Salmon, Michael

Sea turtles are most vulnerable to predators during early growth when they are small and
relatively defenseless. Predation risk might be reduced by evolving effective behavioral as well
as morphological defenses. Loggerhead Caretta caretta and green turtle Chelonia mydas neonates
hide in weed lines. They also become wider faster than they increase in length, a pattern of
positive allometry that may function to minimize the time during growth when they are
vulnerable to gape-limited predators. Virtually nothing is known about how young leatherbacks
grow which might reduce their vulnerability to predators. To find out, we reared 30 hatchlings
from 10 nests in the laboratory for up to 14 weeks, post-emergence. Once weekly, each turtle’s
body proportions straight line carapace length, SCL; straight line carapace width, SCW were
measured to yield an observed pattern of growth. That observed growth pattern was compared to
an expected pattern in which the turtles retained their hatchling proportions as they grew larger
isometric growth. We found that all of the leatherbacks showed allometric growth as their SCW
increased more rapidly than their SCL. Thus as they grew, leatherbacks became proportionally
wider, though this growth was not as pronounced as seen in loggerheads and green turtles. We
also modeled vulnerability to gape-limited predators. Leatherbacks, like loggerhead and green
turtles, were less vulnerable to predation when growing allometrically. These results provide
insight into a little know sea turtle life stage and aids in understanding how morphology in early
development may reduce predation risk.

Loggerhead and green turtle neonates migrate from Florida's coast during a 24-36
h frenzy. Post-frenzy loggerheads are often found in flotsam (Sargassum), while postfrenzy
green turtles "disappear." This study compared the frenzy and post-frenzy activity
of each species, their response to flotsam (in the laboratory and field), and the role of
experience in habitat selection. Both species were most active during day I; activity
thereafter declined (especially in loggerheads). Inactive loggerheads occupied Sargassum
and open water (day or night) whereas inactive green turtles occupied Sargassum by day
and both habitats at night. Exposure to Sargassum had no effect on the later habitat
choices ofloggerheads, while exposed green turtles preferred Sargassum over plastic
plants. In the field, both species preferred flotsam to open water, but occupied distinct
microhabitats. Loggerheads preferred the mat surface while green turtles hid within the
mat. Differences in activity and habitat selection likely reflect species-specific migratory
and anti-predator strategies.

Migratory bird and insect populations show differences in orientation direction, timing,
and distances moved depending upon where they reside in relation to their migratory
goals. These differences presumably occur because of selection for behavioral responses
that promote the most efficient migratory strategies among members of each population.
The purpose of this study was to determine whether migratory behavior in loggerhead
hatchlings differs between populations that exit nesting beaches on the East and West
coast of Florida. When the turtles emerge from the nests, they initially show a swimming
"frenzy" that serves to distance individuals from shallow coastal waters, displacing them
toward oceanic currents that are used to transport the turtles to the North Atlantic Gyre.
On the East coast of Florida, turtles swim eastward toward the Florida Current (western
portion of the Gulf Stream) located relatively close to the shoreline (on average, 2 km
offshore at Miami to 33 km offshore at Melbourne Beach). On the West coast of Florida,
turtles swim westward toward the Loop Current in the Gulf of Mexico, which is located
farther offshore (150 km offshore at St. Petersburg to over 200 km offshore at the Everglades National Park). In a previous study, we demonstrated that for East coast
loggerheads, the frenzy consists of continuous swimming for - 24 h, followed over the
next 5 days by postfrenzy (diurnal, with little nocturnal) swimming activity. No
comparable data exist that characterize the frenzy period of loggerheads from the West
coast ofFlorida.
We used identical methods to quantify the migratory activity of hatchlings from the West
coast of Florida. Hatchlings were captured as they emerged from nests located between
Venice and Sarasota, Florida. They were then tethered in water-filled pools under
laboratory conditions, where temperature and photoperiod could be controlled to
duplicate conditions used when studying the East coast turtles. Activity was continuously
recorded over the next six days. The data were analyzed to determine the proportion of
time the turtles spent swimming every day, and the proportion of that swimming activity
that occurred during the light and dark period of each day. Turtl~s from each coast
showed no statistical difference in the proportion oftime spent swimming each day.
However, after day 1, West coast hatchlings showed statistically lower levels of
swimming activity during the day and statistically higher levels of swimming activity at
night than did turtles from the East coast. We hypothesize that these differences may
reflect a more diffuse period of active "searching" for appropriate oceanic currents by the
West coast turtles, under conditions where greater predation pressures might select for
more movement under conditions of darkness. Such a response may be appropriate when
migratory goals are located at greater distances, and when turtles must migrate farther
from the coast to reach deeper, and presumably less predator-rich, waters.

The pelagic longline fishery is responsible for significant mortality to sea turtles as a
result of foul hooking, entanglement in the lines, and internal injury after consuming the
baited hook. Bait, gear and lights (used to attract the target fishes to the baits at night) are
three variables that could also attract sea turtles to the lines. This study tests the role of
the lights in attracting leatherback (Dermochelys coriacea) turtles and compares their
behavior to the loggerhead (Caretta carelta), shown in previous studies to orient toward
both lightsticks and battery powered LEDs used in the fishery. The same lights were
used in experiments done on leatherbacks reared at Florida Atlantic University's Marine
Laboratory. The leatherbacks were exposed to the lights at night when they were
between 5 and 42 days old. The results show that leatherbacks, unlike loggerheads, either do not orient toward the lights or orient away from them at an angle that enabled
the turtles to keep the light in their peripheral field cf view. Thus, the capture of
leatherbacks in longlines is probably a consequence of other factors (such as attraction to
the odor of the baits, or to natural prey located near the Iines) that need to be investigated
through future research. The results also show that efforts to reduce the incidental capture
and injury of marine turtles in longlines must be based upon a firm understanding of the
similarities, as well as the differences, between turtle species.

