Turtle rookery resembled graveyard, scientists brought it back from the brink

Stunning drone footage of tens of thousands of turtles congregating off Cape York Peninsula captured media attention this week. But this bustling rookery once resembled a turtle graveyard.Key points:Raine Island is the world’s largest green sea turtle rookeryThe majority of eggs started failing to produce hatchlings in the 1990s and thousands of adult females were dying during nesting seasonA major operation to save the rookery has had success but scientists say there is much more work to doThe little coral cay attracts up to 100,000 nesting females some years, and produces about 90 per cent of the region’s green turtles.But in the 1990s, scientists noticed the rookery was struggling.The hatching success rate became unusually low with up to 90 per cent of eggs not producing hatchlings.And thousands of adult females were dying each season, mainly from heat exhaustion and because they were falling off small cliffs.About 2,000 adult turtles died during one nesting season, many after falling off steep sections on the island.(Supplied: Queensland Government)With a population crash looming, a mammoth operation began to save the rookery.Queensland Department of Environment and Science (DES) senior researcher Dr Andrew Dunstan joined the recovery effort in 2011.”The idea was to fence the edge of those cliffs so they couldn’t even get up there.”The second was to shift large amounts of sand to reshape the island, creating higher and flatter beaches so fewer nests would be flooded during high tides.Many nests on Raine Island were being inundated.(Supplied: Great Barrier Reef Marine Park Authority)”One of the big issues with hatching failure is inundation,” Dr Dunstan said.”The island has sort of spread outwards, so the beach has got lower.”The Government began hunting for corporate sponsorship and in 2015 announced a five-year $7.95 million partnership with BHP, the Great Barrier Reef Marine Park Authority, Great Barrier Reef Foundation, and Wuthathi and Meriam traditional owners.Recovery work intensifiesA small team visited the remote island several times a year barging in heavy machinery.They identified “hotspots” for cliff fall deaths and rescued hundreds of stranded turtles each season.The recovery team also used heavy machinery to rescue stranded and overturned turtles.(Supplied: Gary Cranitch/Queensland Museum)”Now we’ve got about 1,750 metres of fencing above that cliff area and that has virtually reduced cliff fall deaths to nothing.” Dr Dunstan said.The team has so far shifted 30,000 cubic metres of sand to re-profile nearly a third of the island.Hatchling production has nearly doubled from those areas.Raine Island is losing less eggs due to flooding but still has problems with hatching success.(Supplied: Queensland Government)Technological innovationThe work has been accompanied by a sophisticated monitoring and research effort using 3D modelling, satellite technology and drones.The team this week published research on how they used drones to count turtles more easily, safely and accurately than traditional methods such as surveying from boats.”Historically what we used to rely on was counting the number of turtles on the beach at night,” co-author Dr Richard Fitzpatrick from the Biopixel Ocean Foundation said.The research found counting turtles using drones was significantly more accurate than counting them from land or from boats.(Supplied: Gary Cranitch/Queensland Museum)”The fact the sea turtles don’t come up every night … it’s not a really accurate count.”The team painted white stripes on 2,000 turtles then filmed them in the water using a drone.By working out the ratio of painted versus unpainted turtles they estimated about 64,000 turtles came to nest on the island last December.Researchers painted a white stripe on 2,000 turtles to help estimate how many were aggregating.(Supplied: Christian Miller)Population crash still expectedDespite the project’s success, Dr Dunstan warned the green turtle population was likely to crash in the near future.”There’s been two or three decades of bad hatching success and low hatchling output, and because they take 35 years to reach maturity we actually should see a crash at some stage reasonably soon,” he said.He said the rookery still faced many threats including lower hatching success during busier nesting seasons as well as climate change impacts.”[We’re] finding no males in new recruits because the sand is just too hot and there’s a sex determination temperature during incubation,” he said.Incubation temperatures below 29 degrees Celsius will produce male turtles while above 29C will result in female turtles.(Supplied: Christian Miller)Dr Dunstan said it was critical recovery efforts continued at the rookery.”It’s not like there are other islands they could just go to. That’s why there’s this big aggregation at Raine — it’s the one great spot,” he said.
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