Indicators of the impact of climate change on migratory species

The Bonn Convention on the Conservation of Migratory Species of Wild Animals adopted a Resolution in 2005 recognising the impacts of climate change on migratory species. It called on Contracting Parties to undertake more research to improve our understanding of these impacts and to implement adaptation measures to reduce foreseeable adverse effects. Given the large diversity of taxa and species affected by climate change, it is impossible to monitor all species and effects thereof. However, it is likely that many of the key ecological and physical processes through which climate change may impact wildlife could be monitored using a suite of indicators, each comprising parameters of species/populations or groups of species as proxies for wider assemblages, habitats and ecosystems. Herein, we identify a suite of 17 indicators whose attributes could reveal negative impacts of climate change on the global status of migratory species: 4 for birds, 4 for marine mammals, 2 for sea turtles, 1 for fish, 3 for land mammals and 3 for bats. A few of these indicators would be relatively straightforward to develop, but most would require additional data collation, and in many cases methodological development. Choosing and developing indicators of the impacts of climate change on migratory species is a challenge, particularly with endangered species, which are subject to many other pressures. To identify and implement conservation measures for these species, indicators must account for the full ensemble of pressures, and link to a system of alerts and triggers for action.

Genetic composition of the Ascension Island green turtle rookery based on mitochondrial DNA : implications for sampling and diversity

In species of conservation concern it is often difficult to be certain that population diversity and structure have been adequately characterised by genetic sampling. Since practical and financial constraints tend to be associated with increasing sample sizes in many conservation genetic studies, it is important to consider the potential for sampling error and bias due to inadequate samples or spatio-temporal structure within populations. We analysed sequence data from the mitochondrial DNA control region in a large sample (n = 245) of green sea turtles Chelonia mydas collected at the globally important rookery of Ascension Island, South Atlantic. We examined genetic diversity and structure among 10 sampling sites, 4 beach clusters and 4 nesting seasons, and evaluated the genetic composition of Ascension against other Atlantic nesting populations, including the well-studied rookery at Tortuguero (Costa Rica). Finally, we used rarefaction and GENESAMP analyses to assess the ability of different sample sizes to provide acceptable genetic representations of a population, using Ascension and Tortuguero as models. On Ascension, we found 13 haplotypes, of which only 3 had been previously observed in the rookery, and 5 previously undescribed. We detected no differentiation among beach clusters or sampling seasons, and only weak differentiation among the 3 primary nesting sites. The increased sample size for Ascension provided higher resolution and statistical power in describing genetic structure among all other known Atlantic rookeries. Our extrapolations showed that a maximum of 18 and 6 haplotypes are expected to occur in Ascension and Tortuguero, respectively, and that current sample sizes are sufficient to describe most of the variation. We recommend using rarefaction and GENESAMP analyses on a rookery-by-rookery basis to evaluate whether a sample set adequately describes mitochondrial DNA diversity, thus strengthening subsequent phylogeographic and mixed stock analyses, and management recommendations for conservation.

Satellite tracking reveals unusual diving characteristics for a marine reptile, the olive ridley turtle : Lepidochelys olivacea

The movements, diving behaviour and thermal environment occupied by 4 adult female olive ridley turtles Lepidochelys olivacea in northern Australia were determined through satellite telemetry. Patterns of behaviour recorded were rather unusual compared to other sea turtles in that dives were mainly deep, largely benthic and exceptionally long (>2 h) in some cases, characteristics typical of over-wintering turtles in colder environments. One individual occupied shallow coastal foraging zones, while the others foraged far from land (probably on the seabed) in relatively deep water (>100 m). Individuals performed long dives (frequently >100 min), but from the short post-dive intervals we suggest that these dives were mainly aerobic. Maximum dive depth recorded was 200 ± 20 m (mean maximum depths ranged from 20.1 to 46.7 m across individuals; n = 17328 dives in total; depths ≥3 m were considered ‘dives’) and the maximum duration was 200 ± 20 min (mean durations ranged from 24.5 to 48.0 min across individuals). Temperature profiles indicate that turtles experienced temperatures ranging from 23 to 29°C at the surface, with the lowest temperature recorded (18.7°C) at a depth of 98 m. Only 6.9% of the dives were in water <20°C. From time-allocation at depth (TAD) scores, we demonstrated that many dives reaching the known or inferred sea bottom were U-shaped, but there was no apparent diel signal in dive depth. This suggests that many benthic dives were not associated exclusively with resting behaviour and likely had a foraging component as well. The ability to perform long benthic dives allows this species to exploit deeper benthic environments in addition to the shallow coastal areas more generally occupied by adult hard-shelled sea turtles (e.g. green and hawksbill turtles). Deep benthic dives also occur in certain marine mammals (e.g. narwhals) and sea birds (e.g. rockhopper penguins) and therefore seem to be a general foraging strategy exploited by animals that can perform long dives.

