Date Awarded

1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Abstract

Immature foraging sea turtles occupy Chesapeake Bay, Virginia annually from May through November. Telemetry was used to monitor the movements and behavior of loggerhead, Caretta caretta, and Kemp's ridley, Lepidochelys kempi, turtles during 1981-1985. Both species utilized the estuary for summer foraging, but exhibited habitat-preference and behavioral differences that amounted to resource partitioning between the species. Loggerheads oriented towards major river outflows and tended to move along channel sides with the tidal flow while ridleys occupied shallower foraging areas and did not range as far with the tide. Strong site tenacity was displayed by both species once foraging areas were established. Differences were apparent in respiratory behavior; ridleys remained on the surface for longer and underwater for shorter periods than loggerheads. Ridleys had a tendency to stay on the surface longer during daylight than night hours, whereas loggerheads surfaced and submerged longer during night than daylight. Estimates of daylight respiration behavior of loggerheads (surface to dive time ratio of 1:17) were used to adjust estimates of population size. Replicated aerial surveys for loggerheads yielded an unadjusted mean population over 1982-1985 of 423. A respiration adjustment factor which accounts for turtles unseen because they are below the surface (17 turtles below the surface for every one seen at the surface) yielded an average annual estimate of 7905. Reported mortality is a small percentage (1.4) of the adjusted population estimate. Mark-recapture, aerial survey and biotelemetric techniques were used in 1980 and 1982-1985 to elucidate migrations of loggerheads and ridleys which are incapable of overwintering in Chesapeake Bay. For both species, the period of residence in the Bay was correlated with water temperature. Migrations to the Bay were linked to vernal warming; the heaviest concentrations of turtles were found south of the 18 C isotherm. Fall migration was linked less strongly with declining water temperature and appeared to be related to the onset of winter storms. Migrating loggerheads remained nearshore in southerly currents in the fall. Contact with most telemetered loggerheads was broken in the vicinity of Cape Hatteras, North Carolina. A satellite-tracked loggerhead spent two months in the vicinity of the Gulf Stream offshore before contact was broken.

DOI

https://dx.doi.org/doi:10.25773/v5-h9nv-c205

Rights

© The Author

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