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By Iain Anderson

Diving the Cumberland

Diving the Cumberland

An emaciated and dehydrated green sea turtle landed on Muriwai Beach in April of 2005. He was a victim of cold shock. Sub-antarctic water from the Tasman had reduced his body temperature to a dangerously low level. The Department of Conservation asked Kelly Tarlton’s Underwater World to help with his rescue. The staff from the aquarium, experts in turtle care, picked him up from the beach and transported him to their aquarium. For a sea turtle this is a luxury hotel where there is plenty to eat and the water in the recovery tanks is maintained at a comfortable sub-tropical 20º C or higher. Turtle patients are also fattened up on a diet of fish, squid and mussels; unusual fare for a species that is vegetarian. In fact green turtles are named for the green colour of their body fat – naturally dyed by the pigments in the marine plants that they ingest. He was given the name Reeve, after the late actor Christopher Reeve who despite crippling back injuries, maintained a positive attitude to life in the belief that one day he would recover from his injuries. There was hope that Reeve would be a tough turtle.

The length of Reeve’s carapace, a system of bony plates that are fused together to form an armour-like shell, has provided a clue to his age. Green turtles reach sexual maturity when they are about 25 years old when carapace length can exceed 76cm. Reeve’s carapace in March 2006 was 55cm long (52cm wide) suggesting that he is sexually immature, perhaps only 10 years old. It was not clear whether Reeve was male or female – one must wait until sexual maturity to easily differentiate the sexes. Sexually mature males, for instance have a long broad tail that comes in handy for holding onto the female during sex at sea.

Reeve probably started life, as one of more than one hundred 4-5cm long hatchlings erupting from a nest on a beach in northern Queensland. He would have instinctively headed for the surf within seconds of hatching, running the gauntlet of birds, crabs and other beach predators. It is not clear how the hatchlings know the way to the water. Some scientists suggest that they use visual cues such as the reflected light of the moon or starlight off the surface of the ocean. While adults survive on a vegan diet of sea grasses and algae, juvenile green turtles are carnivorous and live on a mixed diet of the planktonic animals they encounter near the sea surface.

During the course of his 10 year life, Reeve has probably ranged far and wide for it is known that green turtles can travel up to 40kms per day. It is believed that they navigate by sensing the local intensity and direction of the Earth’s magnetic field along with other cues including sight and smell to find their way to a destination. It is known that they can travel almost direct over 2000 kilometres between foraging and breeding grounds.

Before being returned to the sea in March 2006 local scientists, developed a plan to track his movements. Dan Godoy, a marine researcher with the Auckland University of Technology, attached a New Zealand designed satellite transmitter to Reeve’s back. The device, manufactured by Sirtrack Ltd, a company founded by New Zealand’s former Department of Scientific and Industrial Research* in 1986, is about 200mm long and supports a small antenna. The system starts transmission when two stainless steel screws are out of the water. When the device is placed on top of the shell this will happen whenever the turtle comes up for air. The turtle’s position can then be identified from a system of satellites in high orbit. Coordinate data is then relayed to an organisation in France who email the data to Dan Godoy in New Zealand. Dan will use data from Reeve and other turtles that visit our shores to improve our understanding of turtle behaviour. In addition to the satellite tracking information he is collecting genetic and sighting data for a New Zealand turtle database that is part of a wider South Pacific turtle conservation programme

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I watched Dan as he prepared Reeve’s carapace for attachment of the satellite transmitter. The top surface of the carapace was lightly sanded and some epoxy putty was pressed against it. Working like a baker on pastry dough, Dan moulded the putty onto the shell and around the transmitter. The putty was also progressively thinned toward its edges, to minimise water drag that might slow the turtle down. Once the putty was hard fibreglass was covered across it to ensure that turtle and transmitter would stay together. It was hoped that this would remain intact for at least 11 months, the expected battery life of the system.

On 1 March 2006 Reeve was flown to Kaitaia in the far north and then delivered by four wheel drive to Parengarenga Harbour where the water would be relatively warm for his return to the subtropical north. The group were joined by kids from the local Te Hapua school. Dan answered their questions and then all the kids did a haka. Local kaumatua gave Reeve a blessing before he departed on his journey. All went to plan on the day, but Reeve the turtle had plans of his own! Reeve was going to head south!

By the 6 April he had returned to Auckland, to within half a kilometre of Kelly Tarlton’s Underwater World; a swimming distance of about 500 kilometres. Perhaps Kelly Tarlton’s had left an imprint in his mind map and he was missing the good life with its warm water and great food. After returning to Auckland he has ventured out into the Firth of Thames and back into the harbour. At time of writing (14 April) he has spent the last four days in the upper harbour. He doesn’t need to be anywhere right now anyway. He is not even a teenager yet and can afford time to stay footloose and free to rove wherever he wants to go.

*The Department of Scientific and Industrial Research was dissolved in 1992 to form 10 Crown Research Institutes.

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