Protected species use of a coastal marine migratory corridor connecting marine protected areas

The establishment of protected corridors linking the breeding and foraging grounds of many migratory species remains deficient, particularly in the world's oceans. For example, Australia has recently established a network of Commonwealth Marine Reserves, supplementing existing State reserves, to protect a wide range of resident and migratory marine species; however, the routes used by mobile species to access these sites are often unknown. The flatback marine turtle (Natator depressus) is endemic to the continental shelf of Australia, yet information is not available about how this species uses the marine area. We used a geospatial approach to delineate a coastal corridor from 73 adult female flatback postnesting migratory tracks from four rookeries along the north-west coast of Australia. A core corridor of 1,150 km length and 30,800 km2 area was defined, of which 52 % fell within 11 reserves, leaving 48 % (of equivalent size to several Commonwealth Reserves) of the corridor outside of the reserve network. Despite limited data being available for other marine wildlife in this region, humpback whale migratory tracks overlapped with 96 % of the core corridor, while the tracks of three other species overlapped by 5-10 % (blue whales, olive ridley turtles, whale sharks). The overlap in the distribution ranges of at least 20 other marine vertebrates (dugong, cetaceans, marine turtles, sea snakes, crocodiles, sharks) with the corridor also imply potential use. In conclusion, this study provides valuable information towards proposing new locations requiring protection, as well as identifying high-priority network linkages between existing marine protected areas. © 2014 Springer-Verlag Berlin Heidelberg.

Ontogeny of long distance migration

The movements of some long-distance migrants are driven by innate compass headings that they follow on their first migrations (e.g., some birds and insects), while the movements of other first-time migrants are learned by following more experienced conspecifics (e.g., baleen whales). However, the overall roles of innate, learned, and social behaviors in driving migration goals in many taxa are poorly understood. To look for evidence of whether migration routes are innate or learned for sea turtles, here for 42 sites around the world we compare the migration routes of >400 satellite-tracked adults of multiple species of sea turtle with ∼45 000 Lagrangian hatchling turtle drift scenarios. In so doing, we show that the migration routes of adult turtles are strongly related to hatchling drift patterns, implying that adult migration goals are learned through their past experiences dispersing with ocean currents. The diverse migration destinations of adults consistently reflected the diversity in sites they would have encountered as drifting hatchlings. Our findings reveal how a simple mechanism, juvenile passive drift, can explain the ontogeny of some of the longest migrations in the animal kingdom and ensure that adults find suitable foraging sites.

The accuracy of Fastloc-GPS locations and implications for animal tracking

Over recent years, a major breakthrough in marine animal tracking has occurred with the advent of Fastloc-GPS that provides highly accurate location data even for animals that only surface briefly such as sea turtles, marine mammals and penguins. We assessed the accuracy of Fastloc-GPS locations using fixed trials of tags in which >45 000 locations were obtained. Procedures for determining the speed of travel and heading were developed by simulating tracks and then adding Fastloc-GPS location errors. The levels of detail achievable for speed and heading estimates were illustrated by using empirical Fastloc-GPS data for a green turtle (Chelonia mydas, Linnaeus, 1758) travelling over 3000 km across the Indian Ocean. The accuracy of Fastloc-GPS locations varied as a function of the number of GPS satellites used in the location calculation. For example, when Fastloc-GPS locations were calculated using 4 GPS satellites, 50% of locations were within 36 m and 95% within 724 m of the true position. These values improved to 18 and 70 m, respectively, when 6 satellites were used. Simulations indicated that for animals travelling around 2·5 km h-1 (e.g. turtles, penguins and seals) and depending on the number of satellites used in the location calculation, robust speed and heading estimates would usually be obtained for locations only 1-6 h apart. Fastloc-GPS accuracy is several orders of magnitude better that conventional Argos tracking or light-based geolocation and consequently will allow new insights into small-scale movement patterns of marine animals.

