Sep 26, 2018

By Elisa Chan of the Turtle Island Restoration Network

Over 300 miles off the coast of Costa Rica lies the jewel of the Pacific Ocean, Isla del Coco. Described by Jacque Cousteau as “the most beautiful island on earth,” this oceanic island boasts a rich marine ecosystem, unique flora, and secrets of the deep ocean. In an effort to continue to learn about the mysteries of the Coco Islands, a team of marine biologists from Turtle Island Restoration Network, the crew from Undersea Hunter, and Park Rangers from Cocos Island National Park worked together to document the behavior of one of the most elusive marine visitors—the tiger shark.

Tiger shark encounters are common and welcomed by divers at Cocos. However, in November 2017, visitors experienced the first-ever deadly attack by a tiger shark. While removing the shark involved in the attack was discussed, there is no photographic evidence from the incident, and therefore, no action was taken. Subsequent “close encounters” with tiger sharks have been photo-documented, but further data is needed to determine that only one shark was involved.

While this ultimate question remains unanswered, many additional questions need to be answered to adequately understand what may have led to this behavioral change. For example, did environmental changes—like less available food—lead to the attack?  If it is a single shark that is involved in both the fatal attack and the increasingly aggressive encounters, is it new to Cocos, and where might it have come from? Is it ill perhaps, or maybe it has been habituated to humans by being fed?

Turtle Island and other research colleagues, as well as park managers seek answers to these questions in order to best manage the situation—protecting both wild and human life.

To drive this effort forward, Todd Steiner and Callie Veelenturf, marine biologists from Turtle Island Restoration Network, proposed luring tiger sharks to the surface using a plastic sea turtle mounted with GoPro cameras to capture feeding behavior, provide footage for photo identification, and deploy acoustic tags on the animals from the safety of the boat to better understand the sharks’ movements. This research effort is allowed under special permits from Costa Rican National Park Service.

In August 2018, the team gathered their gear at the end of the dive day and boarded the skiffs to a site known as “Manuelita Coral Garden.” Tiger sharks are known to frequent this area to feed on boobie chicks that often fall from the cliff’s edge. Here the team waited, ready with the turtle lure mounted with GoPros and pole spears loaded with acoustic tags. The plastic sea turtle nervously floated behind the boat, as the team watched intensely for shark shaped shadows in the water.

The first day proved the most successful with five sightings—and distant underwater footage of a tiger shark was captured from the turtle-mounted GoPro cameras. This success provided the team with confidence in their potential new approach for tagging and documenting sharks in the Coco Island region. Additional evenings were spent in the field; however, our team’s schedule didn’t seem to line up with tiger shark feeding time in this area on those days.

Nevertheless, the team at SeaTurtles.org will continue using this method over the coming months in an effort to uncover the full story behind these tiger shark encounters and create a management plan for the safety of both dive visitors and the tiger shark population. Thank you GoPro for supporting these efforts, from everyone with a love for the ocean and our fishy friends. You’re turtle-y awesome.

Click here you’re like to continue to support this incredible team. You can purchase items in-need directly, or contribute to their Microplastic research expedition budget. To learn more about our upcoming Coco Island trips, go here.

Elisa Chan is a friend of Turtle Island Restoration Network, a nonprofit dedicated to mobilizing people in local communities around the world to protect marine wildlife and the oceans and inland watersheds that sustain them. She was a guest on the August Undersea Hunter / TIRN expedition.