Salmon, Michael

Fibropapillomatosis (FP) is a tumor disease that has reached panzootic proportions in green turtles (Chelonia mydas). FP is associated with chelonid alphaherpesvirus 5, although the etiology of FP is likely multifactorial, since high FP prevalence is often observed in degraded habitats. However, specific environmental cofactors for tumor development remain unknown. To explore this, I collated statewide green turtle stranding data from 2000–2020 to evaluate spatiotemporal trends of FP in Florida, and co-analyzed these data alongside patterns of river flow, chlorophyll-a (Chla), sea surface temperature (SST), El Niño (ENSO), and red tide (HAB). I found that FP was stable during 2000–2020. HAB (positively) and SST (negatively) correlated with statewide FP prevalence, as well as several interactions between various factors. These results suggest that SST and HABs may act as cofactors in the development of FP, and future work should be equally interdisciplinary in their investigation of this multifactorial disease

Hatchling loggerhead turtles emerge from subsurface nests on the beach at night, crawl down the beach and enter the sea. Recently, increases in a floating algae (Sargassum) has been reported in the mid-Atlantic and the Caribbean, resulting in large algal wrack on Florida beaches. The purpose of my study was to determine if these accumulations acted as a barrier, preventing hatchlings from completing their crawl to the sea. To address this issue I recorded seasonal changes in Sargassum density and directly observed when, and under what circumstances, hatchlings could cross the wrack. There was a significant overlap between when Sargassum accumulation peaked and when the turtles emerged, with the result that hatchling recruitment was significantly reduced (by~22%) during the 2020 nesting season. I conclude that algal accumulations represent a significant threat that may impede the recovery of loggerhead populations, that are currently threatened or endangered worldwide.

Hatchling marine turtles exhibit a positive phototaxis by crawling toward the lowest and brightest horizon when they emerge from nests on the beach at night, which should lead them to the ocean (“seafinding”). Previous research with cheloniid (loggerhead and green turtle) hatchlings demonstrated that the perceptual spectral sensitivities are well below the light available on the beach regardless of lunar phase. The goal of this research was to determine the perceptual spectral sensitivities of leatherback hatchlings, the most distantly related of all extant sea turtle species. This study revealed that, like cheloniids, leatherbacks are most sensitive to shorter wavelengths (< 500 nm). However, leatherbacks were 10 – 100x less sensitive than cheloniids at all tested wavelengths. This difference in sensitivity corresponds with increased crawl duration and circling behavior under new moon conditions when light levels are lowest and the difference in radiance between the landward and seaward direction is small.

The goal of this study was to determine if hatching synchrony occurs in loggerhead sea turtle nests and if it does, what mechanism(s) promote that synchrony. Synchrony may occur because oviposition takes place during a single evening, and because incubation temperatures within the nest show relatively little variation; thus, rates of embryonic development among the eggs are similar ("temporal synchrony hypothesis"). Alternatively, synchrony might be enhanced through embryo-to-embryo communication that stimulates and synchronizes development ("coordinated hatching hypothesis"). Experiments were designed to distinguish between these two hypotheses. I found that if only a few embryos survive, temporal synchrony occurs. However, if many embryos survive, the duration of incubation and hatching shortens, presumably because embryonic movements inside soft-shelled eggs are detected by and transmitted between eggs and stimulate development, expediting hatching synchrony.

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.

Invasive fire ants are aggressive predators of ground nesting birds and reptiles and are spreading rapidly throughout tropical and temperate climates. Fire ants have been known to prey on a variety of reptile species, including threatened loggerhead sea turtles. The granular fire ant bait AMDRO® is being used on sea turtle nesting beaches to protect nests and hatchlings from these predators, however no studies have been conducted to thoroughly assess its effect on any reptile species. In this field study, I examined the impact of AMDRO® on hatching and emergence success, body condition, and orientation behavior in loggerhead sea turtles (Caretta caretta) in Juno Beach, Florida, USA. Pesticide granules were placed in a one-foot diameter circle directly above nest chambers during the final 5-10 days of incubation, which is representative of typical field applications of this pesticide on nesting beaches. Two controls were used in this study: cornmeal granules in soybean oil served as the vehicle control, and a second group of untreated control nests were left to incubate naturally, undisturbed. After a natural emergence, hatchlings were collected to calculate a body condition index (BCI). For a subset of the nests, 20 hatchlings were collected to perform orientation assays to assess the hatchlings’ ability to orient correctly toward the ocean, a visually mediated process that could be altered by visual impairments resulting from ADMRO® exposure. Three days following a mass emergence event, nests were excavated to collect hatching and emergence success data. Sand samples were collected to determine if the toxicant persisted in the environment or penetrated the egg chamber. Analyses indicated that the toxicant had no effect on hatchling morphology, hatching success, or emergence success. It also had no effect on the ability of hatchlings to orient toward the ocean. However, the pesticide granules attracted more predators than were seen at control nests. Thus, while AMDRO® might not directly impact reproductive success or hatchling behavior, it had the unanticipated effect of possibly increasing nest vulnerability to predators.

