Adaptation of sea turtles to climate warming: Will phenological responses be sufficient to counteract changes in reproductive output?

Sea turtles are vulnerable to climate change since their reproductive output is influenced by incubating temperatures, with warmer temperatures causing lower hatching success and increased feminization of embryos. Their ability to cope with projected increases in ambient temperatures will depend on their capacity to adapt to shifts in climatic regimes. Here, we assessed the extent to which phenological shifts could mitigate impacts from increases in ambient temperatures (from 1.5 to 3°C in air temperatures and from 1.4 to 2.3°C in sea surface temperatures by 2100 at our sites) on four species of sea turtles, under a "middle of the road" scenario (SSP2-4.5). Sand temperatures at sea turtle nesting sites are projected to increase from 0.58 to 4.17°C by 2100 and expected shifts in nesting of 26-43 days earlier will not be sufficient to maintain current incubation temperatures at 7 (29%) of our sites, hatching success rates at 10 (42%) of our sites, with current trends in hatchling sex ratio being able to be maintained at half of the sites. We also calculated the phenological shifts that would be required (both backward for an earlier shift in nesting and forward for a later shift) to keep up with present-day incubation temperatures, hatching success rates, and sex ratios. The required shifts backward in nesting for incubation temperatures ranged from -20 to -191 days, whereas the required shifts forward ranged from +54 to +180 days. However, for half of the sites, no matter the shift the median incubation temperature will always be warmer than the 75th percentile of current ranges. Given that phenological shifts will not be able to ameliorate predicted changes in temperature, hatching success and sex ratio at most sites, turtles may need to use other adaptive responses and/or there is the need to enhance sea turtle resilience to climate warming.

Climate change and marine turtles: recent advances and future directions

Climate change is a threat to marine turtles that is expected to affect all of their life stages. To guide future research, we conducted a review of the most recent literature on this topic, highlighting knowledge gains and research gaps since a similar previous review in 2009. Most research has been focussed on the terrestrial life history phase, where expected impacts will range from habitat loss and decreased reproductive success to feminization of populations, but changes in reproductive periodicity, shifts in latitudinal ranges, and changes in foraging success are all expected in the marine life history phase. Models have been proposed to improve estimates of primary sex ratios, while technological advances promise a better understanding of how climate can influence different life stages and habitats. We suggest a number of research priorities for an improved understanding of how climate change may impact marine turtles, including: improved estimates of primary sex ratios, assessments of the implications of female-biased sex ratios and reduced male production, assessments of the variability in upper thermal limits of clutches, models of beach sediment movement under sea level rise, and assessments of impacts on foraging grounds. Lastly, we suggest that it is not yet possible to recommend manipulating aspects of turtle nesting ecology, as the evidence base with which to understand the results of such interventions is not robust enough, but that strategies for mitigation of stressors should be helpful, providing they consider the synergistic effects of climate change and other anthropogenic-induced threats to marine turtles, and focus on increasing resilience.

Marine mammal conservation: over the horizon

Marine mammals can play important ecological roles in aquatic ecosystems, and their presence can be key to community structure and function. Consequently, marine mammals are often considered indicators of ecosystem health and flagship species. Yet, historical population declines caused by exploitation, and additional current threats, such as climate change, fisheries bycatch, pollution and maritime development, continue to impact many marine mammal species, and at least 25% are classified as threatened (Critically Endangered, Endangered or Vulnerable) on the IUCN Red List. Conversely, some species have experienced population increases/recoveries in recent decades, reflecting management interventions, and are heralded as conservation successes. To continue these successes and reverse the downward trajectories of at-risk species, it is necessary to evaluate the threats faced by marine mammals and the conservation mechanisms available to address them. Additionally, there is a need to identify evidence-based priorities of both research and conservation needs across a range of settings and taxa. To that effect we: (1) outline the key threats to marine mammals and their impacts, identify the associated knowledge gaps and recommend actions needed; (2) discuss the merits and downfalls of established and emerging conservation mechanisms; (3) outline the application of research and monitoring techniques; and (4) highlight particular taxa/populations that are in urgent need of focus.

Leave No Trace ordinances for coastal species management: influences on sea turtle nesting success

Coastal environments provide critical ecosystem services but experience a number of threats including marine debris and abandoned beach equipment. To address this threat, municipalities have begun enacting policy measures such as Leave No Trace ordinances. The impact of these ordinances on coastal species management has not yet been established. To evaluate the effectiveness of Leave No Trace ordinances in coastal species management, sea turtle crawl distribution, nesting success, and the frequency of obstructed crawls pre- and post-ordinance at a loggerhead sea turtleCaretta carettanesting beach in Alabama, USA, were compared between 3 treatment groups: (1) Gulf Shores and Orange Beach with new Leave No Trace ordinances enacted in 2016, (2) Fort Morgan with no ordinance, and (3) the Bon Secour National Wildlife Refuge (NWR) and Gulf State Park with Leave No Trace ordinances but no resident human population. The ordinance had no significant effect on crawl distribution or nesting success across the study site post-ordinance. However, the frequency of obstructed crawls in populated areas declined by 18.1% with the ordinance. The presence of a resident population was a more significant driver of obstructed crawls than the ordinance, as the Bon Secour NWR and Gulf State Park had fewer obstructed crawls than either populated treatment. With time and increased compliance, Leave No Trace ordinances may have the potential to improve coastal species management and increase coastal ecosystem services through reduced marine debris entanglement and ingestion, reduced physical damage to the environment, and increased tourism revenue and environmental education.

