Michael G. Frick

Accounting for Imperfect Detection Is Critical for Inferring Marine Turtle Nesting Population Trends

Assessments of population trends based on time-series counts of individuals are complicated by imperfect detection, which can lead to serious misinterpretations of data. Population trends of threatened marine turtles worldwide are usually based on counts of nests or nesting females. We analyze 39 years of nest-count, female-count, and capture-mark-recapture (CMR) data for nesting loggerhead turtles (Caretta caretta) on Wassaw Island, Georgia, USA. Annual counts of nests and females, not corrected for imperfect detection, yield significant, positive trends in abundance. However, multistate open robust design modeling of CMR data that accounts for changes in imperfect detection reveals that the annual abundance of nesting females has remained essentially constant over the 39-year period. The dichotomy could result from improvements in surveys or increased within-season nest-site fidelity in females, either of which would increase detection probability. For the first time in a marine turtle population, we compare results of population trend analyses that do and do not account for imperfect detection and demonstrate the potential for erroneous conclusions. Past assessments of marine turtle population trends based exclusively on count data should be interpreted with caution and re-evaluated when possible. These concerns apply equally to population assessments of all species with imperfect detection.

Carapace epibionts of loggerhead turtles (Caretta caretta) nesting at Canaveral National Seashore, Florida

A survey of the epibionts inhabiting the carapace of loggerhead sea turtles Caretta caretta (Linnaeus) nesting on Canaveral National Seashore, Florida was conducted from 2003–2004. Epibionts were sampled and identified to the lowest taxonomic level possible. Eleven newly documented epibiont species were observed from 52 individual loggerheads. We present the first records of sea urchins as loggerhead epibionts. Data are presented on the behavioural, physical, and ecological characteristics of some of these newly documented species to understand better the relationship between loggerhead turtles and their epibiota.

Distribution patterns of epibionts on the carapace of loggerhead turtles, Caretta caretta

The spatial distribution of epibionts on carapaces of marine turtles may be influenced by variation in recruitment dynamics, water flow patterns, and levels of disturbance on different regions of the carapace. We determined the distribution of 18 taxa of epibionts among nine zones on the carapace of 18 nesting loggerhead turtles (Caretta caretta) on Wassaw Island, Georgia, USA. Frequency of occurrence (%F) of all epibionts and each taxonomic class was determined for each zone. Distribution patterns were compared with a uniform distribution, and the distribution of each taxonomic class was compared with that of all epibionts combined. The distribution of all epibionts was significantly different from a uniform distribution, with highest densities on the posterior and vertebral zones. Distributions of each class, except Malacostraca and Cirripedia, were not significantly different from a uniform distribution across the carapace. Malacostraca was most dense on the posterior zones, whereas Cirripedia was most dense in the vertebral zones. Distributions of individual classes were all significantly different from the distribution of all epibionts combined. The distribution of all epibionts was strongly influenced by the distributions of the two dominant organisms, the chelonibiid barnacles and the caprellid amphipods.

DIET AND FECUNDITY OF COLUMBUS CRABS, PLANES MINUTUS, ASSOCIATED WITH OCEANIC-STAGE LOGGERHEAD SEA TURTLES, CARETTA CARETTA, AND INANIMATE FLOTSAM

Abstract The digestive tract contents of 85 Columbus crabs, Planes minutus, are presented. Crabs were collected from oceanic-stage loggerhead turtles, Carettta caretta, and inanimate flotsam near the Azores. The numbers of eggs carried by ovigerous crabs (n = 28) are also presented. Numbers of eggs between turtle crabs and flotsam crabs were similar. Dietary analysis yielded 11 food types from P. minutus. Crabs from turtles contained a higher diversity of food items than crabs from inanimate flotsam. The diet of P. minutus was composed primarily of neustonic invertebrates and algae—similar to prey items found from oceanic-stage loggerhead turtles in past studies. The types of food consumed by P. minutus suggest that crabs may obtain food by consuming other epibionts, by hunting neuston from their substrate, or by capturing food particles expelled by host turtles.

Nest Temperatures and Hatchling Sex Ratios from Loggerhead Turtle Nests Incubated Under Natural Field Conditions in Georgia, United States

