Shell-e-brating sea turtle milestones
◀ RETURN TO CONSERVATION & SUSTAINABLE USE SECTION
◀ RETURN TO 2020 ANNUAL REPORT INDEX
Mote Marine Laboratory’s Sea Turtle Conservation & Research Program (STCRP) has been a friend to threatened and endangered sea turtles for 40 years. STCRP monitors 35 miles of southwest Florida beaches from Longboat Key to Venice for sea turtle nesting—the important reproductive process that gives rise to new generations.
With monitoring and field research wrapped up for the 2021 nesting season, Mote scientists have analyzed 40 years of nesting data valuable for conservation and management including:
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133,954 records of sea turtle crawls leaving the ocean with 49% (65,321) resulting in a nest—a chamber dug by the mother turtle where she lays and then covers her clutch of eggs. Of those nests, 98% were laid by loggerhead sea turtles, the primary nesting species in Mote’s monitoring area. Mote’s data reveal that local sea turtle nesting has increased dramatically since 2008, including rapid growth of locally uncommon green sea turtle nests.
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Mote scientists reported that 2021 was the fourth highest nesting in the past four decades. In total there were 3,786 nests, including 89 from the less common green sea turtles. The top three local nesting years were 2019, 2016 and 2017.
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Now, through a deep dive into our 40-year data set, Mote scientists are working to answer important, current questions. For example: Do mother turtles lay larger clutches (groups of eggs) during certain parts of the nesting season? Mote scientists are preparing these data to share with government decision makers who regulate beach nourishment projects. Nourishment (adding sand to beaches) is ideally done outside nesting season but sometimes extends into season and requires moving nests—creating an inherent risk for the developing eggs. If Mote’s data show different clutch sizes over the season, then nourishment timing could adjust to risk fewer eggs.
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Mote’s long-term data are also helping us detect and investigate emerging challenges:
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Is climate change resulting in more female sea turtle hatchlings?
Scientists know that sea turtle nests produce more females during periods of warmer temperatures and more males in cooler temperatures. This temperature-dependent sex determination has scientists wondering if male turtles will become rarer—and if populations will struggle to reproduce—amid human-driven climate change. Since 1970, Earth’s surface temperature has increased faster than in any other 50-year stretch in the last 2000 years.
Thanks to Mote’s long history of research in Sarasota County, Mote scientists and partners at Florida Atlantic University are now able to investigate how climate change might be affecting sea turtle nests. Project partners and interns are comparing sea turtle nest temperatures and hatchling sex ratios (percent of males vs. females) between a past Mote study in 2002 and a new one in 2021.
This year, Mote scientists outfitted 15 sea turtle nests with temperature data loggers, and they collected and released 6,500 hatchlings, collecting biological samples from nearly 2,000 for this project and others. Blood samples will allow us to determine hatchlings’ sex, while DNA samples will be used for paternity tests to help us estimate how many adult males are currently breeding with nesting females that we observe on our beaches. Interns in the National Science Foundation-supported Research Experiences for Undergraduates (REU) program, along with Mote’s own local REU program, will analyze the differences between 2002 and 2021 and work on statistical models to better understand which conditions affect nest temperature the most—such as air temperature, sea surface temperature and rainfall—all conditions that can vary with climate change.
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Mote’s research has revealed an uptick in bacterial dermatitis—lesions and other signs of irritation—on green sea turtles’ carapace (upper shell) on Casey Key, Florida.
Mote scientists and NOAA partners published a preliminary report of this discovery in the Marine Turtle Newsletter in late 2020. To our knowledge, this is the first published record of this health condition in the wild nesting population of green sea turtles. Skin conditions sometimes indicate other, hidden health challenges, necessitating careful monitoring. In 2019, nearly 30% of the nesting green sea turtles documented by Mote had signs of this dermatitis. By summer 2021, that number had increased to 83%.
In 2019 the researchers found 12 types of bacteria on the shells of turtles with dermatitis, but it’s unclear whether those bacteria contributed to, benefited from or simply coincided with the tissue damage.
