the eastern tropical Pacific. Another 400 miles south are the Galapagos Islands. Both are considered safe havens for wildlife, and the waters surrounding each area are protected.
Between the two islands is a busy underwater highway for migratory fish. Species such as sea turtles and sharks move back and forth between the marine reserves, looking for places to nest or foraging for food.
But the underwater highway is open to fishing activities, and with populations of the migratory species declining, scientists and conservationists are campaigning for the entire swimway to be protected.
MigraMar, a network of scientists and environmental groups, has built a strong case for protecting the swimway, by documenting the species that use it. They have attached satellite and acoustic tags to individual species, like the whale shark pictured, so that they are able to follow their migratory pathway.
"We now have six species documented that are moving between these two islands," says Todd Steiner, executive director of Turtle Island Restoration Network and a founding member of MigraMar. "We suspect there's even more."
Steiner adds that the marine reserves surrounding Cocos Island and the Galapagos, pictured here, are good at protecting resident species, but not highly migratory ones.
The route between Cocos and Galapagos follows a chain of seamounts, or underwater mountains, which sharks and turtles rely on for navigation. They are also rich with life, providing vital resting and feeding spots during the long journey.
Endangered green turtles have been found to move between the islands, as they nest in the Galapagos and forage in the Cocos.
Leatherback turtles, which are listed as vulnerable, also use the route. One of the greatest threats to their survival is being caught accidentally by fishing boats or getting entangled in nets.
Scalloped hammerhead sharks travel in schools between the islands. The species is considered critically endangered, with fishing as its main threat. Scientists say that protecting the swimway could help to keep population levels up.
Whale sharks, the largest fish in the world and also endangered, are highly migratory. During an expedition in 2020, scientists tagged a whale shark, named Coco, near Darwin's arch in the Galapagos. Around a month later, Coco arrived at Cocos Island, confirming that the species migrates along the swimway.
Most recently, scientists discovered evidence of a tiger shark using the swimway, as a nine-foot-long female that scientists had tagged in the Galapagos seven years ago surfaced at Cocos Island. As tiger sharks are one of the top predators in the Pacific, their existence is vital to the survival of the entire ecosystem.