As you may have read in my previous blog (Sea Turtles Part 1) or in Alexa’s blog (New England Aquarium Adventure), the National Marine Life Center interns took a trip to the New England Aquarium last week. While we were there, we animal nerds got our fill of marine life from all over the world. For me, of course, the sea turtles were the most exciting part! While visiting the gift shop, I obtained a wonderful book called Sea Turtles of the Atlantic and Gulf Coasts of the United States. It has really been a wonderful resource for me to deepen my understanding of sea turtles biology, behavior, and the things that threaten them in the wild. I’ve learned so much, in fact, that I’ve had to split up my sea turtle blog into several parts. This section deals with the things that threaten turtles, some of these problems are unique to sea turtles, others are quite common among marine animals throughout the ocean: disease, predators, human impacts and the conservation efforts being done to counteract these threats and save these animals.
One of the most common diseases that affect green sea turtles is fibropapillomatosis. Fibropapillomatosis is a debilitating skin disease that affects sea turtles all over the world. This skin disease causes the turtles to develop tumors on their skin. Though it most commonly affects greens, it has also been documented in loggerheads, Kemp’s ridleys, olive ridleys and leatherbacks. This disease can be fatal if it invades the turtle’s internal system, but will often heal if the tumors are superficial. Scientists also think that this could be a virus because herpes was found in 95% of all Florida cases.
There are a number of internal parasites found in sea turtles. Some of the most common ones include flatworms and blood flukes. In fact, 33% of loggerhead sea turtles on the east coast are found with disease-producing blood flukes.
Flatworms are also frequently found in sea turtles. All species of flatworms are found in the gastrointestinal tract except for one that has been found in the bladder. Though these flatworms are parasites, they do not necessarily seem to cause weakness to the turtle. Most wild turtles will have some kind of parasite on or within it, but until the population increases to a high number, the parasite may not be debilitating to the animal.
Roundworms are also found in the stomach or intestinal tract of sea turtles, but frequently the turtle will show no indication of a negative impact caused by these parasites.
Some of the common external parasites found on sea turtles include leeches and a number of different species that reside on the shell called epibiota. Leeches are usually seen around where the flippers attach to the rest of the body.
Epibiota is found on the shell, and these organisms can include barnacles, mollusks, polychaetes, amphipods and algae. Both leeches and epibiota are found most commonly on loggerhead sea turtles. Typically, epibiota doesn’t seem to affect the sea turtle; the organisms and the turtle are in a “commensal” relationship. So, the epibiota benefit from the association, and the turtle receives no benefit or detriment from their presence. A healthy turtle can control the amount of organisms by scraping them off with its flippers. Also, as the turtle grows it sheds the scutes (or shell scales) and so some organisms will be evicted that way. However, if a turtle is sick, it may not be strong enough to control the orgasms, and the internal and external parasites will compound. If too many organisms find a home on the turtle shell it reduces the turtle’s speed and drag it down. If the turtle doesn’t scrape them off right away though, they can potentially become permanent residents. Some barnacles are actually only found on sea turtle shells!
Predators and Dangers
So after a mother sea turtle lays her eggs in a nest chamber on the beach, the dangers begin for the baby turtles. The eggs can be easily trampled by careless humans or other large animals traversing the beaches. If some eggs are trampled or cracked open by predators, it not only releases a scent that makes them easier to find, but can contaminate the clutch and kill far more turtles than were initially consumed. In leatherback and hawksbill nests, “false eggs” are frequently found – these are just shelled albumin. These eggs are often much smaller than eggs containing a developing embryo and are sometimes even dumbbell shaped. The function of the false eggs is currently unknown, but it must have some kind of evolutionary advantage. Some hypotheses include keeping moisture high in the nest or maybe even distracting predators.
When a turtle is hatching from the egg, it uses a caruncle (egg tooth), a hard appendage on the top of its beak to break through the shell.
In order to avoid the most predators, hatchlings usually hatch at night, though this is not foolproof because there are nocturnal predators as well. The hatchlings on the top of the nest can feel if it’s time to rouse the rest of the hatchlings if the sand above the nest is cool or warm, indicating night or day. If the top turtles start digging and wiggling around in the nest, the others will follow. Usually they go about this in spurts, all digging for a while, then all resting, until finally they break through the top and are able to move together out of the nest. Those who hesitate lose the advantage of surprise, and have a less likely chance of reaching the ocean undetected. The most common predators of eggs and hatchlings include ghost crabs, sea birds, bears, raccoon, feral pigs, ants, armadillos, feral/domestic dogs and, of course, humans.
Hatchlings face many of the same predators and dangers that the eggs do, plus some. In the water they face big fish, sharks and much more. Also, once sea turtles reach the ocean, they are solitary animals, though they are sometimes seen in groups because of similar migration routes. Hatchlings face human-caused dangers as well – like light pollution. Hatchlings use the brightest light source as a way to navigate back to the ocean. We think that maybe they’re looking for the moon reflecting off the waves. However, if the brightest light source isn’t the ocean, and it’s actually a street light or house, turtles will head in the wrong direction. If hatchlings are heading away from the ocean their chance of being spotted by terrestrial predators goes up significantly, they also only have a small amount of energy left from the nutrients they received from the egg, so they can starve. They can also fall into holes or gutters and become trapped.
