High Mortality Rates In Mediterranean Loggerhead Turtles Caused By Fishing Nets
Despite the increasing number of marine protected areas, the oceans are becoming an evermore dangerous place to live. By-catch, pollution and climate change are just a small handful of the threats you could expect to face if you called the ocean your home. Although these threats are well-documented, fishing nets are now proving to be a nasty death trap for Mediterranean loggerhead turtles off the coast of the Middle East and North Africa.
Adult loggerhead turtles migrate to these regions in search of food and breeding grounds. However small-scale fisheries have covered the area in fishing nets, which is leading to abnormally high mortality rates from the turtles becoming part of the by-catch.
A ten year study published last month in Diversity and Distributions looked at how loggerhead turtles move in the Mediterranean, and where they feed, as well as what the direct threats to them may be. Led by Robin Snape, a turtle researcher at the University of Exeter, the team tracked 27 female loggerheads using satellite tracking technology between 2001 and 2012.
The study revealed a startling number of facts to the team, including unknown nesting sites. However it also presented an alarming mortality rate amongst the loggerheads, as 3 of the 27 turtles died within the first year giving the team an annual mortality rate of 11%.
Although 11% may not sound unequivocally high, amongst loggerheads a 10-20% annual mortality rate is considered high. “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,” Snape explains.
Whilst Mediterranean loggerheads are currently considered Least Concern under the IUCN Red List, this sort of mortality rate is highly unsustainable. However the solution is nowhere near as simple as just removing the fishing nets.
The areas most at risk contain places of political unrest, and impoverished communities. Whilst conservation efforts are little understood, the small scale fisheries can provide a much needed income to many people thus any action needs to impact upon this as little as possible.
Snape believes that “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.”
Featured Image: Strobilomyces, Wikimedia Commons, CC By-SA 3.0.
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