Somatic growth is an integrated, individual-based response to environmental conditions, especially in ectotherms. Growth dynamics of large, mobile animals are particularly useful as bio-indicators of environmental change at regional scales. We assembled growth rate data from throughout the West Atlantic for green turtles, Chelonia mydas, which are long-lived, highly migratory, primarily herbivorous mega-consumers that may migrate over hundreds to thousands of kilometers. Our dataset, the largest ever compiled for sea turtles, has 9690 growth increments from 30 sites from Bermuda to Uruguay from 1973 to 2015. Using generalized additive mixed models, we evaluated covariates that could affect growth rates; body size, diet, and year have significant effects on growth. Growth increases in early years until 1999, then declines by 26% to 2015. The temporal (year) effect is of particular interest because two carnivorous species of sea turtles-hawksbills, Eretmochelys imbricata, and loggerheads, Caretta caretta-exhibited similar significant declines in growth rates starting in 1997 in the West Atlantic, based on previous studies. These synchronous declines in productivity among three sea turtle species across a trophic spectrum provide strong evidence that an ecological regime shift (ERS) in the Atlantic is driving growth dynamics. The ERS resulted from a synergy of the 1997/1998 El Niño Southern Oscillation (ENSO)-the strongest on record-combined with an unprecedented warming rate over the last two to three decades. Further support is provided by the strong correlations between annualized mean growth rates of green turtles and both sea surface temperatures (SST) in the West Atlantic for years of declining growth rates (r = -.94) and the Multivariate ENSO Index (MEI) for all years (r = .74). Granger-causality analysis also supports the latter finding. We discuss multiple stressors that could reinforce and prolong the effect of the ERS. This study demonstrates the importance of region-wide collaborations.

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To collect data on green turtles Chelonia mydas near the Marquesas Keys, Florida, USA, we conducted haphazard, unmarked, nonlinear transect (HUNT) surveys from a moving vessel. During HUNTs, we recorded green turtle locations and made opportunistic captures. We found a unique foraging assemblage of subadult and adult green turtles in open-water seagrass habitat (3 to 5 m deep) at the eastern Quicksands, west of the Marquesas Keys. At an adjacent area in the Marquesas Keys (Mooney Harbor), we observed juvenile green turtles foraging in shallow seagrass habitat (< 2 m). During 267 km of HUNTs, 370 green turtles (153 adults, 216 subadults, 1 juvenile) were recorded from the eastern Quicksands. At the Mooney Harbor site, 190 juvenile green turtles were sighted during 309 km of transects. Green turtles captured at the eastern Quicksands were adult and subadult animals that ranged from 69.3 to 108.5 cm straight carapace length (SCL; mean ± SD = 88.4 ± 10.6 cm, n = 31). Green turtles captured in Mooney Harbor were juveniles ranging from 27.0 to 59.3 cm SCL (mean = 44.0 ± 7.8, n = 41). Six repeatable, linear transects were surveyed during 3 sampling events at the eastern Quicksands. During these transects, 238 green turtles were observed. These spatial data were used in a nearest-neighbor analysis, which indicated that the distribution of green turtles at the eastern Quicksands was non-random and clumped. We hypothesize that adult and large subadult green turtles use deeper water habitats than juveniles, and this size-class partitioning may be due to differing habitat requirements and predation risk. Our analyses indicate that green turtles found at the eastern Quicksands form foraging herds.

The 2010 Deepwater Horizon (DWH) oil spill posed a severe threat to surface-pelagic sea turtles because the surface convergence zones, which provide vital habitat by aggregating pelagic Sargassum and other floating material, also aggregated floating oil. Following the DWH spill, turtle rescue operations between 17 May and 9 September 2010 documented 937 juvenile sea turtles in the spill area and examined 574 captured turtles. Of the captured turtles, 81% were visibly oiled. Transect searches in convergence zones found Kemp's ridleys (51% of individuals), green turtles (37%), loggerheads (7%), hawksbills (2%), and unidentified sea turtles (2%). Linetransect methods estimated the density of all surface-pelagic sea turtles in surface convergence zones to be 3.32 km −2 (95% CI = 2.82-3.88), and the density of heavily oiled turtles to be 0.24 km −2 (95% CI = 0.15-0.39). Turtle densities and the areal extent of heavy oiling probability were used to estimate total number of turtles exposed to DWH oil. We estimate approximately 402 000 surface-pelagic sea turtles were exposed, and of those, 54 800 were likely to have been heavily oiled. Our estimates formed the basis of surface-pelagic juvenile sea turtle mortality estimates included in the DWH natural resource damage assessment.

In order to provide information to better inform management decisions and direct further research, vessel-based visual transects, snorkel transects, and in-water capture techniques were used to characterize hawksbill sea turtles in the shallow marine habitats of a Marine Protected Area (MPA), the Key West National Wildlife Refuge in the Florida Keys. Hawksbills were found in hardbottom and seagrass dominated habitats throughout the Refuge, and on man-made rubble structures in the Northwest Channel near Cottrell Key. Hawksbills captured (N = 82) were exclusively juveniles and subadults with a straight standard carapace length (SSCL) ranging from 21.4 to 69.0cm with a mean of 44.1 cm (SD = 10.8). Somatic growth rates were calculated from 15 recaptured turtles with periods at large ranging from 51 to 1188 days. Mean SSCL growth rate was 7.7 cm/year (SD = 4.6). Juvenile hawksbills (<50 cm SSCL) showed a significantly higher growth rate (9.2 cm/year, SD = 4.5, N = 11) than subadult hawksbills (50–70 cm SSCL, 3.6 cm/year, SD = 0.9, N = 4). Analysis of 740 base pair mitochondrial control region sequences from 50 sampled turtles yielded 12 haplotypes. Haplotype frequencies were significantly different compared to four other Caribbean juvenile foraging aggregations, including one off the Atlantic coast of Florida. Many-to-one mixed stock analysis indicated Mexico as the primary source of juveniles in the region and also suggested that the Refuge may serve as important developmental habitat for the Cuban nesting aggregation. Serum testosterone radioimmunoassay results from 33 individuals indicated a female biased sex ratio of 3.3 females: 1 male for hawksbills in the Refuge. This assemblage of hawksbills is near the northern limit of the species range, and is one of only two such assemblages described in the waters of the continental United States. Since this assemblage resides in an MPA with intensive human use, basic information on the assemblage is vital to resource managers charged with conservation and species protection in the MPA.