No abstract

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.

Effective management of protected sea turtle populations requires knowledge not only of mean values for demographic and life-history parameters, but also temporal and spatial trends, variability, and underlying causes. For endangered Kemp’s ridley sea turtles (Lepidochelys kempii), the need for baseline information of this type has been emphasized during attempts to understand causes underlying the recent truncation in the recovery trajectory for nesting females. To provide insight into variability in age and size at sexual maturation (ASM and SSM) and long-term growth patterns likely to influence population trends, we conducted skeletochronological analysis of humerus bones from 333 Kemp’s ridleys stranded throughout the Gulf of Mexico (GOM) from 1993 to 2010. Ranges of possible ASMs (6.8 to 21.8 yr) and SSMs (53.3 to 68.3 cm straightline carapace length (SCL)) estimated using the “rapprochement” skeletal growth mark associated with maturation were broad, supporting incorporation of a maturation schedule in Kemp’s ridley population models. Mean ASMs estimated from rapprochement and by fitting logistic, generalized additive mixed, and von Bertalanffy growth models to age and growth data ranged from 11 to 13 yr; confidence intervals for the logistic model predicted maturation of 95% of the population between 11.9 and 14.8 yr. Early juvenile somatic growth rates in the GOM were greater than those previously reported for the Atlantic, indicating potential for differences in maturation trajectories between regions. Finally, long-term, significant decreases in somatic growth response were found for both juveniles and adults, which could influence recruitment to the reproductive population and observed nesting population trends.

Effective management of a rapidly increasing juvenile green sea turtle Chelonia mydas population necessitates an understanding of the foraging grounds utilized throughout ontogeny. We used stomach content (SCA) and stable isotope analyses (SIA) of multiple size classes of green turtles foraging along the middle (MTC) and lower Texas coasts (LTC) in the northwestern Gulf of Mexico to identify ontogenetic shifts in foraging behavior. Spatial differences in diet and habitat residency were examined based on samples gathered from live (n = 55) and deceased turtles (n = 114). Additionally, the isotopic composition of putative forage material within nearshore and inshore habitats was investigated to determine prey contribution to diet. Green turtle recruitment to neritic channel environments in Texas waters at sizes < 25 cm straight carapace length (SCL) was established based on the presence of benthic macroalgae in the diet. Integration of SCA with SIA of carbon and nitrogen in scute material, as well as potential prey, revealed a subsequent inshore shift to seagrass beds before obtaining 35 cm SCL for turtles of the LTC, while turtles from the MTC exhibited considerable variation in size at transition. This study improves our understanding of the feeding ecology of green turtles within critical foraging grounds along the Texas coast. KEY WORDS: Green turtle • Chelonia mydas • Ontogenetic shift • Stomach content analysis • Stable isotope analysis • δ 13 C • δ 15 N • Gulf of Mexico • Texas Resale or republication not permitted without written consent of the publisher

The Kemp's ridley sea turtle Lepidochelys kempii is recovering from declines that reduced nesting from a single-day estimate of 10 000 to 40 000 females in 1947 to < 300 during the entire 1985 nesting season. Although beach monitoring is crucial to estimating nesting population size and activity, in-water data are essential for understanding population dynamics, evaluating management strategies, and ensuring the species' continued recovery. Fifteen immature and 7 adult female ridleys were fitted with platform terminal transmitters and released off the upper Texas coast during 2004 through 2007. Immature individuals were tracked primarily during warmer months and exhibited preferences for tidal passes, bays, coastal lakes, and nearshore waters, although movement patterns varied among years. Females tracked during their internesting intervals remained in the vicinity of the upper Texas coast and, upon entering the postnesting stage, moved eastward along the 20 m isobath to foraging areas offshore of central Louisiana. Satellite telemetry indicated that inshore and continental shelf waters of the northwestern Gulf of Mexico serve as developmental, migratory, inter-nesting, and post-nesting habitat for the Kemp's ridley. Projected population growth will likely lead to increased use of the northwestern Gulf by the species and more frequent encounters with human activities. The extent of such anthropogenic interactions and need for mitigation measures should be examined and considered by natural resource managers to facilitate continued recovery of this and other sea turtle species in the Gulf of Mexico. Likewise, research efforts should be continued to better understand seasonal in-water distributions, abundances, population dynamics, and mortality risks to all life history stages.