If you have visited the National Marine Life Center before, you might have had chance to meet some of our Kemp’s Ridley sea turtle patients. Kemp’s Ridleys travel to the Massachusetts coast in the fall because food is more abundant here this time of year. When winter hits, the turtles know it’s time to head back South, but some get stuck in Cape Cod Bay and get cold stunned. The lucky ones that are spotted are brought to animal rehabilitation centers, like the National Marine Life Center, where they are nursed back to health and released again. Most of the turtles we receive are about two to five years old, but I would like to take a moment to focus on the very beginnings of these turtle’s lives; nesting season.
Kemp’s Ridleys nest from April through July along the Gulf of Mexico, but they may start nesting earlier further south. Most sea turtle species nest at night; however, Kemps Ridley’s are the outliers and nest during the day. They crawl from the ocean and make their way up the beach, looking for the right spot to nest. Once they find a spot they deem worthy, they create a body pit by digging sand away with their back flippers and covering their back ends. Once the body pit is finished, they start to dig down in order to make an egg chamber. This is one of the more intricate stages of nesting because depth of the chamber is important for egg development. If the chamber is too deep, then the eggs will get too cold. If the egg chamber is too shallow, then the eggs will overheat. Not only does the nesting female need to feel out the right depth in order for the eggs to develop, but also she needs to dig to a depth that will produce roughly the same number of males and females. The sex of a turtle is determined during development by the surrounding temperature. When the eggs are warmer, females are produced and when the eggs are colder, males are produced. Digging to the right depth is fortunately instinctual for turtles; however, it can prove to be more difficult for many organizations that relocate nests to hatcheries.
Once the chamber is ready to go, the female will start laying her eggs. While she is depositing her eggs, she will go into a sort of trance, during which it is extremely unlikely that anything will disrupt her. At this point, she is committed to the spot and will finishing nesting. Once all of her eggs are deposited, she will use her back flippers to bury the eggs and then camouflage the nest with the surrounding area. Then she will make her way back to the ocean and leave the nest on the beach. After about 55 days, eggs will start to hatch and little baby turtles start to emerge from the sand. Then they need to make the crawl down the beach to the ocean. During this short period on the beach, they are vulnerable to sea gulls, crabs, and other predators looking for a meal. Once they make it to the ocean, they swim for three days straight using energy they have reserved from their yolk sacs. After the three days, they are safer out in the open ocean and can start to forage and grow into adulthood.
The nesting process is similar amongst most sea turtle species. Most will nest individually; however, Kemp’s Ridleys and their close relatives, Olive Ridleys, have a unique nesting behavior.
While they also nest individually, they are known to nest in groups that can range from hundreds to thousands of turtles at a time. These nesting events are called arribadas, which means “arrival” in Spanish. During an arribada, thousands of females crawl onto the beach all at the same time to nest. These last an average of 3 to 5 days, though one of the largest arribadas recorded lasted 10 days. The first time an arribada was observed was in 1947 in Tamaulipas, Mexico when an engineer happened to be flying along the coast. The footage was somewhat forgotten for the next few years, so arribadas were not recognized by the scientific community until 1961.
This being a new discovery, there is still much to learn about this phenomenon. Scientists aren’t quite sure how all these females know to nests all at the same time, but some theories include that it is based off the lunar cycle, or a hormone may be released into the water prior to nesting. It is advantageous for turtles to nest in such large groups to an extent. When hundreds of thousands of eggs are all deposited at once, there are simply too many eggs for predators to eat them all, and once the eggs hatch, there will be too many hatchlings for the predators to eat too. This increases the likelihood of one mother’s hatchlings surviving to adulthood. However, when the group size increases and there are too many females nesting at once, they end up digging up each other’s nests, destroying the nest before it even has a chance to develop. The nests that were laid at the tail end of the arribada have a better chance of developing since there will not be any more females nesting, but that still leaves hundreds of nests that did not have a chance.
So if you ever find yourself walking the beaches of Texas or Mexico and you see one turtle or thousands crawling up on the beach, now you’ll have an idea as to what is happening.