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CONSERVATION ISSUES - JANUARY 2005

Most people think of Leatherback Turtles as accidental visitors to our seas, having arrived on the gulf stream unintentionally, but this is not the case. Leatherbacks, unlike other reptiles and other sea turtles are warm blooded. It branched off from other sea turtles about 100 million years ago, trading a shell for a rubbery skin and hydrodynamic keels along its carapace, and chose a poisonous diet. It chooses to come here, and it is as much a part of Britain’s wildlife as Swallows or House Martins, and can wander even further north than Britain, up to the Arctic Circle. The biggest one ever recorded was found, (alas dead,) at Harlech in Wales. It was 9½ ft long, and weighed 916 Kg, as much as a car. They are supreme long Distant cruisers, and tests, using data recorders, show that leatherbacks almost never stop moving. and they need to keep moving for the ocean is largely an empty place punctuated by localised blooms of plankton which give rise to their jellyfish prey. It is not known how they find these areas, perhaps they have an exceptional olfactory function. Other turtles caught up in the North Atlantic Drift usually get too cold to eat, and die in British waters, but leatherbacks huge size gives them a lot of volume for relatively little surface area and they are well insulated with fat. They can allow their outer surface to become cold, and like ducks that stand on ice, they use counter–current flow in their limbs to reduce heat loss. Tightly-bunched arteries and veins cool the blood on the way out and warm it on the way back in. One might wonder how an animal of that size can survive on jellyfish which are little more than water and protein, and not very nutritious. In fact jellyfish can be up to 20kg each, and where they do occur can form vast swarms. The fact that they are venomous and difficult to grab, is no problem for the leatherback for it is totally immune to all coelenterate toxins and have double-hooked shearing jaws and a throat lined with spiky papillae, and once anything starts down, it’s a one way street. Only the females return to land, every two to three years to lay their eggs, and when the babies are born, with a giant wingspan relative to their size, they head for deep warm water where they spend their early years.

Large Leatherbacks are sometimes attacked by big sharks and killer whales, but they are not completely defenceless. They turn upside-down and hold their vulnerable flippers up out of the water and one leatherback was filmed rolling over from the upside-down defensive position to chase and bite a large Tiger Shark, and it is thought that they may dive deep to avoid predators, for recorder devices show they routinely dive, straight down, to 300–400 metres for up to 14 minutes. The deepest decent recorded is 1240 metres, but they probably go as deep as 1400m, or a mile. The leatherback is an endangered species, the Pacific numbers has crashed, thanks to long-lining and illegal drift nets. But the Atlantic population is better off, however it is still critically endangered. The leatherbacks outlook depends on us, if we protect vulnerable migratory species in 90% of their range  but not in the remaining 10%, then all our effort could be wasted. Without co-ordinated international measures, some turtle populations may be lost for ever.    

There were 12 reported sightings of Bottlenose Dolphins during October. The largest pod of 12 was off Penzance Harbour on the 15th and 16th Three other reports of dolphins were probably Bottlenose, especially a report of 2 large dark dolphins catching and eating 10lb Bass off The Lizard, and another report of about 30 heading east off The Carracks on the 27th for Bottlenose Dolphins were in St Ives Bay every day for the rest of the month. Two reports of Common Dolphins were of larger numbers, 30 to 40 in Fal Bay on the 5th, and 300 or more travelling across the bay from the Manacles on the 8th.    The only report of Harbour Porpoises was of 20 or more off Doyden Point. Three reports of Grey Seals included one of a seal pup catching and eating Garfish off The Lizard. Other reports were of a Leather Back Turtle off St. Ives and an Amberjack being caught ½ mile off Seaton. I have not received an update of the strandings for October.

Conservation Officer Raymond Dennis

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