Cold-stunned turtles

Banana boxes? Check. Air support? Check. Volunteers? Check. After several years’ experience, conservation groups on Cape Cod know exactly what they need to rescue sea turtles that wash up on their shores every winter. But how do these turtles end up stranded in Massachusetts, USA, a place that seems so far from their usual tropical waters?

Sea turtles come and feed in Cape Cod bay during the warm summer months. Come the colder months, the turtles migrate back to warmer waters in the South. However, due to the geography of the Cape, some turtles cannot navigate their way out of the bay and get trapped. As the water cools these cold-blooded animals suffer from hypothermia, loose their ability to move, and wash up on the shores of the Cape.

Fortunately volunteers patrol the beaches to help the turtles. The cold-stunned turtles are taken to an animal care centre, such as the New England Aquarium, where they receive medical treatment. The turtles’ body temperatures are gradually raised every day and their progress is carefully monitored. Full recovery can take anywhere between a few days and several months, after which the turtles are placed in specially prepared banana boxes and are either flown or driven back South and released in warmer waters.

An improvised turtle centre. (photo courtesy of Liz Maloney)

The cold-stunned turtles are cared for at rescue centres
(photo courtesy of Liz Maloney)

This year, for the first time since the start of the rescue activities, volunteers are recovering turtles from the beach as late as January. This may be due to rising temperatures, which causes the turtles to migrate south later in the season. Already over 500 cold-stunned turtles were reported this season, amongst which are Kemp’s ridley, loggerhead, and green turtles. In 2014 a record of 1200 turtles were recovered from the beaches around the Cape. Thanks to the efforts of the volunteers and rescue centres, the majority of these turtles made it back home safely.

a turtle in a box (photo courtesy of Liz Maloney)

Getting ready for the trip home!
(photo courtesy of Liz Maloney)

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Female-biased sea turtle populations

The temperature at which a sea turtle egg incubates determines the sex of the hatchling. Below a pivotal incubation temperature of about 29.0°C the majority of individuals are born male and above that temperature the majority of individuals are born female. This unique process, known as Temperature-Dependent Sex Determination (TSD), is widespread among reptiles.

What will happen to sea turtle populations when air temperatures rise due to climate change? This is a central question of my latest research, the results of which were published in the Journal of Experimental Marine Biology and Ecology this week.

The study was a collaboration between researchers from Swansea University (United Kingdom) and Deakin University (Australia), and conservationists working on the Dutch Caribbean island of Saint Eustatius. We recorded sand temperatures at a turtle nesting beach where leatherbacks, hawksbill and green sea turtles nest. These data were combined  with temperature projections from the Intergovernmental Panel on Climate Change (IPCC) to model how sand temperatures will change in the next 100 years.

The results showed that sand temperatures are relatively high (ranging from 29.1-33.3°C) at this nesting site and that all three species of sea turtles are female-biased: we estimate that for the current populations of hawksbill, leatherback and green turtles the percentage of turtles born male are 36%, 24%, and 16%, respectively. Projecting into the future, it is likely that the female-skew will be intensified due to warming air temperatures. For example, projections indicate that only 2.4% of green turtle hatchlings will be males by 2030, 1.0% by 2060, and 0.4% by 2090.

Nicole Esteban, a Swansea University researcher and former St Eustatius National Parks (STENAPA) manager, who is a lead author of the paper says that “there is a real concern that there will not be enough males born on Saint Eustatius in the future. If there are too few males, the local population is at risk of collapsing. Another concern is that turtle eggs do not develop above a certain temperature. The study highlights the extinction risks of climate change to species whose biology is closely linked to temperature.”

This research underlines that there is real need for effective conservation measures to be put in place to prevent the localised extinction of these turtle populations. Potential conservation strategies include shading turtle nests on the beach or moving nests to a cooler section of a beach such as a protected hatchery.

fdfa http://www.frogfishphotography.com/index.html

A hawksbill turtle swimming near a wreck in Saint Eustatius
(photo courtesy of Frogfish Photography)


Sand temperatures for nesting sea turtles in the Caribbean: implications for hatchling sex ratios in the face of climate change” was published by the Journal of Experimental Marine Biology and Ecology (2016). Authors: Jacques-Olivier Laloë, Nicole Esteban, Jessica Berkel and Graeme C Hays.

