Ocean Currents » Kemp’s ridley http://blog.oceanconservancy.org News, opinions, photos and facts from Ocean Conservancy Fri, 28 Apr 2017 22:26:28 +0000 en-US hourly 1 http://wordpress.org/?v=3.4.2 5 Things Sea Turtles Need to Survive http://blog.oceanconservancy.org/2016/09/26/5-things-sea-turtles-need-to-survive/ http://blog.oceanconservancy.org/2016/09/26/5-things-sea-turtles-need-to-survive/#comments Mon, 26 Sep 2016 16:14:12 +0000 Rachel Guillory http://blog.oceanconservancy.org/?p=12999

Sea turtles have a strong sense of place—when it’s time to nest, they return to the same beach where they hatched decades before. Many residents of the Gulf Coast share that same sense of place (my own family has lived in Louisiana for more than ten generations!)

That’s why sea turtles are a great mascot for the Gulf Coast. It’s also why Ocean Conservancy’s new video outlining a vision for a healthy Gulf is told from the perspective of a loggerhead sea turtle. In honor of the star of our video, here are five things that sea turtles need to survive and thrive.

1.     A nice beach to nest on

Most sea turtles (with the exception of the Kemp’s ridley) nest at night, and always on the same beach where they were born. If a beach is crowded with lights, noise or debris, a mother sea turtle is less likely to nest there. In 2010, fewer loggerhead sea turtles nested in the Florida Panhandle because workers covered the beaches that summer, cleaning up after the BP oil disaster. Scientists also moved thousands of sea turtle eggs from Alabama and Florida beaches to Florida’s Atlantic Coast that summer, so that the hatchlings wouldn’t be killed by oil as they swam into the Gulf. Because those sea turtles were born on the Atlantic Coast, they may never come back to the Gulf.

2.     The quickest route to the sea

When baby sea turtles hatch, they instinctively run for the bright horizon offshore. But bright lights from roads, buildings and even flashlights can confuse hatchlings, causing them to run in the wrong direction. You can prevent this by using a red filter on your flashlight when you’re on the beach at night, and turning off any lights that face the ocean.

3.     A safe place to grow up

Once they’ve made it to the ocean, many young sea turtles rely on floating seaweed mats, called sargassum, to hide from predators. Sargassum is not just a nursery for little sea turtles—young fish also find safe haven here.

4.     Lots of food to eat

The leatherback sea turtle’s favorite food is jellyfish. But a floating, clear plastic bag can look an awful lot like a jellyfish dinner. When sea turtles consume marine debris by mistake, it can get stuck in their stomachs and cause major damage. Reducing the amount of trash in the ocean means turtles can steer clear of plastic and stick to the jellyfish meals they love.

5.     Your help

All sea turtles are affected by ocean trash, whether mistaking the trash for food, getting a flipper caught in a discarded six-pack ring or being unable to surface for air while accidentally stuck in a fishing net. For every sea turtle that hatches, only one out of 100 will survive to adulthood. Let’s make their chance of survival a little better by keeping our beaches clean and our trash out of the ocean.

Right now, our Gulf leaders are updating a plan to restore the Gulf of Mexico. The new plan is a step in the right direction, but there is more work to be done to protect sea turtles and all who rely on the Gulf.

Send a message to the Gulf Coast Ecosystem Restoration Council today and ask them to ensure a healthy future for the Gulf.

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Creating a Healthy Future for Sea Turtles http://blog.oceanconservancy.org/2016/09/23/creating-a-healthy-future-for-sea-turtles/ http://blog.oceanconservancy.org/2016/09/23/creating-a-healthy-future-for-sea-turtles/#comments Fri, 23 Sep 2016 15:11:54 +0000 Kara Lankford http://blog.oceanconservancy.org/?p=12954

I wasn’t really awake until our all-terrain vehicle bumped its way to the beaches of the Alabama Gulf coast. I held on tight in the dark and wondered whether this adventure had been such a good idea after all.

