2016 End of Season Sea Turtle Update
The first nest of the 2016 season was laid on April 22nd – what a great marker that was to celebrate Earth Day! We were coming off a record year for sea turtles on our beaches, with 522 nests laid on Sanibel and 133 nests laid on Captiva in 2015.
The sea turtles continued to impress us in 2016 and broke historical nesting records on both beaches, with a total of 636 nests laid on Sanibel (including two greens) and 194 nests laid on Captiva. This is the third year in a row that Sanibel has broken records, and the first record breaking year for Captiva since 2000!
The East End of Sanibel has historically been a low density nesting beach, but in recent years has seen a notable spike in nest numbers. The average number of nests laid from 1996-2013 was 38 per season. In 2014 and 2015 there were 110 and 120 nests laid on the East End, respectively. Continuing with this trend, this season 174 loggerhead nests were on the East End, more than quadrupling the 20 year average.
Although statewide numbers do not reflect a corresponding increase in nesting, a statistical analysis of trends indicates that there has been a strong increase (71 percent) over the last ten years (2007-2016). This is especially good news considering it follows a sharp decline in nest counts in the previous decade (1998-2007).
Many years of sea turtle nesting data are needed to analyze sea turtle nesting trends, but it’s really starting to look like the coordinated conservation efforts over the past 20-30 years are starting to pay off, and loggerheads might be in the beginning stages of recovery.
The 2016 volunteer hours were nothing short of staggering. In less than 7 months, our 107 volunteers reported 4,752 hours on the beach. This is approximately 119 fourty-hour work weeks! Even on the long and hot days of July, these folks are always willing to help with huge smiles on their faces. We are so grateful to have such an amazing team!!
This year we were proud to launch our nighttime tagging project to learn more about the nesting patterns of individual females on Sanibel. Our Nighttime Tagging Team, Andrew Glinsky and Jennifer Gooch, came to SCCF with a combined 6 seasons of tagging experience. Andrew worked on 3 tagging beaches in Costa Rica and most recently tagged leatherbacks in Western Africa. Jennifer also spent one season tagging in Costa Rica and then Grenada before coming to Sanibel. They were an excellent team that worked very well together, with the public, and with the turtles.
After obtaining the necessary permits, we were so appreciative that Mark and Gretchen Banks generously funded the entire project. Our only remaining limitation was finding housing for the additional staff needed to complete the project, and we were so fortunate to have the Wilmeth Cottage to accommodate our tagging interns!
The goal of the project was to monitor the movement of individual nesting females. In addition to working with the turtles, Jennifer and Andrew were able to educate beach goers every night by encouraging sea-turtle friendly behaviors. They distributed red filters for flashlights, tagged furniture left on the beach to remind beachgoers of the hazards to nesting and hatchling sea turtles, and shared information about the mission of our sea turtle program.
The project was more successful than any of us imagined! Between May 1 and July 27, Andrew and Jennifer encountered 239 turtles (representing 157 unique individuals). Of the 239 crawls, 50 were on the East End and 189 were on the West End. Preliminary data from the tagging project suggest that the East End turtles are generally distinct from the West End turtles (with a few exceptions). The lack of crossover between the East End and West End turtles could be great news for conservation efforts. Since sea turtles take about 30 years to reach reproductive age, the spike in nests we have been seeing on the East End could be from females that were protected as hatchlings 30 years ago and are now returning to the East End to lay their eggs. More crossover between West End and East End turtles could mean many things, including a potential shift in preferred habitat from the West to the East End. Several more years of data would be required to explore the alternatives, but if the results remain consistent, it would be fantastic news for the turtles!
Additional highlights from our results include:
- One loggerhead was originally tagged on Sanibel in 1993 (23 years ago!) when she nested just 3 miles from where she was seen in 2016
- Another was encountered 10 times from May 27th- July 16th. She was originally tagged on Sanibel in 2014 by a student from FAU and this season she typically only laid between 1-15 eggs ( the average number laid is 110 eggs).
- A turtle that nested on May 26 was originally tagged on Melbourne Beach. It’s very unusual for loggerheads to nest on both coasts of Florida!
Tagging data on Sanibel also helps fill in the gaps and broaden the spatial scope of the long term datasets collected by Mote Marine Lab and the Conservancy of Southwest Florida. The results of the project are providing additional data to help prioritize management initiatives and conservation efforts both on Sanibel and statewide.
One of the recent changes in the nesting habitat on Sanibel involves colonization by coyotes in 2011. Coyotes are emerging as predators throughout the Southeast United States and it is important to learn more about their behavior and the impacts on nesting and hatchling sea turtles. We are in a unique position on Sanibel to further enhance our understanding of coyote/sea turtle dynamics.