Terrestrial basking and climate change

Terrestrial basking is a rare behavior observed in populations of green sea turtles in Hawai’i, Western Australia, and the Galápagos Archipelago. Being cold-blooded, the main reason why turtles bask on land is probably to regulate their body temperature but scientists speculate that terrestrial basking may also aid immune function, predator avoidance, and may even prevent unwanted courtship.

New research published in Biology Letters examined the relationship between terrestrial basking and climate. Having counted the number of turtles that bask on one Hawaiian beach every day for six years, the researchers found that terrestrial basking peaks in the year when the sea surface temperatures are lowest. Terrestrial basking generally happens when sea surface temperatures fall below 23°C. This suggests that terrestrial basking is a response to seasonally cool ocean temperatures.

Picture 2

Basking varies seasonally in concert with cool SST. Green circles are standardized anomalies of the number of turtles observed basking weekly at Laniakea, Oahu. Blue circles are weekly AVHRR SST data for this location. Thick dark lines are the Fourier series for each timeseries. (Source: Biology Letters)

However, since the sea surface temperatures at the sites where turtles bask on land is warming on average 0.04°C per year, the researchers predict that in the future the waters will be warm enough that the turtles will no longer come on land for warmth. The researchers estimate terrestrial basking may cease in Hawaii by 2039, in Australia by 2086, and in the Galápagos by 2102. Since other populations of marine turtles are successful without having to resort to terrestrial basking, this will probably not have drastic negative impacts on these green turtle population, but this does mean that beach goers of the future will not have the privilege of sharing the beach with napping turtles.

Sea level rise

Climate change challenges conservation efforts worldwide. Different aspects of climate change are affecting sea turtle populations across the globe. Rising temperatures are an obvious problem for a species with temperature-dependent sex determination. Similar to crocodiles, the incubation temperature of a sea turtle egg determines the sex of the hatchling. The pivotal temperature is close to 29°C: nests that incubate below this temperature produce a majority of males and nests that incubate above it produce a majority of females. Therefore, a warming world would cause a female-bias in sea turtle populations.

Another dangerous aspect of climate change for sea turtles is rising sea levels. A risk of rising sea levels is that turtle nesting beaches will be lost and this could push local turtle populations over the brink unless new suitable nesting beaches are found. A new study that will be published in the December issue of the Journal of Experimental Marine Biology and Ecology looks at the predicted effect of sea level rise on the hatching success of leatherback turtles nesting in Colombia.

The study was conducted on La Playona Beach and looks at the effect of water content of sand on the hatching success of turtle nests. The results of the study show that high sand water content was correlated with reduced hatching success: the wetter a nest, the fewer hatchlings survive from that nest. Projected climate change may therefore be detrimental to the breeding success of sea turtles as nests will have higher exposure to water due to sea level rise and an increase of hurricane events (another predicted consequence of climate change).

Scatterplot showing the relationship between percent sand water content and hatching success (the proportion of eggs that produced live hatchlings that emerged from the nest at the sand surface) in leatherback turtle nests A) in-situ (r = − 0.73, F1,28 = 32.48, P < 0.0001) and B) in experimental clutches in five different sand water content treatments (r = − 0.84, F1,19 = 45.59, P < 0.0001). Black lines shows linear fitted lines. (Source: The Journal of Experimental Marine Biology and Ecology)

The authors of the study conclude that “projected climate change and sea level rise may thus negatively affect leatherback turtle nesting success, although there are several avenues for adaptation to such future change.” They also recommend studying whether or not similar results are found with other species of sea turtles.

Another interesting result of the study is that hatchlings born in wetter nests were smaller in size. They did not appear to have less vigour, though. This last part of the study was measured by “racing” different-sized baby turtles on the beach!