Drivers of change in the relative abundance of dugongs in New Caledonia

Context Sound understanding of temporal changes in the abundance of wildlife species is required for assessing their status and for effective conservation and management. In New Caledonia, a single baseline aerial survey of dugongs in 2003 estimated a population of 2026 (± 553 s.e.) individuals. A second, similar survey in 2008 produced a lower estimate of 606 (± 200 s.e.) individuals, leading to concerns that the dugong population was experiencing a decline. Aims This study used data collected from additional aerial surveys with the aim of updating information on the current size of the dugong population in New Caledonia and investigating the drivers of change in the estimates. Methods Four additional surveys were conducted: one in each of the cool (June) and warm (November) seasons of 2011 and 2012 around the main Island of New Caledonia. Dugong relative abundance and density were calculated and compared among survey years and survey regions. Drivers of change in the dugong population size were then investigated. Key results The abundance estimates obtained from our four surveys ranged from 649 (± 195 s.e.) to 1227 (± 296 s.e.) dugongs. These new results were not significantly different to the 2008 estimate but were significantly lower than the 2003 estimate. There was no significant variation in the proportion of calves throughout the entire time series of surveys. Conclusions The dugong population of New Caledonia was relatively stable between 2008 and 2012. We could not find sufficient evidence to show whether the discrepancy between 2003 and the remainder of the time series is due to a real decline in the population or the result of the confounding effects of variation in environmental conditions, animal behaviour and sampling biases. Implications The stability of the dugong population between 2008 and 2012 is a positive outcome for local conservation and management of dugongs. This study also highlights the advisability of replicating baseline surveys to enable robust interpretation of temporal variation in population size estimates, and in turn, to improve the management of wildlife species.

A decision framework for prioritizing multiple management actions for threatened marine megafauna

Resources for conserving biodiversity are invariably insufficient. This situation creates the need for transparent, systematic frameworks to help stakeholders prioritize the allocation of resources across multiple management actions. We developed a novel framework that explicitly prioritizes actions to minimize the impacts of several threats across a species' range. The framework uses a budget constraint and maximizes conservation outcomes from a set of management actions, accounting for the likelihood of the action being successfully applied and accepted by local and Indigenous communities. This approach is novel in that it integrates local knowledge and expert opinion with optimization software, thereby minimizing assumptions about likelihood of success of actions and their effectiveness. To test the framework, we used the eastern Gulf of Carpentaria and Torres Strait population of the flatback turtle, Natator depressus, as a case study. This approach allowed the framework to be applied in a data-poor context, a situation common in conservation planning. The framework identified the best set of actions to maximize the conservation of flatback eggs for scenarios with different budgets and management parameters and allowed comparisons between optimized and preselected scenarios. Optimized scenarios considered all implementable actions to explore how to best allocate resources with a specified budget and focus. Preselected scenarios were used to evaluate current allocations of funds and/or potential budget allocations suggested by different stakeholders. Scenarios that used a combination of aerial and ground strategies to reduce predation of eggs performed better than scenarios that focused only on reducing harvest of eggs. The performances of optimized and preselected scenarios were generally similar among scenarios that targeted similar threats. However, the cost-effectiveness of optimized scenarios was usually higher than that of preselected scenarios, demonstrating the value of conducting a systematic optimization approach. Our method provides a foundation for more effective conservation investments and guidance to prioritize actions within recovery plans while considering the sociopolitical and cultural context of decisions. The framework can be adapted easily to a wide range of species, geographical scales, and life stages.

Using expert opinion to prioritize impacts of climate change on sea turtles' nesting grounds

Managers and conservationists often need to prioritize which impacts from climate change to deal with from a long list of threats. However, data which allows comparison of the relative impact from climatic threats for decision-making is often unavailable. This is the case for the management of sea turtles in the face of climate change. The terrestrial life stages of sea turtles can be negatively impacted by various climatic processes, such as sea level rise, altered cyclonic activity, and increased sand temperatures. However, no study has systematically investigated the relative impact of each of these climatic processes, making it challenging for managers to prioritize their decisions and resources. To address this we offer a systematic method for eliciting expert knowledge to estimate the relative impact of climatic processes on sea turtles' terrestrial reproductive phase. For this we used as an example the world's largest population of green sea turtles and asked 22 scientists and managers to answer a paper based survey with a series of pair-wise comparison matrices that compared the anticipated impacts from each climatic process. Both scientists and managers agreed that increased sand temperature will likely cause the most threat to the reproductive output of the nGBR green turtle population followed by sea level rise, then altered cyclonic activity. The methodology used proved useful to determine the relative impact of the selected climatic processes on sea turtles' reproductive output and provided valuable information for decision-making. Thus, the methodological approach can potentially be applied to other species and ecosystems of management concern.