Effect of North Atlantic climate variability on hawksbill turtles in the Southern Gulf of Mexico

Somatic growth dynamics are an integrated response to environmental conditions. Hawksbill sea turtles (Eretmochelys imbricata) are long‐lived, major consumers in coral reef habitats that move over broad geographic areas (hundreds to thousands of kilometers). We evaluated spatio‐temporal effects on hawksbill growth dynamics over a 33‐yr period and 24 study sites throughout the West Atlantic and explored relationships between growth dynamics and climate indices. We compiled the largest ever data set on somatic growth rates for hawksbills – 3541 growth increments from 1980 to 2013. Using generalized additive mixed model analyses, we evaluated 10 covariates, including spatial and temporal variation, that could affect growth rates. Growth rates throughout the region responded similarly over space and time. The lack of a spatial effect or spatio‐temporal interaction and the very strong temporal effect reveal that growth rates in West Atlantic hawksbills are likely driven by region‐wide forces. Between 1997 and 2013, mean growth rates declined significantly and steadily by 18%. Regional climate indices have significant relationships with annual growth rates with 0‐ or 1‐yr lags: positive with the Multivariate El Niño Southern Oscillation Index (correlation = 0.99) and negative with Caribbean sea surface temperature (correlation = −0.85). Declines in growth rates between 1997 and 2013 throughout the West Atlantic most likely resulted from warming waters through indirect negative effects on foraging resources of hawksbills. These climatic influences are complex. With increasing temperatures, trajectories of decline of coral cover and availability in reef habitats of major prey species of hawksbills are not parallel. Knowledge of how choice of foraging habitats, prey selection, and prey abundance are affected by warming water temperatures is needed to understand how climate change will affect productivity of consumers that live in association with coral reefs.

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“…), hawksbills in the Gulf of Mexico (del Monte‐Luna et al. ), and Atlantic loggerheads (Arendt et al. ).…”

Section: Discussionmentioning

confidence: 99%

Somatic growth dynamics of West Atlantic hawksbill sea turtles: a spatio‐temporal perspective

et al. 2016

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“…Baron et al 2013). For example, annual breeding probability is correlated with sea surface temperatures (Chaloupka 2001, Saba et al 2007, Mazaris et al 2009, del Monte-Luna et al 2012, which may correlate with favourable conditions. Whilst the shift in energy allocation starts a few years prior to sexual maturity, it persists for an unknown number of years after.…”

Section: Energy Allocation Shiftmentioning

confidence: 99%

Growth rates of adult sea turtles

Omeyer¹,

Godley²,

Broderick³

2017

Endang. Species. Res.

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Indeterminate growth, i.e. growth that persists throughout life, is common in longlived reptiles. Because fecundity and body size tend to be correlated in such species, individuals face a life-history trade-off at sexual maturity. Saturation tagging and intensive monitoring at nesting grounds can potentially provide opportunities to accumulate data on individual measurements and reproductive output. Until recently, however, shortcomings from these methods have prevented the testing of theories on resource allocation between growth and reproduction at sexual maturity in wild populations of sea turtles. Here, we review the state of knowledge of growth rates in adult sea turtles and potential life-history trade-offs. We found that post-maturity growth rates varied among ocean basins. They appeared highest in the Atlantic Ocean for both green turtles Chelonia mydas and hawksbill turtles Eretmochelys imbricata, and highest in the Mediterranean Sea for loggerhead turtles Caretta caretta. For other species, there are too few studies at present to allow for intraspecific comparison. Additionally, we found no significant difference in mean female compound annual growth rates among species and ocean basins. Although captive studies have provided great insight into changes in energy allocation at sexual maturity and life-history trade-offs, this review highlights the lack of data on wild animals regarding changes in post-maturity growth rates and reproductive output over time. Such data are desirable to further our understanding of energy allocation, growth and ageing in wild sea turtles. They are further required to assess the status of species and to understand population dynamics for both conservation and management.

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“…, del Monte‐Luna et al. ). If juvenile age classes were disturbed and trend estimates occur during the recovery phase, then trend durations exceeding 20 yr are necessary to improve accuracy.…”

Section: Discussionmentioning

confidence: 99%

“…MoSE can be used as a tool to provide prognostic advice for how to improve monitoring to increase accuracy for estimating population status indicators, namely population trend. For example, our model suggests that at least 10 yr of monitoring data is necessary to accurately estimate population trend, regardless of biological impact, underlying process errors, detection level, and population phase; but, this would be influenced by the duration of cycles in breeding probability (Solow et al 2002, Saba et al 2007, del Monte-Luna et al 2012). If juvenile age classes were disturbed and trend estimates occur during the recovery phase, then trend durations exceeding 20 yr are necessary to improve accuracy.…”

Section: Discussionmentioning

confidence: 99%

Fathoming sea turtles: monitoring strategy evaluation to improve conservation status assessments

Piacenza

Richards

Heppell

2019

Ecological Applications

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Population monitoring must be accurate and reliable to correctly classify population status. For sea turtles, nesting beach surveys are often the only population‐level surveys that are accessible. However, process and observation errors, compounded by delayed maturity, obscure the relationship between trends on the nesting beach and the population. We present a simulation‐based tool, monitoring strategy evaluation (MoSE), to test the relationships between monitoring data and assessment accuracy, using green sea turtles, Chelonia mydas, as a case study. To explore this first application of MoSE, we apply different treatments of population impacts to virtual true populations, and sample the nests or nesters, with observation error, to test if the observation data can be used to diagnose population status accurately. Based on the observed data, we examine population trend and compare it to the known values from the operating model. We ran a series of scenarios including harvest impacts, cyclical breeding probability, and sampling biases, to see how these factors impact accuracy in estimating population trend. We explored the necessary duration of monitoring for accurate trend estimation and the probability of a false trend diagnosis. Our results suggest that disturbance type and severity can have important and persistent effects on the accuracy of population assessments drawn from monitoring nesting beaches. The underlying population phase, age classes disturbed, and impact severity influenced the accuracy of estimating population trend. At least 10 yr of monitoring data is necessary to estimate population trend accurately, and >20 yr if juvenile age classes were disturbed and the population is recovering. In general, there is a greater probability of making a false positive trend diagnosis than a false negative, but this depends on impact type and severity, population phase, and sampling duration. Improving detection rates to 90% does little to lower probability of a false trend diagnosis with shorter monitoring spans. Altogether, monitoring strategies for specific populations may be tailored based on the impact history, population phase, and environmental drivers. The MoSE is an important framework for analysis through simulation that can comprehensively test population assessments for accuracy and inform policy recommendations regarding the best monitoring strategies.

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Effect of North Atlantic climate variability on hawksbill turtles in the Southern Gulf of Mexico

Cited by 24 publications

References 43 publications

Somatic growth dynamics of West Atlantic hawksbill sea turtles: a spatio‐temporal perspective

Somatic growth dynamics of West Atlantic hawksbill sea turtles: a spatio‐temporal perspective

Growth rates of adult sea turtles

Fathoming sea turtles: monitoring strategy evaluation to improve conservation status assessments

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