seaturtle.org : MTN : ARCHIVES : Sign In

The rehabilitation and release of juvenile and subadult Kemp’s ridleys at IMMS presented an opportunity to examine the movements of these poorly understood life history stages in an understudied region of the Kemp’s range, the north central Gulf of Mexico. Twelve rehabilitated sea turtles were selected for satellite tracking. During the fall of 2010, six of these turtles were released in Mississippi waters, two miles south of East Ship Island. Due to the high number of sea turtle strandings along the Mississippi coast during the spring of 2011, the other six rehabilitated turtles were released near documented immature Kemp’s ridley feeding grounds in Cedar Key, Florida (Schmid et al. 2003) rather than in Mississippi, in an attempt to prevent re-stranding. The movements of the two groups were compared to examine the possible effects of translocating immature Kemp’s ridleys by releasing them in a different location from where they were found. This analysis is presented to provide an initial assessment of site fidelity within the north central Gulf of Mexico.

In the fall of 2010, six rehabilitated immature Kemp’s ridleys were released near the Mississippi Sound off Ship Island (N 30° 20.82’ W 88° 91.60’) (Table 1). In the spring of 2011, an additional six immature Kemp’s ridleys were released off Cedar Key, Florida (N 29° 13.335’ W 82° 97.76’). The individuals released in 2010 were fitted with a Sirtrack KiwiSat K2G - 202 series platform terminal transmitter (PTT), 371A (n = 3) and 271B (n = 3). The individuals released in 2011 were fitted with a 271B (n = 6) PTT. The battery from each PTT 371A had a lifetime of approximately 115 days at constant power and weighed approximately 170 grams. The battery from the PTT 271B had a battery life of approximately 80 days and weighed approximately 98 grams. Transmitter sizes were consistently less than 3% of each individual’s release weight. Each PTT was painted with Tempo Marine, a clear antifouling paint. Prior to application of the transmitter, each turtle’s anterior vertebral and costal scutes were sanded and cleaned with acetone. Transmitters were attached following the procedures outlined in Seney et al. (2010). Once the epoxy had cured, two coats of the brush-on antifouling paint Interlux Micron were applied to the cured adhesives as well as the non-metal surfaces of the PTT.

Table 1. Lengths, weights and tracking data for the 12 satellite-tagged immature Kemp’s ridely sea turtles released in Mississippi and Florida. *=Straight-line notch-tip carapace length; ^=Curved carapace notch-tip length; #=An active track as of manuscript preparation.

Each PTT was set to a duty cycle of 6 hours on followed by 6 hours off to conserve the battery. Messages received from the satellites were processed by CLS America (www.clsamerica.com) to give Doppler-derived locations classified by the number of messages used for processing. Location classes included LC 3, 2, 1, 0, A, B, and Z. LC 3, 2, 1, and 0 were derived from a minimum of 4 messages. These classes had estimated accuracies of < 250 m, < 500 m, < 1500 m and > 1500 m respectively. LC A and LC B were calculated from 3 and 2 messages respectively and did not provide accuracy estimation. LC Z indicated an invalid location (Argos 2009).

The Satellite Tracking and Analysis Tool (STAT) (Coyne & Godley 2005) was used to exclude locations in the following categories: 1) LC Z; 2) locations that recorded swimming speeds of 5 km hr-1 or greater; 3) locations that were recorded at elevations at 0.5 m or greater; and 4) locations that were recorded on dry or over land areas. Incorrect readings (points that crossed land or large areas of water) that were not filtered by STAT were removed manually in ArcMap 9.3. In both release groups the Pearson’s correlation coefficients were used to compare the distance from the hooking/ stranding and release locations to the time the first transmission was run at an α level of 0.05. A two- tailed t-test was conducted at an α level of 0.05 with the average swimming speeds for the two groups. The slopes of the regressions were also analyzed to examine any differences in overall movements. Microsoft© Excel was utilized for these analyses. The time period that was analyzed was constrained to 60 days to reduce possibilities of statistical bias from the few turtles with exceptionally longer track durations.

Figure 1. Satellite tagging tracks of the turtles released in Mississippi (left) and Florida (right).

Tracking paths for the turtles released in Mississippi indicated that they migrated to warmer waters offshore when water temperatures decreased; but they did not travel far. These individuals stayed in the general area of the Mississippi Sound and adjacent Louisiana waters during the 60-day tracking period, moving farther away from both their hooking/stranding location (r = 0.55, p < 0.01) and their release location (r = 0.48, p < 0.01) (Fig. 1). However, they did not travel farther than 183 km (Crush, 55.63 days after release) from their hooking/stranding locations within the 60-day period covered in this analysis.

In contrast, the majority of the turtles released in Florida did not remain in the area where they were initially released. Within days of the release, four out of six turtles quickly began swimming up the coastline toward Alabama and Mississippi, moving away from their release site (r = 0.58, p < 0.01) and closer to their hooking/ stranding sites (r = -0.40, p < 0.01).

