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Tag Returns from Loggerhead Turtles from Wassaw Island, GA
Kristina L. Williams and Michael G. Frick

Southeastern Naturalist, Volume 7, Number 1 (2008): 165–172

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2008 SOUTHEASTERN NATURALIST 7(1):165–172 Tag Returns from Loggerhead Turtles from Wassaw Island, GA Kristina L. Williams1,* and Michael G. Frick1 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 saturationtagging 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. Introduction The southeastern United States is considered one of the most important Caretta caretta Linnaeus (Loggerhead Sea Turtle ) rookeries in the world (Bowen and Karl 1997). The majority of Loggerheads nesting in this region occurs in Florida (≈90%), including the Florida Panhandle, while the remaining 10% of the population deposit their eggs on barrier island beaches north of Florida (Bowen and Karl 1997). These relatively small islands allow biologists an opportunity to develop and implement research practices and monitoring efforts that may not be considered cost effective or feasible on larger beaches where turtles nest en masse (Richardson 1999). There are at least three subpopulations of Loggerhead sea turtles that nest along the southeastern coast of the United States each summer: the “Florida Panhandle” subpopulation, the “South Florida” subpopulation, which nests south of Amelia Island to approximately Sarasota, FL, and the “Northern” subpopulation, which nests north of Florida to Virginia (Bowen 2003). The subpopulations are genetically distinct and may be ecologically and behaviorally different, although some overlap has been recorded through tag returns and genetic studies (Plotkin and Spotila 2002). The Caretta Research Project (CRP) has tagged almost 1300 Loggerhead Sea Turtles on Wassaw Island since 1973. The purpose of this paper is to report sources of tag returns and dispersal data from Loggerheads nesting on Wassaw Island and identify possible adult foraging areas utilized by turtles away from the nesting beach. 1Caretta Research Project, PO Box 9841, Savannah, GA 31412. *Corresponding author - WassawCRP@aol.com. 166 Southeastern Naturalist Vol.7, No. 1 Methods Study site Wassaw Island is part of the Wassaw National Wildlife Refuge (31.905N, 80.981W) located 12 km south of the South Carolina/Georgia border. The 10.7-km beach has been consistently patrolled nightly since 1973. Standard beach monitoring data collections Monitoring for nesting Loggerheads begins in early May and ends by the middle of August, after nesting activity ceases. Patrols begin at dusk (2100 h) and usually end at dawn (0600 h). Two teams of up to 4 people per team patrol the beach using two 4-wheeled vehicles or by walking, depending on tide stage, weather conditions, and vehicle performance. Turtles were approached and checked for tags only after egg deposition had begun. Since 1973, there have been 6 types of tags used: monel, rototags, Reise, inconel, Floy, and Destron PIT (Passive Integrated Transponder) tags. In 1992, PIT tags were introduced to supplement double tagging with inconel tags since the external metal tags are frequently lost. Turtles were tagged in 3 fashions. Singly tagged turtles were outfitted with a tag on either the first or second large scale on the posterior edge of the right front fl ipper. Double-tagged turtles received tags in either the first or second large scale on the posterior edge of each front fl ipper. Triple-tagged turtles received an additional tag on the right or left back fl ipper. All PIT tags were implanted subcutaneously just proximal to the center elbow region of the right front fl ipper. Tag returns were recorded in cooperation with National Marine Fisheries Service, Southeastern Fisheries Science Center, the Archie Carr Center for Sea Turtle Research at the University of Florida at Gainesville, and the Georgia Ddepartment of Natural Resources (GADNR). Results and Discussion Since 1973, we have identified 1295 individual turtles and have received 152 returns from 143 individuals (11.7% tag-return rate) (Fig. 1, Table 1). Table 1. Summary of tag returns from Loggerhead Sea Turtles tagged on Wassaw Island, GA from 1973–2006. Return Location State Nesting beach Dead on beach In-water capture New York 0 1 0 Delaware 0 1 0 Virginia 0 2 2 North Carolina 4 0 1 South Carolina 20 5 2 Georgia 92 4 12 Florida 3 0 2 Alabama 0 0 1 Total 119 13 20 2008 K.L. Williams and M.G. Frick 167 These returns were analyzed in three ways: source of tag return, dispersal, and potential adult foraging areas (AFAs). Source Tag returns come from three primary sources: turtles encountered on a nesting beach, captured by commercial fishing industry (trawlers), or dead on the beach. Figure 1. Locations of tag returns from in-water captures and stranded (dead on the beach) Loggerhead Sea Turtles originally tagged on Wassaw National Wildlife Refuge between 1973–2006. 