225 Adult Migrations and Habitat Use Pamela Plotkin CONTENTS 8.1 Introduction 225 8.2 Leatherback, Dermochelys coriacea 226 8.3 Olive Ridley, Lepidochelys olivacea 227 8.4 Kemp’s Ridley, Lepidochelys kempii 228 8.5 Hawksbill, Eretmochelys imbricata 229 8.6 Flatback, Natator depressus 230 8.7 Loggerhead, Caretta caretta 231 8.8 Green, Chelonia mydas 231 8.9 East Pacific Green, Chelonia agassizi 232 8.10 Conclusions 233 References 233 8.1 INTRODUCTION Adult sea turtles are among the largest living reptiles and the only reptiles that exhibit long-distance migrations that rival those of terrestrial and avian vertebrates. Many details of these large-scale movements are poorly understood because sea turtles swim over vast areas. Data accumulated from several decades of mark–recap- ture and telemetry studies demonstrate that adult sea turtle migrations are resource- driven, with migrants traveling hundreds to thousands of kilometers between estab- lished feeding and breeding areas at regular or seasonal intervals. For some species, however, resources are not always predictable in time and space. For example, food resources can vary spatially and temporally, and critical breeding habitats may be ephemeral. Thus, some sea turtles have evolved special migratory behaviors to compensate for environmental variability and unpredictability. The mechanisms that adult sea turtles employ as they travel through seemingly featureless ocean have been an enigma since Archie Carr first described the amazing trans-Atlantic journey of female green turtles to nesting beaches on Ascension Island (Carr, 1965). Results from laboratory studies using hatchling sea turtles have been extrapolated to explain the environmental cues used by adults 8 © 2003 CRC Press LLC 226 The Biology of Sea Turtles, Vol. II during migration. Hatchlings can perceive and respond to several environmental cues, including magnetic field intensity (Lohmann and Lohmann, 1996), magnetic inclination angle (Lohmann and Lohmann, 1994), visual cues (Mrosovsky and Shettleworth, 1968), water temperature gradients (Owens, 1980a), wave direction (Lohmann et al., 1990; Wyneken et al., 1990), and chemicals in the water (Grass- man et al., 1984). Despite this wealth of information, it is quite tenable that hatchlings rely on different cues than do adult turtles. In the last decade, we have gained a much better understanding of the naviga- tional abilities of adult sea turtles, but the mechanisms used to guide them during migration remain speculative (Papi and Luschi, 1996; Papi et al., 2000). Movements of sea turtles to specific sites (Papi et al., 1995; 1997) and their return to these areas even after displacement (Luschi et al., 1996; Papi et al., 1997) confirm that sea turtles do indeed navigate. Recent studies have suggested or demonstrated that these nav- igational feats may be guided by biological compasses (Papi and Luschi, 1996; Luschi et al., 1998), currents (Morreale et al., 1996; Papi et al., 2000), waterborne chemicals (Luschi et al., 1998; Papi et al., 2000), windborne information (Luschi et al., 2001), bathymetric features (Morreale et al., 1994), and water temperature (Plotkin, 1994). Sea turtles evolved distinct migratory strategies during their evolutionary history as they adapted to different ocean habitats (Hendrickson, 1980). These adaptations are illustrated by the migratory and habitat use patterns that are beginning to emerge following several decades of research. Interspecific and intraspecific variation in migratory behavior exists among contemporary sea turtles, and it is probable that considerable variation exists in navigational mechanisms used among and within species as well. The remainder of this chapter provides a summary of the current state of knowl- edge of adult sea turtle migration patterns and habitat use by each species and, where available, the potential navigational mechanisms employed. Most of our knowledge comes from studies conducted on postnesting females because these turtles are easy to capture, mark, and tag. Overall, very little is known about adult male sea turtles. 