Sea Turtles! Part 1: General Sea Turtle Biology and Behavior
Photo credit: http://www.theanimalfiles.com/reptiles/tortoises_turtles/green_sea_turtle.html
My ultimate goal for interning at the National Marine Life Center this summer is to get some marine animal care and education experience for my future. In two years I will be entering graduate school, and looking to further my education in sea turtle conservation. On Monday, the other interns and I took a field trip out to Boston to check out the New England Aquarium to get a chance to see some animals and “nerd out” together. It was truly a great experience for all of us because we got a chance to learn from each others’ backgrounds. Last summer I worked as a reptile care intern at Omaha’s Henry Doorly Zoo, so I felt like my trip to the aquarium worked like a bridge to connect my previous experience with animal care and husbandry with my current work trying to learn about marine animals and education. While we were at the aquarium, I bought a great book called Sea Turtles of the Atlantic and Gulf Coasts of the United States. Though I’ve only read bits and pieces of it, I’ve learned so much already, and so for this week, we’re going to talk about some things that I knew, and some things that I’ve learned. My passion: sea turtles!
To start off, sea turtles are reptiles. The main characteristics of reptiles are:
1. They are air-breathing, so they have lungs just like humans.
2. Reptiles are “cold-blooded,” or ectothermic, which means that the temperature of their body is greatly affected by the temperature of the air or water around them.
3. Reptiles lay eggs.
4. They have scales covering their skin.
Sea turtles are unique among freshwater turtles and tortoises because they can’t withdraw their head or limbs into the shell. Their shell is designed to be hydrodynamic, as many may never leave the ocean unless they are ill or nesting. Evolution sacrificed the space necessary for the added defense of pulling into the shell for the added speed of the sea turtle shell design.
General Turtle Anatomy
Sea turtles, like other turtles and tortoises, do not have teeth. They have a hard beak called the rhamphotheca, and in some species the lower jaw is serrated, while in other’s it is smooth but sharp.
Photo credit: http://www.scubadivinginplayadelcarmen.com/playa-del-carmen-marine-life-guide/sea-turtles.htm
The top part of the turtle’s shell where the “back” is is called the carapace.
The bottom part of the shell where the “belly” is, is called the plastron.
Green sea turtle showing plastron. Photo credit: http://www.vims.edu/newsandevents/topstories/archives/2009/green_sea_turtle_release.php
The area on the side that connects the two is called the bridge. The scales on the shell are called scutes.
It is very difficult to tell a live sea turtle’s age. You can take an estimate based on size, but the size may not always be an accurate description of age in sea turtles. Especially once adults have reached sexual maturity, their growth slows greatly and nearly stops, so unless you’ve tagged it, you may be completely unable to tell the age of the animal.
A researcher putting a tag in the flipper of an Olive Ridley sea turtle. Photo credit: http://www.visualphotos.com/image/1x9147179/olive_ridley_sea_turtle_lepidochelys_olivacea
Adult male sea turtles can be distinguished from females by looking at the tail. In males, the tail is quite long, extending far from the back edge of the shell. This is because residing within the tail is the male sex organ used for copulation.
You may be curious about how a sea turtle is able to process all the salt that it ingests from the salt water it lives in. Sea turtles have special glands near their tear ducks called lachrymal glands. These glands excrete excess salt in their bodies so the animal doesn’t get dehydrated.
There are 7 species of sea turtles, 5 of which we see in Cape Cod. These are the leatherback, green, loggerhead, Kemp’s Ridley, Hawksbill, Olive Ridley, and flatback.
Sea turtles are polygamous, which means that both males and females may mate with many partners. Sea turtles don’t only have many partners in a lifetime, but they will have many partners in each nesting season. In fact, a clutch of turtle eggs may be the product of many fathers.
Sea turtles mating. Photo credit: http://www.archelon.gr/eng/biology.php
Females choose who they mate with. If they are approached by a partner that is not suitable, she will frequently cover her cloaca (the hole where waste is excreted and where copulation takes place) with her back flippers and settle on the ocean bottom until the male goes away or until she needs to surface to breathe. Mating is not a fun task for adult turtles. Males will often bite females on their neck and flippers, leaving open wounds that heal slowly, often taking weeks to do so. Males will compete to mate with the female, so if one male is mating with a female, another male will frequently approach and try to pry the male off, or bite his head, flippers, or even his tail.
Males competing for access to a female. Photo credit: http://seapics.com/new-pictures/2008/2008-01-new-pictures.html
Males in many species use the claws that appear on their front flippers to hang on to the female’s carapace during mating.
Females will produce hundreds of eggs during a nesting season, and it takes a toll on the animal’s body. This is why females don’t participate in nesting every year, they will usually lay eggs every 2-4 years. Females must leave the ocean and come out on the beach to lay their eggs. Most sea turtles lay their eggs at night in order to expose their eggs to fewer predators. Also, turtles don’t put all their eggs in one basket – so to speak.
A female leatherback returning to the ocean after nesting. Photo credit: http://seaturtles.photoshelter.com/gallery-image/Sea-Turtle-Images/G0000_8GK4yEUHhc/I0000ga8IbbcTvGo
Sea turtles will lay many nests in a season, with approximately 100 eggs per nest. She will come out, dig a hole in the sand with her back flippers, deposit the eggs in the sand, and then cover the eggs and fling sand everywhere in order to disguise the nest. She then returns to the ocean and will mate again and come back to the beach in a few days or a few weeks and lay another nest. If a female attempts to come up on land to lay her eggs, but is scared by the presence of humans or potential egg predators, she will return to the sea and lay her eggs somewhere else along the beach or at a later time, and these tracks are referred to as “false crawls.” Females also tend to return to the same beach that they hatched from to lay their eggs, this is called “nest fidelity.”
As in other reptiles, turtles have temperature dependent sex determination. What this means is that the temperature of the nest determines whether there will be more males or more females in the nest, and after certain temperatures the nest will be all male or all female. For sea turtles, warmer temperatures produce females and cooler temperatures produce males. A phrase I use to remember which temperature produces which sex is “hot chicks and cool dudes.”
Green sea turtle nest. Photo credit: http://www.allposters.com/-sp/Green-Sea-Turtle-Eggs-in-a-Nest-on-a-Beach-Chelonia-Mydas-Pacific-Ocean-Borneo-Posters_i6011847_.htm
The turtle eggs will incubate for 50-65 days before they begin to hatch. Find out more details about the life cycle of sea turtles and the dangers they encounter in my next blog: Sea Turtles! Part 2.