Cocos Expedition 2024: Part 3 – Sharks and Rays

Cocos Island Expedition – August-September 2024

Cocos Log Blog Part 3 Sharks and Rays

The iconic species that everyone comes to Cocos for is the scalloped hammerhead shark. These aggregations occur in large schools, sometimes 200 or more, and consist almost entirely of females averaging 8 feet in length. Many of the bottom-up “background” photos were taken in Cocos and this is a photographer’s dream shot.

Video by Luis Fallas.

In Cocos you have the opportunity to see hammerhead sharks up close as they come into “cleaning stations” to collect parasites and dead skin from “cleaner fish”, mainly butterflyfish, but also king angels and the occasional juvenile hogfish. Shark behavior is to slow down and enjoy the spa treatment, but they can be wary of diving bubbles. During the summer, the female hammerhead sharks have fresh mating scars and the butterflyfish seem to focus on eating the dead skin in these scar areas.

In the video below the yellow dots are the butterflyfish, but on this day the hammerheads didn’t slow down enough to achieve a “good” clean.

Video by Diego Jimenez.

There are also Galapagos and blacktip shark cleaning stations in Cocos. Blacktips seem to be the shyest of all, moving away soon after divers show up.

Video by Luis Fallas.

On the Galapagos Islands, however, the presence of divers is not important and encounters are common at the cleaning stations.

Video by Marta Torne.

Tiger sharks are also most often seen cruising the sand-coral reef ecotone, but their abundance can vary seasonally. On this trip, only one juvenile was observed swimming across the sandy bottom of the coral garden from a school of hammerhead sharks.

(Watch me tag a large tiger shark on an expedition in 2019 in this short documentary from The Economist film team )

The most common and ignored shark are the whitetip reef sharks, which can be seen hanging from the sandy bottom or swimming by on almost every dive, sometimes in small schools. They can easily be approached for close-up photos, or in our case, to secure tissue samples for research purposes.

Other sharks occasionally seen include whale sharks, silvertip sharks and silky sharks; the latter two were spotted on this trip.

Cocos is also home to four rays.

Marbled rays, a type of stingray, beautiful and graceful, with beautiful black, brown and white spots on their circular disc, are common in Cocos. Females can reach over 9 feet in size and their tail is longer than their body. When it is mating season, you will often see many smaller males chasing females. On this trip we only observed individuals.

Video by Marta Torne.

Several eagle rays were also spotted on this trip, swimming gracefully across the sandy bottom, likely searching for their food source of molluscs and crustaceans.

While diving on this trip, a sicklefin devil ray and several giant manta rays were observed. Both species are filter feeders and can reach enormous sizes, up to 22 feet for the giant manta ray and 12 feet for the devil ray.

While the abundance and biomass of sharks and rays in Cocos is spectacular, so is the abundance and diversity of fish that provide food for these and other predators.

The amazing diversity of other coconut fish will be explored in the next Cocos Log blog Part 4. In Part 5we will discuss our research goals for this expedition.

Again, if you haven’t already, please take action to protect Cocos’ wildlife by clicking link and to tell the government of Costa Rica that we need more action to protect the migration route of critically endangered marine life in the Caribbean.