8.2 LEATHERBACK, DERMOCHELYS CORIACEA The leatherback is widely distributed throughout the world’s oceans from boreal to tropical waters. Leatherbacks inhabit the oceanic zone, are highly migratory (Prit- chard, 1973; 1976; Morreale et al., 1996; Hughes et al., 1998), and are capable of transoceanic migrations (Eckert, 1998) and diving to great depths (Eckert et al., 1989). Much of the details of leatherback migrations remain elusive, in part because the turtles occur far from land and travel such great distances; however, recent and ongoing studies will soon provide more specific information regarding the migratory behavior of this ocean traveler (Eckert and Sarti, 1997; Eckert, 1998; Lutcavage et al., in press). Little is known of the prereproductive migrations of leatherbacks and the location of breeding grounds; it is believed that they conform to the generalized model for sea turtle reproduction (Owens, 1980b). Females migrate to nearshore waters of tropical beaches several weeks prior to the nesting season. Most female leatherbacks © 2003 CRC Press LLC Adult Migrations and Habitat Use 227 undertake reproductive migration to nesting beaches every 2–3 years, where they oviposit on average five to six clutches at 9-day intervals (Boulon et al., 1996; Steyermark et al., 1996). Estimating fecundity for leatherbacks is challenging because females do not display strong beach fidelity. Females may travel among adjacent (Steyermark et al., 1996) or distant beaches (Keinath and Musick, 1993) within a nesting season. After the nesting season, females migrate long distances across deep oceanic waters (Morreale et al., 1994; 1996; Eckert and Sarti, 1997; Eckert, 1998; Hughes et al., 1998; Lutcavage et al., in press) and in some instances across ocean basins (Eckert, 1998). In some regions, migratory corridors along deepwater bathymetric contours have been described, with multiple postnesting females from the same beach migrating through these areas in subsequent years (Morreale et al., 1994; 1996). How- ever, in other regions no such corridors have been detected for postnesting female cohorts (Eckert, 1998). Leatherbacks do not migrate to resident feeding grounds, as has been well described for some species. Instead, leatherbacks appear to swim con- tinuously (Eckert and Sarti, 1997; Eckert, 1998), possibly to areas of high food concentration (Grant et al., 1996; Eckert and Sarti, 1997), where they appear to feed on organisms associated with the deep scattering layer (Eckert et al., 1989). Navigational cues used by leatherbacks during migration are not known, but potentially important cues suggested thus far include ocean currents, ocean fronts, bathymetric features, and magnetic cues (Morreale et al., 1994; 1996; Lutcavage, 1996). 8.3 OLIVE RIDLEY, LEPIDOCHELYS OLIVACEA The olive ridley has a circumtropical distribution, occurring in the Atlantic, Pacific, and Indian Oceans (Pritchard, 1969). Knowledge of olive ridley migrations is frag- mentary throughout most of its range, with the exception of the eastern Pacific and the northern Indian Ocean. The olive ridley is highly migratory and spends most of its nonbreeding life cycle in the oceanic zone (Cornelius and Robinson, 1986; Pitman, 1990; 1993; Arenas and Hall, 1992; Plotkin, 1994; Plotkin et al., 1994; 1995; Beavers, 1996; Beavers and Cassano, 1996). Olive ridleys occupy the neritic zone during the breeding season. Reproductively active males and females migrate toward the coast and aggregate at nearshore breeding grounds located near beaches where mass nesting emergences (commonly known as arribadas) also occur (Pritchard, 1969; Hughes and Richard, 1974; Cor- nelius, 1986; Dash and Kar, 1990; Plotkin et al., 1991; 1996; Kalb et al., 1995; 1997; Pandav et al., 2000). A significant proportion of the breeding also takes place far from shore (Pitman, 1990; Kopitsky et al., 2000), and some males and females may not migrate to nearshore breeding aggregations. Some males appear to remain in oceanic waters, are nonaggregated, and mate opportunistically as they intercept females en route to nearshore breeding grounds and nesting beaches (Plotkin, 1994; Plotkin et al., 1994; 1996; Kopitsky et al., 2000). After mating, females remain nearshore for several weeks to several months. Solitary nesters emerge onto beaches to lay eggs individually throughout much of the species’ range. Solitary nesters have weak site fidelity (Kalb, 1999), lay two © 2003 CRC Press LLC 228 The Biology of Sea Turtles, Vol. II clutches annually at 14-day intervals (Pritchard, 1969; Kalb, 1999), and may use multiple, geographically distant beaches within a nesting season (Kalb, 1999). Arri- bada nesting females emerge onto beaches to lay eggs en masse at a few select beaches in the Atlantic, Pacific, and Indian Oceans. The arribada nesters have strong site fidelity (Plotkin et al., 1995; Kalb, 1999), lay two clutches approximately every 28 days (Pritchard, 1969; Kalb, 1999), and may delay nesting for 6–8 weeks when environmental conditions are unfavorable (Plotkin et al., 1997). Once mating and nesting is completed, olive ridleys quickly migrate back to oceanic waters. The postreproductive migrations of olive ridleys are unique and complex. Their migratory pathways vary annually (Plotkin, 1994), there is no spatial and temporal overlap in migratory pathways among groups or cohorts of turtles (Plotkin et al., 1994; 1995), and no apparent migration corridors exist. Unlike other marine turtles that migrate from a breeding ground to a single feeding area, where they reside until the next breeding season, olive ridleys are nomadic migrants that swim hundreds to thousands of kilometers over vast oceanographic stretches (Plotkin, 1994; Plotkin et al., 1994; 1995). Despite the multitude of cues that may be used in long-distance navigation, operation of a specific cue has not been demonstrated. However, Plotkin (1994) suggested that water temperature might be the predominant cue used during post- reproductive migrations to oceanic feeding areas in the eastern Pacific because of the spatial and temporal correspondence between turtle movements and the locations of divergence and convergence zones, thermal fronts, and cool water masses. 8.4 KEMP’S RIDLEY, LEPIDOCHELYS KEMPII The Kemp’s ridley has a relatively restricted range, occurring in the neritic zone of the Gulf of Mexico and western Atlantic (Marquez, 1994). Evidence accumulated from several decades of tag returns and telemetry studies has demonstrated that Kemp’s ridley is a neritic migrant that swims along the U.S. and Mexican coasts, nearshore in continental shelf waters (Byles, 1989; Byles and Plotkin, 1994; Mar- quez, 1994; Renaud, 1995; Shaver, 1999; 2001). Narrow migratory corridors extend along the entire U.S. and Mexican gulf coast (Byles and Plotkin, 1994). Reproductively mature females undertake annual migrations from the western Atlantic and Gulf of Mexico (Renaud et al., 1996) to their principal nesting beach, Rancho Nuevo, located near the central Mexican gulf coast in the state of Tamaulipas. Females aggregate nearshore Rancho Nuevo in advance of the nesting season, and mating takes place approximately 30 days prior to first oviposition for the season (Chavez et al., 1967; Pritchard, 1969; Mendonca and Pritchard, 1986; Rostal, 1991). Mating also occurs elsewhere in coastal and inshore waters from south Texas to areas south of Rancho Nuevo in Tamaulipas and Veracruz, Mexico (Shaver, 1992). Nesting begins in late April and may last until mid-August (Marquez, 1994). The vast majority of females emerge en masse to nest at Rancho Nuevo during the May, June, and July arribadas. The arribadas at Rancho Nuevo typically occur every 28 days (Pritchard and Marquez, 1973). Females lay approximately three nests per season (Rostal et al., 1997) and remain relatively close to the nesting beach during the internesting period between clutches (Mendonca and Pritchard, 1986). © 2003 CRC Press LLC Adult Migrations and Habitat Use 229 Solitary nesting also occurs at Rancho Nuevo (Rostal et al., 1997) and other beaches. A small number of females regularly nest on the Texas coast (Shaver, 1998), and very rarely on western Atlantic beaches such as Florida (Fletemeyer, 1990; Meylan et al., 1990a; Libert, 1998; Johnson et al., 2000), North Carolina (T. Conant, unpublished data cited in Bowen et al., 1994), and South Carolina. Nesting has been documented as far south as Colombia (Chavez and Kaufmann, 1974); however, Kemp’s ridleys rarely nest south of the tip of the Yucatan Peninsula (Marquez, 1994). After the last clutch is oviposited, females begin postnesting migrations away from their nesting beach, traveling north or south along the coast (Mysing and Vanselous, 1989; Byles, 1989; Shaver, 1999; 2001). Postnesting migrations have been recorded as far south as Colombia (Marquez, 1994) and as far north as Virginia; however, most Kemp’s ridleys migrate to areas concentrated between north Texas coastal waters and Campeche, Mexico (Chavez, 1969; Pritchard and Marquez, 1973; Byles, 1989; Shaver, 1999; 2001). These long-distance migrations encompass hundreds of kilometers (Byles, 1989) and occur primarily in shallow waters less than 50 m deep (Byles, 1989; Renaud, 1995; Renaud et al., 1996; Shaver, 1999; 2001). Females may establish relatively circumscribed ranges in coastal waters for several months (Byles, 1989; Byles and Plotkin, 1994), suggesting that resident feeding