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A study of clutch frequency was conducted at a loggerhead turtle rookery on Casey Key, Florida (27.1°N, -82.5°W) during 2006-2008. Female loggerhead turtles (Caretta caretta) were approached after nesting for attachment of satellite tags (Sirtrack Kiwisat 101 or Wildlife Computers SPOT-5) to the carapace along with standard Inconel flipper tags and PIT tags. Clutch frequency and site fidelity were subsequently derived from characteristics of the tracking histories.

Movements were reconstructed from fixes of Location Classes 3, 2, 1, 0, or A (and omitted Location Classes of B or Z). Location data were preprocessed in Satellite Tracking and Analysis Tool (STAT: Coyne & Godley 2005) to filter locations for depth > 0.5m, speed > 4 km/hr, locations < 4hr apart, or for angles < 15 degrees. The filter process discarded errant points far inland, for improbable speeds, or excluded obvious outlier points from the vector of the movement path. Multiple criteria were then applied to identify each presumed emergence: (1) emergences were only considered within the expected inter-nesting intervals for loggerheads (9-15d), (2) emergence locations were associated with depths of -0.5 to 0.5, (3) when the turtle movements were directed onshore followed by an immediate offshore vector, (4) an improvement in location classes such as multiple LC 2 or 3 within a short time span, (5) evidence of an increased surface interval in the PTT data, (6) verification by nocturnal patrols if the female emerged on the same beach as the patrols (7) or verification by parental assignment using DNA microsatellite markers (B. Shamblin, unpubl. data).

Among the loggerheads tracked during the 2008 season was a female (102.9 cm curved carapace length) that established a new record of clutch frequency that was determined empirically by a combination of the satellite tracking history (ARGOS ID 72441) combined with periodic verification by nocturnal tagging personnel or molecular techniques of matching DNA samples from the first and last nests. The female’s annual reproductive output of eight nests (Table 1) was readily determined by the displacement and daily movements relative to shore (Fig. 1) during each internesting interval. Site fidelity was to the same regional rookery, though not specifically to the same beach, with all eight nests deposited within 15.9 km measured between the most distant nests (measured in Google Earth). A distinctive behavioral trait of the tracked female contributed to clarity in verifying all nests: her displacement distance perpendicular to shore across the inter-nesting periods illustrated a pattern of directed movements toward shore followed by a distant offshore movement after nesting (Fig. 2) accounting for the movement sequence in Fig. 1.

Figure 1. Displacement from shore by loggerhead 72441 as it leaves and returns from first nest at May 20 to the eighth nest on August 9. During a post nesting migration the turtle swam steadily toward a distant foraging residency on the Yucatan Banks, Mexico.

Table 1. Dates of nesting for loggerhead 72441 tracked by Argos satellites. Abbreviations in the verified column (Ver) are NP = verified by night patrols, G = verified genetically, * = nest was unverified because raccoons destroyed all eggs that same night before nest was discovered. Distances between nests were determined in Google Earth.

The present account establishes a new maximum clutch frequency of eight nests for loggerhead turtles of the Western Atlantic compared to a previous record of seven clutches documented for Georgia loggerheads (Lenarz et al. 1981). We note that an earlier study had suggested the potential for eight nests in southwest Florida loggerheads, based on internesting intervals (Addison 1991). Our approach differed from Sato et al. (1998) who used archival time depth data loggers to determine nesting activity of females by verifying nesting emergences. However logistically speaking, satellite transmitters seem better suited than archival data loggers to illuminate the entire nesting season profile of animals since they do not have to be recovered.

Figure 2. Daily movement vectors to and from each nesting event (N). Since the female was tagged at the first nest, movements preceding that cannot be indicated. Positive values indicate the turtle moving away from the release site or negative when moving towards the release site.

The marine turtle community has expressed skepticism as to whether the uncertainty errors in ARGOS satellite tracking (contrasted with the higher frequency and accuracy of locations with GPS tags) allow locations to be recorded with sufficient precision to document nesting emergences. This study demonstrates that a combination of data filtering and multiple criteria matching can afford reliability in detecting loggerhead emergences, whether nesting or false crawls, provided that individual turtles have a distinctive pattern of inshore-offshore directed movements. Related studies for other turtle species are now required to more extensively test this method of estimating clutch frequency. In particular, species or individuals that linger near shore during an inter-nesting period may be more problematic to interpret a movement pattern than was illustrated by this loggerhead female (cf. Fig. 1 and 2).

Acknowledgments: The study was partly supported by grant 08-019R from the Florida Sea Turtle Grants Program (<http://www.helpingseaturtles.org>) which is funded by sales of the Florida Sea Turtle License Plate. Animals were handled in accordance with IACUC permit 08-04-AT1 and Marine Turtle Permit #126 from the Florida Fish and Wildlife Conservation Commission. Location data were filtered and analyzed in STAT developed by seaturtle.org We thank staff and interns of the Sea Turtle Conservation and Research Program for dawn patrols and L. Flynn, A. Oeding, and K. Martin for nocturnal patrols. B. Shamblin conducted the genetic testing.

ADDISON, D.S. 1996. Caretta caretta (Loggerhead Sea Turtle). Nesting frequency. Herpetological Review. 27: 76.

COYNE, M.S., & B.J. GODLEY. 2005. Satellite Tracking and Analysis Tool (STAT): an integrated system for archiving, analyzing and mapping animal tracking data. Marine Ecology Progress Series 301:1-7.

LENARZ, M.S., N.B. FRAZER, M.S. RALSTON & R.B. MAST. 1981. Seven nests recorded for loggerhead turtle (Caretta caretta) in one season. Herpetological Review 12: 9.

SATO, K., Y. MATSUZAWA, H. TANAKA, T. BANDO, S. MINIMIKAWA, W. SAKAMOTO, & Y. NAITO. 1998. Internesting intervals for loggerhead turtles, Caretta caretta, and green turtles, Chelonia mydas, are affected by temperature. Canadian Journal of Zoology 76:1651-1662.