Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
John A. Musick
Aerial surveys are commonly used to evaluate in-water sea turtle abundances. A correction is applied to account for turtles diving below the observed surface. Historically, observations of summer/fall surfacing behavior were used for this correction, assuming constant behavior among seasons. Using radio/acoustic telemetry, seasonal differences in sea turtle surfacing behavior were determined among Kemp's ridleys and loggerheads. Mean time spent at surface in the spring ranged between 9.9%-30.0% with significant differences among individuals. Observed surfacing times were higher than historic summer/fall observations (Byles 1988; 5.3%), indicating that historic springtime abundances were overestimated by 50%-80%. Aerial surveys (2001-2004) indicated a 65%-75% decline in the Chesapeake Bay sea turtle population since the 1980's. Current sea turtle estimates range between 2,500-5,500 turtles compared to 6,500-9,000 turtles observed in the Lower Bay alone in the 1980's. Satellite telemetry was used to track long-term movements of adult and juvenile turtles utilizing Virginia's waters. Loggerheads and Kemp's ridleys were found to exhibit significant fidelity to Bay and coastal waters south to Cape Hatteras. Several individuals established winter habitat off Cape Hatteras, adjacent to the outer continental shelf and Gulf Stream. Fall migrations commenced when surface temperatures dropped below 20??C. Some turtles migrated south to Georgia, Florida and the Gulf of Mexico. Two turtles were transported by the Gulf Stream to the north Atlantic and the Grand Banks, indicating some plasticity in habitat use. Virginia's pound net fishery was considered a primary source of sea turtle mortality in the 1980's. Fisheries surveys (2000-2002) indicated a significant reductions in fishery effort and hazardous large mesh and string leaders. No subsurface bycatch mortalities were observed during side scan sonar surveys (2001-2002). Pound nets are no longer a significant source of sea turtle mortality in Virginia. Pound net recaptures of live turtles (1979-2002) indicated strong philopatry to specific foraging areas, including strong inter-annual site fidelity. Over 20% of tagged loggerheads were recaptured in study nets during 1-11 seasons. Satellite telemetry was used to track the movements of one adult loggerhead captured multiple times from 1999-2002. Home range analyses indicated a 73.9% overlap in the total range over a three-year period.
© The Author
Mansfield, Katherine Lamont., "Sources of mortality, movements and behavior of sea turtles in Virginia" (2006). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1539616760.