To observe the ecology and behavior of coyotes that have colonized the beach habitat, five wildlife cameras were mounted behind sea turtle nests on Sanibel in 2014 – 2016. Ongoing data indicate that coyotes are considerably more active on the West End than the more densely developed and populated East End. Photos of coyotes are captured on the undeveloped stretches of beach on the West End almost every night. In addition to nest depredation, they may also be causing sea turtles to abandon their nesting attempts and creating other negative impacts in the quality of nesting habitat. In fact, one of the tagging project goals was to characterize potential shifts of nest sites away from coyote-dense stretches of beach in response to these pressures, but based on 2016 data we do not see any indication this is happening.
Wildlife camera data revealed a drop in overall coyote activity on the beach in 2016, and coyotes were seen twice as often in 2015 compared to 2016 (0.75 photos/day vs. 1.5 photos/day in 2015). A corresponding decrease in depredation rates was also observed this season, and we are now below the 10% threshold recommended by the Federal Loggerhead Recovery Plan. Previous studies suggest that night patrols on the beach significantly decrease the amount of coyote depredation on nests (for example, Eskew, 2010) and it is possible that our tagging surveys contributed to the drop in activity this year.
Another major factor that contributed to the decreased depredation rate is nest screening, a management technique that has been implemented on Sanibel since 2015. Our screening efforts increased this season with 88% of nests screened in 2016 compared to 64% in 2015. Only 6% of the screened nests were depredating, so all of our hard work seems to be paying off – many thanks to the volunteers that put in so much time to help protect these eggs!!
It is relevant to note that in 2015, the City of Sanibel contracted the University of Georgia to conduct a fecal genotyping project to estimate coyote population size and density on Sanibel. In light of this study, Sanibel biologists are now in a unique position to provide a comprehensive assessment of the coyote population on Sanibel. The collaborative effort among Sanibel biologists will make us well equipped to evaluate the true impacts that coyotes are having on both eggs and hatchlings on our beaches. These data will make it possible to prioritize management objectives and develop effective plans that have the greatest positive impact on sea turtle nesting success.
Tropical Storm Colin and Hurricane Hermine produced strong storm surge and extreme tides for Sanibel and Captiva’s beaches in 2016, completely washing away 145 nests 34 on Captiva, 15 on the East End, and 96 on the West End) and severely inundating many more. Storms are natural events in coastal ecosystems and sea turtles have a nesting strategy that accommodates for these pressures. Each female turtle deposits several nests throughout the nesting season, essentially hedging bets to make sure that even if a storm hits at some point during the nesting season, there is a high probability that at least a few of the nests will incubate successfully. For example, one of our tagged females was identified nesting on Sanibel three times in 2016, and while one of her nests washed away in TS Colin, her two other nests produced a total of 153 hatchlings.
Despite some challenges this season, especially with storms, over 25,000 hatchlings were produced on our beaches this summer!
Jake Lasala, Florida Atlantic University: The purpose of the project is to determine the mating behavior of sea turtles nesting in southern Florida. Specifically they want to find out how many males and females are actively contributing to the population, known as the breeding sex ratio. From 2013-2015 samples were collected from over 60 individual nesting females and 850+ hatchlings. All of the nests have had multiple paternal contributions, and on average 2.5 fathers are contributing to each clutch of eggs. Our tagging information allowed Jake to examine changes in paternity of an individual female’s clutches over the course of the season.
Simona Ceriani, Florida Fish and Wildlife Conservation Commission: Simona is using a stable isotopes analysis to determine where the turtles that nest on Sanibel are foraging over the winter. Last year she focused on green sea turtles, and this year she incorporated our tagging data to use samples from 60 unique loggerheads. The results will contribute to protecting their overwintering habitat (potentially including federal critical habitat designation, closing the areas to threats such as commercial fisheries, etc.).
Clear Your Gear: Sadly, according to CROW records, more than 100 wildlife are currently lost each year due to monofilament or hook injuries. In response to this increasing threat, seven Sanibel-Captiva area conservation groups have united to create a new environmental campaign called “Clear Your Gear.” The organizations collaborating on Clear Your Gear include: City of Sanibel Natural Resources Department, CROW (the Clinic for the Rehabilitation of Wildlife), J.N. “Ding” Darling National Wildlife Refuge, J.N. “Ding” Darling Wildlife Society, Monofilament Busters, The Sanibel-Captiva Conservation Foundation and the Sanibel Sea School. Clear Your Gear will work to educate the fishing public on the harmful effects of fishing line (monofilament) and other fishing gear discarded in the environment, and thereby reduce the number of injured or destroyed wildlife. Currently, Clear Your Gear has established more than 20 monofilament recycling stations on Sanibel and the Sanibel Causeway.
Operating support for the SCCF Sea Turtle Program comes from a wide variety of donors and grants. Two generous donors made significant gifts this season. Kirsten Recker funded the balance for two new beach vehicles, and Mark and Gretchen Banks funded our entire tagging project as well as matching all donations to the Adopt-A-Beach program.
As with the time and talent contributions of our volunteers, we could not be as effective as we are without the financial support of all these most appreciated donors.