areas exist. In contrast to the females, adult males appear to be nonmigratory. Shaver et al. (in press) tracked 11 adult male Kemp’s ridleys, and most of them remained resident in coastal waters near Rancho Nuevo for several months after the nesting season. Only one male migrated away from the breeding grounds; he migrated to the north Texas coast near Galveston. This is quite different from the generalized pattern that has been described for male sea turtles (Rostal, 1991). Most males depart the breeding grounds by the time the greatest number of females emerge to lay eggs (i.e., when most females have already copulated) (Hendrickson, 1958; Booth and Peters, 1972; Ehrhart, 1982; Frazier, 1985) and migrate to distant feeding grounds (Plotkin et al., 1995; 1997; Hays et al., 2001b). 8.5 HAWKSBILL, ERETMOCHELYS IMBRICATA Hawksbills are distributed in tropical waters throughout much of the Atlantic, Pacific, and Indian Oceans (Witzell, 1983). Hawksbills live in close association with hard- substrate communities such as coral reefs, where they forage primarily on sponges (Meylan, 1988), and may also occur in coastal lagoons and bays. Hawksbills were once believed to be nonmigratory residents of reefs adjacent to their respective nesting beaches (Hendrickson, 1980; Witzell, 1983; Frazier, 1985), but postrepro- ductive tagging, telemetry, and genetic studies have revealed that hawksbills do indeed migrate and that many are highly migratory, traveling hundreds to thousands of kilometers between nesting beaches and foraging areas (Meylan, 1982; Parmenter, 1983; Broderick et al., 1994; Byles and Swimmer, 1994; Groshens and Vaughan, 1994; Miller et al., 1998; Meylan, 1999; Prieto et al., 2001). Data from one adult male hawksbill marked and later recaptured indicate that males are also highly migratory (Nietschmann, 1981). © 2003 CRC Press LLC 230 The Biology of Sea Turtles, Vol. II Very little is known about hawksbill reproductive migrations from foraging areas to breeding grounds. Females migrate to nest at their natal beaches (Bass, 1999) every 2–3 years (Witzell, 1983). Females inhabiting the same foraging area do not all migrate to the same nesting beach (Miller et al., 1998). Mating is not well documented for this species, but it has been observed in the shallow waters adjacent to nesting beaches (Witzell, 1983) and probably occurs approximately 30 days prior to first nesting (Owens, 1980b). Hawksbills are solitary nesters that lay four to seven clutches every 14–16 days (Witzell, 1983). Females remain nearshore the nesting beach during the internesting period (Starbird, 1993; Starbird et al., 1999). As soon as the last nest is oviposited, females begin postnesting migrations back to foraging areas (Starbird, 1993; Starbird et al., 1999; Mortimer and Balazs, 2000; Horrocks et al., 2001). Postnesting hawksbills migrate to specific foraging areas within short range (25–200 km) (Ellis et al., 2000; Hillis-Starr et al., 2000; Mortimer and Balazs, 2000; Horrocks et al., 2001; Lageux et al., in press) and long range (200 km or more) (Byles and Swimmer, 1994; Miller et al., 1998; Horrocks et al., 2001; Prieto et al., 2001; Lageux et al., in press) of their nesting beaches. Such variation in migratory behavior is found among females nesting at the same beaches (Miller et al., 1998; Horrocks et al., 2001; Prieto et al., 2001). No apparent patterns have emerged to explain why some females migrate short distances while others bypass reefs close to their nesting beaches and migrate greater distances. Both short-distance and long-distance migrations appear to be relatively quick, directed movements that may occur across deep oceanic waters or channels (Ellis et al., 2000; Horrocks et al., 2001) or shallow coastal waters (Ellis et al., 2000). Once a female reaches her foraging ground, she remains resident there (Ellis et al., 2000; Mortimer and Balazs, 2000), presumably until her next reproductive migration. 