Loggerhead turtle

Recent studies have shown that hatchling loggerhead sea turtles possess the ability to orient to the earth's magnetic field. These experiments did not identify the specific component of the field used by turtles to determine direction. One of the field's most important characteristics, inclination, has been implicated as the specific property used by birds to orient. This study investigated the possibility that sea turtles use the inclination of the earth's field in a similar manner. Results show that turtles determine direction with the use of an inclination compass similar to the one used by birds to orient. This study has important implications regarding the mechanisms used by animals to orient and navigate.

The impact of coastline development on nesting sea turtles, nest contents,
and hatchlings was investigated in southeastern Florida. There were
95-128 loggerhead (Caretta caretta) nests per mile on six miles of beach.
Seventeen green turtle (Chelonia mydas) nests were found. Nesting females
did not avoid lighted, developed beaches in favor of undeveloped beaches.
Hatchling emergence bearings were measured at 397 nests, and ambient
light intensities were correlated with the incidence of misorientation. Most hatchlings emerging where artificial light sources were visible
were misoriented inland. From 0-96% of misoriented hatchlings were killed
by automobiles, ghost crabs, or dessication. Mortality was greatest
where hatchlings were able to enter roadways, and lowest where barriers
prevented this. Analysis of post-emergence contents of 422 nests
revealed that mortality within nests was greater on soft beaches with
large-grained sand than on fine-grained, firmer beaches, and was increased
by human footfalls and beach-cleaning machinery.

Pole-mounted street lighting on coastal roadways is often visible in adjacent areas. At roadways near sea turtle nesting beaches, these lights can disrupt the nocturnal orientation of hatchlings as they crawl from the nest to the sea. Our objective was to determine if an alternative lighting system (light-emitting diodes, embedded in the roadway pavement) prevented orientation disruption of loggerhead hatchlings. Hatchlings at the beach oriented normally when the embedded lights were on, or when all lighting was switched off. However, turtles showed poor orientation when exposed to pole-mounted street lighting. Light measurements revealed that street lighting was present at the beach, whereas embedded lighting was absent. I conclude that embedded lighting systems restrict light scatter, leaving adjacent habitats dark, and therefore protect the turtles from artificial lighting allowing for normal seafinding.

This study's objective was to determine if the transfer of a crawling direction to a magnetic compass in loggerhead hatchling sea turtles ( Caretta caretta L.) was facilitated by how long the turtle crawled (an "endogenous timing" component). I first determined how long it took hatchlings to crawl from their nest to the ocean. Two types of experiments were then carried out. In the first, crawling time varied. In the second, both crawling time and direction varied. I found that at most beaches hatchlings crawled to the ocean in less than 5 min. My experiments showed that if crawls are too short (1 min), or too long (5 min), vector transfer is weakened compared to a 2 min crawl. I also found that a period of non-directional crawling interfered with the ability of a 2 min crawl to promote calibration. These results confirm that efficient transfer of a crawling vector, maintained by visual compass, to a swimming vector, maintained by a magnetic compass, depends upon an endogenous timing program in hatchlings. The temporal properties of that program are, in turn, apparently shaped by where their mothers place nests on the beach.

In the ocean, lighting varies with habitat; the eye's spectral sensitivity must vary with visual ecology. Green turtles are the only sea turtle whose spectral sensitivity has been studied. Loggerheads and leatherbacks see visible light between 340 and 700 nm. However, the wavelengths detected with the greatest sensitivity by both species are those best transmitted at the specific depths where food, mates and predators are likely to be encountered. Both species have trichromatic vision, but the species differ in the concentration and peak sensitivity of each visual pigment resulting in either a broadly tuned (loggerhead) or finely tuned (leatherback) spectral sensitivity. Spectral sensitivity of leatherbacks overlaps both bioluminescence of prey, and light available in clear, deep, oceanic waters.

Hatchling sea turtles use visual cues to orient to the water. Streetlights placed on coastal roadways can attract the turtles inland. Filters were designed to be used with coastal roadway lighting to eliminate the more harmful wavelengths of light. I tested the General Electric 2422 and NLW filters in a laboratory setting with hatchling loggerhead and green turtles. Both species of turtles were attracted to the amber filtered lighting in arena experiments. Loggerhead hatchlings were used in T-maze experiments where they were given a choice between amber filtered and unfiltered lighting. The turtles preferred the unfiltered lighting to the filtered lighting, even when it was 100 to 1000 times dimmer. I conclude that amber filtered lighting does afford some protection to sea turtles, although it must be used in conjunction with other light management techniques to prevent the disruption of hatchling turtle orientation.

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.

The calcium requirement in captive-raised hatchling loggerhead sea turtles (Caretta caretta) was investigated. Comparisons were made among turtles on 6 experimental diets and between captive and wild turtles. Diets consisted of trout chow diets containing 1%, 2%, 3%, or 4% calcium and 1.65% phosphorous, AquaMax 500RTM (2% Ca), and shrimp. Feeding trials lasted 28 days and changes in body size and bone density were measured. The calcium and phosphorous content of foods eaten by post-hatchlings in the sargassum were compared with captive diets. Results showed that shrimp was high in protein and low in calcium, with nearly twice as much P as Ca. The growth trials showed that turtles fed shrimp versus all other diets grew larger. There was no difference in total bone density of any treatment over the study. No signs of hypocalcemia were present, therefore, no lower limit for calcium requirement was determined in this study.

South Florida's loggerhead (Caretta caretta), green (Chelonia mydas) and leatherback (Dermochelys coriacea) sea turtles hatchling have environmentally determined sex. The in situ nest mean hatchling sex ratios (SR) were highly female-biased : loggerhead F=0.89) and green turtle F=0.81; leatherback's SR was nearly balanced (0.55F). Nest temperatures and SRs differed between leatherbacks and loggerhead and green turtles. The latter two did not differ. The loggerhead response parameters were estimated within biological limitations by both 50-65% of incubation and mean middle 1/3 temperature. The maximum middle 1/3 temperature was the best-fit predictor for green turtles. No best-fit sex ratio-temperature response could be identified for leatherbacks. Clutches incubating under natural conditions can vary greatly in SR ; TRT differences may account for differences among species' sex ratios.