Every night from October to March, PhD student Mark Hamann and research assistant Matt Forrest work from dusk to dawn on the tropical Heron Island beach, their yellow miner's helmet lamps showing the way for up to 100 tourists at a time to follow.
Even in pouring rain, these University of Queensland researchers circumnavigate the 16-hectare coral cay about five to 20 times nightly, unlikely Pied Pipers conducting scientific research and providing eco-education to fascinated followers.
They search the inky black night for the eerie sights and sounds of green and loggerhead turtles laying their clutches.
Tell-tale tracks and scratching in the sand signal success - another green turtle has made it to shore. She lays a clutch of 115 eggs over three hours, and exhausted, is oblivious to scientific scrutiny and the curiosity of ecotourists. She then bulldozes inexorably down to the shoreline to prepare her next clutch to be laid in a fortnight.
For Mr Hamann, Heron Island has come full circle from its notorious origins as a turtle soup factory in 1925, to one of the largest nesting colonies of green turtles in eastern Australia.
The processing factory was replaced by a resort in 1932, currently operated by P&O. Heron Island is also home to the University of Queensland's research station - one of the main coral reef research centres in the world - providing a permanent base for a diversity of marine studies.
Inadequate knowledge of sea-turtle population dynamics allowed turtle hunting in Australia until low numbers of nesting adults prompted legislative protection in 1950. Green turtles are now protected by law, with the exception of sustenance fishing by indigenous groups.
Australia is now one of the last refuges for globally declining sea-turtle populations.
While an estimated 3000 green turtles are lost a year in Australia to sustenance fishing, some 20,000 green turtles are harvested annually in Papua New Guinea and 70,000 in Indonesia. In Malaysia, scientists estimate that apart from those eggs laid on protected beaches, such as Rantau Abang, or those purchased and incubated by the Malaysian Fisheries Department, every egg laid in the past 50 to 60 years has been legally taken by collectors.
The turtles are their own worst enemies. Their flesh makes good eating, the skin makes good leather, and other parts are used in making ornaments and perfumes. The beautifully patterned mosaic shell is highly prized in many cultures.
Only one in 1000 hatchlings will survive to reach sexual maturity at age 30 to 40 years. Forty percent will be lost between the beach and the coral rim, most to hungry large fish, sharks and sea birds.
Others will be innocent victims of intensive fishing practices. Scientists believe loggerheads (Caretta caretta) are particularly under pressure from trawlers, fishing lines, recreational boating, entanglement in ropes discarded by boats, and from disease. For green turtles, there are the unknown variables of cyclones, El Ni?o and other climatic events, and variations in seagrass and algae availabilities for these marine vegetarians.
'The next few years could be crunch time for the loggerheads as numbers appear to be reduced by up to two-thirds in some Queensland rookeries,' Mr Hamann said.
'The Queensland Department of Environment is trying to get a better picture of turtle population dynamics, building on accurate data collected since 1974. My research on the green turtle (Chelonia mydas) is a small part of the State-wide network of information.'
His work is supervised by Dr Joan Whittier (University of Queensland Anatomical Sciences Department) and Dr Col Limpus, of the Queensland Department of Environment, who is also an adjunct associate professor in the University's Zoology Department.
Mr Hamann is studying the role of hormones in metabolism and mobilisation of the green sea turtle. He said much remained to be known about green turtles, particularly their internal physiology.
'It is known that green turtles are slightly larger, females growing to 105cm long, and weighing to 150 kg, compared with loggerheads which grow to 95cm and weigh to 100kg,' he said.
'Males and females travel short, to extraordinarily long, distances to mate in courtship areas on offshore islands and cays. Some may travel only 2kms from the adjoining Wistari Reef; others make the long trek from up to 2500 kms away, according to tagged turtles recovered from feeding area research and international tag recoveries.'
Females mobilise massive levels of testosterone and triglycerides once courtship finishes, while the male's sperm is viable up to six months. If mating is successful in October-November, the males retire, their work done.
Scientists believe turtles may use some form of magnetic imprinting to locate birth areas. They may mobilise magnetic compounds in the brain to follow the earth's magnetic lines. During summer months the females go ashore to lay eggs in dunes above the high-tide line. If nesting is successful, they will repeat the process five to six times during a season, returning again to breed in another five to seven years.
Scientists are not sure why, but suspect the influence of abundant food supplies led to a record nesting season last year with an estimated 1500 green turtles visiting Heron Island. This year, some 300 turtles have nested so far - 140 of which were not previously tagged. Mr Hamann has observed from tagged specimens that some turtles are coming ashore for their fourth nesting season.
Despite a life dictated by tide times, turtle nesting patterns, and broken day-time sleeps, Mr Hamann is consumed by his work. He would not swap it for his earlier careers as a sea bird and wading bird research assistant, or as a herpetologist on the Birdsville track fauna surveys.
Funded by an Australian Research Council large grant to Dr Whittier and Dr Limpus for sea turtle physiology research, he admits he would happily work for free, but needs money to buy food.
'I like talking about turtles to tourists, but the best part is studying turtles in their own environment,' he said.
'They just blow me away with their beauty.'
For further information, contact Mr Hamann, telephone 07 3365 2518, email: m.hamann@mailbox.uq.edu.au