Then a pop of orange and red burst across the Gulf of Mexico. All that had been asleep was now vivid and busy. Sea gulls and terns swooped above the waves scanning for breakfast. A pod of dolphins broke the surface offshore. Salty fishermen appeared as the mist lifted, persistent, patient. I remember being on the beach early each morning during the BP oil disaster. Even through all the chaos the mornings were always magical as the sun rose over the Gulf. Six years later it is reassuring to see so much is well, but we know that there is still work ahead to restore this environment to its natural state. As I took in all these sights, I reminded myself: I’m here to do a job.

I had signed up with Share the Beach, a volunteer conservation program that monitors and helps protect sea turtles as they are about to hatch. The Gulf is home to many sea turtle species, including: loggerhead, leatherback, hawksbill, green and Kemp’s ridley. Each of these five species is listed as threatened or endangered and could become extinct if measures aren’t taken to support their populations.

One way to help these iconic creatures is to protect their nests and give young turtles the best chance to survive and return to the sea. If we find a nest, we lay metal fencing on the sand to protect the eggs from predators and flag the area so people know it shouldn’t be disturbed. On rare occasions, mother turtles lay their eggs too close to the high tide mark. In those cases, we carefully move the nest and eggs to higher ground so the nest won’t be inundated with water, which might kill the hatchlings.

When the eggs have been incubating in the sand for 55 days, we begin to “nest sit.” Volunteer teams watch the nests around the clock until the babies hatch. Our goal is to make sure the baby turtles reach the Gulf waters without a hitch. Many times, the baby turtles become disoriented, confusing street lights and porch lights on the land with the horizon offshore. If they head to manmade lights, we redirect them to the water. This year, Alabama had a record nesting year, which means there is hope for recovery, resilience and restoration in spite of the many stressors on the environment.

Ocean Conservancy’s new video focuses on that hope. It begins with a sea turtle that hatched in 2010 during the height of the BP oil disaster. Skipping ahead to the year 2045, the sea turtle returns to the same beach where she hatched to lay her own eggs. But, thanks to the efforts of people like you to restore the Gulf, she doesn’t find an oil laden beach; she finds a pristine environment teeming with life. That’s the future Ocean Conservancy works to achieve each day.

Join Ocean Conservancy to help create a healthy future for sea turtles and all who rely on the Gulf.  Last month, the Gulf Coast Ecosystem Restoration Council released its updated plan to restore the Gulf of Mexico. Please join us in thanking the Council for their work and asking them to take the plan a step further. Help us generate 20,000 comments to the Council to ensure a healthy future for Gulf species like sea turtles.


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10 Things to Know About Sea Turtles http://blog.oceanconservancy.org/2016/06/16/10-things-to-know-about-sea-turtles/ http://blog.oceanconservancy.org/2016/06/16/10-things-to-know-about-sea-turtles/#comments Thu, 16 Jun 2016 13:00:48 +0000 Guest Blogger http://blog.oceanconservancy.org/?p=12205

This blog was written by Roger Di Silvestro, a field correspondent for Ocean Conservancy.

Sea turtles are among the world’s most ancient vertebrates. When on land, they look cumbersome and awkward, their powerful front flippers struggling to pull their weight across ocean shores. But in the water, where they spend most of their lives, sea turtles fly through the water much as birds soar through the sky. Their flippers become wings, their disk-shaped bodies cut through the sea like torpedoes.

Sea turtles remain one of nature’s great mysteries—scientists have only begun to discover secrets of sea turtle life. Here are ten things science can tell you about these marine animals.

1. Sea turtles are reptiles, like snakes and lizards, and breathe air. They first evolved about 150 million years ago, making them survivors of the Age of Dinosaurs. The first turtles were land animals that probably looked much like the tortoises of today, with powerful, column-like legs designed to support a heavy body. Evolution turned these elephantine legs into flippers as the creatures adapted to a life of swimming. Today turtles swim in all oceans except those in the chilly Polar Regions.

