Global Conservation Priorities for Marine Turtles

Assessing conservation status and pursuing applicable management priorities for marine megafauna across multiple scales pose significant challenges. Because marine turtles exemplify these challenges, the IUCN Marine Turtle Specialist Group (MTSG) developed the ‘conservation priorities portfolio’ (CPP) framework in 2011 to evaluate population risk and threats for regional management units (RMUs). Here, the MTSG has updated the 2011 CPP framework through an inclusive assessment process. Expert elicitation results involving 145 individuals from 50 countries suggests that marine turtle conservation status appears to be improving, but significant challenges remain. Since the previous assessment, long-term abundance trends increased on average, and threat impact scores improved for nearly twice as many RMUs (53%) as worsened (28%) (≥10% threshold for changes in numeric scores). While expert-assessed threat impacts have generally decreased, fisheries bycatch remains the highest scored threat across regions and species. Risk-threat staus improved for most (54%) RMUs. Over 40% of RMUs were scored as low risk-low threats, of which 8 were green turtles Chelonia mydas RMUs. Less than 20% of RMUs were scored as high risk-high threats, of which 4 were leatherback turtles Dermochelys coriacea. Most high risk-high threats RMUs were in the Pacific Ocean, while most low risk-low threats RMUs were in the Atlantic Ocean. Eleven RMUs were evaluated as having critical data needs. Our results—also provided through an interactive data dashboard—underscore the importance of context-specific planning to effectively target limited conservation resources. Future assessments should further prioritize inclusion of under-represented topics, researchers, and regions to better address multi-faceted conservation challenges.

Socio-economic drivers affecting marine turtle conservation status: causes and consequences

Conservation and Enforcement Capacity index (CECi): Integrating human development, economy, and marine turtle status

Long-term trends in abundance of green sea turtles (Chelonia mydas) assessed by non-lethal capture rates in a coastal fishery

Stable isotope analyses have become popular in sea turtle literature over the past decade, with an increasing year-to-year trend in published studies reporting insights into food web structure, diet, trophic interactions, ontogenetic shifts, geographic distributions, and more. Understanding the geographic distribution of migrating taxa within their sub-populations could enhance conservation and management, especially for threatened populations. For sea turtles, stable isotope analyses can potentially be used to quickly assess foraging distributions across large proportions of a nesting population, examining high numbers of turtles at low cost and/or effort relative to satellite telemetry and mark-recapture studies. We systematically assessed the literature, aiming to identify the current state of research into sea turtle isotope ecology, including key knowledge gaps and the level of geographic assessment within regional management units (RMUs). Sea turtle RMUs listed as Least Concern by the IUCN (6.5 studies per RMU) have been studied at a rate 13 times higher than those considered Threatened (0.5 studies per RMU). Loggerhead turtles Caretta caretta and green turtles Chelonia mydas are the most studied species. Comparatively, flatback Natator depressus and Kemp’s ridley Lepidochelys kempii turtles return a paucity of analyses. This is the first review of sea turtle isotope studies and helps to refocus future isotope research to prioritise conservation outcomes throughout the world. The mismatch between effort and conservation priority may be a testimony to the effectiveness of research and management in these areas but suggests a need to now realign the focus of sea turtle isotope ecological studies towards more threatened RMUs.

Fisheries bycatch is considered the most serious threat globally to long‐lived marine megafauna (e.g., mammals, birds, turtles, elasmobranchs). However, bycatch assessments to date have not evaluated population‐level bycatch impacts across fishing gears. Here, we provide the first global, multi‐gear evaluation of population‐level fisheries bycatch impacts for marine turtles. To compare bycatch impacts of multiple gears within and among marine turtle populations (or regional management units, RMUs), we compiled more than 1,800 records from over 230 sources of reported marine turtle bycatch in longline, net, and trawl fisheries worldwide that were published between 1990–2011. The highest bycatch rates and levels of observed effort for each gear category occurred in the East Pacific, Northwest and Southwest Atlantic, and Mediterranean regions, which were also the regions of highest data availability. Overall, available data were dominated by longline records (nearly 60% of all records), and were non‐uniformly distributed, with significant data gaps around Africa, in the Indian Ocean, and Southeast Asia. We found that bycatch impact scores—which integrate information on bycatch rates, fishing effort, mortality rates, and body sizes (i.e., proxies for reproductive values) of turtles taken as bycatch—as well as mortality rates in particular, were significantly lower in longline fishing gear than in net and trawl fishing gears. Based on bycatch impact scores and RMU‐specific population metrics, we identified the RMUs most and least threatened by bycatch globally, and found wide variation among species, regions, and gears within these classifications. The lack of regional or species‐specific patterns in bycatch impacts across fishing gears suggests that gear types and RMUs in which bycatch has the highest impact depend on spatially‐explicit overlaps of fisheries (e.g., gear characteristics, fishing practices, target species), marine turtle populations (e.g., conservation status, aggregation areas), and underlying habitat features (e.g., oceanographic conditions). Our study provides a blueprint both for prioritizing limited conservation resources toward managing fishing gears and practices with the highest population impacts on sea turtles and for enhancing data collection and reporting efforts.