Prioritizing climate change adaptation options for iconic marine species

© 2015, Springer Science+Business Media Dordrecht. Adaptation options in response to climate impact scenarios for marine mammals and seabirds were developed based on the IPCC vulnerability framework. Under this framework, vulnerability to the physical effects of climate change can be reduced by adaptation options that reduce exposure of individuals, reduce the sensitivity of individuals, and increase the adaptive capacity of individual/species to cope with climate change. We evaluated options in each vulnerability category with three screening tools collectively forming an approach we term sequential adaptation prioritization for species. These tools were designed to evaluate (i) technical aspects (cost-benefit-risk, CBR), (ii) institutional barriers, and (iii) potential social acceptability. The CBR tool identified which adaptation options were high cost and low benefit, might be discarded, and which were high benefit and low cost, might be rapidly implemented (depending on risk). Low cost and low benefit options might not be pursued, while those that are high cost, but high benefit deserve further attention. Even with technical merit, adaptation options can fail because of institutional problems with implementation. The second evaluation tool, based on the conceptual framework on barriers to effective climate adaptation, identifies where barriers may exist, and leads to strategies for overcoming them. Finally, adaptation options may not be acceptable to society at large, or resisted by vocal opponents or groups. The social acceptability tool identifies potentially contested options, which may be useful to managers charged with implementing adaptation options. Social acceptability, as scored by experts, differed from acceptability scored by the public, indicating the need to involve the public in assessing this aspect. Scores from each tool for each scenario can be combined to rank the suite of adaptation options. This approach provides useful tools to assist conservation managers in selecting from a wide range of adaptation strategies; the methodology is also applicable to other conservation sectors.

Predicting climate warming effects on green turtle hatchling viability and dispersal performance

Ectotherms are taxa considered highly sensitive to rapid climate warming. This is because body temperature profoundly governs their performance, fitness and life history. Yet, while several modelling approaches currently predict thermal effects on some aspects of life history and demography, they do not consider how temperature simultaneously affects developmental success and offspring phenotypic performance, two additional key attributes that are needed to comprehensively understand species responses to climate warming. Here, we developed a stepwise, individual-level modelling approach linking biophysical and developmental models with empirically derived performance functions to predict the effects of temperature-induced changes to offspring viability, phenotype and performance, using green sea turtle hatchlings as an ectotherm model. Climate warming is expected to particularly threaten sea turtles, as their life-history traits may preclude them from rapid adaptation. Under conservative and extreme warming, our model predicted large effects on performance attributes key to dispersal, as well as a reduction in offspring viability. Forecast sand temperatures produced smaller, weaker hatchlings, which were up to 40% slower than at present, albeit with increased energy stores. Conversely, increases in sea surface temperatures aided swimming performance. Our exploratory study points to the need for further development of integrative individual-based modelling frameworks to better understand the complex outcomes of climate change for ectotherm species. Such advances could better serve ecologists to highlight the most vulnerable species and populations, encouraging prioritization of conservation effort to the most threatened systems.

Using climatic suitability thresholds to identify past, present and future population viability

Often climatic niche models predict that any change in climatic conditions will impact species abundance or distribution. However, the accuracy of models that just incorporate climatic information to predict future species habitat use is widely debated. Alternatively, environmental conditions may simply need to be above some minimum threshold of climatic suitability, at which point, other factors drive population size. Using the example of nesting sites of loggerhead sea turtles (Caretta caretta) in the Mediterranean (n = 105), we developed climatic niche models to examine whether a climatic suitability threshold could be identified as a climatic indicator in order for large populations of a widespread species to exist. We then assessed the climatic suitability of sites above and below this threshold in the past (∼1900) and future (∼2100). Most large sites that are currently above the climatic threshold were above the threshold in the past and future, particularly when future nesting seasonality shifted to start 1–2 months earlier. Our analyses highlight the importance of future phenological shifts for maintaining suitability. Our results provide a positive outlook for sea turtle conservation, suggesting that climatic conditions may remain suitable in the future at sites that currently support large nesting populations. Our study also provides an alternative way of interpreting the outputs of climatic niche models, by generating a threshold as an index of a minimum climatic suitability required to sustain large populations. This type of approach offers the possibility to benefit from information provided by climate-driven models, while reducing their inherent uncertainties.