2. The most obvious characteristic of any turtle is its shell. It evolved from the ribs into a box of bone covered in tough skin that protects all but the head, tail and flippers. The shell is part of the turtle’s spine and forms a sort of outer skeleton reminiscent of the exoskeletons of insects and spiders.

3. The ocean is home to seven turtle species: the leatherback, loggerhead, olive ridley, hawksbill, flatback, green and Kemp’s ridley.

4.  Sea turtles begin life in leathery-shelled eggs laid in holes dug by their mothers in sand. Depending on the species, a female may produce 50 to 200 eggs at a time, most species laying them at night. About 60 days later, the eggs hatch within a few minutes of each other and the babies races to the sea, often assaulted by a gamut of predators like crabs, gulls, raccoons and sharks. A female may lay as many as eight clutches per breeding season. On average, about one hatchling per 1,000 survives to adulthood.

5. The largest sea turtle is the leatherback, which possesses a flexible, leathery shell. It reaches a length of four to eight feet and weighs 500-2,000 pounds—not bad for a reptile that feeds mostly on jellyfish. Its search for food can take it down to 4,000 feet and across hundreds of miles: they can easily migrate 3,600 miles each way.

6. The smallest sea turtle is the Kemp’s ridley, which measures less than 30 inches long and weighs less than 100 pounds. The Kemp’s has the most-restricted nesting range of any sea turtle species—one beach, about 15 miles long, near Rancho Nuevo in Mexico. Unlike other sea turtles, Kemp’s ridleys usually lay eggs during the day and in massive groups, called arribadas (Spanish for “arrival”). In the 1940s, an arribada typically would number around 40,000 females. By the 1980s, as a result of uncontrolled collection of eggs and meat for human food, the entire The Mexican government has enforced stricter provisions on egging, and the United States has a  nesting beach in Texas where more than 100 females have laid eggs yearly for the past decade. Biologists raise the hatchlings in captivity until they are large enough to have an edge on survival, then release them from the beach where they hatched.

7. Young turtles head to the open sea, returning later to offshore and reef areas to feed. Some species travel hundreds of miles. The flatback sea turtle, however, restricts its activities to seas off Australia.

8. Sea turtles can rest underwater without breathing for up to two hours. When seeking food or evading predators, they need to surface for air more frequently.

9. All sea turtles are omnivorous when young, but the green sea turtle becomes purely herbivorous as an adult. As omnivores, the turtles will scarf down seaweed, sponges, mollusks, worms, fish and other sea life. However, leatherbacks tend to eat almost exclusively jellyfish, some of which can grow to be several feet across.

10. The average lifespan for a sea turtle is hard to nail down, given that they live for several decades and few research projects last that long. Current conventional wisdom suggests that they reach breeding age anywhere between age 3 and 50 and may live 80 to 100 years, though these figures are ballpark.


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Ocean Plastic Pollution: Groundhog Day, But This Time with Sea Turtles http://blog.oceanconservancy.org/2015/09/15/ocean-plastic-pollution-groundhog-day-but-this-time-with-sea-turtles/ http://blog.oceanconservancy.org/2015/09/15/ocean-plastic-pollution-groundhog-day-but-this-time-with-sea-turtles/#comments Tue, 15 Sep 2015 18:08:27 +0000 George Leonard http://blog.oceanconservancy.org/?p=10737

Olive Ridley sea turtle. Photo by: Matthew Dolkas.

I got a kick out of Groundhog Day, the comedy starring Bill Murray and Andie MacDowell that was released in 1993. With Murray waking each day to relive Groundhog Day alongside Punxsutawney Phil and his co-anchor, the movie was lighthearted and fun. But the science of ocean plastic pollution is starting to feel a lot like Groundhog Day. And the storyline is becoming much more troubling with each new publication.

This week a new study in the peer-reviewed journal Global Change Biology calculates that over half of the world’s sea turtles have ingested plastic; this follows on the heels of a publication last month by some of the same scientists that predicted that nearly all of the world’s seabirds would be contaminated with plastics by 2050 unless action is taken soon. With each new publication, the case for a global strategy to stem the tide of plastics into the world’s oceans becomes ever more vital.