- Only one out of 100 hatchlings will survive because of the many obstacles they face. One attempt to help these animals is through headstart programs. These are done for many turtles, such as the red-bellied cooters that the NMLC has participated in. This program involves taking hatchlings from the wild and raising them in a facility that keeps them safe from predators and allows them to grow up so that they are not as easily preyed upon. Once they reach a certain size they are then released back into the wild to hopefully proliferate!
Adults and juveniles face similar dangers. Human caused issues stem frequently from pollution, bycatch, entanglement, destruction of habitat (including nesting beaches) and active harvest.
Pollution is a huge issues for turtles, specifically littering. Turtles often mistake plastic bags floating at the surface for food, and this is fatal. It can either cause an obstruction in the digestive tract, or it will make the turtle feel as though it’s full even though it’s not getting any nutrients, and it will starve to death. If fishermen do not responsibly dispose of their fishing line, turtles can easily become entangled. Fishing line may look relatively harmless, but it can easily cut into marine animals’ skin and cause deep wounds, infections, and even painful amputation. For more information on entanglement or how to properly dispose of fishing line, see my previous blog: Monofilament Recycling Program Underway.
The fishing industry also takes a toll on sea turtle numbers. Sea turtles are frequently victims of boat strikes. In fact, back home in the midwest, the Omaha Henry Doorly Zoo in Omaha, Nebraska is currently caring for a sea turtle that was hit by a boat in 2002 and deemed unreleasable. Her name is Bubbles and she is a 15-20 year old green sea turtle. For more information on this particular turtle please see: Omaha World Herald News Article or Omaha Zoo\’s press release.
Turtles are frequently caught in fishing nets as “bycatch” – this means that they were accidentally caught. Because turtles breathe air, if they get stuck in fishing nets and are unable to surface, they easily drown. Even if they somehow manage to get out in time, they often die of shock. TEDs (turtle excluder devices) became a mandatory piece of equipment for all trawlers fishing in US waters. These are a device that attaches to the net so that large objects (like sea turtles) will be released from the net without affecting the fisherman’s catch size. This is somewhat of a controversial issue. Because turtles experience shock from going through the fisherman’s nets, many of those that are freed from the nests will still die. Some say that the TEDs are greatly reducing turtle mortality, others, such as the author of my new sea turtle book, say that turtle deaths are actually increasing since use of the TEDs was implemented.
Of course, there is also a continuing problem with deliberate hunting in many countries. There’s still a market for sea turtle eggs and meat, and though education around the world about the need to conserve these animals is increasing, many people still kill nesting females and harvest eggs.
In addition to human caused dangers, turtles also face natural dangers. Even adult sea turtles have a couple predators like sharks and orcas. But don’t think that turtles are by any means an easy food source: Sea turtle vs. Shark.
The last threat I want to discuss is a huge issue in Cape Cod – cold stunning. If you haven’t heard, Cape Cod is a stranding hotspot – in fact it’s the third in the world next to a place in Australia and another in New Zealand! This is due to the unique geographic feature that is the Cape Cod hook.
Turtles follow the Gulf Stream up north to the Cape, and find a great foraging area here. However, when it comes time for the turtle to go south for the winter, its instincts tell it to go south, and the turtle can’t figure out that it needs to go north to escape the hook and get out into open ocean.
Because turtles are reptiles, they are ectothermic or cold-blooded. This means that their body temperature depends on the temperature of the environment around them. So, as winter approaches and the water temperature drops, so does the turtles’ body temperature. Eventually they will go into hypothermic shock, this is also called cold stunning. Their heart rates drop and they wash up on the beaches, and then they are taken to rehabilitation facilities (such as the National Marine Life Center!) where their body temperatures are warmed up very slowly (just a couple of degrees a day) until they are warm enough to be put into a tank. They are then housed until spring/early summer when they are released on the southern side of the cape toward open ocean.
YOU CAN HELP!
There are things great and small that everyone can do to help sea turtles and all wildlife.
- Donate: the NMLC needs your help to complete our hospital so we can care for our turtles that are entangled, struck by boats, or cold-stunned. Our timeline is not based on what needs to be done – but rather how we’re going to fund it!
- Volunteer: Organizations such as the NMLC and Mass Audubon Society always need help. Mass Audubon is a sea turtle rescue program. There are plenty of great wildlife programs that could use your experience/expertise in whatever field you’re in!
- Don’t litter: Obviously, please discard of your garbage and fishing line responsibly, especially your plastic bags! If you come across trash, please help by cleaning it up!
- Pass it on: teach your friends, relatives, and colleagues about the trials turtles and other marine animals face so that we can make a difference together.
- Enjoy wildlife from a distance: Your presence is stressful to the animals and your respect is much appreciated.
- Call the professionals: If you come across a wounded or stranded animal, NEVER approach a wild animal without professional assistance or permission. Sea turtles and marine mammals are protected by the federal government and these animals can carry a wide array of zoonotic diseases!
For more specific information on each turtle species, see my next blog: Sea Turtles! Part 3.