Loggerhead: The Bulldog of the sea


With a carapace often covered by living organisms resembling an old log at sea, flesh that tastes fishy and relatively standard nesting behaviours, the loggerhead turtle (Caretta caretta) is often regarded as just been ‘the other turtle’. Possessing a large head and powerful crushing jaws, the loggerhead is the bulldog of the sea turtles. However, the loggerhead is perhaps the most-studied of the marine turtles and so has become a symbol of the conflict between fishing activities and beach development against the sea turtle survival in general.


The size of the head-jaw combination allows the loggerhead to feed on large shellfish and unlike the other turtles, loggerhead females will use this powerful jaw to their advantage and try and bite anything that disturbs them during the nesting process. Archie Carr relates to a story from 1905 where 5 men set out in a rowing boat to catch a 280kg loggerhead in Connecticut. Several hours later they limped back into port after a drawn out fight with the turtle. The loggerhead nearly overturned the boat with it flippers, chewed the oars into stumps and tore a gash in one of the men’s arms. The turtle got away and the men resolved never again to hunt loggerheads. It is for these reasons the loggerhead got its reputation as the bulldog of the sea.


Despite its bad reputation, in reality the loggerhead is a beautiful species. The turtle’s carapace is reddish-brown blended with olive and its plastron cream to yellow. Living organisms such as barnacles, skeleton shrimp and algae often cover the carapace of adults and older juveniles. On close inspection their shells are full of life, mobile islands transporting marine hitchhikers across the oceans, essentially a swimming ecosystem. More than 100 species of animals from 13 phyla and 37 kinds of algae live on the back of loggerheads. It is unclear what benefit the turtle will get from this relationship, but this small army of live could be providing camouflage from the turtle’s predators.


These turtles can be considered as a keystone species in the marine world. Often eating its way through invertebrate populations the turtle plays a central role in the food chain, managing the food source. This diet heavily reliant on invertebrates mean that shells get broken down and some come out of the digestive system, falling back to the benthos. The small pieces of shell are thus available for other animals to eat as a source of calcium. Moreover, females transfer substantial amounts of nutrients – their eggs- to the terrestrial ecosystems around nesting reaches. For example, up 28% of the energy and 26% of the nitrogen put into egg clutches in Florida is transferred to predators. A substantial number of hatchlings become food for fish, birds and some small mammals, playing important roles in the food web.


Loggerheads are ecologically generalized with broad ecological requirements. They nest over the greatest geographic range of any sea turtle, from the tropics to the temperate zone, foraging in both open waters and in nearshore regions of all tropical and temperate oceans. With 67,000 nests a year in Florida, 15,000 in Oman, 3000 in Greece to name a few, the loggerhead is wide spread.


There are however some obvious differences among the loggerhead populations around the world. Mediterranean turtles are smaller than their Atlantic Cousins and those in the south and north pacific do not mix. Likewise, those in the Indian Ocean appear to be distinct from those in Oman and same for the population in Southern Africa. Water temperature is a critical environmental cue for these turtles, using changes to time their movements in and out of shallow water. They move from offshore to inshore and from south to north in spring and reverse the movement in autumn.


In Oman and South Africa, loggerheads nest on isolated, exposed beaches, while in Australia they nest on open sand beaches. In Florida and the Mediterranean there are not many isolated beaches left so loggerheads are forced to nest on resort beaches and in front of apartment buildings. There are only about 10,000 nesting female loggerheads each year and so reduction in suitable nesting beaches is a serious problem. For example, in Greece the nesting beaches are at such a premium due to extensive urbanization and resort development, turtles have been forced to compete with beachfront lighting, noise, and heavy human and vehicular traffic at night. All of these disturbances could have a large detrimental impact on the females nesting ability.


Further pressure on populations comes from marine activity. Huge longline and gill net fisheries in the Pacific and Atlantic have put populations in jeopardy. Thousands of loggerheads are killed each year in Egypt alone from fishing pressure. In general populations are in decline. In 1977 Australia boasted around 3,500 loggerheads nesting a year, now this figure is more like 500. The population in Japan has also declined 50-90% during the last half of the 20th century.


Despite rapidly declining populations, conservation efforts for this turtle are strong. Some communities in the US and Europe have enacted lighting ordinances to keep beaches dark. Resorts in Greece are fined if they do not stack their sun lounges at night time, allowing more room for turtles to nest. TEDs are reducing trawling deaths, Australia’s enhanced use of TEDs has led to local population gains for loggerheads in recent years. Projects across the loggerheads range work hard to safe guard nests in hatcheries allowing as many hatchlings to grow and get to the sea.


It takes 25-35 years for loggerheads to reach sexual maturity, in that time they must survive the natural and human dangers in the open ocean and then in the nearshore waters were it battles with humans. The advent of TEDS in many nations will increase odds for survival for this species, but this is offset by the effect of increasing longline fishing. We need to continue the study of biology and conservation actions in order to ensure that both the loggerheads vulnerable and most productive populations continue to survive through the 21st century.

#Marine #Turtle #Asia

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