624 



Abstract— Loggerhead sea turtles (Ca- 

 retta caretta ) are migratory, long-lived, 

 and slow maturing. They are difficult to 

 study because they are seen rarely and 

 their habitats range over vast stretches 

 of the ocean. Movements of immature 

 turtles between pelagic and coastal de- 

 velopmental habitats are particularly 

 difficult to investigate because of in- 

 adequate tagging technologies and the 

 difficulty in capturing significant num- 

 bers of turtles at sea. However, genetic 

 markers found in mitochondrial DNA 

 (mtDNA) provide a basis for predict- 

 ing the origin of juvenile turtles in 

 developmental habitats. Mixed stock 

 analysis was used to determine which 

 nesting populations were contributing 

 individuals to a foraging aggregation 

 of immature loggerhead turtles (mean 

 63.3 cm straight carapace length 1SCL| ) 

 captured in coastal waters off Hutchin- 

 son Island, Florida. The results indi- 

 cated that at least three different 

 western Atlantic loggerhead sea turtle 

 subpopulations contribute to this group: 

 south Flonda leg's i, Mexico (20'7f), 

 and northeast Florida-North Carolina 

 (10%). The conservation and manage- 

 ment of these immature sea turtles 

 is complicated by their multinational 

 genetic demographics. 



Origin of immature loggerhead sea turtles 

 {Caretta caretta) at Hutchinson Island, Florida: 

 evidence from mtDNA markers 



Wayne N. Witzell 



National Marine Fisheries Service, NOAA 



75 Virginia Beach Drive 



Miami, Florida 33149 



E-mail address maynewitzelhg'noaagov 



Anna L. Bass 



Department of Fisheries and Aquatic Sciences 

 7922 NW 71 St Street 

 Gainesville, Flonda 32653 



Michael J. Bresette 



David A. Singewald 



Jonathan C. Gorham 



Quantum Resources, Inc. 

 6451 South Ocean Dnve 

 Jensen Beach, Flonda 34957 



Manuscript accepted 23 January 2002. 

 Fish. Bull. 100:624-631 (2002). " 



North Atlantic loggerhead sea turtles 

 have extended and complex devel- 

 opmental life histories (Musick and 

 Limpus, 1997). After emerging from 

 their nests, hatchling loggerhead sea 

 turtles enter the surf and eventually 

 move into the pelagic environment 

 for several years before returning to 

 inshore benthic coastal waters. The 

 accepted hypothesis is that these 

 hatchlings are passively transported 

 to the eastern Atlantic by major cur- 

 rent systems and these turtles would 

 eventually return to coastal benthic 

 habitats in the western Atlantic by 

 the North Atlantic gyre when they 

 attain 25-60 cm or an estimated 3-10 

 years old (Carr, 1986, 1987; Musick and 

 Limpus, 1997). 



The loggerhead sea turtle (Caretta 

 caretta) is listed as threatened under 

 the United States Endangered Species 

 Act of 1973 and subsequent amend- 

 ments. Although the loggerhead sea 

 turtle nesting population in the south- 

 eastern United States is one of the 

 largest in the world, other distinct nest- 

 ing populations (as defined by genetic 

 divergence) exist in the northwestern 

 Atlantic Ocean. These known sub- 

 populations are found in the Yucatan. 



northwest Florida, south Florida, and 

 from north Florida to North Carolina. 

 The east central coast of Florida sup- 

 ports the largest nesting subpopulation 

 of loggerhead turtles and is a highly 

 dynamic coastal area with multiple sea 

 turtle species in various postpelagic 

 developmental stages (Witzell. 1987). 

 Sea turtles may hatch in one country, 

 grow through adolescence in a second 

 or more countries, feed and reproduce 

 as adults in a third jurisdiction, and 

 swim through a dozen more territorial 

 waters enroute to and from these des- 

 tinations (Bowen et al., 1995). Tagging 

 studies, unfortunately, are only capable 

 of providing glimpses of these complex 

 changes in developmental habitats 

 because of high tag loss rates and rare 

 opportunities of recapturing tagged 

 turtles thousands of kilometers away in 

 the pelagic environment several years 

 later (Chaloupka and Musick. 1997). 



The likelihood that turtles from ge- 

 netically distinct stocks share coastal 

 and pelagic developmental habitats may 

 raise doubts regarding the effectiveness 

 of conservation strategies based on geo- 

 graphical or political boundaries (Carr 

 and Stancyk, 1975; Bowen and Witzell, 

 1996). Consequently, sea turtle biolo- 



