Tiger sharks tagged, monitored

Marine biologists working with the Department of Environment to study the area’s predator species caught and tagged two tiger sharks last week and fitted each shark with two types of electronic tracking devices.

One is a satellite tag that includes a GPS receiver and transmitter and signals via satellite the location of the shark.

The other is a small acoustic tag, or pinger, that transmits a signal that can be detected by a permanent or handheld receiver, showing that the animal is near.

The acoustic tags can be used to detect movements on a finer scale, providing a more detailed picture of the behaviour and movement of the tiger sharks while they are in Cayman. They will show which sea areas they actually use, and at what time of day.

The sharks — a 10-foot female called Tina and a seven-foot younger, immature female Luiza — will help the researchers understand their species’ migration patterns, movements and behaviour when they are in Cayman.

“Both of them seem to be doing fine. Tina has reported in several times a day while moving around the island; she seems to be deep during the day, coming into shallower water at night to look for the stingrays and turtles on which these species normally feed,” said lead researcher Mauvis Gore.

Endangered

“Tiger sharks, like many other species, are increasingly endangered as a result of intense over-fishing globally. In fact, large shark species are becoming so scarce globally that in many countries they are either fully protected, or else their fishing quotas have been reduced to zero,” she said.

Only in the last few years have scientists discovered that tiger sharks can make extensive annual migrations between countries or even across oceans.

The tracks revealed by the satellite tags results will show whether the tiger sharks that are sometimes observed in the Cayman Islands move around or between the islands, and whether, as suspected, they are here for only part of the year and then migrate elsewhere.

International efforts to protect dwindling shark populations have come to the fore in the last few years because of the dramatic decline in shark populations globally.

Unlike bony fish, sharks mature very slowly and reproduce only once every one to two years, producing only a small number of pups. Over the last decade or two, 70 million sharks per year have been fished and killed, almost entirely for their fins that are in demand as a component of shark fin soup.

“Even if we agree to exploit sharks,” said Ms Gore. “We want to do it sustainably, not in this crazy way that will see the resource completely destroyed in another 10 years. As it is, sharks are now far more valuable in the sea than in the fishing boat. Divers will pay good money to dive in places where they have a chance of seeing such iconic wildlife, and the same sharks can be seen over and over again – whereas once it’s dead that’s it, and it fetches very little in the market.”

A favourite of Harvey’s

“Tiger sharks are one of my favourite animals,” added Guy Harvey, whose Ocean Foundation provided the satellite tags, and who helped the team catch Luiza.

“They are the most handsome of all the sharks, and I just love painting them. It’s just unfortunate they have these stripes that give rise to their name, making people think they are much more dangerous than they really are.”

Harvey, a well-known artist and resident, has also assisted with tagging tiger sharks in Bermuda and the Bahamas.

The tiger shark study is part of a project by a team from Marine Conservation International led by Ms Gore. It is funded by UK Overseas Territories Environment Programme, the Cayman Islands DoE, the Save Our Seas Foundation, and the Guy Harvey Ocean Foundation.

The team have been working in the Cayman Islands over the past 18 months to assess the species and abundance of sharks and rays, as well as whales and dolphins.

“We are very pleased with the preliminary results of this work,” stated Gina Ebanks-Petrie, director of the DoE. “It makes sense to find ways of managing our resources so they benefit us in the long-term, not destroy them; and we also have international obligations to protect these threatened species.”

The resident project officer, Oliver Dubock, said people’s fear of sharks is out of proportion.

“Of course they can be dangerous,” he said. “But no more than fierce dogs. You need to know how to behave and how to handle them. Just as an example, in Florida on average over 70 people per year die from boating accidents, but less than one every two years as a result of shark attack.”

Tim Austin, deputy director at the DoE, added, “We urge fishermen and divers to join this important conservation effort and help look after these two beautiful animals.”

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