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Life Studying the Sea Turtles with Dr. Melania López-Castro

Updated: Sep 16, 2020

Location of foraging area centroids in the northern GoM computed from satellite tracking data for Kemp's ridley sea turtles (identified by nest number) that nested in 2 areas of Texas (PAIS: Padre Island National Seashore, open symbols; UTC: upper Texas Coast, solid symbols) during 2010 to 2012. Also shown are the source of the MC252 oil and the maximum extent of the oiled area (gray shading) (ERMA 2016). Numbers in parentheses indicate overlapping centroids of the same turtle; numbers separated by forward slashes are nest numbers for turtles that nested more than once in the indicated year

Humans occupy a very small portion of the Earth’s timeline, but have manipulated it drastically, creating changes that will affect the rest of the timeline for centuries to come. Our impact has led to air and water pollution, deforestation, and decreased biodiversity. According to the Environmental Defense Fund, “humans have driven at least 680 vertebrate species to extinction since the 16th century” and currently threaten another one million animal and plant species. In a natural world governed by the Theory of Evolution and the principle of “Survival of the Fittest”, humans have pushed hundreds of species to the brink, despite their incredible history of survival, including sea turtles - animals which have roots back to the age of the dinosaurs.

However, humans have the ability to recognize their mistakes and take action for the future regarding environmental conservation. One of those impact-oriented scientists is Dr. Melania López-Castro, a marine biologist working on sea turtle research for 23 years and counting, and the Sea Turtle Conservation Program coordinator at Pronatura Península de Yucatán, A.C.

“I was taking a class in college about marine vertebrates. When we started talking about sea turtles, what struck me was that this group of species, that has been on the planet for over 100 million years, were on the brink of extinction because of humans and in a matter of just decades. Just a few years back, in 1990, Mexico had declared a total ban on these species but numbers were not increasing, so I wanted to learn how I could help in their recovery.”

Sea turtles act as keystone species. They have a significant role in the balance of the ocean's ecosystem; the grazing of sea turtles maintains biodiversity. For instance, "the Hawksbill turtles eat sponges, preventing them from out-competing slow-growing corals." If sea turtles went extinct, it would cause a decline in all the species who depend on the seagrass beds and coral reefs for shelter and food.

The impact of the sea turtles extends to humans too. Many marine species that humans harvest depend on the seagrass beds, whose growth is controlled by the sea turtles. Sea turtles that mainly prey on jellyfish, like the leatherbacks, prevent large blooms of jellyfish, whose drifting can block coastal power stations and tear fishnets.

Though there is so much media coverage and common public talk about sea turtles (don’t use plastic straws! #fortheturtles), little is known about their lives once they leave the beaches they’re born on - a period known as the lost years - , and the science behind the research is quite complex.

“Sea turtles use different habitats through their life cycle and they are all interconnected but we still don't know how and to what extent,” says Dr. López-Castro. “The lost years are spent in the open ocean and occur right after the hatchlings enter the sea and before they recruit into coastal foraging areas approximately 5 to 12 years later. There might be important aggregation areas that if threatened might seriously affect the recruitment to coastal foraging areas and thus to nesting grounds.”

Dr. López-Castro specifically researches the use of biochemical markers, particularly trace elements and lead stable isotopes, to understand population connectivity of marine organisms. Though small, these trace elements play an important role in the lives of many marine organisms. Bodies of water have unique chemical makeups, like a fingerprint. Various marine life, like shad, detect the presence of these chemicals to find their way back to where they were born, their nesting site. While most of these animals track their birthplace, Dr. López-Castro uses it to detect the whereabouts of her sea turtles.

“Have you heard the phrase "you are what you eat"? Well, it is the same principle with biochemical markers. Depending on what and where you eat, you obtain a set of trace elements and lead isotopes. This can be "saved" in inert tissues such as hair, feathers, bones, and in the case of turtles, carapace (the shell). If we analyze each layer of the carapace, we can see if an organism spends its time in the same place or if it is moving to other areas, this of course if the areas are different enough and if they have been characterized, that is, we know what trace elements and what concentrations are there. With lead isotopes what we look at is the ratio of four of its stable isotopes that can be different depending on their geographic origin.”

This data collection process is not simple. “At a nesting beach, it requires long hours of surveying the beach at night, for over 6 months of the nesting season, to record females and their nests. If a female is found, it has to be measured and tagged with a unique ID so we can identify it later and obtain other types of information like growth rates, reproductive output, and movements. Of the nests we obtain information after the hatching date, what we collect is the number of eggs laid, the number of hatchlings (dead or alive) and number of dead embryos so we can estimate emergence and hatching success. All of this information is entered in a huge database that is later analyzed.” While getting to spend time at the beach might initially sound like all play and no work, the beaches get hot and buggy during the day, and very cold at night. All the while, the researchers have an important responsibility on their shoulders - science and theories are backed up by data, so it must be accurate and carefully preserved.