8.6 FLATBACK, NATATOR DEPRESSUS The flatback has the most restricted migratory range of all sea turtles. It is endemic to the tropical waters of the Australian continental shelf (Limpus et al., 1981), occurring in shallow, turbid waters and bays (Limpus et al., 1983; 1989). Flatbacks were once characterized as nonmigratory (Hendrickson, 1980), but tagging studies have confirmed that they do undertake long-distance migrations between foraging and breeding areas (Limpus et al., 1981; 1983). Flatbacks nest on mainland beaches, continental island beaches, and sand cays within Australian territorial waters on the northeast coast (Limpus, 1971; Limpus et al., 1981; 1989), north coast (Limpus et al., 1983; Guinea et al., 1991; Guinea, 1994), and west coast (Prince, 1994). Foraging areas extend just beyond the Australian territorial waters into adjacent waters of the Indonesian archipelago and Papuan coast (Parmenter, 1994). Females migrate from foraging areas to nesting beaches on average every 1–3 years (Limpus et al., 1984; Parmenter, 1994). Females show strong site fidelity to their nesting beaches (Limpus et al., 1984; Parmenter, 1994). Mating occurs in the vicinity of the nesting beach approximately 1 month prior to the start of the nesting season (Limpus et al., 1989; 1993). Nesting occurs year-round at some beaches (Limpus et al., 1983; 1989) and seasonally at others (Limpus, 1971; Limpus et al., © 2003 CRC Press LLC Adult Migrations and Habitat Use 231 1984; 1989; Guinea, 1994). Flatbacks are solitary nesters that lay an average of three clutches per season at approximately 16-day intervals (Limpus et al., 1984). Females presumably remain nearshore during the internesting period and return to foraging grounds after the last clutch has been oviposited; no published data exist to support this assumption. Postnesting flatbacks migrate hundreds to thousands of kilometers to their for- aging grounds, located primarily in turbid, shallow, inshore waters of northern Queensland and along the north Australian coast (Limpus et al., 1983; Parmenter, 1994) and possibly northward to the Irian Jaya coast (Limpus et al., 1993). 8.7 LOGGERHEAD, CARETTA CARETTA Loggerheads occur in subtropical and temperate waters across continental shelves and estuarine areas in the Atlantic, Pacific, and Indian Oceans (Dodd, 1988). Throughout this range, loggerheads spend most of their time in nearshore and inshore waters, sometimes associated with reefs and other natural and artificial hard sub- strates (Dodd, 1988). Loggerheads are highly migratory, capable of traveling hun- dreds to thousands of kilometers between foraging and breeding areas (Caldwell et al., 1959; Bell and Richardson, 1978; Timko and Kolz, 1982; Meylan et al., 1983; Limpus et al., 1992; Papi et al., 1997; Plotkin and Spotila, 2002). Female loggerheads do not appear to migrate to just one foraging area. Rather, they move continuously and thus appear to forage at a series of coastal areas (Timko and Kolz, 1982; Papi et al., 1997; Plotkin and Spotila, 2002). Females migrate to nest at their natal beaches (Schierwater and Schroth, 1996) about every 3 years (Limpus, 1985; Dodd, 1988). Both females and males migrate asynchronously from foraging areas to breeding areas several weeks to months prior to the nesting season (Limpus, 1985). Males arrive a few weeks in advance of the females (Henwood, 1987). Some males appear to be nonmigratory and may reside in breeding areas throughout the year (Henwood, 1987). Mating occurs during or immediately after migration to breeding areas located nearshore nesting beaches (Caldwell et al., 1959; Limpus, 1985; Wibbels et al., 1987). Females lay an average of four clutches approximately every 2 weeks (Dodd, 1988). During the internesting period, females remain nearshore (Hopkins and Mur- phy, 1981; Stoneburner, 1982; Sakamoto et al., 1990; Hays et al., 1991; Tucker et al., 1996). Females begin postnesting migrations as soon as their last clutch is oviposited (Stoneburner, 1982; Tucker et al., 1996; Plotkin and Spotila, 2002). Females typi- cally migrate nearshore, moving north or south of their nesting beach (Papi et al., 1997; Plotkin and Spotila, 2002), but may also make brief offshore movements after the nesting season into deep oceanic waters (Byles and Dodd, 1989). 8.8 GREEN, CHELONIA MYDAS Green turtles occur in tropical and subtropical waters of the Atlantic, Pacific, and Indian Oceans. They inhabit the neritic zone, occurring in nearshore and inshore waters where they forage primarily on sea grasses and algae (Mortimer, 1982), and © 2003 CRC Press LLC 232 The Biology of Sea Turtles, Vol. II temporarily inhabit the oceanic zone during migrations from foraging areas to breeding areas and back. Some of these long-distance reproductive migrations are spectacular feats, with turtles swimming thousands of kilometers across the open ocean directly to beaches located on small, isolated oceanic islands (Carr, 1965; Luschi et al., 1998). Female green turtles migrate from foraging areas to their natal beaches (Meylan et al., 1990b) every 2–4 years and