Is it Time?

Most animal species reproduce during certain periods of time, or seasons during the year. But how many species lay eggs at the exact same time and place? Probably only a rare few. One of these animals is the Olive Ridley sea turtle.

The Olive Ridley sea turtle is native to tropical areas in the Pacific, Indian, and Atlantic Oceans. They are one of the smaller sea turtles, weighing less than 100 pounds. They have a unique behavior not seen among other sea turtles. The females lay their eggs at the same time. There are certain beaches along Costa Rica that are referred to as “arribadas” or “arribazones”. "Arriba" is spanish for arrival. Local human populations around the Olive Ridleys' breeding beaches chose "arriba" or arrival to describe how hundreds to thousands of female turtles return to the exact same beaches at the same time every year. Mating with males usually takes place right near the beaches where the females lay their eggs. The Olive Ridley sea turtles are monogamous and only have to mate once for the female to lay hundreds of eggs multiple times during the breeding season. This is because the female is able to store the male's sperm inside her so she can "save" it for future fertilization. At the same time, thousands of female Olive Ridley sea turtles will travel to these “arribazones” between one and three times a year to lay eggs. It is thought that the female turtles return to the same beach they were born at. Some suggest that they remember the scent of the beach and chemosensors help guide them to it. A typical Olive Ridley female will lay about 110 eggs over a 28 day period. It is not uncommon for the females to lay over a million eggs on one beach. The eggs will hatch about two months after being laid and all the young turtles will find their way to the ocean while dodging possible predators.

Scientists believe that the Olive Ridley females lay eggs at the same time as a defense against predators. But how do they all know what time to lay their eggs? Scientists speculate that these turtles receive some “signal” from the environment that it’s time to lay eggs. Some hypotheses say that changes in tide, phases of the moon, or changes in wind cue the turtles to head to the “arribadas”.

Although the Olive Ridley was taken off the Endangered Species list, people have been reconsidering putting them back on the list due to a large decline in numbers. Humans and fishing nets are mostly to blame for their decline. The turtles’ eggs are considered a delicacy and humans have destroyed many of the “arribadas” trying to collect them.

Though we know the breeding behavior of the Olive Ridleys, it would be helpful to know why they breed that way. What is the actual cue they receive to lay eggs? Is the large grouping of females more than just a defense against predators? If we continue to destroy their breeding grounds, eventually we will destroy their species. We can learn a lot from the environment and how living organisms interact with it. We need to preserve our environments and the species that live in them so we can answer questions, like the ones we still have about the Olive Ridley sea turtles.

http://animaldiversity.ummz.umich.edu/site/accounts/information/Lepidochelys_olivacea.html
http://www.fws.gov/northflorida/SeaTurtles/Turtle%20Factsheets/olive-ridley-sea-turtle.htm
http://animal.discovery.com/fansites/caught/conservation/costa_rica.html

Posted by: Christine McConville (3)