AimHurricanes bring wind and rainfall that can have dramatic effects on coastal ecosystems, which provide important nesting locations for some migratory species. We investigated the frequency with which hurricanes impact spatially and biologically distinct sea turtle nesting populations to understand whether the reproductive biology of sea turtles can buffer population‐level impacts of these disturbances.LocationNorth‐western Atlantic and north‐eastern Pacific Oceans.MethodsHistorical hurricane paths from 1970 to 2007 were combined into a spatial layer of seasonal storm frequency, which we used to quantify the frequency of impacts on sea turtle nesting sites. This was done by comparing spatio‐temporal patterns of hurricane frequency among nesting sites used by different species and spatially/biologically distinct populations (‘regional management units’).ResultsHurricanes affected 97% of sea turtle nesting beaches (n = 2444) over four decades, and the seasonal incidence of these storms overlapped substantially with sea turtle nesting and egg incubation periods. The spatial distribution of storms, in relation to the distribution of species and regional management units, determined relative exposure to large storm events. Green (Chelonia mydas), hawksbill (Eretmochelys imbricata) and leatherback (Dermochelys coriacea) turtle nesting beaches experienced relatively frequent storms; loggerhead (Caretta caretta) and Kemp's ridley (Lepidochelys kempii) turtle nesting beaches experienced relatively fewer storms; and olive ridley turtle (Lepidochelys olivacea) nesting sites were least affected.Main conclusionsExtreme weather events are common features of coastal environments and may impact sea turtles by altering nesting habitat quality (through sand erosion and accretion) and lowering within‐season reproductive success by drowning incubating embryos or eroding nests. The unique reproductive attributes of sea turtles (i.e. individual females reproduce at 2–5‐year intervals, and when reproducing lay 2–7 clutches of c. 100 large eggs at c. 2‐week intervals) may be uniquely suited to exploiting highly disturbed nesting habitats. The impacts of hurricanes on sea turtle populations may be limited because even in severe storm seasons only a proportion of adult females are reproducing, and only those eggs incubating at the time of storm impact will be directly affected. Understanding whether the frequency of large storms influences long‐term population dynamics will aid in the development of effective local and regional management plans for sea turtle recovery efforts.

BackgroundResolving threats to widely distributed marine megafauna requires definition of the geographic distributions of both the threats as well as the population unit(s) of interest. In turn, because individual threats can operate on varying spatial scales, their impacts can affect different segments of a population of the same species. Therefore, integration of multiple tools and techniques — including site-based monitoring, genetic analyses, mark-recapture studies and telemetry — can facilitate robust definitions of population segments at multiple biological and spatial scales to address different management and research challenges.Methodology/Principal FindingsTo address these issues for marine turtles, we collated all available studies on marine turtle biogeography, including nesting sites, population abundances and trends, population genetics, and satellite telemetry. We georeferenced this information to generate separate layers for nesting sites, genetic stocks, and core distributions of population segments of all marine turtle species. We then spatially integrated this information from fine- to coarse-spatial scales to develop nested envelope models, or Regional Management Units (RMUs), for marine turtles globally.Conclusions/SignificanceThe RMU framework is a solution to the challenge of how to organize marine turtles into units of protection above the level of nesting populations, but below the level of species, within regional entities that might be on independent evolutionary trajectories. Among many potential applications, RMUs provide a framework for identifying data gaps, assessing high diversity areas for multiple species and genetic stocks, and evaluating conservation status of marine turtles. Furthermore, RMUs allow for identification of geographic barriers to gene flow, and can provide valuable guidance to marine spatial planning initiatives that integrate spatial distributions of protected species and human activities. In addition, the RMU framework — including maps and supporting metadata — will be an iterative, user-driven tool made publicly available in an online application for comments, improvements, download and analysis.

