Caretta caretta

Meylan, Peter A., Meylan, Anne B. & Gray, Jennifer A., 2011, The Ecology And Migrations Of Sea Turtles 8. Tests Of The Developmental Habitat Hypothesis, Bulletin of the American Museum of Natural History 2011 (357), pp. 1-70 : 38-42

Caretta caretta

PANAMA: SECRETARY STUDY SITE: Eightytwo Caretta were captured at this site. About one-quarter (n 5 17) were laparoscoped and a single 98 cm SCL adult male was identified. This turtle had recently lost an entire foreflipper and its occurrence at the site may have been atypical. The size distribution of the remaining 81 Caretta is shown in figure 17.

Wibbels et al. (1991b) used 76 cm SCL as a minimum size of sexual maturity of western Atlantic loggerheads on the basis of laparoscopy of 22 immature animals in Florida, laparoscopy of a large number of immature and adult animals in Australia, and the minimum reported size of nesting females in Florida. The average size of nesting female Caretta in the Atlantic Ocean is greater than 90 cm ( Dodd, 1988). Bjorndal et al. (1983) reported a minimum size of 74.9 cm SCL for nesting females at Melbourne Beach, Florida; Kaufmann (1975) measured nesting females in Colombia as small as 70 cm SCLn-t (5 68.6 cm SCLmin; see table 9). This size (68.6 cm) is used as the minimum size at sexual maturity in figures 17 and 18. This is a very conservative estimate, given that loggerheads as large as 85.3 cm SCL were immature at the Zapatilla Cays (fig. 18). However, this low value is used in this paper because it is possible that Colombian loggerheads may occur in developmental habitat in Panama. Buritaca, Colombia, is one of the few known Caretta nesting beaches in the southwest Caribbean, although at present it appears to be extremely depleted ( Amorocho et al., 1999).

Only 12 Caretta captured at Secretary were larger than 68.6 cm. In addition to the outlier mentioned above, the largest was 76.5 cm SCL. One of these 12, a 72.1 cm female, was laparoscoped and was determined to be pubescent (stage 2). Additional laparoscopy of Caretta in the 65–85 cm size range is

TABLE 11 Summary of foraging ground data for Eretmochelys imbricata from the literature

needed for corroboration; however, the eastern end of the Chiriqui Lagoon appears to support immature-dominated, benthic developmental habitat for Caretta caretta (see also Engstrom et al., 2002).

A sample of laparoscoped immature loggerheads (n 5 22) from the two Panama sites suggests that maturation of Caretta in Panama begins at about 65 cm SCL in both sexes (fig. 18). Two stage 2 males from the Zapatilla Cays were about 15 cm larger than the very conservative minimum size at sexual maturity used here.

THE LITERATURE: The large minimum size of loggerheads observed at the Secretary study site (45.2 cm SCL), relative to that seen for Chelonia and Eretmochelys , reflects the extended pelagic stage in this species ( Carr, 1986; Bolten et al., 1993, 1995, 1998; Bolten, 2003). The minimum size for this species at other Atlantic, immature-dominat- ed, inshore, foraging grounds varies from 41.5–47.5 cm SCL except for Chesapeake Bay, which apparently receives occasional (, 1 %) epipelagic-stage individuals (table 12). Caretta also appears to have regular overlap of adults with immature-dominated, benthic developmental habitats. In all studies listed in table 12 and figure 26, some adults were present, and they made up a variable portion of the sample, from 1.2 % at Secretary in Panama to about 20 % (based on size) at two sites along the eastern seaboard of the United States ( Epperly et al., 1995; Schmid, 1995). However, only the Secretary study used laparoscopy, so the number of matures in the remaining studies is likely an overestimate. In some cases, the presence of adults may result from juxtaposed internesting and immature foraging habitats (fig. 23B), and in others, overlap between the adult foraging grounds and benthic developmental habitat (fig. 23C, D). However, sites like Secretary (fig. 17), Indian River Lagoon (fig. 26 A), Mosquito Lagoon, and Charleston Harbor have very few adults and thus support the observations that benthic developmental habitats for Caretta , like those for other cheloniid species, can be immature dominated.

There are clear exceptions to the use of benthic developmental habitat by immature Caretta in the North Atlantic. Some Atlantic- Mediterranean Caretta remain pelagic until they enter adult foraging grounds, as appears to be the case in the Pacific. In the western Mediterranean, off the coast of Spain, large immature loggerheads of all size classes up to adult size are regularly captured in a longline fishery ( Gasau and Ninou, 2000: fig. 1). Alternatively, some (or all) individual loggerheads in a population may switch between benthic and epipelagic feeding. This pattern of polymodal foraging is now well established for Caretta (Witzell, 2002; Morreale and Standora, 2005; Hawkes et al., 2006; McClellan and Read, 2007; Reich et al., 2010). It appears to occur regularly in a small subset of loggerheads that forage in benthic habitats along the east coast of the United States (Morreale and Standora, 2005; McClellan and Read, 2007; Mansfield et al., 2009). This subset migrates off shore into the Gulf Stream Current instead of migrating south along the coast as water temperatures drop in the fall. Switching between epipelagic and benthic foraging may be the norm for Caretta in the Atlantic. To reflect this Casale et al. (2008) proposed a relaxed life history model for Caretta , which may be more prevalent in the Mediterranean than western Atlantic Ocean.

In the Pacific, immature Caretta are known to remain pelagic until just before reaching sexual maturity. The work of Limpus et al. (1994b) in Moreton Bay, Queensland, and studies of pelagic Caretta in the north Pacific (Polovina et al., 2000), suggest that the benthic developmental stage may be absent in Pacific loggerhead populations. Limpus et al. (1994b) reported that there are very few records of Caretta in the 30–70 cm size class from eastern Australia, and they suggested that Caretta recruit to the Moreton Bay foraging grounds at about 70 cm CCL, while still immature. They then mature and remain resident at this site, which is considered adult foraging habitat. A similar population structure exists for Caretta in the southern Great Barrier Reef ( Limpus, 1992). Studies of Caretta caught as bycatch in the longline fisheries in the North Pacific include animals up to 83 cm SCL (Polovina et al., 2004).

Florida Bay also offers intriguing evidence bearing on the developmental habitat hypothesis. A preliminary report by Schroeder et al. (1998), suggested the possibility that this area is occupied mainly by Caretta that are mature or nearly mature. Although there were a few individuals as small as 50 cm, most were in the 80–100 cm range. The smallest nesting females in Florida are about 75 cm SCL ( Dodd, 1988). Thus, Florida Bay may represent an adult foraging ground into which large immatures recruit and then go through the maturation process.

TABLE 12

Summary of foraging ground data for Caretta caretta from the literature