168 Southeastern Naturalist Vol.7, No. 1 Nesting beaches The majority (78.3%, n = 119) of the tag returns come from encounters on nesting beaches, and nearly half (48.7%, n = 58) of these are from 2 major nesting beaches south of Wassaw Island: Blackbeard and Ossabaw Islands. Blackbeard Island has reported the highest number of Wassaw’s turtles (31.9%, n = 38). Blackbeard Island only recently started a saturation tagging program to facilitate research with Georgia Southern University, and therefore tag returns from Blackbeard have increased considerably since 2001. The beach that has given us the second highest number of returns is Ossabaw Island (16.8%, n = 20), just south of Wassaw. Tagging and patrolling at night have been sporadic on Ossabaw, yet a significant number of returns come from this island. This percentage would have been much higher if they monitored the beach for nesting females in addition to conducting their nest-protection practices. The remaining 61 tag returns from nesting beaches are split between beaches north (n = 28) and south (n = 33) of Wassaw Island. Most tag returns from northern beaches come from other programs that conduct nightly education walks (i.e., Hilton Head, Folly Beach, Pritchard’s Island, and Cape Romain in South Carolina). South Florida beaches do not host many beachmonitoring projects, but projects in Keywaydin and Sanibel Island, where nightly patrols occur, have not yielded any tag returns for our project. It is not surprising that inter-island shifting was so frequently observed both within and between an individual’s nesting seasons. While many turtles do show a high level of site fidelity to Wassaw throughout the nesting season, approximately 60% of “Wassaw’s” turtles were seen only once on Wassaw. We receive many reports of turtles tagged on Wassaw observed nesting on neighboring islands. Inter-island shifting in Georgia is common among Loggerheads and occurs both within a nesting season and between seasons as reported by Bell and Richardson (1978) and Williams and Frick (2001). This shift may be explained by the dynamic nature of Georgia’s barrier islands or by offshore changes (i.e., sandbars) that defl ect turtles from one nesting beach to another. Additionally, Loggerhead sea turtles tagged on Bald Head Island, NC have also been identified nesting on other beaches from North Carolina to Florida (Hawkes et al. 2005). Changes in nesting densities illustrate the ability of turtles to shift their nesting efforts to neighboring beaches. Brunswick, GA residents reported large historical numbers of Loggerhead nests on St. Simon’s Island (Caldwell 1962). However, as erosion destroyed most of the suitable nesting areas on St. Simon’s Island, turtles shifted their nesting efforts to the south, confirmed by aerial surveys conducted in 1958 and 1959 (Caldwell et. al. 1959), which also demonstrated that, in Georgia, the most concentrated nesting occurred on Jekyll and Little Cumberland Islands (LCI). As development increased on Jekyll Island, nesting shifted again to LCI and Cumberland Island (CMBI), also confirmed by the Georgia Game and Fish Commission in 1960–1961 (Caldwell 1962). Little Cumberland Island began its saturationtagging program in 1964. At its peak in 1972, LCI hosted the highest density 2008 K.L. Williams and M.G. Frick 169 of nests/km in Georgia (A. Mackinnon, GADNR, pers. comm.). Dahlen et al. (2000) reported that between 1982 and 1997, nesting on LCI and CMBI decreased by 7 and 4 nests/year respectively, and nesting on the southern portion of CMBI has increased by 2.5 nests/year. In-water recaptures. Approximatly 17% of all returns (n = 20) were captured within a fishing industry (primarily shrimp trawlers). Sixty percent (n = 12) of these captures were within 50 km of Wassaw Island. The remaining 8 returns were from more distant locations, further demonstrating the extent of travel of Loggerhead Sea Turtles. While 19 of 20 in-water encounters were reported from shrimp trawlers, one was from a shark fisherman who found the flipper with the tag attached in the stomach of a small Galeocerdo cuvier (Péron and Lesueur in Lesueur) (tiger shark) off of North Carolina. Returns such as these are especially interesting since they document sea turtles as a prey item of tiger sharks. We occasionally observe turtles on Wassaw with tiger shark bites through their carapace with shark teeth remaining within the bite. Shark teeth are identifiable to species so we can confidently determine which species attacked the turtle. Dead on the beach. Only 13 (8.6%) of the returns were reported from Loggerheads found dead on various beaches. This result may be a great underestimation of