551 research outputs found
Migration and habitat use of sea turtles in the Bahamas
Objectives:
Evaluate movement and distribution patterns of sea turtles in our series of study sites
in The Bahamas. This objective includes the questions of where do the turtles come
from, how long are they resident in these sites, and where do they go when they
leave.
Collect data that will allow us to develop techniques to compare habitat quality and to
serve as a foundation for studies of the role of green turtles in seagrass ecosystems.
Evaluate models for estimating growth rates and carrying capacities for sea turtles
based on our data from a long-term study of immature green turtles in the southern
Bahamas. (Document has 7 pages.
Biology of pelagic sea turtles: effects of marine debris
Objectives:
1. Quantify the sub-lethal effect of debris ingestion (nutrient dilution) on nutrient gain
2. Model sub-lethal effects of debris ingestion on nutrient intake and growth
3. Evaluation of stress from entanglement on the loggerhead sea turtle
4. Movement patterns and behavior of pelagic-stage loggerheads in the eastern Atlantic
5. Document the genetic relationships of pelagic-stage loggerheads in the eastern
Atlantic with rookeries in the southeast US (Document has 14 pages; lists publications resulting from research
Home range and habitat use by Kemp's Ridley turtles in West-Central Florida
The Kemp's ridley turtle (Lepidochelys kempii) is an endangered species whose recovery depends in part on
the identification and protection of required habitats. We used radio and sonic telemetry on subadult Kemp's ridley
turtles to investigate home-range size and habitat use in the coastal waters of west-central Florida from 1994 to
1996. We tracked 9 turtles during May-August up to 70 days after release and fou.ld they occupied 5-30 km2 foraging
ranges. Compositional analyses indicated that turtles used rock outcroppings in their foraging ranges at a
significantly higher proportion than expected. based on availability within the study area. Additionally. turtles used
live bottom (e.g .• sessile invertebrates) and green macroalgae habitats significantly more than seagrass habitat. Similar
studies are needed through'mt the Kemp's ridley turtles' range to investigate regional and stage-specific differences
in habitat use. which can then be used to conserve important foraging areas
Evaluating trends in abundance of immature green turtles, Chelonia mydas, in the Greater Caribbean
Many long-lived marine species exhibit life history traits. that make them more vulnerable to overexploitation. Accurate population trend analysis is essential for development and assessment of management plans for these species. However, because many of these species disperse over large geographic areas, have life stages inaccessible to human surveyors, and/or undergo complex developmental migrations, data on trends in abundance are often available for only one stage of the population, usually breeding adults. The green turtle (Chelonia mydas) is one of these long-lived species for which population trends are based almost exclusively on either numbers of females that emerge to nest or numbers of nests deposited each year on geographically restricted beaches. In this study, we generated estimates of annual abundance for juvenile green turtles at two foraging grounds in the Bahamas based on long-term capture-mark-recapture (CMR) studies at Union Creek (24 years) and Conception Creek (13 years), using a two-stage approach. First, we estimated recapture probabilities from CMR data using the Cormack-Jolly-Seber models in the software program MARK; second, we estimated annual abundance of green turtles. at both study sites using the recapture probabilities in a Horvitz-Thompson type estimation procedure. Green turtle abundance did not change significantly in Conception Creek, but, in Union Creek, green turtle abundance had successive phases of significant increase, significant decrease, and stability. These changes in abundance resulted from changes in immigration, not survival or emigration. The trends in abundance on the foraging grounds did not conform to the significantly increasing trend for the major nesting population at Tortuguero, Costa Rica. This disparity highlights the challenges of assessing population-wide trends of green turtles and other long-lived species. The best approach for monitoring population trends may be a combination of (1) extensive surveys to provide data for large-scale trends in relative population abundance, and (2) intensive surveys, using CMR techniques, to estimate absolute abundance and evaluate the demographic processes' driving the trends
Estimates of survival probabilities for oceanic-stage loggerhead sea turtles (Caretta caretta) in the North Atlantic
Estimates of instantaneous mortality rates (Z) and annual apparent survival probabilities (Φ) were generated from catch-curve analyses for oceanic-stage juvenile loggerheads (Caretta caretta) in the waters of the Azores. Two age distributions were analyzed: the “total sample” of 1600 loggerheads primarily captured by sighting and dipnetting from a variety of vessels in the Azores between 1984 and 1995 and the “tuna sample” of 733 loggerheads (a subset of the total sample) captured by sighting and dipnetting from vessels in the commercial tuna fleet in the Azores between 1990 and 1992. Because loggerhead sea turtles begin to emigrate from oceanic to neritic habitats at age 7, the best estimates of instantaneous mortality rate (0.094) and annual survival probability (0.911) not confounded with permanent emigration were generated for age classes 2 through 6. These estimates must be interpreted with caution because of the assumptions upon which catch-curve analyses are based. However, these are the first directly derived estimates of mortality and survival probabilities for oceanic-stage sea turtles. Estimation of survival probabilities was identified as “an immediate and critical requirement” in 2000 by the Turtle Expert Working Group of the U.S. National Marine Fisheries Service
