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Stable isotope tracking of endangered sea turtles: validation with satellite telemetry and δ15N analysis of amino acids.

Seminoff JA, Benson SR, Arthur KE, Eguchi T, Dutton PH, Tapilatu RF, Popp BN - PLoS ONE (2012)

Bottom Line: Among the 78 turtles studied, we found a distinct dichotomy in δ(15)N values of bulk skin, with distinct "low δ(15)N" and "high δ(15)N" groups. δ(15)N analysis of amino acids confirmed that this disparity resulted from isotopic differences at the base of the food chain and not from differences in trophic position between the two groups.These findings confirm that prevailing marine isoscapes of foraging areas can be reflected in the isotopic compositions of marine turtle body tissues sampled at nesting beaches.Our forensic approach validates the use of stable isotopes to depict leatherback turtle movements over broad spatial ranges and is timely for establishing wise conservation efforts in light of this species' imminent risk of extinction in the Pacific.

View Article: PubMed Central - PubMed

Affiliation: National Oceanic and Atmospheric Administration-National Marine Fisheries Service, Southwest Fisheries Science Center, La Jolla, California, United States of America. jeffrey.seminoff@noaa.gov

ABSTRACT
Effective conservation strategies for highly migratory species must incorporate information about long-distance movements and locations of high-use foraging areas. However, the inherent challenges of directly monitoring these factors call for creative research approaches and innovative application of existing tools. Highly migratory marine species, such as marine turtles, regularly travel hundreds or thousands of kilometers between breeding and feeding areas, but identification of migratory routes and habitat use patterns remains elusive. Here we use satellite telemetry in combination with compound-specific isotope analysis of amino acids to confirm that insights from bulk tissue stable isotope analysis can reveal divergent migratory strategies and within-population segregation of foraging groups of critically endangered leatherback sea turtles (Dermochelys coriacea) across the Pacific Ocean. Among the 78 turtles studied, we found a distinct dichotomy in δ(15)N values of bulk skin, with distinct "low δ(15)N" and "high δ(15)N" groups. δ(15)N analysis of amino acids confirmed that this disparity resulted from isotopic differences at the base of the food chain and not from differences in trophic position between the two groups. Satellite tracking of 13 individuals indicated that their bulk skin δ(15)N value was linked to the particular foraging region of each turtle. These findings confirm that prevailing marine isoscapes of foraging areas can be reflected in the isotopic compositions of marine turtle body tissues sampled at nesting beaches. We use a Bayesian mixture model to show that between 82 and 100% of the 78 skin-sampled turtles could be assigned with confidence to either the eastern Pacific or western Pacific, with 33 to 66% of all turtles foraging in the eastern Pacific. Our forensic approach validates the use of stable isotopes to depict leatherback turtle movements over broad spatial ranges and is timely for establishing wise conservation efforts in light of this species' imminent risk of extinction in the Pacific.

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Marginal posterior distributions of δ15N values for the two assumed foraging grounds (bell-shaped curves) and individual assignments to one of the two foraging grounds (filled circles in horizontal arrangement) with color-coded probabilities of belonging to the eastern Pacific foraging area.Panel A is from Model 4, whereas the Panel B is from Model 6. For both models, posterior distributions depicted in red are from the ‘low δ15N’ (i.e. putative western Pacific foragers), whereas those in blue represent the ‘high δ15N’ group (i.e., putative eastern Pacific foragers).
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pone-0037403-g005: Marginal posterior distributions of δ15N values for the two assumed foraging grounds (bell-shaped curves) and individual assignments to one of the two foraging grounds (filled circles in horizontal arrangement) with color-coded probabilities of belonging to the eastern Pacific foraging area.Panel A is from Model 4, whereas the Panel B is from Model 6. For both models, posterior distributions depicted in red are from the ‘low δ15N’ (i.e. putative western Pacific foragers), whereas those in blue represent the ‘high δ15N’ group (i.e., putative eastern Pacific foragers).

Mentions: The disparate bulk skin δ15N values between known (i.e. satellite-tracked) eastern and western Pacific foragers combined with CSIA-corroboration that these differences were due to baseline isotope values in each region allowed us to characterize the foraging area destinations for each individual based on its skin δ15N value using a Bayesian mixture-model analysis. Among the six models considered (Table 3), all models performed well and no model stood out as the best according to our model selection method. Models 1 through 4 performed well in terms of the mean of the differences (near zero - unbiased), but Models 5 and 6 performed well with respect to the variability in the differences (good precision). Estimated variances of the two normal distributions were different (Figure 5), indicating two-variance models (Models 2, 4, and 6), were more appropriate than the one-variance models (Models 1, 3, and 5). One turtle (72489; Table S1) exhibited an eastern Pacific δ15N value (i.e. ‘high’ δ15N: 15.05‰) but was tracked to the western Pacific (Figure 1). Consequently, the results of the models that used the known foraging locations were influenced by this turtle, and resulted in more-precautionary foraging region assignments. Because of the likelihood that the proportion of foraging destinations changes annually, we use Model 4 (known foraging destinations, time-independent) and Model 6 (unknown foraging destinations, time-dependent) (Table 3) to assign foraging region to each turtle.