Larval release by adult fiddler crabs occurs during the ebbing tides, but its timing
relative to the day-night and tidal amplitude cycles depends upon tidal form (e.g., shows
phenotypical plasticity). Crabs (Uca thayeri) from Florida's East Coast are exposed to
semidiurnal tides and release their larvae at night, whereas crabs from Florida's West
Coast exposed to mixed tides release their larvae during the afternoon. The purpose of
this study was to determine whether the larvae could hatch at times other than those
correlated with the tidal form at their location. Clusters of eggs at similar stages of
development, 24-72 h in advance of release, were reciprocally transferred between
females from each coast. Release ofboth the transferred larvae and maternal clutch
occurred synchronously, and at the time dictated by the female's tidal regime. These
results suggest that larvae are phenotypically plastic with respect to hatching time and
can either delay (West coast) or advance (East coast) their response to release signals
from females.

The cues used by marine turtles to locate foraging areas in the open ocean are largely
unknown though some species (especially the green turtle [Chelonia mydas], the
loggerhead [Caretta caretta], and the leatherback [Dermochelys coriacea]) somehow
locate areas of high productivity. Loggerheads can detect airborne odors, but a capacity
to orient has not yet been investigated. In this comparative study, tethered loggerheads
and leatherbacks were exposed to dimethyl sulfide (DMS) or food odors in a laminar
flow of air. Turtles did not orient into the air current. Free-swimming loggerheads and
green turtles were also exposed to air- or waterborne food (squid) odor plus a neutral
visual stimulus. Both species showed increases in swimming activity and biting behavior
to both stimuli. These results suggest that airborne odors are likely not used to locate
distant areas, but that they are used in localized food searching efforts.

Marine turtles produce many offspring which offsets the high mortality
experienced by turtles during early development. Juvenile mortality might be reduced by
evolving effective behavioral as well as morphological anti-predator defenses. Body
proportions of three species (Caretta caretta, Chelonia mydas, Dermochelys coriacea) of
turtles were measured in the first fourteen weeks of development to examine how growth
may mitigate predation by gape-limited predators. Growth was categorized as isometric
if shape did not change during development or allometric if body shape did change. All
three species showed allometric growth in carapace width; however it was less
pronounced in the larger D. coriacea turtles. Allometric growth in carapace width
decreased as all three species grew in size. When high predation occurs in early
development, many species will favor rapid growth into a size refuge. Juvenile sea turtles
may optimize their survival by growing allometrically when predation risk is the greatest.

Juvenile green turtle (Chelonia mydas) abundance differs among nearshore reefs,
but why some sites are preferred over others is unknown. My study had two objectives:
to quantify differences in abundance over time (one year) and to determine what
ecological factors were correlated with those differences. I conducted quarterly surveys
on reefs in Palm Beach and Broward Counties and compared reef sites with respect to (i)
water depth, (ii) algal abundance and composition, and (iii) changes in reef area (caused
by sand covering) through time (11 years). Turtles were most abundant on shallow reefs
exposed to high light levels that remained stable (uncovered by sand) for long periods of
time. These reefs had the highest diversity of algal species, in part because cropping by
the turtles prevented any one species from becoming dominant. My results suggest that
both physical and biological factors make some reefs more attractive to turtles than
others

The younger life history stages of marine turtles (eggs, hatchlings) often fail to survive. To compensate, sea turtles nest several times/season and produce large clutches of eggs. The hawksbill produces the largest clutches (150 eggs) and the smallest hatchlings of any marine turtle. My study, done at Jumby Bay in Antigua, West Indies, was designed to determine whether they did so to compensate for loss in the nest, hatchling loss in the water, or both factors. I
found that most of the eggs (79 %) survived to become hatchlings that left the nest and entered the sea. However, 88 % of the hatchlings swimming offshore were taken by predators within minutes after they began their migration. These results suggest that at Jumby Bay, large clutch size is favored in hawksbills because of predation pressures on the hatchlings.

Endogenous rhythms allow most organisms to synchronize their behavior and physiology with physical cycles that vary on a daily, lunar or annual cycle. Populations within species often show variation in the timing of functionally identical rhythms. This variation occurs because physical cycles may differ with geography. The purpose of this study was to determine whether hatching rhythms shown by fiddler crabs (Genus Uca) on one coastline could be entrained by the different tide patterns present at another coastline. To test this I transferred breeding females (Uca thayeri) from mangroves on the west coast of Florida to mangroves on the east coast. On the west coast, females are exposed to "mixed" tides; most release their larvae during the day or night (early summer), or during the day (mid- to late summer). On the east coast, females are exposed to "semidiurnal" tides; they release their larvae between dusk and midnight. After four weeks of exposure to the East Coast tides, crabs from the West Coast showed hatching rhythms identical to the resident crabs. This change indicates that the crabs show behavioral (phenotypic) "plasticity". These observations provide further evidence for the adaptive value of behavioral plasticity.