Distribution patterns of Kemp's ridley sea turtles in the southeast US

A project of SCDNR in conjunction with the partners and sponsors detailed below.

Subscribe to receive daily project updates

Click on an animal's name for maps and more information.

Introduction

Despite known occurrence of juvenile Kemp’s ridley sea turtles along nearly the entire U.S. Eastern Seaboard, the importance of seasonal foraging grounds for this species in the Atlantic Ocean is often under-valued in comparison with Gulf of Mexico (GoM). The reason for the relegation of Atlantic foraging grounds is that nearly 100% of nesting for Kemp’s ridley sea turtles occurs on GoM beaches (mostly near the U.S./Mexico border); after nesting, adult females take up residence at foraging grounds throughout the entire GoM; and because oceanic currents favor the initial settlement of young juvenile Kemp’s to the continental shelf of the GoM when they seek out coastal habitats.

Trawl research conducted by the National Marine Fisheries Service near Cape Canaveral, FL and off South Carolina and Georgia between 1978 and 1984 captured 61 Kemp’s ridley sea turtles in coastal waters, five of which seen again as far away as Virginia, providing the first insight into the seasonal distribution patterns for this species in this region(Henwood and Ogren, 1987).

In contrast, coastal trawl research conducted from north Florida through central South Carolina by the South Carolina Department of Natural Resources (SCDNR), in partnership with the University of Georgia Marine Extension Service/Sea Grant (UGA), captured 260 Kemp’s ridley sea turtles between 2000 and 2015, only one of which was ever seen again. Furthermore, nearly all of those captures occurred in the shallowest waters sampled, suggesting that perhaps Kemp’s ridley sea turtles spend most of their time closer to shore and in shallower waters than can be sampled by this survey, and hence why they are infrequently captured relative to loggerhead sea turtles.

To answer this question, the sampling design of the SCDNR-UGA survey was modified in spring/summer 2016 and 2017 to concentrate trawling efforts on the shallowest waters possible to trawl over near Brunswick, GA. This modified study area was selected because Kemp’s ridley sea turtles were consistently captured there during the previous 15 years, but also because of close proximity to the homeport of the research vessel (RV Georgia Bulldog) and to a state of the art rehabilitation facility (Georgia Sea Turtle Center) should any of the captured sea turtles require shore-based treatment.

The modified sampling design captured Kemp’s ridley sea turtles at a rate that was eight times faster than prior trawling efforts, which also enabled deployment of 16 satellite transmitters on Kemp’s ridley sea turtles (41.9 to 61.5 cm minimum straight-line carapace length, SCLmin). Although track durations were much shorter than the 9-mo battery life of the transmitter, the data collected were invaluable for establishing that tagged Kemp’s largely remained within the latitudinal boundaries of the multi-state coastal survey, as well as spent 75% of their time throughout all water depths sampled by that survey. These tracks also revealed summertime connectivity of foraging grounds between north Florida and South Carolina, which previously was thought to only represent seasonal movement to/from over-wintering grounds (Henwood and Ogren, 1987; Renaud, 1995; Gitschlag, 1996). One tracked Kemp’s (aptly named “Schmid”) also established connectivity between Georgia and the west coast of Florida, where satellite telemetry previously documented year-round residence of Kemp’s ridleys but seasonal movement along nearly that entire coast (Schmid and Witzell, 2006).

Telemetry research into the distribution patterns of Kemp’s ridley sea turtles captured by the SCDNR-UGA survey will continue through at least 2018. Greatest future emphasis will be placed on documenting the distributional patterns of Kemp’s ridley sea turtles captured off South Carolina, to include estuarine captures. During 2000–2015, Kemp’s ridley sea turtles were captured as far north as the SCDNR-UGA survey samples (i.e., Winyah Bay, SC), but greatest catch rates for this species occurred from central Georgia through southern South Carolina, consistent with satellite tracking in 2016 and 2017.

Future emphasis will also be placed on documenting the over-wintering location of Kemp’s ridley sea turtles captured off South Carolina during the summer; however, due to short track durations this aspect of data collection will almost certainly require attaching transmitters in the fall. Renaud (1995) and Gitschlag (1996) each tracked one Kemp’s ridley sea turtle through the winter following fall tag-and-release off Mayport, FL and Brunswick, GA, respectively. Both Kemp’s ridleys over-wintered between central and south Florida, one of which foraged off South Carolina the following spring/summer.

On October 9, our first fall release track was initiated with “Peach”, a 57.8 cm (SCLmin) female Kemp’s ridley that was captured on June 1 in the Charleston, SC shipping channel, but required four months of rehabilitation following surgical removal of ingested monofilament and healing of external wounds that resulted from severe monofilament entanglement.1 We are anxious to see if “Peach” will also head south to over-winter; perhaps she’ll move east and over-winter in the same mid-shelf waters as loggerheads captured in the Charleston, SC shipping channel in the spring (Arendt et al., 2012); maybe she’ll head north and over-winter off southern North Carolina similar to juvenile Kemp’s tagged in Long Island Sound, NY (Morreale, 1999); or possibly she’ll show us something completely different. Stay tuned…

References:

1 http://www.postandcourier.com/business/doomed-sea-turtle-gets-some-lucky-breaks-with-dnr-and/article_dbc8de66-5041-11e7-8dc1-db6d4d874d01.html (Accessed 8 October 2017)

Arendt, M.D., A.L. Segars, J.I. Byrd, J. Boynton, J.D. Whitaker, L. Parker, D.W. Owens, G. Blanvillain, J.M. Quattro, and M.A. Roberts. 2012. Seasonal distribution patterns of juvenile loggerhead sea turtles (Caretta caretta) following capture from a shipping channel in the Northwest Atlantic Ocean. Marine Biology 159(1): 127 –139.

Gitschlag, G.R. 1996. Migration and diving behavior of Kemp's ridley (Garman) sea turtles along the southeastern Atlantic coast. Journal of Experimental Marine Biology and Ecology 205: 115-135.

Henwood, T.A., and L.H. Ogren. 1987. Distribution and migrations of immature Kemp's ridley sea turtles (Lepidochelys kempi) and green turtles (Chelonia mydas) off Florida, Georgia, and South Carolina. Northeast Gulf Science 9(2): 153-159.

Morreale, S.J. 1999. Oceanic migration of sea turtles. Dissertation. Cornell University, 160 p.

Renaud, M.L. 1995. Movements and submergence patterns of Kemp’s ridley turtles (Lepidochelys kempii). Journal of Herpetology 29(3): 370–374.

Schmid, J.R., and W.N. Witzell. 2006. Seasonal migrations of immature Kemp’s ridley turtles (Lepidocheyls kempii Garman) along the west coast of Florida. Gulf of Mexico Science 2006(1/2): 28–40.

Project Partners

This research is being conducted in partnership with the University of Georgia Marine Extension Service which owns and operates the RV Georgia Bulldog, the vessel that is used to capture sea turtles off Georgia and north Florida under federal and state permits.