show a high degree of nest site fidelity (Miller, 1997). Mating may occur en route to the nesting beach (Meylan et al., 1992), far from the nesting beach at distant mating grounds (Limpus, 1993), or nearshore the nesting beach (Carr and Ogren, 1960; Booth and Peters, 1972; Broderick and Godley, 1997; Godley et al., 2002). Females oviposit an average of three clutches at 10- to 17-day intervals (Miller, 1997) and remain near the nesting beach during the internesting period (Carr et al., 1974; Dizon and Balazs, 1982). Postnesting females migrate hundreds to thousands of kilometers from their nesting beach to resident coastal foraging areas (Balazs, 1994; Balazs et al., 1994; 2000; Papi et al., 1995; Schroeder et al., 1996; Cheng and Balazs, 1998; Luschi et al., 1998; Papi et al., 2000; Luschi et al., 2001). Postbreeding males also migrate long distances from breeding areas to foraging grounds at the end of the mating season (Hays et al., 2001a) or may remain in the vicinity of the nesting beach (Garduno et al., 2000). In general, these migrations can be characterized as relatively fast, directed movements toward specific locations (Schroeder et al., 1996; Luschi et al., 1998), which may occur nearshore (Schroeder et al., 1996) or in deep oceanic water (Balazs, 1994; Luschi et al., 1998), with cohorts traveling along similar path- ways during part of the migration (Luschi et al., 2001). The navigational mechanisms used by green turtles migrating from Ascension Island to coastal foraging grounds in Brazil have provided insights into the naviga- tional abilities of adult sea turtles. These studies have demonstrated that green turtles are able to maintain straight courses over long distances in the open ocean (Luschi et al., 1998), can correct their course during the migration according to environmen- tal information (Luschi et al., 1998), may be guided in part by currents (Luschi et al., 1998) or windborne information (Luschi et al., 2001), do not rely on sea surface temperatures (Hays et al., 2001b), and can navigate in the absence of magnetic cues (Papi et al., 2000). 8.9 EAST PACIFIC GREEN, CHELONIA AGASSIZI East Pacific green turtles are restricted to the coastal waters, lagoons, and bays along the west coast of America from Baja California and the Gulf of California to southern Peru and the Galapagos Islands (Alvarado and Figueroa, 1998), where they feed primarily on sea grasses and algae (Seminoff et al., 2000). Females migrate from foraging areas to nesting beaches on average every 3–4 years (Alvarado et al., 2000). The primary nesting beaches are located in Michoacan, Mexico; however, sporadic nesting also occurs elsewhere along the Mexican and Central American coast. Mating takes place nearshore the nesting beach (Alvarado and Figueroa, 1989). Females oviposit between one and seven clutches per season at 11- to 13-day intervals (Alvarado et al., 2000). Females remain nearshore the © 2003 CRC Press LLC Adult Migrations and Habitat Use 233 nesting beach during the internesting period and return to foraging grounds after the last clutch has been oviposited (Byles et al., 1995). Postnesting females migrate north and south of their nesting beaches to foraging areas in the Gulf of California and to coastal areas in Central and South America (Byles et al., 1995). 8.10 CONCLUSIONS Distinct migratory patterns exist among extant sea turtles, and these patterns are best understood in the context of the locations and sizes of their foraging areas. The first pattern is exhibited by leatherbacks and east Pacific olive ridleys. These turtles migrate to oceanic waters where they forage over very broad areas, seeking out highly productive waters such as fronts and convergence zones. These foraging areas vary spatially and temporally, and are frequently unpredictable. The second pattern is exhibited by Kemp’s ridleys, loggerheads, and flatbacks. These species migrate to highly productive neritic foraging areas located on continental shelves. Many forage over broad areas, typically swimming along a coastline; however, some establish small, circumscribed foraging areas. Their foraging areas are fairly pre- dictable in space and time, however small-scale variations are possible. The third pattern is exhibited by green and hawksbill turtles. These species migrate to well- established, fixed foraging areas located nearshore. Their foraging range is relatively small and virtually no spatial or temporal variation exists. 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