Project Title: Discovering new migratory pathways and the relationship between feeding ecology and reproductive output in loggerhead turtles (Caretta caretta, L.) nesting at the Archie Carr National Wildlife Refuge
Project Manager: Dr. L.M. Ehrhart
Organization: University of Central Florida (Research and Educational Institute)
Grant Amount: $29,895.00
Completion Date: 2014-05-22
Summary: Loggerhead nest numbers in Florida have been declining since 1998, raising concern among the scientific community and the general public because approximately 90% of all loggerhead nesting in the Southeastern U.S. occurs in Florida. The reasons for such decline are unclear. As population estimates are based on nesting activity, the decline in nest numbers may reflect a decline in the adult nesting population. However, reduction in nest numbers might reflect a change in the relationship between feeding ecology and reproductive output. Here, we will continue and expand the research we started in 2009. This project intends to investigate reproductive parameters, life history trade offs, movements and feeding habits of loggerheads nesting at the Archie Carr National Wildlife Refuge (ACNWR) using satellite tags in cooperation with the Caribbean Conservation Corporation, stable isotope analysis and more traditional techniques. The information gained from this study will improve estimates of adult nesting population size, identify movement patterns and expand the knowledge on feeding ecology. Moreover, the combination of satellite tracking and stable isotope analysis has the potential to elucidate the relationship between foraging activities and reproductive output, addressing one of the hypotheses for the apparent decline in loggerhead nest activities. Thus, this study will ultimately facilitate the ability of managers to make important conservation and management decisions for this threatened species that has incurred a 43% decline since 1998.
Results: The Sea Turtle Grant Program provided funds for the deployment of 6 SPOT 5 satellite tags (Wildlife Computers) during the 2011 nesting season. All satellite units were deployed as a part of the collaboration between the UCF Marine Turtle Group and the Sea Turtle Conservancy. Four units were deployed at the beginning of May, while the remaining two were deployed at the end of July in conjunction with the Tour de Turtle, an educational event organized by the Sea Turtle Conservancy. We are very pleased to announce that on May 31st, we encountered Bitey, one of the loggerheads equipped with a satellite tag (sponsored by this program) in 2009. After two years spent in the Great Bahamas Bank, Bitey was found nesting at the Archie Carr NWR carrying a FastLoc GPS tag still transmitting. We replaced her tag with a new tag and sent the old unit to Wildlife Computers for refurbishment. Bitey was first tagged by the UCF MTRG in 1992 and has been seen nesting 9 times since 1992.One of our objectives was to assess intra-seasonal clutch frequency. To maximize the chances of selecting first time nesters and increase the probability of re-sampling those individuals, we deployed four tracking units at the beginning of the nesting season and only on turtles previously flipper tagged by the UCF Marine Turtle Research Group and found nesting for the first time in the 2011 season. Moreover, the four units were deployed within a two-day period in an attempt to concentrate the re-nesting episodes over weekly intervals, thus reducing the need to continuously cover the beach with an ATV. To encounter and sample the tracked turtles during subsequent nesting episodes we physically covered the beach with an ATV in days of expected return and use the “Argos almost real time email service”. Over the season we were able to re-encounter and sample 5 of the tracked turtles several times (Table 1). Each time we collected samples for stable isotope analysis (blood, skin, scute biopsy and one freshly laid egg). In addition, we weighed and measured a subsample of eggs from each clutch. The two loggerheads taking part in the Tour de Turtles were sampled just once at the end of July. In 2011, we continued the collaboration with Dr. Valdes at The Disney Animal Kingdom to assess the nutritional status of the female and of her eggs and how it changes over the course of the nesting season. We are waiting for the results of the nutritional analysis and have started processing the samples collected for stable isotope analysis. With regard to post-nesting migratory movements, only 5 of the 7 tags we deployed in 2011 are still transmitting as of today (November 23, 2011). Sade stopped transmitting on June 30 after we cut the unraveled strand of the antenna. Mayorita stopped transmitting on September 19 and was last seen in Cuban waters. Tracking data suggest a failure of the tag and not incidental capture. Bubbles stopped transmitting on Oct 7, shortly after reaching North Carolina and after spending the last part of the summer months in the waters offshore the Delmarva Peninsula. The majority (n=5) of the loggerheads we tagged in 2011 headed to Southern foraging areas and in particular to the Bahamas. Of the 7 individuals for which post-nesting migration destination is known, only 2 migrated North to Virginia and Delaware, where they spent the rest of the summer and then migrated to the North Carolina Outer Banks, where they are overwintering. The two females followed the same migration pattern observed in 6 loggerheads we satellite tracked between 2008 and 2010. The preliminary stable isotope results showed that individuals that headed to northern foraging grounds in 2011 have the same isotopic signature found in loggerheads that took up residence in those areas in previous years. Moreover, all the females that utilize the northern foraging ground (n=2 in 2011, n=3 in 2010, n=2 in 2009 and n=1 in 2008) have isotopic signatures similar to the loggerhead population of the Pamlico-Albemarle estuarine complex of the North Carolina coast (Wallace et al. 2009, McClellan 2010). Loggerheads that took up residence in the Bahamas have isotopic signatures comparable to those we observed in the past in loggerheads heading to southern foraging grounds. The preliminary results support the relationship between latitude of the foraging ground and stable isotope signatures that we have found over the course of our study. The data we have been collecting since 2008 support the use of stable isotopes to infer post-nesting migration destinations of loggerheads nesting at the Carr refuge in lieu of more expensive satellite units. The next step will be to finish the isotopic analysis of all the tissues collected from the satellite turtles and to use the relationship we identified between latitude and isotopic signature to assign foraging grounds to the larger pool of nesting females we have sampled for stable isotope analysis (n=180). This will provide a better representation at the population level.