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A visit to St. Lucia in South Africa during the sea turtle breeding season will allow you the chance to see the age-old nesting habits of loggerhead and leatherback turtles. In particular, the coastline of the iSimangaliso Wetland Park is the one of the major nesting site areas in Africa where these two species lay their eggs.
Sea turtles swim incredible distances – loggerhead turtles can easily migrate over 10,000 km a year, while leatherback turtles reach over 16,000 km (1). However, when the time comes to lay their eggs they are able to migrate back to the exact same beach they hatched out from.
Loggerhead turtles can sense Earth’s magnetic field, and their brains behave like a compass which allows them to navigate the huge distances between their nesting and feeding grounds. Their magnetic compass is so finely tuned that it can even sense the different rocks underneath the sands of its nest – making a ‘magnetic fingerprint’ that allows them to remember their exact place of origin forever.
Leatherback turtles, the greatest long-distance migrators, use an extremely accurate sun compass. Their circadian rhythm (the sense of what time of the day it is) is so accurate that they are able to align it to the position of the sun in the sky to orientate themselves. Leatherbacks also have a thin spot in their skulls that allows sunlight to stimulate a gland which helps them determine the season, and thus migration times, based on the length of daylight.
Research indicates that the temperature of the sand affects the ratios of male and female hatchlings. A temperature difference of as little as 0.5 degrees centigrade can change the sex of a turtle. Long exposure to high temperatures puts the eggs under stress and this affects the amount of eggs that hatch, as well as the sex ratio of the hatchlings.
The beaches along the iSimangaliso coastline encompass the most important nesting sites of the loggerhead and leatherback turtles. The sedimentary features of the nesting sites (mineral composition of the sand) impact incubation duration and hatching success. The heavy mineral sands (rutile, ilmenite and titanium) found along these shores are very dark and therefore keep the temperature of the sand higher than areas where these minerals in the sand are not prevalent. Nests in darker sands absorb more solar radiation and therefore have increased temperatures when compared with nests that lie in lighter sand, which reflects more of the incoming radiation. Shadowing may also affect sand temperature and cause differences in sex ratio within the same nesting site (2,3).
Turtle tours are offered from November to February. If you’re interested in seeing these amazing animals then contact us and we can set up an unforgettable experience for you.
- SEE Turtles – Sea turtle migration – https://www.seeturtles.org/sea-turtle-migration
- Howard, R et al (2014). Thermal tolerances of sea turtle embryos: current understanding and future directions. Endangered Species Research. Vol 2: 75-86
- Laloe, J et al (2016). Sand temperatures for nesting turtles in the Caribbean: Implications for hatchling sex ratios in the face of climate change. Journal of Experimental Marine Biology and Ecology. 474: 92 -99
- iSimangaliso Wetland Park – https://isimangaliso.com/activity/turtle-tours/
- Marine Protected Areas – https://www.marineprotectedareas.org.za/turtles