Stable isotope tracking of endangered sea turtles: validation with satellite telemetry and δ15N analysis of amino acids.

Seminoff JA, Benson SR, Arthur KE, Eguchi T, Dutton PH, Tapilatu RF, Popp BN - PLoS ONE (2012)

Marginal posterior distributions of δ15N values for the two assumed foraging grounds (bell-shaped curves) and individual assignments to one of the two foraging grounds (filled circles in horizontal arrangement) with color-coded probabilities of belonging to the eastern Pacific foraging area.Panel A is from Model 4, whereas the Panel B is from Model 6. For both models, posterior distributions depicted in red are from the ‘low δ15N’ (i.e. putative western Pacific foragers), whereas those in blue represent the ‘high δ15N’ group (i.e., putative eastern Pacific foragers).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3362573&req=5

pone-0037403-g005: Marginal posterior distributions of δ15N values for the two assumed foraging grounds (bell-shaped curves) and individual assignments to one of the two foraging grounds (filled circles in horizontal arrangement) with color-coded probabilities of belonging to the eastern Pacific foraging area.Panel A is from Model 4, whereas the Panel B is from Model 6. For both models, posterior distributions depicted in red are from the ‘low δ15N’ (i.e. putative western Pacific foragers), whereas those in blue represent the ‘high δ15N’ group (i.e., putative eastern Pacific foragers).
Mentions: The disparate bulk skin δ15N values between known (i.e. satellite-tracked) eastern and western Pacific foragers combined with CSIA-corroboration that these differences were due to baseline isotope values in each region allowed us to characterize the foraging area destinations for each individual based on its skin δ15N value using a Bayesian mixture-model analysis. Among the six models considered (Table 3), all models performed well and no model stood out as the best according to our model selection method. Models 1 through 4 performed well in terms of the mean of the differences (near zero - unbiased), but Models 5 and 6 performed well with respect to the variability in the differences (good precision). Estimated variances of the two normal distributions were different (Figure 5), indicating two-variance models (Models 2, 4, and 6), were more appropriate than the one-variance models (Models 1, 3, and 5). One turtle (72489; Table S1) exhibited an eastern Pacific δ15N value (i.e. ‘high’ δ15N: 15.05‰) but was tracked to the western Pacific (Figure 1). Consequently, the results of the models that used the known foraging locations were influenced by this turtle, and resulted in more-precautionary foraging region assignments. Because of the likelihood that the proportion of foraging destinations changes annually, we use Model 4 (known foraging destinations, time-independent) and Model 6 (unknown foraging destinations, time-dependent) (Table 3) to assign foraging region to each turtle.

Bottom Line: Among the 78 turtles studied, we found a distinct dichotomy in δ(15)N values of bulk skin, with distinct "low δ(15)N" and "high δ(15)N" groups. δ(15)N analysis of amino acids confirmed that this disparity resulted from isotopic differences at the base of the food chain and not from differences in trophic position between the two groups.These findings confirm that prevailing marine isoscapes of foraging areas can be reflected in the isotopic compositions of marine turtle body tissues sampled at nesting beaches.Our forensic approach validates the use of stable isotopes to depict leatherback turtle movements over broad spatial ranges and is timely for establishing wise conservation efforts in light of this species' imminent risk of extinction in the Pacific.

View Article: PubMed Central - PubMed

Affiliation: National Oceanic and Atmospheric Administration-National Marine Fisheries Service, Southwest Fisheries Science Center, La Jolla, California, United States of America. jeffrey.seminoff@noaa.gov

ABSTRACT
Effective conservation strategies for highly migratory species must incorporate information about long-distance movements and locations of high-use foraging areas. However, the inherent challenges of directly monitoring these factors call for creative research approaches and innovative application of existing tools. Highly migratory marine species, such as marine turtles, regularly travel hundreds or thousands of kilometers between breeding and feeding areas, but identification of migratory routes and habitat use patterns remains elusive. Here we use satellite telemetry in combination with compound-specific isotope analysis of amino acids to confirm that insights from bulk tissue stable isotope analysis can reveal divergent migratory strategies and within-population segregation of foraging groups of critically endangered leatherback sea turtles (Dermochelys coriacea) across the Pacific Ocean. Among the 78 turtles studied, we found a distinct dichotomy in δ(15)N values of bulk skin, with distinct "low δ(15)N" and "high δ(15)N" groups. δ(15)N analysis of amino acids confirmed that this disparity resulted from isotopic differences at the base of the food chain and not from differences in trophic position between the two groups. Satellite tracking of 13 individuals indicated that their bulk skin δ(15)N value was linked to the particular foraging region of each turtle. These findings confirm that prevailing marine isoscapes of foraging areas can be reflected in the isotopic compositions of marine turtle body tissues sampled at nesting beaches. We use a Bayesian mixture model to show that between 82 and 100% of the 78 skin-sampled turtles could be assigned with confidence to either the eastern Pacific or western Pacific, with 33 to 66% of all turtles foraging in the eastern Pacific. Our forensic approach validates the use of stable isotopes to depict leatherback turtle movements over broad spatial ranges and is timely for establishing wise conservation efforts in light of this species' imminent risk of extinction in the Pacific.

Show MeSH