While the condition did not affect turtle survival or nesting success, based on analyses completed for the 2019 season, Mote scientists collected additional samples in 2021 to continue monitoring it closely. The research team is working to identify the bacteria causing the dermatitis, which would allow them to test antibiotics against those bacteria, with the goal of developing a treatment for turtles that enter rehabilitation facilities with this condition. Skin abnormalities in wildlife can reflect changes in water quality, temperature, turtles’ diet, immune function and more.
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Mote scientists tagged 10 sea turtles with satellite-linked transmitters this year—including three adult male and three adult female loggerheads, and four adult female green turtles.
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Two male loggerhead turtles that were rescued and tagged by Mote in the past—nicknamed JT and Bobby—were re-stranded and rescued again by Mote staff after suffering from red tide toxicity this year. Both were rehabilitated and released again, and JT received a new satellite tag. Scientists have relatively little data on where male sea turtles migrate and feed, so tracking them is particularly important for identifying areas to conserve and protect males. Because male turtles spend life at sea, not coming ashore as nesting females do, it’s critical to tag males that are rehabilitated and released.
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Adult green turtles were tracked to identify the number of nests they lay and important migratory routes and foraging grounds.
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Adult female loggerheads were tracked in collaboration with FWC to determine whether foraging ground and stable isotope signatures have changed over time.
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Follow all of Mote’s satellite-tagged turtles at: mote.org/seaturtletracking
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On local nesting beaches, where sea turtles emerge at night, Mote’s nighttime tagging team had 730 encounters with 423 individual turtles this year. Those individuals were 397 loggerheads (263 newly seen on our beaches, 134 we’ve tagged before) and 26 greens (9 newly tagged on our beaches and 17 tagged before). In total, Mote scientists tagged 377 turtles for identification this year.
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This year across Longboat Key, Mote provided endangered species monitoring for five beach nourishment projects (sand being added to maintain beaches and groin construction to reduce erosion) that overlapped with sea turtle nesting season. To prevent nourishment impacts to turtle nests, Mote scientists carefully relocated nests from nourishment sites, in accordance with state and federal law, and they monitored nests for hatch/emergence success, depredation (damage by predatory animals) and disorientation (when hatchlings emerge from the nest but fail to crawl toward the ocean because they are drawn to artificial lights on land). These efforts help us provide a full picture of nourishment impacts.
Mote provided its data on nesting activity and outcomes to the Florida Fish and Wildlife Conservation (FWC), Florida Department of Environmental Protection (DEP) and the U.S. Fish and Wildlife Service (USFWS). Florida’s DEP provides permits for nourishment projects with comments from FWC and USFWS, the state and federal agencies responsible for protecting nesting sea turtles, while FWC issues Marine Turtle Permits to Mote for our monitoring. Mote, an independent, nonprofit, research institution, has long been a vital source of unbiased data about how beach activities affect turtles, informing government decisions on how to protect these imperiled species.
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Mote research this year also suggested that some tools for maintaining shorelines are better for nesting turtles than others. Specifically, Mote scientists found evidence that a “geotextile container” (or “geotube”) beach armoring structure was likely better for local nesting sea turtles than a seawall that later replaced it. Seawalls are common, hard structures commonly used along the Gulf of Mexico coast. The geotextile container—made of flexible casing filled with sediment and covered with at least 3 feet of sand to help it imitate a beach dune—appeared to decrease the chances of false crawls (turtles emerging from sea and returning without nesting) and nests being washed out, compared with nearby beaches with seawalls or the unarmored, eroded beach that existed before the geotube was installed in 2010. With more time and data collection, Mote will also directly compare the geotube with the seawall that replaced it in 2021. Details from this study will be shared through a future peer-reviewed publication.
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Successful sea turtle research and conservation depends on a community of scientists, management authorities, volunteers and others working together. This year alone, more than 15 research and conservation partners are benefiting from Mote’s sea turtle data and samples collected from Sarasota County’s nesting turtles.
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Just one example: Mote scientists have been collecting epibionts (organisms like sponges, shrimp and crabs that live on the turtles’ shells) and sharing them with the Yale Peabody Museum of Natural History for their growing collection. Such a collection is valuable for documenting any changes over time—for example, before and after sea turtles encounter environmental contaminants.
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Top photo by: isabelle_bonaire - Fotolia / Adobe Stock