Environmental Engineering Reference
In-Depth Information
occurs in coastal waters all around the British Isles. The colour varies from translucent through pale yel-
low, pale brown, pale grey to light blue or purple. In faintly coloured specimens the blue tends to outline
the pattern of the internal sculpting of the bell, which can grow up to 30 centimetres in diameter. The
tentacles, arising from the underneath of the bell, are arranged in eight horseshoe or rectangular-shaped
groups each with 40 to 60 tentacles.
Other species frequently recorded include the common jellyfish Aurelia aurita , which is almost cer-
tainly the most abundant of them all, and the compass jellyfish Chrysaora hysoscella .
TURTLES
While there is little information about jellyfish around Gower, it is known that they are the staple diet
of the critically endangered leatherback turtle Dermochelys coriacea , which has been recorded from the
area, together with loggerhead turtle Caretta caretta and Kemp's ridley turtle Lepidochelys kempii . The
leatherback breeds in shallow tropical waters and it is clear that its extensive migrations are the result of
following swarms of jellyfish. One of the mysteries of leatherbacks is how they can thrive almost entirely
on jellyfish, which are composed for the most part of water. In British waters they occur seasonally and
the majority of sightings, usually of adults, are between August and October.
A particularly large specimen was seen off Gower in September 1966 and was described in the news-
papers as being 'the size of a small car with a head as big as a football'. Similarly in September 2003
a large turtle was seen in the Loughor Estuary, swimming at the surface in a westerly direction together
with large blooms of dustbin-lid jellyfish. The leatherback is the world's largest sea turtle and the most
widely distributed reptile; it has a shell normally up to 2 metres in length, and can weigh half a tonne.
They are spectacular animals, and the largest specimen ever recorded was found stranded at Harlech in
1988. The turtle weighed 916 kilograms and was 2.91 metres long, and can now be seen in the National
Museum in Cardiff. The same year a plastron, the underpart of a leatherback shell, was found in Three
Cliff Bay, one of a number of occasions when dead animals have been washed up on the Gower beaches
(Fig. 67). The leatherback's characteristic feature, as its name suggests, is a blackish leathery shell with
seven longitudinal ridges along the back, three of which are clearly visible when the animal is swimming
at the surface. The skin is also black and relatively smooth with pale spots. The black leathery skin, large
size, and prominent ridges on the back make them easy to identify. The leatherback is warm-blooded (en-
dothermic), maintaining a body temperature of around 25°C, which is unusual as most reptiles are cold-
blooded (ectotherms).
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