Qamar Schuyler is lead author on this study alongside Chris Wilcox and Denise Hardesty (members of an independent scientific working group at the National Center for Ecological Analysis and Synthesis that Ocean Conservancy convened in 2011) and four other ocean experts. The team applied the same analytical approach used in Dr. Wilcox’s seabird analysis, with disturbingly similar results. By integrating global maps of plastic in the ocean and sea turtle distribution, they showed that these endangered animals are most at risk of plastic ingestion in hotspots along the coastlines of southern China and Southeast Asia, and the east coasts of Australia, the United States and southern Africa. Olive Ridleys are the species at greatest risk because of its broad diet, oceanic life style, and its tendency to selectively ingest plastics. Kemp’s Ridleys are the species least at risk because of its tendency to eat animals that live on the bottom of the ocean, rather than forage at the ocean surface.

Due to limited data, the authors couldn’t determine the population and species level impacts of their findings; but given that as little as 0.5 gm of ingested plastic can kill a juvenile turtle, there is clearly cause for concern. Just as for seabirds, contamination rates for sea turtles have increased over time and Schuyler estimates that 52% of the world’s remaining sea turtles have plastics in their gut. That number is 62% for the world’s seabirds. Groundhog Day indeed.

At Ocean Conservancy, we are responding decisively to this onslaught of new science. We are now leading an effort to stem the tide of plastics from the regions that are the greatest source of plastics to the ocean, currently rapidly industrializing countries in Asia. Schuyler’s study confirms that this region is a critical beachhead in our campaign against ocean plastic pollution. Our team is also actively planning a November 2015 meeting of our Trash Free Seas Alliance ® to confront the consequences of this emerging science head-on and to advance plans to solve this problem at scale. The Alliance brings together conservationists, industry leaders, and scientists with a common purpose of keeping marine debris out of our ocean and waterways. Long the responsibility of individual consumers and cash-starved governments, plastics in the ocean is increasingly a problem that requires private sector leadership and resources to help solve, an issue that is at the center of our work with the Alliance.

The good news is Groundhog Day came to an end and Bill Murray and Andie MacDowell lived happily ever after. In the ocean, sea turtles and seabirds can have a happy ending too, but only if we collectively commit to stemming the tide of plastics that is increasingly contaminating the ocean’s wildlife.

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Interview: Dr. Blair Witherington on Oil’s Impact on Turtles in the Gulf of Mexico http://blog.oceanconservancy.org/2013/12/23/interview-dr-blair-witherington-on-oils-impact-on-turtles-in-the-gulf-of-mexico/ http://blog.oceanconservancy.org/2013/12/23/interview-dr-blair-witherington-on-oils-impact-on-turtles-in-the-gulf-of-mexico/#comments Mon, 23 Dec 2013 14:50:33 +0000 Matt Love http://blog.oceanconservancy.org/?p=7230

Dr. Witherington with an oiled Kemp’s ridley turtle in the Gulf of Mexico.

(This blog is part of a series of interviews with scientists who are championing marine research in the Gulf of Mexico.)

A research scientist with more than 24 years of experience in sea turtle biology and conservation, Dr. Blair Witherington has worked with the Florida Fish and Wildlife Conservation Commission’s Fish and Wildlife Research Institute since 1992. He is also an adjunct assistant professor, department of zoology, University of Florida; served as president of the 20th International Sea Turtle Symposium; and is vice chair of the Northwest Atlantic region of the Marine Turtle Specialist Group of the International Union for Conservation of Nature. He has authored or contributed to more than 40 scientific articles, monographs and book chapters. In addition, he has written five books on sea turtles and other natural history subjects.

The BP Deepwater Horizon oil disaster had an immediate and particularly harmful effect on early juvenile sea turtles in the Gulf of Mexico. The worst marine oil spill in history also served to highlight a compelling need for assessments of open-sea habitats – research critically lacking in 2010, yet essential for conservation efforts and restoration planning.