Sea turtles disease risk analysis and discovery of the first Australian green turtle (Chelonia mydas) papillomavirus

Previous studies show that conservation actions have prevented extinctions, recovered populations, and reduced declining trends in global biodiversity. However, all studies to date have substantially underestimated the difference conservation action makes because they failed to account fully for what would have happened in the absence thereof. We undertook a scenario-based thought experiment to better quantify the effect conservation actions have had on the extinction risk of the world's 235 recognized ungulate species. We did so by comparing species' observed conservation status in 2008 with their estimated status under counterfactual scenarios in which conservation efforts ceased in 1996. We estimated that without conservation at least 148 species would have deteriorated by one International Union for Conservation of Nature (IUCN) Red List category, including 6 species that now would be listed as extinct or extinct in the wild. The overall decline in the conservation status of ungulates would have been nearly 8 times worse than observed. This trend would have been greater still if not for conservation on private lands. While some species have benefited from highly targeted interventions, such as reintroduction, most benefited collaterally from conservation such as habitat protection. We found that the difference conservation action makes to the conservation status of the world's ungulate species is likely to be higher than previously estimated. Increased, and sustained, investment could help achieve further improvements.

We document a tendency for published estimates of population size in sea turtles to be increasing rather than decreasing across the globe. To examine the population status of the seven species of sea turtle globally, we obtained 299 time series of annual nesting abundance with a total of 4417 annual estimates. The time series ranged in length from 6 to 47 years (mean, 16.2 years). When levels of abundance were summed within regional management units (RMUs) for each species, there were upward trends in 12 RMUs versus downward trends in 5 RMUs. This prevalence of more upward than downward trends was also evident in the individual time series, where we found 95 significant increases in abundance and 35 significant decreases. Adding to this encouraging news for sea turtle conservation, we show that even small sea turtle populations have the capacity to recover, that is, Allee effects appear unimportant. Positive trends in abundance are likely linked to the effective protection of eggs and nesting females, as well as reduced bycatch. However, conservation concerns remain, such as the decline in leatherback turtles in the Eastern and Western Pacific. Furthermore, we also show that, often, time series are too short to identify trends in abundance. Our findings highlight the importance of continued conservation and monitoring efforts that underpin this global conservation success story.

Towards reducing the data gap in the conservation efforts for sea turtles in Bangladesh

Global trends in sea turtle research and conservation: Using symposium abstracts to assess past biases and future opportunities

Assessing the linkage between breeding and non-breeding areas has important implications for understanding the fundamental biology of and conserving animal species. This is a challenging task for marine species, and in sea turtles a combination of stable isotope analysis (SIA) and satellite telemetry has been increasingly used. The Northwest Atlantic (NWA) loggerhead (Caretta caretta) Regional Management Unit, one of the largest sea turtle populations in the world, provides an excellent opportunity to investigate key biological patterns as well as methodological aspects related to the use of stable isotopes to infer spatial distribution of turtles in foraging areas. We provide the first comprehensive assessment of the annual distribution of NWA adult female loggerheads among foraging areas and investigate the efficacy of various analytical approaches as well as the effect of sample size in these types of studies. A total of 5168 individual females were sampled from seven Management Units (MUs) between 2013-2018. We provide the first estimate of the proportion of females originating from each MU that uses each foraging area and show how this proportion varies over time. We also estimate the relative importance (in terms of number of turtles) of each foraging area to the overall loggerhead breeding aggregation nesting in Florida and in the NWA for each year of the study. The foraging area used by reproductively active females differs considerably across MUs. One of these, the Subtropical NWA, is by far the most important foraging area in terms of both number of individuals and genetic diversity, and therefore this region may be considered as a conservation priority. Through simulations, we show that limited sizes of sample groups (unknowns; training; priors) may result in false geographic differentiation and consequently mislead interpretations. We provide thresholds and methodological recommendations for future studies. This study establishes a fundamental baseline for monitoring the annual contribution of foraging area to a terrestrial-based breeding aggregation of a marine animal in a cost-effective way. This type of monitoring allows for early detection of changes in foraging distributions—a possible effect of climate change on marine ecosystems or of area-specific anthropogenic threats.

A global sea turtle climate vulnerability assessment