Habitat utilization and migration in juvenile sea turtles.

Sea turtles are basically creatures that spend their entire lives in marine or estuarine habitats.Their only remaining reptilian ties to terrestrial habitats are for nesting and restricted cases of basking. Consequently.physiological. anatomical. and behavioral adaptations have evolved largely in response to selection in the aquatic environment and sea turtles share many common elements with liirger tislics and cetaceans in their habitat utilization and migrations. A generalized habitat model may he con- structed for sea turtles based on ontogenetic stages (Figure 6.1):

I. Early juvenile nursery habitat (usually pelagic and oceanic).
2. Later juvenile developmental habitat (usually demersal and neritic).

3. Adult foraging habitat.
4. Adult inter-nesting andfor breeding habitat. 

All sea turtles move immediately to the sea after hatching, usually after dark, and swim actively offshore. Most then undertake a mostly passive, denatant {sensu Jones)' migration drifting pelagically in oceanic gyre systems. Subsequently, after a period of years, these now larger and older juveniles actively recruit to demersal neritic dcvelopmentai habitats in the tropical and temperate zones. Demersal juve- niles in some temperate zone populations make seasonal migrations to foraging areas at higher latitudes in summer and lower latitudes in winter (see below) while those in tropical areas are more localized in their movements, When approaching maturity, pubescent turtles move into adult foraging habitats. In some populations adult habitats are geographically distinct from juvenile developmental habitats;24in others they may overlap or coin~ide.U~p.~on maturity as the nesting season approaches adults make a contranatant migration toward the nesting beaches. Most mating occurs t poorly defined courtship areas that are clone KÃthe nesting beaches relitlive lo the distant foraging areas. Afler mating the females move to their respcclivc nesting beaches.'-* Courtship areas may be directly HITthe nesting beaches,*or remote from the beaches,'" depending on the population. During the nesting season, females usually become resident in the internesting habitat in the vicinity of the nesting beach." The focus of the present paper is habitat utilization and migration of juvenile sea turtles and nursery and developmental habitats. 


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