Compensatory growth in oceanic loggerhead sea turtles: response to a stochastic environment
Compensatory growth (CG, accelerated growth that may occur when an
organism that has grown at a reduced rate as a result of suboptimal environmental
conditions is exposed to better conditions) is considered an adaptation to variable en vironments. Although documented thoroughly under captive conditions, CG has rarely
been studied in wild populations. In their first years of life, oceanic-stage loggerhead
sea turtles (Caretta caretta) have relatively little control over their geographic position
or movements and thus have an extremely stochastic lifestyle with great variation in
food availability and temperature. This environmental variation results in variable
growth rates. We evaluate somatic growth functions of oceanic-stage loggerheads from
the eastern Atlantic based on skeletochronology that allowed us to assign age and cohort
to each individual. We demonstrate CG in these turtles based on three different analytical
approaches: changes in coefficients of variation in size-at-age, generalized additive
model regression analyses of somatic growth, and linear regression of age-specific
growth rates. As a result of CG, variation in size-at-age in these juvenile loggerheads
is substantially reduced. Thus, size is a better predictor of age than expected based on
variation in growth rates. CG decreases with age, apparently as loggerheads gain greater
control over their movements. In addition, we have evaluated for the first time in wild
sea turtles the time-dependent nature of somatic growth by distinguishing among age,
year, and cohort effects using a mixed longitudinal sampling design with assigned-age
individuals. Age and year had significant effects on growth rates, but there was no
significant cohort effect. Our results address critical gaps in knowledge of the demog raphy of this endangered species.info:eu-repo/semantics/publishedVersio
Green turtle somatic growth model: evidence for density dependence.
Abstract. The green turtle, Chelonia mydas, is a circumglobal species and a primary herbivore in marine ecosystems. Overexploitation as a food resource for human populations has resulted in drastic declines or extinction of green turtle populations in the Greater Caribbean. Attempts to manage the remaining populations on a sustainable basis are hampered by insufficient knowledge of demographic parameters. In particular, compensatory responses resulting from density-dependent effects have not been evaluated for any sea turtle population and thus have not been explicitly included in any population models. Growth rates of immature green turtles were measured during an 18-yr study in Union Creek, a wildlife reserve in the southern Bahamas. We have evaluated the growth data for both straight carapace length (SCL) and body mass with nonparametric regression models that had one response variable (absolute growth rate) and five potential covariates: sex, site, year, mean size, and recapture interval. The SCL model of size-specific growth rates was a good fit to the data and accounted for 59% of the variance. The body-mass model was not a good fit to the data, accounting for only 26% of the variance. In the SCL model, sex, site, year, and mean size all had significant effects, whereas recapture interval did not. We used results of the SCL model to evaluate a density-dependent effect on somatic growth rates. Over the 18 yr of our study, relative population density underwent a sixfold increase followed by a threefold decrease in Union Creek as a result of natural immigration and emigration. Three lines of evidence support a density-dependent effect. First, there is a significant inverse correlation between population density and mean annual growth rate. Second, the condition index (mass/(SCL) 3 ) of green turtles in Union Creek is positively correlated with mean annual growth rates and was negatively correlated with population density, indicating that the green turtles were nutrient limited during periods of low growth and high population densities. Third, the population in Union Creek fluctuated around carrying capacity during our study and thus was at levels likely to experience densitydependent effects that could be measured. We estimate the carrying capacity of pastures of the seagrass Thalassia testudinum, the major diet plant of the green turtle, as a range from 122 to 4439 kg green turtles/ha or 16-586 million 50-kg green turtles in the Caribbean. Because green turtle populations are probably regulated by food limitation under natural conditions, carrying capacity can serve as a baseline to estimate changes in green turtle populations in the Caribbean since preColumbian times and to set a goal for recovery for these depleted populations. Finally, we compare the growth functions for green turtle populations in the Atlantic and Pacific oceans. Not only does the form of the size-specific growth functions differ between the two regions (monotonic declining in the Atlantic and nonmonotonic in the Pacific), but also small juvenile green turtles in the Atlantic have substantially higher growth rates than those in the Pacific. Research is needed to evaluate the causes of these differences, but our results indicate that demographic parameters between ocean basins should only be extrapolated with great caution
Transatlantic developmental migrations of loggerhead sea turtles demonstrated by mtDNA sequence analysis
Molecular markers based on mitochondrial (mt) DNA control region se quences were used to test the hypothesis that juvenile loggerhead sea turtles (Caretta
caretta) in pelagic habitats of the eastern Atlantic are derived from nesting populations in
the western Atlantic. We compared mtDNA haplotypes from 131 pelagic juvenile turtles
(79 from the Azores and 52 from Madeira) to mtDNA haplotypes observed in major nesting
colonies of the Atlantic Ocean and Mediterranean Sea. A subset of 121 pelagic samples
(92%) contained haplotypes that match mtDNA sequences observed in nesting colonies.