The slope of the regression line that best fits the data for the correlations between hours after release and distance from stranding sites were in opposite directions and almost twice as large for the Florida turtles (slope = -0.12) as for the Mississippi turtles (slope = 0.059). However, the average swimming speed was significantly faster for the Mississippi turtles (1.48 km/hr) than for the Florida turtles (1.16 km/hr; t (9) = 2.43, p < 0.05). This indicates that the Florida turtles were not moving as fast as the Mississippi turtles but were moving in a more direct line, in this case toward the hooking/stranding location, whereas the Mississippi turtles were moving generally away from their hooking/stranding site and not in a direct line.

The results indicated that the juvenile and subadult Kemp’s ridleys released in Mississippi waters displayed a significant degree of site fidelity to the north central Gulf of Mexico. They stayed in the general area of Mississippi and Louisiana waters whereas several turtles that were released from Cedar Key, FL displayed western directional movements. These conclusions were supported by a home range analysis of the Mississippi-released turtles (Broadway et al. 2012 in prep), which detected a 100% utilization range from 5,570 to 12,134 km2 (mean = 8,787 km2 ± 2,294 SD) for individual turtles. They went no farther south than 28.7 °N during the winter months (Broadway et al. in prep). It is important to note that three of the four Florida-released turtles showing directional movements stopped transmitting before they reached their original hooking/ stranding locations, and the fourth continued to its hooking/stranding location but did not spend considerable time there. Overall, the results of this study imply that it is best to release turtles near their hooking/stranding location when possible.

Interestingly, one of the Florida-released turtles, Strider, was tracked past its original hooking/stranding location to the vicinity of Rancho Nuevo, Mexico, which is the main nesting location for this species (Hildebrand 1963). Strider remained in this area for approximately two weeks in March before returning north to waters along the Texas/Louisiana border. Based on serum testosterone levels measured prior to release in April 2011 (0.846 ng/ml), and compared to typical levels (Rostal et al. 1998), Strider was determined to be male. Although Strider’s carapace (curved notch-tip) was measured to be 54.5 cm at the time of release, which is lower than the widely accepted 60 cm threshold for categorizing Kemp’s ridleys as mature, Gregory & Schmid (2001) suggested that maturation could occur prior to reaching this size. Shaver et al. (2005) showed that even though the majority of males reside near Rancho Nuevo year round some males can migrate away post-mating. Adult females have been tracked migrating from the Atlantic coast of Florida (Schmid 1995) and northern Gulf of Mexico (Renaud et al. 1996) to Rancho Nuevo, but the authors believe this is the first instance of tracking a newly mature Kemp’s ridley male on its migration to mating grounds near the nesting beach.

Previous studies have examined the movements of immature Kemp’s ridley sea turtles in other regions (Renaud & Williams 2005; Schmid et al. 2003; Seney & Landry 2011). Schmid et al. (2003) tracked subadult Kemp’s ridleys via radio and sonic telemetry in west central Florida to investigate home range sizes and habitat use. Turtles preferred to forage around rock outcroppings and in live benthic habitats, and several turtles displayed relatively small home ranges during the summer months (Schmid et al. 2003). Renaud & Williams (2005) tracked the movements of wild-caught and rehabilitated turtles in the northwestern Gulf of Mexico, Gulf coast of Florida and Atlantic seaboard from North Carolina to Florida. The majority of the monitored juvenile turtles remained within 15 km of their nearshore capture site and were characterized as habitat faithful. The authors also detected offshore movements as water temperatures cooled seasonally (Renaud & Williams 2005). More recently, Seney & Landry (2011) tracked rehabilitated immature Kemp’s ridleys via satellite telemetry in the northwestern Gulf of Mexico and observed concentrated movements near tidal passes, fishing piers and within bay systems. The conclusions of these studies correspond with the movements observed from the Mississippi-released turtles. These turtles seasonally migrated to offshore waters; however, five of the six were observed returning to the nearshore waters of the Mississippi Sound the next year (Broadway et al. in prep). The sixth turtle, Terry, stopped transmitting signals after only 23 days. Future analyses will examine summer movements and specific habitat use of juvenile Kemp’s ridley sea turtles in the Mississippi Sound.

This is the first study to examine the movements of immature Kemp’s ridley sea turtles via satellite telemetry in the north central Gulf of Mexico. Other satellite telemetry studies have provided insight into the use of poorly understood developmental grounds by juvenile loggerhead (Polovina et al. 2006) and juvenile green sea turtles (Hart & Fujisaki 2010). The revised recovery plan for the Kemp’s ridley sea turtle (NMFS, USFWS & SEMARNAT 2011) calls for a better comprehension of habitat use of all life history stages. The north central Gulf of Mexico has been identified in the past to represent important developmental habitat for this species (Ogren 1989), yet data regarding habitat use and site fidelity are deficient. Additionally, as the Kemp’s ridley population continues to recover, the chances for adverse human interactions, notably fishery interactions, may increase (Seney & Landry 2011). This potential has been underscored by the abnormally high number of Kemp’s ridley strandings since 2010 (NOAA 2012), even though the cause(s) for this mortality is not fully understood. Therefore, more current data on the habitat use and movements of all life history stages of Kemp’s ridley turtles will aid effective conservation and management throughout its range. The long-term study recently initiated by the Institute for Marine Mammal Studies will serve to fill this knowledge gap in the north central Gulf of Mexico and will contribute to the continued recovery of Kemp’s ridleys.