Movements of migrating green turtles in relation to AVHRR derived sea surface temperature

Previous studies have shown that for some populations of marine turtle, individuals move along narrow migration corridors in the open ocean. It has been suggested that these migration corridors may correspond with nearsurface oceanographic features that can be detected by remote sensing. This idea is examined by superimposing the tracks of green turtles (Chelonia mydas) migrating from Ascension Island to Brazil, on sea surface temperature (SST) data derived from Advanced Very High Resolution Radiometer (AVHRR) images. The turtles did not follow specific isotherms during migration nor make turns en-route where specific thermal cues were encountered. These results suggest that for this population, SST plays a minimal role in influencing the exact route that individuals follow.

Trophic status drives interannual variability in nesting numbers of marine turtles

Large annual fluctuations are seen in breeding numbers in many populations of non–annual breeders. We examined the interannual variation in nesting numbers of populations of green (Chelonia mydas) (n = 16 populations), loggerhead (Caretta caretta) (n =10 populations), leatherback (Dermochelys coriacea) (n = 9 populations) and hawksbill turtles (Eretmochelys imbricata) (n = 10 populations). Interannual variation was greatest in the green turtle. When comparing green and loggerhead turtles nesting in Cyprus we found that green turtles were more likely to change the interval between laying seasons and showed greater variation in the number of clutches laid in a season. We suggest that these differences are driven by the varying trophic statuses of the different species. Green turtles are herbivorous, feeding on sea grasses and macro–algae, and this primary production will be more tightly coupled with prevailing environmental conditions than the carnivorous diet of the loggerhead turtle.

Movement patterns of green turtles in Brazilian coastal waters described by satellite tracking and flipper tagging

The movements of 8 green turtles Chelonia mydas in Brazilian coastal waters were tracked using transmitters linked to the Argos system for periods of between 1 and 197 d. These were the first tracking data gathered on juveniles of this species in this important foraging ground. Information was integrated with that collected over a decade using traditional flipper-tagging methods at the same site. Both satellite telemetry and flipper tagging suggested that turtles undertook 1 of 3 general patterns of behaviour: pronounced long range movements (>100 km), moderate range movements (<100 km) or extended residence very close to the capture/release site. There seemed to be a general tendency for the turtles recaptured/tracked further afield to have been among the larger turtles captured. Satellite tracking of 5 turtles which moved from the release site showed that they moved through coastal waters; a factor which is likely to predispose migrating turtles to incidental capture as a result of the prevailing fishing methods in the region. The movements of the 3 turtles who travelled less than 100 km from the release site challenge previous ideas relating to home range in green turtles feeding in sea grass pastures. We hypothesise that there may be a fundamental difference in the pattern of habitat utilisation by larger green turtles depending on whether they are feeding on seagrass or macroalgae. Extended tracking of 2 small turtles which stayed near the release point showed that small juvenile turtles, whilst in residence in a particular feeding ground, can also exhibit high levels of site-fidelity with home ranges of the order of several square kilometers.

Long-term satellite telemetry of the movements and habitat utilisation by green turtles in the Mediterranean

There is a relative paucity of data regarding the at-sea distribution and behaviour of marine turtles. This is especially true for the critically endangered green turtle Chelonia mydas population in the Mediterranean. Six adult female green turtles were equipped with satellite transmitters and tracked for periods of between 28 and 293 d following their final nesting of the season in northern Cyprus. Data elucidated hitherto unknown migratory pathways and highlighted the importance of North African coastal waters as feeding habitat for adults of this species. For three individuals, instruments transmitted detailed information on dive depth, dive duration and water temperature which afforded novel insights into behaviour during different stages of migration, feeding in the foraging grounds and most remarkably, during a period of midwinter diapause when water temperatures were generally below 25°C. Turtles showed fidelity to specific shallow inshore feeding areas and moved offshore to deeper wintering sites.