Ocean Conservancy:  Turtle researchers call the post-hatchling and juvenile life stages “the lost years.” With the exception of one species, loggerhead juveniles, the early open-sea surface lives and distribution of juvenile green turtles, hawksbills and Kemp’s ridleys have been poorly understood. Your recent research is changing that. Tell us how.

Dr. Witherington:  Many other researchers have been intrigued by the mystery of the so-called “lost years.” Work I am doing with colleagues Shigetomo Hirama and Robert Hardy builds on the accomplishments of others who have inferred from indirect evidence how the youngest sea turtles disperse from land and live on the open sea. The importance of our recent contribution may be in the opportunity we’ve had to study these turtles directly. We hypothesized where we might find these “lost” turtles, went out to locate them there, and there they were. In observing these turtles within their sea-surface habitat and capturing them to allow measurements and assessment of their diet, we’ve learned definitively how these turtles live.

OC:  How does knowing more about the distribution of juvenile sea turtles in the open waters of the Gulf help guide conservation and protection efforts?

Dr. W.:  One of the most important conclusions we’ve drawn concerns the nature of the habitat that young turtles depend on. The early life stages of at least four sea turtle species in the Gulf are closely tied to surface convergence zones. As the name suggests, these zones are places at the sea surface where water converges and things accumulate. One of the most important accumulations is of the brown alga (a seaweed) called pelagic Sargassum, a floating plant that is the basis for a diverse community of unique organisms. Young sea turtles are closely tied to Sargassum, float within it, and feed on the animals that drift within these open-sea rafts. To fully protect sea turtles it will be essential to understand how Sargassum drift habitat is distributed and what threatens it. Some threats are direct, like the harvest of Sargassum for livestock feed (a practice that has been stopped in U.S. waters). But most threats are indirect and come from the nature of the oceanography where the Sargassum floats—oceanic convergence zones. These zones collect many bad things, including plastics and petroleum. We are just beginning to understand how extensively these pollutants threaten turtles with entanglement and ingestion hazards.

A juvenile green turtle within a seaweed mat in the Gulf of Mexico.
Photo: Blair Witherington

OC:  You spent time in the Gulf rescuing turtles and studying how they were injured by the BP Deepwater Horizon well blowout, the worst oil spill in history. What did you see and learn?

Dr. W.:  The Gulf spill harmed young surface-pelagic turtles profoundly. My involvement with response efforts during the spill was with a team of scientists and field workers whose job it was to rescue turtles at sea in a quantitative way. By this I mean that we carefully recorded our search effort and where we observed turtles so that we could not only tally the numbers of animals affected by the oil, but we could also estimate turtle numbers from places we couldn’t get to. The spill was enormous, and unfortunately we could only get vessels and search teams to a thin fraction of the event’s area and time period. Storms periodically threatened crew safety and much of the area that could be searched was over a hundred miles offshore and inaccessible to the small vessels we had available. What we learned was that our fears of the vulnerability of small sea turtles to oil were well founded. The convergence zones where Sargassum habitat collects and where young turtles live were the areas of surface water where petroleum concentrated the most. In the convergence zones we searched, we collected hundreds of oiled juvenile sea turtles representing four species: green turtles, Kemp’s ridleys, hawksbills and loggerheads. Most were 1- to 2-year-old turtles, about the size of a coconut and a kilo in weight. In the worst cases, the turtles were imbedded in mats of congealed grease and covered so thickly with tenacious oil that they were barely recognizable as turtles. In addition to external oiling, turtles also had oil lining their esophagus. It was pretty bad. The live oiled turtles we rescued were taken to facilities for cleanup and rehab. Hundreds of turtles were saved. It was difficult but rewarding work.

OC:  What risks are posed by an oil spill to the widely scattered seaweed-raft habitats occupied by these young turtles?

