Sea turtles--Nests

Sea level rise threatens loggerhead sea turtle (Caretta caretta) nests laid close to the high tide line (HTL) with inundation from washover. Boca Raton, Florida is a relatively steep, dynamic beach with changes in beach morphology even during nonactive hurricane seasons. One potential solution to conserve sea turtle nests is to relocate nests laid at or below the HTL closer to the dune. In this study, I examined reproductive success for in situ vs relocated nests. Relocation did not decrease reproductive success, while nests left near the HTL were at risk of washout. During a dry season, nests that experienced one to three days of washover had significantly higher reproductive success than nests that experienced no washover. Relocation can be a useful method to preserve nests against sea level rise, but nonrelocated nests near the HTL may sometimes benefit from washover to cool the nests during hot and dry years.

This study examined the environmental and anthropogenic factors that may influence loggerhead sea turtle nest site selection and how these factors vary between successful nesting attempts and false crawls on a high-density sea turtle nesting beach in Boca Raton, Florida. Beach morphology, sand texture, and nests’ proximity to artificial structures were measured using a combination of drone-based photogrammetry, traditional surveys with Real Time Kinematic Global Positioning System (RTK GPS), and sediment granulometry. Proximity to dune crossover stairs was significantly different between nests and false crawls, and the probability of a false crawl occurring decreased as proximity to dune crossover stairs increased. The results of this study will provide researchers with a new tool for nest monitoring and a better understanding of the microhabitat cues that may influence loggerhead sea turtle nest site selection and aid in guiding beach and sea turtle management decisions.

Sea turtle nest success, defined as the number of eggs in a nest that successfully hatch and emerge, is closely linked to environmental conditions. Interacting biotic and abiotic factors influence hatching and hatchling emergence success. To date, combinations of multiple factors interacting together, which result in highly successful sea turtle nests are not well understood. Using 25-years of historic nest data and local expert experience, I identified five historically successful loggerhead (Caretta caretta) nesting beaches (hotspots) along the Florida (USA) Atlantic coast and measured nest environments along with nest success. Principal component analysis was used to reduce 12 environmental variables so that the relative contributions of sand characteristics, nest temperature, sand moisture, and nest location were considered. The nest environments differed among nesting beaches and were broadly segregated into two distinct climates: subtropical (hot and humid) and warm-temperate (warm and dry). I found that nests at subtropical sites, compared with the warm-temperate sites, were characterized by environmental gradients in contrasting ways. Nest locations were predominantly mid-beach in subtropical sites but clustered at higher elevations and closer to the base of the dune at warm-temperate climate sites. Collectively, highly successful nest hotspots represent a mosaic of abiotic factors providing conditions that promote successful hatching and emergence. This new perspective on consistently successful loggerhead nesting beach traits demonstrate that the key traits of sea turtle nesting habitat vary with prevailing climate type and should be managed accordingly.

As climate change threatens with sea-level rise and more storms, increased erosion could increase the need for beach nourishment. Alterations to sand characteristics may result in changes to the sea turtle nest microenvironment, impacting the temperature and oxygen levels which may affect hatchling performance. In this study, leatherback, loggerhead, and green nests were sampled from two sites with different sand characteristics in Juno Beach, Florida, USA. Gas exchange was higher in green turtle nests with a greater mixture of sediment. Darker sediment elevated nest temperatures. Finer sediment and a greater mixture of sediment in leatherback nests elevated the nest temperatures; conversely finer sediment, and a greater mixture of sediment decreased loggerhead and green nest temperatures. Elevated nest temperatures reduced leatherback, loggerhead, and green turtle hatchling performance. Understanding the relationships between beach composition, nest environment, and hatchling performance will aid management decisions essential to sea turtle conservation.

Few studies on marine turtles focus on the variation in reproductive performance of individual females. I use a long-term nesting data set (1986 – 2018) of individual loggerheads including information on 1,854 individuals, of which 853 were seen nesting multiple times. During this time, emergence success has declined while the number of females nesting, and the number of nests deposited has increased. Declining emergence success can be linked to an increase in predation in most recent years; however, this does not fully explain the decline in emergence success over all years. Females were found to vary in productivity. Successful females were larger and deposited more eggs in nests. This study shows that an increasing in nesting numbers does not mean that productivity is increasing proportionally and that recovery efforts are uniformly successful. This study is also a powerful tool for understanding the reproductive strategies of individual female loggerheads.

