Oct-Nov 2008

Shark Tagging in Mexico

Jurassic Shark

Some folks like to spend their holidays sunning themselves on the beach. I prefer a more hands on style of break and so took myself off to Mexico for three weeks to assist with an ongoing research project into the migration and ecology of great white sharks, scalloped hammerhead sharks and whale sharks.

This trip was carried out under the auspices of a Joint Services adventurous training exercise, named Exercise Jurassic Shark 2, building upon the work carried out in 2006 tagging scalloped hammerhead sharks in the Cocos Islands.

Funding for the expedition was through a combination of sponsorship and individual contributions. The Defence Sports and Recreation Association were kind enough to provide sponsorship of £700 towards the costs of the return flight to and from Mexico.

Great White Shark

The wider research is to log the movements of sharks along the Pacific coast of Central and South America and investigate the DNA of the sharks with the aim of developing a management plan for these wide ranging species. Currently great white sharks and whale sharks are protected in Mexican waters. However, once they leave the protected area they are subject to pressure from a number of shark fisheries along the Pacific coast. Scalloped hammerheads have no protection and are a target species for the Asian fin trade, providing the base material for shark fin soup.

The aim of the exercise was to place a number of radio receivers around Guadalupe and the Revillagigedo Islands, to deploy up to 20 radio tags, 2 satellite tags and to take tissue samples from a number of individual sharks for mitochondrial DNA analysis.

Tagging the great white sharks was carried out from a small boat, known locally as a Panga. To attract the sharks to the boat, a dead fish was attached to a cord and suspended in the water. As the shark approaches, the cord is drawn in so that the left hand side of the shark is close to the boat. The tag is then inserted just below the dorsal fin of the shark. At the

same time as the shark is tagged a photograph is taken of the shark. This is then used to identify the particular shark from a database of known individuals.

Whale Sharks

Unlike the great white sharks, the scalloped hammerhead sharks and the whale sharks were tagged in open water using both open circuit (SCUBA) and closed circuit breathing apparatus. The benefit of the closed circuit rebreather is that it does not produce bubbles.

Over the course of the expedition a total of 10 great white sharks, 8 scalloped hammerheads, 3 Galapagos sharks and 1 Silvertip shark were tagged by the team. It is believed that this is the first time that a silvertip shark has ever been tagged. Unfortunately no whale sharks were tagged on this expedition although the satellite tags have been left with the local researchers and will hopefully be deployed in the not too distant future.

Further details about the expedition can be found at http:\\www.jurassic-shark.org.uke.

Tagging was carried out using a spear gun with a modified shaft. The tag that holds the radio transmitter in place slots into a groove on the spear shaft and the radio tag is held in place with rubber bands. The operator then hangs onto the rocks close to a cleaning station, which are easily identified by the presence of a small yellow fish called a barber fish. This was made difficult by the 3 – 4m swell that buffeted the divers when in the water and the presence on numerable sharp sea urchins, aggressive moray eels and the fact that the rock face was covered in sharp barnacles. Deploying the tag required the operator getting within 1 – 2 metres of the shark selected. As with the great whites the target area was at the base of the dorsal fin.

WGuy Hagg Senior Environmental Advisor DE Ops (South) LMS Environmental Support Team.

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