Dr. W.:  Although there is a lot to be learned from massive events like the BP spill, many hundreds of smaller spills occur in the Gulf each year. These releases of petroleum result in floating oil and tar that is carried by surface water into pelagic turtle habitat. We see evidence of this in the years with no headline oil spills, when young turtles on the open sea float amongst tar balls and have their mouths gummed by sticky tar. Apparently, the indiscriminant feeding style of young sea turtles promotes accidental ingestion of many things that are not good for them. We know that large oil spills are disastrous, but the chronic effects from small spills, multiplied by thousands of events over time, may be a greater cumulative threat.

OC:  How does petroleum affect a transient young turtle in the open sea?

Dr. W.:  Oil is sticky. It adheres to the outsides of turtles and if it is extensive enough it can keep them from swimming and feeding, and it can suffocate them. Oil also gets very hot in the sun and can raise the temperature of a turtle into the lethal range. Turtles also ingest oil, which contains numerous toxic compounds that have the potential to affect life functions both in the short and long term.

[See Ocean Conservancy’s “Restoring the Gulf of Mexico: Establishing a Platform for Success” for a statistical snapshot of sea turtles recovered from the BP Deepwater Horizon oil impact area; also “Restoring the Gulf of Mexico: A Framework for Ecosystem Restoration in the Gulf of Mexico” for a deeper dive into Gulf ecology, sea turtle life and more.]

OC:  Have we seen a dwindling of the sea turtle population in the Gulf? Has the health of the population been established for loggerheads, green hawksbills and Kemp’s ridleys? Do we have a baseline for any of the species?

Dr. W.:  You’d think that we would know a lot about that, but we don’t. A population’s health (that is, its ability to persist) has to do with the number of its members at all life stages, their probability of survival and how many new turtles are produced. With this information, population biologists can forecast population changes for better or for worse. We do a pretty good job of counting sea turtle nests on their nesting beaches, but we know much less about survival at sea. For example, Kemp’s ridley sea turtles nest mostly on one stretch of beach in northern Mexico. We know that there were once many tens of thousands of ridleys nesting on those beaches and that the population declined dramatically. Beginning in the 1980s, workers counting nests recorded that numbers were increasing, a trend that has continued until the last few years when the upward arc of nest counts has flattened. These changes likely reflect rates of survivorship and sources of mortality where sea turtles live most of their lives—the sea. If we had measurements of these survival rates that we could depend on, we could predict interruptions to sea turtle recovery… and ideally, do something about it. Right now, we’re a little in the dark and cannot recognize the results of some threats until many years after they occur. As for baselines on any sea turtle population, we have mostly just nest counts on beaches to turn to. These represent an index of just one life stage: adult females. And as baselines go, we find ourselves unsatisfied with the time span of our information. Most nest-count time periods have yet to approach the generation time of loggerheads and green turtles, which is about 45 years. Still, through our brief window in time, we can say that the oldest members of the population have been increasing for green turtles living in the Gulf of Mexico. For ridleys, we’ve seen a similar increase until recently, which may be only a statistical blip. Loggerheads have had nest counts with considerable ups and downs, but have shown no definitive recovery. Hawksbill nest numbers are either up or down depending on which nesting beach one examines.

[See Ocean Conservancy’s “The Gulf of Mexico Ecosystem: A Coastal and Marine Atlas” for maps and information on Kemp’s ridley turtles (pages 94-97) and pelagic Sargassum (pages 36-38). These two maps are also included at the end of the blog.]   

OC:  So what is the state of current Gulf turtle research? What don’t we know but we will need to know to undertake effective Gulf restoration efforts? And what about protection and conservation planning?

Dr. W.:  Scientists concerned with sea turtles in the Gulf have begun to consider how an organized network of research locations could contribute the information that population biologists, resources managers and regulators need to assess populations and bring about their recovery. Sea turtles live in many locations, and each of these is likely to be biologically unique. A hope we have is that a network of index sites could contribute the information needed for a collective understanding of populations—information like how quickly turtles grow and their probability of survival to the next life stage. Of course, we also need to understand the factors that dictate growth and survival, like availability of food resources and intersections with threats.

