SCDNR Marine Resources Division In-Water Study
Blood Work
Since the 1970’s, the South Carolina Department of Natural Resources Marine Resources Division (SCDNR MRD) has been involved in numerous research projects to assess population parameters of sea turtles collected in the water by trawling. Because sea turtles are long-lived, slow-growing, and late-maturing species, the benefits of recovery efforts can take decades to become evident. Furthermore, because sea turtles spend 99% of their lives in the water and only the adult females venture onto the beaches to nest, in-water studies address a critical data void that nesting beach or aerial surveys can not.
During the summers of 2000-2003, three vessels collectively trawled an average of 650 stations annually, from Winyah Bay, SC, to St. Augustine, FL, using modified shrimp nets (i.e., no turtle excluder devices, large webbing to reduce bycatch). Trawl stations were 30 minutes in duration (to prevent turtles from drowning) and were conducted in water depths of approximately 10-45 feet. In total, 933 individual loggerheads (including 12 loggerheads tagged by other studies) were collected. Catch rates were comparable to trawl studies conducted in the early 1990’s at ‘turtle-rich’ environments such as shipping channels, and about 10 times higher than open-water trawl surveys to collect sea turtles in the mid-1970’s. Consistent with high catch rates, recapture rates were very low (16 of 933 loggerheads re-encountered to date), perhaps due to an effective ‘dilution’ of tagged loggerheads in a sea of untagged loggerheads.
During the summers of 2004-2006, the research focus shifted to study the seasonal distributional patterns of juvenile loggerheads collected from the Charleston, SC, shipping entrance channel. Twenty-four juvenile loggerheads have been studied using satellite transmitters to date. Although collected in the channel, these turtles spent considerably more time on the shoals adjacent to the channel, consistent with previous acoustic tracking studies at this same location in the early 1990’s. Furthermore, very little time (about 30% overall) was spent in the areas trawled by the project during the summers of 2000-2003, which could also explain low recapture rates. Most of these loggerheads left Charleston coastal waters in December to over-winter on the middle and outer continental shelf of SC & GA, but returned to Charleston coastal waters in April.
The in-water research project has also begun addressing the seasonal distributional patterns of adult male loggerheads. Nine adult male loggerheads have been satellite-tagged to date, of which some have remained in the vicinity of where they were collected (Cape Canaveral, FL), while others have traveled as far north as NJ. As many as 20 additional adult males may be satellite-tagged during April 2007, which should greatly increase our knowledge of the reproductive biology and ecology of this very elusive life history stage. Future research interests also include distributional patterns of debilitated loggerhead sea turtles following release. To date, only one rehabilitated sea turtle (collected by the project in May 2005 and released following rehabilitation at the SC Aquarium three months later) has been satellite-tagged by the project, but more may be studied in upcoming years. To learn more about the satellite telemetry projects, go to www.seaturtle.org.
Page Content: Michael Arendt and Julia Byrd