Shark tagging study aims to reveal secrets of Cayman’s apex predators

The Department of Environment and Marine Conservation International are working to reveal the hidden secrets of our reefs’ apex predators.

In ten years of partnership, more than 80 sharks have been outfitted with special tags that track their location.

Last week, Cayman 27’s Joe Avary joined the shark tagging team in the waters off of East End to learn more.

“We wanted to know what species they have around here, what sort of numbers, is there a seasonality to it, and we also wanted to know how healthy the population was,” explained Professor Mauvis Gore of Marine Conservation International.

She told Cayman 27 that a decade of research has netted valuable insight into Cayman’s shark populations, but there’s still more to learn.

“You need long-term data to try to work out any information, and this is where the ten years comes in now, we have ten years, and we can begin to say what is happening,” said Professor Gore.

Acoustic tracking devices help researchers better understand the behaviours of these apex predators. Tagged sharks’ movements are recorded by a network of strategically placed acoustic receivers around our three islands.

“We are going to take some measurements so we know what sort of sizes we’re getting around here, see what sex it is,” said Professor Gore.

Professor Gore and her team were back on the water last week, tagging sharks. The first step: catching one.

After a short wait, an adult male Caribbean reef shark took the bait. Once secured to the stern of the boat, researchers begin their work collecting scientific data.

“Once we pull it in we need to move very fast to get all this information as quickly as possible so that we are not stressing out the shark anymore than we need to,” said Professor Gore.

The shark is measured, and a tissue sample is collected before the shark is turned upside-down, putting the animal into a state of ‘tonic immobility.’

“It’s almost if it has been given a tranquilizer, it is a natural physiological response to being turned upside down in most sharks, and that gives us a chance to work on the shark without it being stressed,” said Professor Gore.

With the shark immobilised, Professor Gore inserts the acoustic tag.

“We put them in a small split underneath the skin, not in the body, but just underneath the skin,” explained Professor Gore. “When they go anywhere near one of our many receivers around the islands, we know where that shark was and when.”

A visual marker is attached to the dorsal fin, and the shark is released. This shark wasted no time in returning back to the reef.

“He was in very good condition, there was no parasites, he was blemish free, and he looked very healthy, he’s also sexually active, at the moment, he’s a big male, a big adult male, and that is quite good to know that these guys are out there,” said Professor Gore.

She told Cayman 27 data gleaned from this shark and more than 80 others tagged over the past decade can help unravel the remaining mysteries of these dynamic and fascinating creatures.

Professor Gore said one question she hopes can be answered is whether shark protections implemented in 2015 as part of the National Conservation Law have led to an increase in shark populations. That analysis is still underway.