Genetic Analysis, Movement, and Nesting Patterns of the Green Sea Turtle (Chelonia Mydas) in St. Croix, Virgin Islands (USA): A Regional Analysis for the Caribbean.
Department of Marine Sciences
Green Sea Turtle
The green sea turtle Chelonia mydas is listed as endangered by the IUCN Red List of 2004. The Endangered Species Act now classifies the green turtle species into 11 distinct population segments (DPSs) with most segments being classified as threatened and only three (Mediterranean, Central West Pacific, and Central South Pacific) being listed as endangered. More information needs to be obtained about the foraging, nesting, and movement behaviors of the different green turtle rookeries worldwide to implement the best management practices. The main purpose of this study was to track internesting and post-nesting movements, categorize the benthic habitat types utilized during these periods, identify the dominant genetic haplotype, and provide summary statistics of female green sea turtles nesting on the East End beaches, including the beaches within Jack, Isaac, and East End Bays, of St. Croix, US Virgin Islands. Seven Wildlife Computers™ SPOT-352A platform transmitter terminals (PTTs) were attached to female green sea turtles on the East End beaches of St. Croix in August and October 2015. The females were tracked using the Satellite Tracking and Analysis Tool (STAT) on seaturtle.org and movement patterns were mapped. Kernel density estimation (KDE) was utilized to calculate 50% core use and 95% activity areas during their internesting and post-nesting periods. Minimum convex polygons (MCPs) were created when KDE could not be completed. Habitat utilization was identified in the core use areas and MCPs. Tissue biopsies were collected from 60 nesting female green turtles on the East End beaches from 2012-2015. The ~820-bp mtDNA control region was sequenced to identify the haplotypes present within this rookery. Summary statistics were calculated for nesting data collected on the East End beaches from 2003-2015 to identify some of the life history characteristics of the green turtle rookery on the East End beaches. Recommendations were provided for better ways to conduct long-term nesting surveys with uniformity, so that population estimation models can be applied. Female green turtles were tracked between 16-241 d (mean=160.9±10.6) for a total of 1,126 PTT days transmitted before analyses were conducted. Kernel density estimation and a MCP could not be created when less than ten detections of the highest location class were received. Three females were residents of the waters around St. Croix, remaining within the same areas during both their internesting and post-nesting periods. Three females were classified as migrants as two transitioned to the waters near St. Kitts and Nevis during their post-nesting periods and one moved to the waters to the northwest of Vieques. The haplotypes identified on the East End beaches of St. Croix were CmA3.1, CmA5.1, and CmA5.2. The haplotype CmA5.1 was most common (91.4%, n=58). The average number of green sea turtle nests was 263.9±53.5 between 2003 and 2015. The mean clutch size was 107.9±3.4 eggs with an average hatching success of 86.7%±2.0%. Nesting survey effort varied greatly over the survey period, which limited the power of the data collected. The major finding of this study was that there are resident and migrant green turtles on the East End beaches of St. Croix. The dominant haplotype on the East End beaches was identified as CmA5.1. While a population estimation was not able to be calculated from the nesting beach monitoring data, significant knowledge was gained about the large rookery present on East End beaches, which will allow conservation managers to evaluate other ways to protect this population. Future researchers should utilize additional satellite transmitters equipped with depth recorders to monitor dive profiles of both male and female green turtles throughout the Caribbean. Additional genetic analyses should be conducted on the East End beach rookery to adequately determine if there is significant enough genetic differentiation to classify it as a separate management unit (MU) from the Buck Island rookery. The nest monitoring program on the East End beaches should continue with a focus of collecting data on the total number of nesting females, clutch size, and hatching success. Continued collaborative research involving satellite telemetry, genetic analyses, and nest monitoring is vital for protecting this threatened and endangered species.