Acknowledgements. Special thanks to the volunteers and interns who helped collect the data. Additional thanks go to the two anonymous reviewers for helpful comments to this manuscript.

ARGOS, S. 2009. Argos user's manual, CLS.

COYNE, M.S. & B.J. GODLEY. 2005. Satellite Tracking and Analysis Tool (STAT): an integrated system for archiving, analyzing and mapping animal tracking data. Marine Ecology Progress Series 301: 1-7.

CROWDER, L.B. & S.S. HEPPELL. 2011. The decline and rise of a sea turtle: How Kemp's ridleys are recovering in the Gulf of Mexico. Solutions Journal 2: 67-73.

GREGORY, L.F. & J.R. SCHMID. 2001. Stress responses and sexing of wild Kemp's ridley sea turtles (Lepidochelys kempii) in the Northeastern Gulf of Mexico. General and Comparative Endocrinology 124: 66-74.

HART, K.M. & I. FUJISAKI. 2010. Satellite tracking reveals habitat use by juvenile green sea turtles Chelonia mydas in the Everglades, Florida, USA. Endangered Species Research 11: 221-232.

HEPPELL, S.S., P.M. BURCHFIELD & L.J. PENA. 2007. Biology and Conservation of Ridley Sea Turtles. P.T. Plotkin. Baltimore, MD, Johns Hopkins University Press. 368 pp.

HILDEBRAND, H.H. 1963. Halazgo del área de andación de la tortuga maria “lora” Lepidochelys kempi (Garman), en la costa occidental del Golfo de México. Sobretiro de Cienci (México) 22: 105-112.

NMFS, USFWS & SEMARNAT. 2011. Bi-National Recovery Plan for the Kemp's Ridley Sea Turtle (Lepidochelys kempii), Second Revision. N.M.F.S. Silver Spring, Maryland: 156 pp. + appendices.

NOAA. 2012. Sea turtle strandings in the Gulf of Mexico, NOAA Fisheries Office of Protected Resources. Retrieved from <http://www.nmfs.noaa.gov/pr/species/turtles/gulfofmexico.htm> Accessed August 23, 2012.

OGREN, L. 1989. Distribution of juvenile and subadult Kemp’s ridley turtles: Preliminary results from the 1984-1987 surveys. Proceedings of the First International Symposium on Kemp’s ridley sea turtle biology, conservation and management. C.W. Caillouet Jr. & A.M. Landry, Jr. College Station, TX, Texas A&M Sea Grant College Program: p. 116-123.

POLOVINA, J., I. UCHIDA, G. BALAZS, E.A. HOWELL, D. PARKER & P. DUTTON. 2006. The Kuroshiro Extension Bifurcation Region: A pelagic hotspot for juvenile loggerhead sea turtles. Deep-Sea Research II 53: 326-339.

RENAUD, M.L., J.A. CARPENTER, J.A. WILLIAMS & A.M. LANDRY, JR. 1996. Kemp's ridley Sea Turtle (Lepidochelys kempii) tracked by satellite telemetry from Louisiana to nesting beach at Rancho Nuevo, Tamaulipas, Mexico. Chelonian Conservation & Biology 2: 108-109.

RENAUD, M.L. & J.A. WILLIAMS. 2005. Kemp's ridley sea turtle movements and migrations. Chelonian Conservation & Biology 4: 808-816.

ROSTAL, D.C., D.W. OWENS, J.S. GRUMBLES, D.S. MACKENZIE & M.S. AMOSS, JR. 1998. Seasonal reproductive cycle of the Kemp's ridley sea turtle (Lepidochelys kempi). General and Comparative Endocrinology 109: 232-243.

SCHMID, J.R. 1995. Marine turtle populations on the east-central coast of Florida: results of tagging studies at Cape Canaveral, Florida, 1986-1991. Fishery Bulletin 98: 189-191.

SCHMID, J.R., A.B. BOLTEN, K.A. BJORNDAL, W.J. LINDBERG, H.F. PERCIVAL & P.D. ZWICK. 2003. Home range and habitat use by Kemp's ridley turtles in West-Central Florida. Journal of Wildlife Management 67: 196-206.

SENEY, E.E., B.M. HIGGINS & A.M. LANDRY, JR. 2010. Satellite transmitter attachment techniques for small juvenile sea turtles. Journal of Experimental Marine Biology & Ecology 384: 61-67.

SENEY, E.E. & A.M. LANDRY, JR. 2011. Movement patterns of immature and adult female Kemp's ridley sea turtles in the northwestern Gulf of Mexico. Marine Ecology-Progress Series 440: 241-254.

SHAVER, D.J. 2005. Analysis of the Kemp’s ridley imprinting and headstart project at Padre Island National Seashore, Texas, 1978–88, with subsequent nesting and stranding records on the Texas coast. Chelonian Conservation & Biology 4: 846-859.