the number of tagged turtles that strand dead on beaches, because strandings are often too decomposed to retain their tags or lack fl ippers due to marine scavengers. Six were found within 50 km on neighboring islands, and three were located farther north in South Carolina. The remaining four were found in Virginia, Delaware, and New York. This result is not surprising as turtles are commonly seen from the Chesapeake Bay to the Long Island Sound throughout summer and early fall. Dispersal North. Forty-five (29.6%) of 152 tag returns were reported north of Wassaw Island. Twenty-eight of the 45 northern returns were seen on nesting beaches, eight were found in the water, and nine were found dead on the beach. The distances of northern nesting beaches utilized by Loggerheads observed on Wassaw Island range from 10–400 km (mean = 95.4 km), with the northernmost nesting beach being Onslow Beach, NC. The distances of turtles caught in the water ranged from 0–860 km (mean = 286.6 km), with the farthest off of Hog Island, VA. The distances of turtles reported dead on the beach ranged from 40–1191 km (mean = 425.5 km), with Montauk Point, NY being the farthest north. Satellite telemetry studies have also demonstrated the northern movement of Georgia’s turtles after completing their nesting season. Twelve of 13 Loggerheads that were satellite tagged on Wassaw Island traveled north (CRP, unpubl. data; Plotkin and Spotila 2002). Movements of these turtles commonly led to the Chesapeake Bay/Delmarva Peninsula area before returning southward (to South and North Carolina area) in late fall (autumn), presumably as water temperatures began to drop (Coles and Musick 2000, 170 Southeastern Naturalist Vol.7, No. 1 Shoop and Kenney 1992). The Chesapeake Bay has long been documented as a productive foraging area for juvenile Loggerheads (Coles and Musick 2000). However, the importance of this area to post-nesting Loggerheads is not well known (Plotkin and Spotila 2002). South. One hundred and seven (70.4%) of 152 tag returns were reported south of Wassaw Island. Ninety-one of these returns were seen on nesting beaches, 12 were found in the water, and 4 were found dead on the beach. Distances of southern nesting beaches utilized by Loggerheads observed on Wassaw Island range from 14–410 km (mean = 57.6 km), with the southernmost nesting beach being Cape Canaveral, FL. Distances of turtles caught in the water ranged from 14–1935 km (mean = 264.2 km), with the most distant one occurring off of Gulf Shores, AL. The distances of turtles reported dead on the beach ranged from 12–48 km (mean = 25.3 km), with Blackbeard Island, GA being the farthest south. Most of this study’s southbound turtles were seen within Georgia and the northern subpopulation boundaries. However, 6 were seen farther south. As previously mentioned, 1 of these returns was from a turtle caught in a trawler off Gulf Shores, AL. While it is uncommon to receive a Wassaw tag return from the Gulf of Mexico, there have been 7 previously documented individuals that were originally tagged on the east coast of the United States and reported in the Gulf of Mexico. One of these turtles was tagged on CMBI, GA and reported in Tampa Bay, FL (in the Gulf of Mexico; Bell and Richardson 1978). The remaining 6 turtles were tagged in the Cape Canaveral area, FL. Two were found dead near West Port St. Joe and Sanibel Island (Meylan et. al. 1983). Two were caught by trawls off of Longboat Key and Charlotte Harbor, FL, and 2 were caught in a shrimp trawler off Mississippi (Caldwell et. al. 1959, Meylan et. al. 1983). While this sample size is small, it illustrates the range of movements by Loggerheads that nest on the east coast. Potential adult foraging areas Three (2.1%) of the 142 returns were caught in trawls the year after the turtles were seen on Wassaw Island. While there are reports of sea turtles nesting in consecutive years, it is not common. Since turtles usually have a 2–3 year remigration period, we expect that these recaptures represent potential adult foraging areas for these individuals. Two of these 3 were far from the nesting beach: 1 near Cape Canaveral, FL, a second off Gulf Shores, AL, and the third was off of Sapelo Island, GA. Collectively, these tag returns show that the northern subpopulation of Loggerheads will utilize beaches and foraging grounds covering many kilometers along the southeastern United States. Meylan et. al. (1983) reports incidental sea turtle mortality in fishing gear set for commercial species. Such occurrences emphasize the need for the protection of turtles during their migrations to and from breeding, nesting, and foraging areas. Research on Australian Loggerhead Turtles indicates that at the end of the 2008 K.L. Williams and M.G. Frick 171 nesting season, it is important for females to migrate