Hatchling marine turtles use visual cues to orient from their nest to the sea at
night. However, the wavelengths of light that carry this information have not been
properly documented, nor do we understand why they are favored. I measured
wavelength irradiance at 20 nm intervals between 340 – 600 nm at a dark nesting beach
and then, in the laboratory, determined the thresholds of the hatchlings for each λ that
evoked a positive phototaxis. In this study, I show that green turtle hatchlings are (i) most
sensitive to the shorter (360 – 480 nm) light wavelengths. Those light energies (ii)
dominated the available natural lighting at the nesting beach. They also (iii) presented a
steep gradient in irradiance between a landward and seaward view, an important cue for
orientation. I attribute the phototactic responses to “stimulus filtering”, the outcome of
natural selection that optimizes behavioral responses (seafinding) according to their
function, as well as when and where they occur.

For highly migratory species, it is important to understand what habitats are used and what
requirements are essential for growth and development. These migrations often span different political
and regulatory boundaries, complicating conservation strategies. The hatchlings and post-hatchlings of
most sea turtle species migrate to oceanic habitats where they remain for several years before
returning to shallow developmental habitats. For critically endangered hawksbill turtle, Eretmochelys
imbricata, most research has concentrated on nesting ecology and very little is known about the posthatchling
migration. Many sea turtles then spend years in different foraging habitats before reaching
sexual maturity, and such foraging grounds typically represent a mixed stock of turtles from different
nesting beaches. Mitochondrial DNA analysis can be used to estimate genetic stock structure of mixedstock
foraging populations for sea turtles, and the duration of the post-hatchling oceanic stage can be
estimated using stable isotope analysis and satellite telemetry. Our objectives are to determine the
duration of the post-hatchling oceanic stage of development, to determine if the turtles sampled in a
particular foraging habitat represent a biased or unbiased assortment of matrilineages, and to infer
potential migratory pathways by investigating ocean currents between nesting beaches and the
foraging site. Here we discuss our methods, to determine the duration of the post-hatchling oceanic
stage and stock structure for immature hawksbills at a developmental foraging ground.

Most marine organisms partition particular activities, such as growth, migration, reproduction, and
hatching, to particular seasons, times of the day or night, or phases of the lunar cycle. The result is
characterized as a “rhythm”. Scientists who study these rhythms generally ask two kinds of questions:
why do they occur when they do that is, what is their survival value, and how are they controlled,
physiologically? Hatchling marine turtles almost always emerge from their nests at night, then crawl
down the beach to the sea and migrate offshore. By doing so at night they avoid lethally warm beach
sands and diurnally active predators in the shallows. But these “survival value” explanations do not
account for how the turtles, digging their way upward inside the nest toward the beach surface, know
that it’s dark and time to emerge. The classic explanation for how they “know” is based upon surface
sand temperatures. During the day, these sands can be very warm 50° C. When hatchlings digging
upward encounter these heated sands, they stop digging until the sand cools, after sunset. But these
observations fail to explain why in most studies, hatchlings rarely emerge from their nests at dawn or in
the early morning, when the sand is still cool. To account for those observations, we hypothesize that
the turtles must also possess a time sense that inhibits emergence during inappropriate times, such as
shortly before or after sunrise.

The cues used by marine turtles to locate foraging areas in the open ocean are largely
unknown, though field observations suggest that some species [especially the green turtle
[Chelonia mydas], the loggerhead [Caretta caretta], and the leatherback [Dermochelys coriacea]]
somehow locate areas of high productivity. Do they do so by orienting toward chemical cues in
air, water, or both air and water? Previous studies have shown that loggerheads are capable of
detecting airborne odors from synthetic food [turtle pellets] as well as natural dimethyl sulfide
[DMS], which is found in productive oceanic areas. However, responses were brief, and a
capacity to orient was not investigated. We presented tethered loggerheads and leatherbacks to a
laminar airflow that contained DMS or natural food odors [squid, shrimp, sargassum, and moon
jellyfish]. We observed no tendency to orient upwind. Additional experiments examined if freeswimming
loggerhead and green turtles would respond to squid odor presented in air or water
with a visual stimulus [a small plastic ball suspended in the water present]. Both species showed
significant increases in biting behavior when exposed to squid odor in air or water. We conclude
that i. air currents carrying DMS or food do not induce turtles to orient upwind, ii. turtles can
detect and respond to food odors either in air or underwater, and iii. only odors from food
stimulate turtles to initiate feeding behavior. None of our results provide support for the
hypothesis that turtles can locate distant sources of food in the ocean using odor cues.