As many of you may know, loggerhead sea turtles deposit around 112 eggs within a nest. However, here in Kefalonia our nests have an average of around 88 to 94 eggs per clutch. Sea turtle eggs are spherical in shape and are the size of a ping pong ball. Each egg, as it is laid, has already been fertilized by a male sea turtle the female encountered in the breeding season. A nest can have up to five contributing fathers. This is due to the females’ ability to store sperm from multiple males within the folds of her oviduct.
However, not every egg is perfectly spherical. Egg sizes can range from miniature to extra-large, they can even come in different shapes such as oblong. Although it is rare, some eggs may not even have a shell (composed of aragonite), as we have seen once this 2014 season. Shell-less eggs only have a thin membrane protecting them from the elements. Typically both miniature and shell-less eggs only contain albumen (egg white) with possibly some small granules of yolk material and have no propensity to develop. Shell-less eggs are very hard to spot and can only be observed if the female is witnessed laying her eggs or if a relocation is performed soon after the nest was laid. Miniature and shell-less eggs are actually not counted as part of the clutch, as these eggs are not viable and contain no yolk.
Misshaped eggs can be anywhere from oval shaped to odd shapes that resemble a banana - we’re not jokin’! This is also a good time to introduce chain-form eggs. These types of eggs are linked together by small connections of aragonite (egg shell) creating a chain-like appearance and each yolk is encased in each egg within the chain. This makes them different from the oblong eggs, as oblong eggs are often one large egg with multiple yolks inside. The constriction between yolks inside these large eggs can vary and it is thought that the closer the yolks are together, the higher the chance of hatching.
When we see misshaped and abnormal eggs within a clutch, it indicates that there is a problem with the oviduct of the nesting female. More research is needed on this topic to draw further conclusions, which makes it important to monitor throughout our sea turtle nesting seasons.