The eggs of all sea turtle species develop in underground nests on oceanic nesting beaches. Eggs are unattended and their incubation conditions are subject to effects of the environment. Nest temperature influences various aspects of hatchling biology, including sex determination. Past studies identified that sea turtle embryos have a warm female cool male response pattern and rainfall has been thought to cool nest temperature. The effects of rainfall or periods of drought were often inferred but not verified. Using laboratory and field studies, I examined how changes in environmental factors during incubation, particularly sand moisture, can affect nest conditions and hatchling biology. I derived temperature-sex ratio response curves for eggs incubated at different moisture levels to determine the effect of moisture on how embryos respond to temperature. I also studied how increasing moisture levels in relocated nests through daily watering influence nest conditions and discuss if this method is an effective mitigation strategy for the detrimental effects of increasing temperatures on embryo survival and sex ratios. I investigated how environmental factors, nest conditions, and hatchling biology can differ among sites on a nesting beach. Extreme moisture conditions, both low and high, result in a narrower transition between one sex ratio bias to another. I demonstrated that watering nests decreases nest temperatures and increases hatching success but watering has a minimal impact on sex ratios. Ambient beach conditions vary slightly in air temperature, rainfall, solar radiation, and humidity, depending on beach location. Nest conditions such as nest temperature and moisture also differ, but hatching success and sex ratios do not vary among different sites on the same nesting beach in Boca Raton, Florida. Ultimately, these studies together help identify and demonstrate how these environmental factors and drivers can affect the nest environment during incubation. Further developing our understanding of environmental factors, particularly nest moisture, and their variability will provide better predictions of future climate change effects and perhaps create more effective mitigation strategies.

Sea turtle hatchlings emerge from their nest and quickly crawl to the surf. During the crawl, hatchlings may encounter threats, biotic and abiotic, which can affect their ability to successfully reach the surf. The impact of these threats on hatchling survival during that crawl is largely undocumented. Current methods used to estimate cohort recruitment rely heavily on nest inventory data. This method, however, does not account for post-emergent hatchling mortality that occurs during the crawl. During the 2017-2018 nesting seasons, I quantified the fates of 1,379 loggerhead (Caretta caretta) hatchlings from 26 nest emergences during their crawl from the nest to the surf on the east and west coasts of Florida. I documented hatchling fates at 5 Florida nesting beaches: Wabasso, Boca Raton, Keewaydin Island, Naples, and Anna Maria Island. Overall, 6.5% of all emergent hatchlings died during the crawl from the nests to the surf. Ghost crabs, night herons, foxes, and coyotes killed hatchlings and photopollution and barriers on the beach (both abiotic threats) caused hatchling mortality. Anthropogenic (abiotic) threats accounted for more mortality than did predators. In order to assess how beach urbanization impacts hatchling mortality, I categorized each study site as urban (Wabasso and Naples), intermediate (Anna Maria Island and Boca Raton), or natural (Keewaydin Island) based on the relative levels of shoreline development and human activity at each beach. Sites with intermediate levels of urbanization accounted for greater levels of hatchling mortality than at other beaches due to the absolutely larger numbers of hatchlings lost to a disorientation event and to a beach barrier. Given the small numbers of emergences, at all sites, only a small proportion of the hatchlings mortalities (e.g., between 3 and 12 percent), site type could not be rigorously used as a discriminator. My results provide a better understanding of how specific environmental threats contribute to hatchling mortality. While nest-to-surf mortality is relatively low, its cumulative costs add up to several hundreds of thousands of hatchlings. Armed with this information, nesting beach managers can assess risks and focus their efforts to implement the most effective management practices to minimize losses of this imperiled species.

Caging of sea turtle nests has used by City of Boca Raton's sea turtle conservation program to deter terrestrial predators and reduce human disturbance. The juxtaposition of nest cages and artificial lighting may pose serious threats to hatchlings. I addressed possible negative effects of cages on sea turtle hatchlings' seafinding abilities and potential "cage-trapping" under natural and artificially illuminated conditions. Cages did not effect hatchling orientation on artificially illuminated or dark beaches. Hatchlings did not experience any delay in cage escape on dark beaches, but a significant number were trapped inside the cages on artificially illuminated beaches. The highest incidence of trapping occurred on nights surrounding a new moon. Disoriented hatchlings exited cages either after city lighting was reduced (past midnight) or as natural levels of illumination increased shortly before sunrise. When cages were darkened all turtles escaped but many still exhibited signs of disorientation.

The purpose of this study was to determine if filtered street lighting affected the nesting behavior of loggerhead sea turtles ( Caretta caretta L.). My study site was a nesting beach at Carlin Park, Jupiter, Florida. During the 1999 nesting season, portions of the beach were either kept dark or were illuminated by four 70 W high-pressure sodium (HPS) streetlights, each housed in a cut-off fixture covered by an acrylic (model #2422) filter. These filters excluded all light wavelengths below 540 nm. The excluded wavelengths repel nesting females. Daily counts of nesting and non-nesting crawls were made. Data from the 1999 nesting season were compared to historical records of nesting at the site between 1990 and 1998. I found no evidence that filtered lights affected nesting densities, or the ratio of successful to unsuccessful crawls. These results suggest that at Carlin Park, the nesting behavior of loggerhead females is unaffected by exposure of the beach to filtered street lighting.