to foraging areas in order to replenish their fat reserves since they feed little or not at all for several months during their nesting cycle (Limpus and Limpus 2003). It is presumed the same is true for Atlantic Loggerheads as well. Currently these foraging areas and the routes turtles use to travel to these areas are being revealed through satellite telemetry and tag returns in the United States. Morreale et. al. (1996) state the importance of locating post-nesting foraging areas and migration routes between foraging and nesting areas, primarily because the clustering of turtles in one area or route may render an entire population vulnerable to extirpation. More data on the migratory movements and preferred foraging habitats of Loggerhead Sea Turtles are needed in order to protect turtles from in-water threats. Acknowledgments The Caretta Research Project would like to thank Randy Isbister, Charles Warnock, United States Fish and Wildlife Service Savannah Coastal Refuges, Georgia Department of Natural Resources, and Wassaw Island, LLC for making our work on Wassaw Island possible. We would also like to thank 34 years of staff, assistants, interns, and over 2000 volunteers who have donated sweat, time, and money in order to protect Georgia’s Loggerheads. We appreciate the comments and suggestions from three anonymous reviewers which greatly improved this manuscript. Literature Cited Bell, R., and J.I. Richardson. 1978. An analysis of tag recoveries from Loggerhead Sea Turtles (Caretta caretta) nesting on Little Cumberland Island, Georgia. Florida Marine Research Publications. 33:20–24. Bowen, B.W. 2003. What is a Loggerhead Turtle? The genetic perspective. Pp. 7–27, In A.B. Bolten and B.E. Witherington (Eds.). Loggerhead Sea Turtles. Smithsonian Books, Washington, DC. 319 pp. Bowen, B.W., and S.A. Karl. 1997. Population genetics, phylogeography, and molecular evolution. Pp. 29–50, In P.L. Lutz and J.A. Musick (Eds.). The Biology of Sea Turtles. CRC Marine Science Series, CRC Press, Inc., Boca Raton, FL. 432 pp. Caldwell, D.K. 1962. Comments on the nesting behavior of Atlantic Loggerhead Sea Turtles, based primarily on tagging returns. Quarterly Journal of the Florida Academy of Science 25(4):287–302. Caldwell, D.K., A. Carr, and L.H. Ogren. 1959. The Atlantic Loggerhead Sea Turtle Caretta caretta (L.), in America. I. Nesting and migration of the Atlantic Loggerhead Turtle. Bulletin of the Florida State Museum 4(10):295–308. Coles, W.C., and J.A. Musick. 2000. Satellite sea surface temperature analysis and correlation with sea turtle distribution off North Carolina. Copeia 2:551–554. Dahlen, M.K., R. Bell, J.I. Richardson, and T.H. Richardson. 2000. Beyond D-0004: Thirty-four years of Loggerhead (Caretta caretta) research on Little Cumberland Island, Georgia, 1964–1997. Pp. 60–62, In F.A. Abreu-Grobois, R. Briseno-Duenas, R. Marquez, L. Sarti (Compilers). Proceedings of the Eighteenth International Sea Turtle Symposium. US Department of Commerce, Miami, FL. NOAA Technical Memorandum NMFS-SEFSC-436, 293 pp. 172 Southeastern Naturalist Vol.7, No. 1 Hawkes, L.A., A.C. Broderick, M.H. Godfrey, and B.J. Godley. 2005. Status of nesting Loggerhead Turtles, Caretta caretta, at Bald Head Island (North Carolina, USA) after 24 years of intensive monitoring and conservation. Oryx 39(1): 65–72. Limpus, C.J., and D.J. Limpus. 2003. Biology of the Loggerhead Turtle in western South Pacific Ocean foraging areas. Pp. 93–113, In A.B. Bolten and B.E. Witherington (Eds.). Loggerhead Sea Turtles. Smithsonian Books, Washington, DC. 319 pp. Meylan, A.B., K.A. Bjorndal, and B.J. Turner. 1983. Sea turtles nesting at Melbourne Beach, Florida. II. Post-nesting movements of Caretta caretta. Biological Conservation 26(1):79–90. Morreale, S.J., E.A. Standora, J.R. Spotila, and F.V. Paladino. 1996. Migration corridor for sea turtles. Nature 384:319–320. Plotkin P.T., and J.R. Spotila. 2002. Post-nesting migrations of Loggerhead Turtles Caretta caretta from Georgia, USA: Conservation implications for a genetically distinct subpopulation. Oryx 36(4):396–399. Richardson, J.I. 1999. Priorities for Studies of Reproduction and Nest Biology. Pp. 9–11, In K.L. Eckert, K.A. Bjorndal, F.A. Abreu-Grobois, and M. Donnelly (Eds.). Research and Management Techniques for the Conservation of Sea Turtles. IUCN/SSC Marine Turtle Specialist Group, Washington, DC. Publication No. 4. 235 pp. Shoop, C.R., and R.D. Kenny. 1992. Seasonal distributions and abundances of Loggerhead and Leatherback Sea Turtles in waters of the northeastern United States. Herpetological Monographs 6:43–67. Williams, K.L., and M.G. Frick. 2001. Results from the long-term monitoring of nesting Loggerhead Sea Turtles (Caretta caretta) on Wassaw Island, Georgia: 1973–2000. NOAA, Miami, FL. Technical Memorandum NMFS-SEFSC-446. Jan. 2001. 32 pp.