Researchers tracked 27 female loggerhead turtles using satellite devices over a ten-year period from 2001 to 2012.
The year-long survey revealed, for the first time, that the turtles were using multiple nesting sites hundreds of kilometres apart, researchers say.
Three of the 27 turtles died within the first year of being followed due to entanglement in fishing nets, suggesting an annual mortality rate of 11 percent, which the team says is “alarmingly high”.
The waters off the coast of Middle East and North Africa are proving to be death traps for the Mediterranean loggerhead turtles.
As adult loggerhead turtles migrate to these regions in search of food and nesting sites, they get entangled in fishing nets used by small-scale fisheries, leading to their early death, according to a new study published last month in Diversity and Distributions.
The high adult turtle mortality rate in the region has conservationists worried.
“The mortality rate and level of bycatch in these countries is very concerning,” lead author Robin Snape, a turtle researcher at the University of Exeter, said in a statement.“There is poor understanding of the need for conservation and of the impacts that fishing practices can cause.”
Previously, by monitoring turtle strandings on beaches of North Cyprus and interviewing fishermen, Snape and his colleagues estimated that as many as 1000 turtles were being accidentally caught annually by small-scale fisheries in waters off North Cyprus.
To get a more complete picture of how loggerhead turtles move in the Mediterranean, where they feed, and the threats they face, Snape and his team tracked 27 female loggerhead turtles from North Cyprus nesting beaches using satellite devices over a ten-year period from 2001 to 2012.
The ten year-long tracking revealed a number of previously known — and unknown – nesting and feeding sites of the turtles off Cyprus, Egypt, Libya, Tunisia, Turkey, Syria and Israel. The team also found that the turtles were often nesting in different countries instead of returning to the place of their birth to lay their eggs.
“This is the first time that nesting events hundreds of kilometres apart and among multiple geopolitical units have been documented for Mediterranean loggerheads,” the authors write in the paper.
Three of the 27 female turtles, however, died within the first year of being followed, suggesting an annual mortality rate of 11 percent. Researchers say that these turtles were killed as a result of getting entangled in fishing nets used by small-scale fisheries.
This mortality rate is alarmingly high, Snape told Mongabay. “A relatively high proportion of our study girls were getting killed very quickly.”
“Ten to twenty percent annual mortality is considered to be high for adult loggerheads and suggests high anthropogenic mortality,” he explained. “Consider that an adult female loggerhead may lay around 280 eggs once in every two to four years. Half of these eggs could be lost to predation or washed away at the nesting beach. Even when protected by conservation efforts many nests will fail to hatch. Then of hatchlings only a fraction will survive it to adulthood. An adult female needs at least 10 years, probably more, to produce enough successful young to replace herself with one adult in the population. At 10 percent annual mortality the turtles are barely achieving that. Given that our estimate is likely conservative the picture is worrying.”
The IUCN currently classifies the Mediterranean loggerhead turtles as Least Concern on the basis of their overall population estimates, the authors write. But this status is a product of decades of intensive conservation efforts at nest sites, they add, which could be reversed should these efforts cease.
To protect these turtles, researchers need to better understand the small scale fisheries sector and halt development at nesting sites, Snape said.
“Since small scale fisheries are so diverse, involving many people, often some of least affluent community groups, they are difficult to understand and manage,” he said. “More studies are needed to better understand how these fisheries operate and to mitigate their impacts as best as possible, whilst impacting the livelihoods of as few people as can be.”
“At the same time, since this mitigation can not be achieved within a short time frame due to political unrest and lack of country-specific information, the nest protection schemes in Greece, Cyprus, Turkey need to be better supported and beefed up,” Snape added. “Unfortunately nesting habitat is still being lost to development in Greece and Turkey and there are examples in both the Turkish and Greek communities of Cyprus.”
- Snape, R. T. E., Broderick, A. C., Çiçek, B. A., Fuller, W. J., Glen, F., Stokes, K. and Godley, B. J. (2016), Shelf life: neritic habitat use of a turtle population highly threatened by fisheries. Diversity Distrib.. doi:10.1111/ddi.12440