Witzell et al.. Origin of Caietta catena at Hutchinson Island 



629 



Table 4 



Doiiiograpliic compositions of coastal juvenili' loggerhead sea turtles from U.S. coastal foraging habitats by using RFLP analysis, n 

 = number of turtles in sample. SFL = south Florida; NEFL-NC = northeast Florida to North Carolina. 



Location 



SFL 



NEFL-NC 



Literature source 



Chesapeake Bay 

 South Carolina 



0.64 

 0.50 



0.36 

 0.50 



62 

 33 



Norrgard and Graves ( 1995) 

 Scars ctal. (1995) 



inadequate sample sizes or sampling errors, or possibly 

 changes between year classes. However, the differences are 

 undoubtedly an artifact and are more likely due to the poor 

 resolution and small sample sizes of the RFLP studies. 



Comparisons of estimates generated by using different 

 methods are problematic for several reasons. Recently, 

 Encalada et al. (1998) published the results of a survey of 

 nesting locations using sequences from the control region 

 of the mtDNA. This region exhibits a sixfold increase in di- 

 vergence rates when compared to estimates of divergence 

 based on RFLP analysis. More variation was detected 

 and consequently more haplotypes were identified than 

 previously in Bowen et al. (1993). Encalada et al. (1998) 

 also included several other nesting subpopulations in the 

 Atlantic Ocean, in particular nesting subpopulations in 

 northwest Florida and the Yucatan of Mexico. 



The manner and routes of dispersal of posthatchling 

 loggerhead sea turtles from the Yucatan and NWFL are 

 undoubtedly complex and probably follow the same disper- 

 sal scenarios as proposed for the Kemp's ridley sea turtle 

 (Lepidochelys kempii) by Collard and Ogren ( 1990). These 

 loggerhead turtles either stay in the Gulf of Mexico or 

 are transported into the Atlantic by the Florida Current. 

 Once in the Atlantic, they either stay on the Continental 

 shelf area or are entrained in major current systems and 

 are transported to the eastern Atlantic Ocean for an un- 

 determined amount of time before presumably returning 

 to western Atlantic coastal benthic habitats. The SFL and 

 NEFL-NC rookeries are all situated near the western 

 boundary of the Gulf Stream where the hatchlings are 

 quickly transported away from beaches. Juvenile logger- 

 head sea turtles leave their pelagic habitat over a range of 

 sizes, and presumably ages, depending on feeding success. 

 This estimate size range (SCL) was from 25 to 60 cm (Carr, 

 1986, 1987; Martin et al, 1989; Musick and Limpus, 1997). 

 Hays and Marsh (1997) deduced from drift studies that 

 the pelagic phase ended "at least for some loggerheads in 

 the north Atlantic" when they were around 50 cm. These 

 postpelagic turtles are thought to become coastal benthic 

 crustacean foragers (Musick and Limpus, 1997) and to 

 move up and down the U.S. East Coast seasonally. 



Movements of juvenile loggerhead sea turtles tagged 

 at the St. Lucie Power Plant indicate that a substantial 

 portion of these turtles appear to reside in the immediate 

 vicinity of Hutchinson Island (M. Bresette, unpubl. data). 

 However, a few turtles have been documented from as far 

 north as North Carolina and as far south as Florida Bay 

 in southwest Florida. Most recaptured juvenile logger- 

 head sea turtles were from the north and may indicate 



that Hutchinson Island is near the southern boundary 

 of the seasonal migration (Ernest et. al., 1989). Relatively 

 few southern movements were recorded to Florida Bay. 

 Over 47% of 3142 turtles under 85 cm captured at the St. 

 Lucie Power Plant were captured from January through 

 April 1976-2000 (Fig. 3). Captures then tapered off until 

 December, consistent with seasonal north and south move- 

 ments as suggested for immature turtles at nearby Cape 

 Canaveral (Henwood, 1987). There has previously been no 

 tagging evidence to indicate movements of these immature 

 turtles outside the continental United States, yet these 

 mtDNA data indicate a large contribution from Mexico. 



The Hutchinson Island juvenile loggerhead sea turtles 

 settle into this important coastal habitat at the same size, 

 and presumably age, whatever their genetic origins are. 

 This finding indicates that this particular coastal habitat 

 may be critical for several western Atlantic populations of 

 juvenile sea turtles, both loggerhead and green. 



Management implications 



The NEFL-NC population is of particular interest to some 

 U.S. conservation biologists because of an apparent decline 

 in nesting females prior to 1990 (Turtle Expert Working 

 Group, 2000). The goal of protecting these turtles while in 

 various developmental habitats is extremely complex, par- 

 ticularly when they intermingle with large numbers of sea 

 turtles from a healthy (large) breeding population (SFL), 

 as well as with small (NWFL) and foreign populations 

 (Yucatan). Management measures affecting immature 

 loggerhead sea turtles in the east-central Florida forag- 

 ing habitats need to take into account the contributions 

 from other source populations that may not be as robust 

 as that of the south Florida population. Specific measures 

 will depend largely on the demographic composition of 

 stranded turtles with known sources of mortality. The 

 genetic compositions of juvenile loggerhead sea turtles 

 that are impacted by disease, boat collisions, anthropo- 

 genic debris, channel dredging, and recreational and com- 

 mercial fisheries need to be determined before resource 

 managers can take appropriate action. Unfortunately it 

 is difficult to determine specific causes of mortality from 

 stranded individuals, and researchers are unable to accu- 

 rately determine the activities that affect specific nesting 

 aggregations. The conservative approach would be to regu- 

 late all known sources of mortality to immature coastal 

 loggerhead sea turtles until more data become available 

 through aggressive genetic sampling and necropsies of 

 stranded animals. 