For Dr. López-Castro, a typical day at work can go in two different ways. “A typical day in the field for in-water monitoring starts around 6 am. We get into our small boat and go to our study areas to count and catch juvenile sea turtles for the next 4 hours. Of course, this includes bringing the captured turtles on board to measure and weigh them so we can determine its body index (which we use to evaluate general population health), tag them and release them back into the water. After that, we return to land for a well-deserved shower and meal.”

“A typical day in the field for nest monitoring starts around 7 pm. We get our gear, jump to the ATV and start surveying the beach looking for turtles nesting or recent nests. The length of the beach varies between 22 and 31 km and on a good night, we can find 40 or more nests. We stop at every new nest to confirm that eggs were laid, we mark them, record their location with a GPS and move to the next. If we also find a female, then we need to wait for her to finish laying her eggs so we can measure its carapace and tag her. We finish the survey around 4 am, go to bed, sleep a bit and then around 11 am, right after breakfast we proceed to wash the ATV, prepare more stakes (we use them to mark the nests) and enter all the information of the data sheets into our database. After that, there are a few hours of more rest and then at 7 pm we get ready to start all over again.”

Expediting this nest monitoring process is where Kashmir World Foundation’s MiSHELL project comes in. The project uses YOLO, an image detection software, to detect the sea turtle tracks of different species in real time so that researchers know exactly where nests are and what species of turtle laid them, making the data collection process faster.

Dr. López-Castro has written sixteen publications about foraging areas of multiple sea turtle species revealed through studying trace elements and predicted distributions of their “lost years” areas. “[The publication process] all starts with a question. It could be about a certain aspect of the biology of an organism that is not well known, of a new technique or methodology. Then, you propose your hypotheses, which are possible answers or solutions to your question. You set the methodology following the scientific method, which are all the steps you are going to follow to obtain information that might help you test your hypothesis.”

“ Once you have all that, you go out to the field and start collecting your data. This is my favorite part because I get to go to the beach and see some turtles. How you collect your data is crucial, you need to be meticulous and careful while recording data because the quality of this will dictate how reliable your results are. Once you have all your data, they have to be organized and analyzed to get your results which in turn, will help you test your hypothesis and write your discussion. Once you have a solid document, you send it to a scientific journal where it will be peer-reviewed. This means other experts will evaluate the robustness of your methods and the coherence of your results. They will also give you comments to improve the paper and once these have been incorporated in your document, they will decide if it is worthy of publishing.”

All of Dr. Castro’s publications, which cover “three different species in two different geographical areas” all aim to provide better insight into sea turtle populations. “I hope this information has been used to develop better conservation strategies and management options”, she says.

There’s a reason why the Yucatan Peninsula is a unique environment and perfectly suited for sea turtles. “I think part of it is the climate. It is perfect for sea turtles as they prefer tropical weather. The waters around the Península provide feeding areas for sea turtle species such as the green and hawksbill turtles. Furthermore, its sandy beaches provide suitable nesting habitat for the green, hawksbill, and loggerhead turtles. These beaches are considered among the 14 most important for the recovery of these species in the Atlantic ocean.”

Just like the Yucatan Peninsula, ProNatura Peninsula de Yucatan is a unique and multifaceted organization. “Our experience [is definitely what makes us special]. In 2020, our organization turned 30 years old - one of the oldest organizations working for the conservation of biodiversity in the region. We are a group of very dedicated people of different backgrounds and professional experience working towards a common goal: the development of society in harmony with nature.” ProNatura Peninsula de Yucatan has multiple projects, including the conservation of birds, whale sharks, and big cats like jaguars and pumas. Their three pillars include work in biodiversity and associated environmental services, transversality in environmental policy, and good environmental practices in economic activities.

Covid19 has made it difficult for ProNatura Peninsula de Yucatan to continue their projects, but environmental conservation cannot and will not stop for a pandemic.

“Our planet is suffering a great loss of biodiversity. This pandemic is an example of what can happen if we keep losing our natural resources. We have forgotten that we depend on nature and all the services it provides: water, clean air, food. It is time for us to reevaluate our relationship with nature and start working towards its recovery. There are many ways to help nature without being an expert biologist or scientist either by taking small actions to reduce pollution, volunteering with local conservation groups or supporting these conservation groups with a small donation if it is within your possibilities. Small actions are better than no actions at all.”

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