Maximum likelihood analyses (UCON, SHADRACQ) estimate that 100% of these pelagic
juveniles are from the nesting populations in the southeastern United States and adjacent
Yucatan Peninsula, Mexico. Estimated contributions from nesting populations in south
Florida (0.71, 0.72), northern Florida to North Carolina (0.19, 0.17), and Quintana Roo,
Mexico (0.11, 0.10) are consistent with the relative size of these nesting aggregates. No
contribution was detected from nesting colonies in the Mediterranean (Greece) or South
Atlantic (Brazil), although samples sizes are insufficient to exclude these locations with
finality. The link between west Atlantic nesting colonies and east Atlantic feeding grounds
provides a more complete scientific basis for assessing the impact of subadult mortality in
oceanic fisheries. Demographic models for loggerhead turtles in the western Atlantic can
now be improved by incorporating growth and mortality data from juvenile turtles in pelagic
habitats. These data demonstrate that the appropriate scale for loggerhead turtle conservation
efforts is vastly larger than the current scale of management plans based on political
boundaries.info:eu-repo/semantics/publishedVersio
Once and Future Gulf of Mexico Ecosystem: Restoration Recommendations of an Expert Working Group
The Deepwater Horizon (DWH) well blowout released more petroleum hydrocarbons into the marine environment than any previous U.S. oil spill (4.9 million barrels), fouling marine life, damaging deep sea and shoreline habitats and causing closures of economically valuable fisheries in the Gulf of Mexico. A suite of pollutants—liquid and gaseous petroleum compounds plus chemical dispersants—poured into ecosystems that had already been stressed by overfishing, development and global climate change. Beyond the direct effects that were captured in dramatic photographs of oiled birds in the media, it is likely that there are subtle, delayed, indirect and potentially synergistic impacts of these widely dispersed, highly bioavailable and toxic hydrocarbons and chemical dispersants on marine life from pelicans to salt marsh grasses and to deep-sea animals. As tragic as the DWH blowout was, it has stimulated public interest in protecting this economically, socially and environmentally critical region. The 2010 Mabus Report, commissioned by President Barack Obama and written by the secretary of the Navy, provides a blueprint for restoring the Gulf that is bold, visionary and strategic. It is clear that we need not only to repair the damage left behind by the oil but also to go well beyond that to restore the anthropogenically stressed and declining Gulf ecosystems to prosperity-sustaining levels of historic productivity. For this report, we assembled a team of leading scientists with expertise in coastal and marine ecosystems and with experience in their restoration to identify strategies and specific actions that will revitalize and sustain the Gulf coastal economy. Because the DWH spill intervened in ecosystems that are intimately interconnected and already under stress, and will remain stressed from global climate change, we argue that restoration of the Gulf must go beyond the traditional "in-place, in-kind" restoration approach that targets specific damaged habitats or species. A sustainable restoration of the Gulf of Mexico after DWH must: 1. Recognize that ecosystem resilience has been compromised by multiple human interventions predating the DWH spill; 2. Acknowledge that significant future environmental change is inevitable and must be factored into restoration plans and actions for them to be durable; 3. Treat the Gulf as a complex and interconnected network of ecosystems from shoreline to deep sea; and 4. Recognize that human and ecosystem productivity in the Gulf are interdependent, and that human needs from and effects on the Gulf must be integral to restoration planning. With these principles in mind, the authors provide the scientific basis for a sustainable restoration program along three themes: 1. Assess and repair damage from DWH and other stresses on the Gulf; 2. Protect existing habitats and populations; and 3. Integrate sustainable human use with ecological processes in the Gulf of Mexico. Under these themes, 15 historically informed, adaptive, ecosystem-based restoration actions are presented to recover Gulf resources and rebuild the resilience of its ecosystem. The vision that guides our recommendations fundamentally imbeds the restoration actions within the context of the changing environment so as to achieve resilience of resources, human communities and the economy into the indefinite future
Activity patterns of Kemp's ridley turtles, Lepidochelys kempii, in the coastal waters of the Cedar Keys, Florida
Radio and sonic telemetry were used to investigate
the tidal orientation, rate of movement
(ROM), and surfacing behavior of nine Kemp's ridley
turtles, Lepidochelys kempii, tracked east of the Cedar
Keys, Florida. The mean of mean turtle bearings on
incoming (48 ± 49 0) and falling (232 ± 41 0) tides was
significantly oriented to the mean directions of tidal flow
(37±9°, P<0.0025, and 234±9 0, P<0.005, respectively).
Turtles had a mean ROM of 0.44±0.33 km/h
(range: 0.004-1.758 km/h), a mean surface duration of
18± 15 s (range: 1-88 s), and a mean submergence duration
of 8.4± 6.4 min (range: 0.2-60.0 min). ROM was
negatively correlated with surface and submergence
durations and positively correlated with the number of
surfacings. Furthermore, ROMs were higher and surface and submergence durations were shorter during the day.
Daily activities of turtles were attributed to food acquisition
and bioenergetics
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