Abstract We examined loggerhead nest temperatures and hatchling sex ratios in an effort to more accurately predict hatchling sex ratios produced from 2 barrier islands in the northern management unit (Blackbeard Island National Wildlife Refuge and Wassaw National Wildlife Refuge, Georgia, United States) from 2000 to 2004. Temperature data loggers were placed into 169 nests to monitor incubation temperatures. Average critical period temperatures ranged from 26.3°C to 33.2°C (mean ± SE, 29.2° ± 0.1°C) and indicated seasonal variation in sex ratios. The sex of 669 hatchlings found dead in nests was histologically evaluated (n  =  212 nests; 14–90 nests/yr). The sex ratios varied from 0% to 100% female per nest (n  =  1–53 hatchlings/nest) and average sex ratio for all nests ranged from 55.5% female in 2003 to 85.4% female in 2002. In addition to monitoring nest temperature, 10 hatchlings per nest were euthanized to verify sex during 2003 on Blackbeard Island National Wildlife Refuge (n  =  10 nests) and 2004 on Wassaw National Wildlife Refuge (n  =  9 nests). Sex ratios were analyzed by using an advanced statistical program for evaluating temperature-dependent sex determination and indicated a 1∶1 temperature (temperature that produces a 1∶1 sex ratio) of 28.9°C. We offer an equation for predicting northern management unit hatchling loggerhead sex ratios by using critical period temperature and tested its validity. Sixteen of 18 nests (n  =  10 hatchlings/nest) showed no significant difference between the predicted sex ratios based on the equation vs. sex ratios obtained through histology. Our data indicated that rookery beaches north of Florida are important areas for the production and recruitments of male loggerhead hatchlings into the overall western North Atlantic Ocean and nests deposited earliest within a nesting season are primary contributors of male turtles. We suggest that nest monitoring programs grant such nests particular protection to increase their survivability and the production of hatchlings.

New Records and Observations of Epibionts from Loggerhead Sea Turtles

Abstract Loggerhead sea turtles Caretta caretta (Linnaeus) were sampled (n = 304) for epibionts while nesting in Georgia from 1998–2003. Twelve newly documented epibiont species were observed and represent the first records of a hermit crab and a sea star as sea turtle epibionts. We report some physical, behavioral and ecological characteristics of the newly documented epibionts, particularly because nothing is known of their life history in Georgia as sea turtle epibionts. We also discuss the role of epibiotic crabs as facultative associates of loggerhead turtles.

Tag Returns from Loggerhead Turtles from Wassaw Island, GA

Abstract Much of what is known about sea turtle biology is attributed to research conducted on nesting females, due to the accessibility of these animals when on the beach. Long-range tag-return data obtained from individual loggerheads are helpful when determining population estimates, nesting ranges, seasonal dispersal patterns, and possible foraging areas. The Caretta Research Project has run a saturation-tagging project on Wassaw National Wildlife Refuge, GA since 1973. Tag returns received from the east coast of the United States to the Gulf of Mexico provide evidence that while some female turtles demonstrate site fidelity, others utilize multiple beaches during a nesting season as well as throughout their reproductive lifetimes and travel extensively between nesting seasons.

First Authentic Report of the Turtle Barnacle Cylindrolepas darwiniana Since its Description in 1916

Abstract An analysis of museum specimens reveals that reports of the chelonophilic barnacle Cylindrolepas darwiniana are misidentifications of the similar turtle barnacle Platylepas decorata. As a result, contemporary collections from loggerhead and hawksbill sea turtles represent the first report of this turtle barnacle since its description nearly a century ago. Novel morphological characters that clearly distinguish C. darwiniana from other turtle barnacles have been ascertained from the recent specimens and are reported.

A New Stomatolepas Barnacle Species (Cirripedia: Balanomorpha: Coronuloidea) from Leatherback Sea Turtles

ABSTRACT A new species of the commensal barnacle genus Stomatolepas has been collected from leatherback turtles in the southern Atlantic Ocean. It is described here as S. pilsbryi n. sp. and compared to its congeners S. elegans (Costa, 1838) and S. praegustator Pilsbry, 1910. A neotype is also designated for S. elegans.

Marine Snake Epibiosis: A Review and First Report of Decapods Associated with Pelamis platurus

Under circumstances in which area for settlement is limited, the colonization of living substrata may become a highly valuable strategy for survival of marine invertebrates. This phenomenon, termed epibiosis, results in spatially close associations between two or more living organisms. Pelamis platurus, the yellow-bellied sea snake, is the only exclusively pelagic marine snake and its propensity for foraging along ocean slicks facilitates its colonization by pelagic epibionts. Herein, we report epibionts associated with P. platurus inhabiting the waters off the northwestern Pacific coast of Costa Rica. These associations include the first records of decapod epibionts from any marine snake. Decapod epibionts were found on 18.9% of P. platurus, and size of snake (total length) had a significant positive effect on the frequency and intensity of epibiosis. We discuss the spatial and ecological mechanisms that facilitate these interactions, as well as the suite of factors that either promote or deter epibiosis and ultimately dictate the frequency and intensity of these interactions. Finally, we provide a review of marine snake epibiosis. The intention of this review is to (1) provide contemporary researchers with a single, accessible reference to all known reports of epibionts associated with marine snakes and (2) discuss what is currently known with respect to diversity of epibionts from marine snakes.