Loggerheads, leatherbacks, nesting and badgers…

Turtle “spoor” on the beaches of Sodwana.

Imagine a dark night, with only the stars to light the way for any living creature. The white foam of waves breaking on a lonely, pristine beach is all that differentiates the shore from the ocean. From the water, a large black shape emerges, dragging itself up the sand like a cripple. Here there is none of the abundant grace it has in the water – only herculean effort. In a rite as old as time, she excavates a hole using her rear flippers and, when she senses it’s deep enough, lays about 110 eggs which are pure white and look like ping pong balls. The nest is then carefully covered, and she drags herself laboriously back down to the ocean, disappearing into the dark waves. The eggs and baby turtles are now entirely alone with no protection. Driven by instinct, this sacred ritual is repeated over the entire productive life of the turtles.

A turtle nest quite some way up the beach.

Leatherback females will stop at as many as eleven sites (away from their actual nest) to create “decoy” nests to confuse predators. A leatherback can lay 7 to 11 individual nests per season, laying a new nest every 10 days, whilst loggerheads lay between four and six clutches in a season, before they both become quiescent (meaning they will not reproduce) for two or three years. During January and February, the baby turtles break out of their eggs and head back to the sea. To see these miniature turtles is nothing short of miraculous and absolutely awe-inspiring.

Ghost crabs are recognised as a major predator of sea turtle eggs and hatchlings around the world. Dogs, cats, ants, badgers, mongooses, gulls, rats and jackals all prey on the eggs. On my trip up the beach with Parks Board we came upon a turtle nest which had been raided. The tracks suggested that a honey badger was the culprit this time…

This nest was raided by what we suspect was a honey badger.

Sodwana falls within the iSimangaliso Wetland Park, which was listed as one of South Africa’s first World Heritage Sites in December 1999 (in recognition of its superlative natural beauty and unique global values). The park begins at Mphelane in the South and extends to the border of Mozambique in the North. It is one of the most outstanding wetland and coastal sites in Africa. Covering an area of 3 280 km², it includes a wide range of pristine marine, coastal, wetland, estuarine, and terrestrial environments. This pristine environment includes coral reefs, long sandy beaches, coastal dunes, lake systems, swamps, and extensive reed and papyrus wetlands. One of its natural spectacles is this nesting of the leatherback and loggerhead turtles.

Sodwana is one of the sites where both loggerhead and leatherback turtles return to the beaches of their birth to nest, usually somewhere between November and March. Turtles can swim incredible distances. Loggerheads can easily migrate over 10 000 km a year, and leatherbacks can cover over 16 000 km annually. Yoshi, a large loggerhead turtle released by the Two Oceans Aquarium swam 40 011 km in 1003 days (see info block to read story). Yet the females still find their way back to the beaches where they hatched. How do they do this? Well, they use a number of methods – but magnetoreception is the answer given by the latest research.

Ghost crabs contribute significantly to the casualties of both the eggs and the baby turtles.

Magnetoreception is a sense which allows an organism to detect a magnetic field to perceive direction, altitude or location. Studies show that female sea turtles can imprint or learn their home beach’s distinctive magnetic signatures at birth – through geomagnetic imprinting. Each coastline has a unique magnetic signature, and this allows the turtles to remember and use it as an internal compass in the future. Which is how turtles use their magnetoreception sense to migrate long distances (often several thousand kilometres) to their natal beach to reproduce. Why would they choose to do this? Returning to their beach of birth to breed is associated with the advantages in parasite resistance and diseases. Parent turtles can pass down their genetic makeup to help young turtles fight off local parasites and diseases – thus enabling them to have a greater chance of survival.

Next week we’ll share some rather startling facts about these incredible animals…

Jacqui Ikin & The Cross Country Team

INFO BLOCK:

Criteria for IUCN classifications:
http://cmsdocs.s3.amazonaws.com/keydocuments/summary_sheet_en_web.pdf

Yoshi the loggerhead turtle sends her last transmission after 40 000km swim!
https://www.aquarium.co.za/news/yoshi-the-loggerhead-turtle-sends-her-last-transmission-after-40-000km-swim

Evidence that Magnetic Navigation and Geomagnetic Imprinting Shape Spatial Genetic Variation in Sea Turtles”
https://www.cell.com/current-biology/fulltext/S0960-9822(18)30351-8

Watch turtle digging nest and laying eggs:
https://www.ameliaislandseaturtlewatch.com/aistw-videos.html

How do sea turtles navigate?
https://www.youtube.com/watch?v=9scOgtXTNfQ

Sea Turtle Navigation
https://www.youtube.com/watch?v=mZzS_QRUEiI