OC:  Given that so much more awaits research, how would you map the research that needs to be carried out the most urgently? What would that look like and why is it needed?

Dr. W.:  This is where the population biology of the animal helps a bit. Because very few sea turtles live the decades required to mature and reproduce, these older turtles on the cusp of maturity are the most valuable members of the population. Losing them hits the population hard. So understanding how to reduce threats that take these subadult turtles is critical. The chief threat in the Gulf to this life stage, especially in loggerheads and Kemp’s ridleys, is incidental drowning in trawl and long-line fisheries. But some threats of high magnitude to younger life stages are also critical to conservation. For all life stages it will be important for regulators to understand where sea turtles intersect with threats we can manage. Technology that allows both tracking of turtles and monitoring of our own behavior (fishing, boating, release of pollutants) should be in our long-term plan.

OC:  Which species of turtles are found in significant numbers in the area of the Deepwater Horizon spill? You propose in your research that the open waters of the northern and eastern Gulf are of “unique importance” to Kemp’s ridleys. So do we know yet precisely how they have been harmed?

Dr. W.:  The Gulf is unique for its role in fostering the Sargassum drift community of organisms, which includes young sea turtles. I’ve mentioned four species (green turtle, Kemp’s ridley, hawksbill, loggerhead), but a fifth species also occurs in the Gulf. This is the leatherback turtle, which remains in the open sea for its entire life. Harm from the BP spill on all of these species is still being assessed, and as one might imagine, the task is under intense scrutiny. It’s also cloaked within a legal veil that does not permit me to say much about it. Sorry.

OC:  When you investigated the diets of turtles occupying mats of Sargassum you found they had ingested marine animals and Sargassum, etc., but you also reported an “alarming indicator of mortality,” which was that approximately 8 to 21 percent of the dry mass of ingested material was “debris,” and mostly plastic.

Dr. W.:  Yes, this was an alarming result. Sea turtles eat floating plastic. It can reduce their growth and kill them, but we don’t fully know the magnitude of this threat. Post-hatchling loggerheads and green turtles that strand dead following tropical cyclones show plastics in about 90 percent of necropsied specimens. The plastics are typically shards of plastic containers degraded in sunlight and broken up by waves. The shards stack up in the intestine, block the gut, and puncture it. Unfortunately, the sea is full of plastic and the floating bits accumulate precisely where little turtles live—in the convergence zones I described.

OC:  You also found that the mortality rate of these turtles is difficult to gauge, pointing out that there are few “strandings” of dead turtle carcasses on shorelines. Thus, understanding threats to early juveniles and post-hatchlings has been a missing element in management efforts. How is this to be remedied?

Dr. W.:  This is tricky. One way to measure mortality is to put marks on lots of turtles and make repeated observations of how many you see again. We are currently putting tiny injectable encapsulated radio tags into the juveniles we catch, but we have had so few returns we can’t say anything about survival. We simply have not tagged enough. Another method may be to give turtles broadcasting tags (satellite transmitters) that are small enough not to be a burden and affect survival. Then, turtles that go missing could be assumed to be dead (given a numerical model to account for error). We’ve put satellite tags on small pelagic juveniles, and we’ve gotten interesting movement data, but because the tags sink if they pop off the turtle, we can’t conclude much about turtles that go off the air. More advanced floating tags that archive data will need to be developed that are small enough to not cause trouble for these small turtles. I look forward to that future.

OC:  Without this research into the mortality risks posed by plastics and petroleum is it even possible to assess damage from catastrophic oil spills?

Dr. W.:  Yes. Given measurements of where turtles are, how many there are, and extent of oiling observed, and given assumptions about mortality given the intersection of turtles and oil, we can estimate mortality within intervals of statistical confidence. It’s much more helpful to our understanding of the disaster than simply claiming we don’t know.

Pelagic Sargassum map.

Kemp’s Ridley sea turtle

More from This Blog Series:

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