Growth rates of adult sea turtles

This is the final version of the article. Available from Inter Research via the DOI in this record.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

So excellent a fishe: A global overview of legal marine turtle fisheries

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordAim: We provide a global assessment of the current legal direct take of marine turtles, including the scale and species breakdown at country level, and investigate the significance of legal take to marine turtle populations within the wider context of global threats. Location: World-wide. Methods: We undertook a comprehensive review of the literature (>500 publications) and contacted over 150 in-country experts to collate data for countries that permit the legal take of marine turtles (as of 1 January 2013). Current annual take for each country and species was estimated, and estimates were generated for the 1980s, 1990s and 2000s. Results: Currently, 42 countries and territories permit direct take of turtles and collectively take in excess of 42,000turtles per year, the majority of which (>80%) are green turtles Chelonia mydas (Linnaeus 1758). Ten countries account for more than 90% of legal take each year with Papua New Guinea (36.1%) and Nicaragua (22.3%) accounting for more than half of the total global take. Since 1980, we estimate that more than 2million turtles have been legally taken in these countries, with current levels <60% of those in the 1980s. Main conclusions: Our results provide the most comprehensive global synthesis of the legal take of turtles in recent years and suggest that legal take has the potential to be a driver of marine turtle population dynamics, comparable to mortality estimates through recorded bycatch. However, it is likely that illegal take, along with bycatch, is significantly under-recorded and far greater than the total level of directed legal take. This hampers the ability to assess the relative impacts of these threats to marine turtles

Evidence of overfishing in small-scale fisheries in Madagascar

This is the final version. Available from the publisher via the DOI in this record.The datasets generated for this study are available on request to the corresponding authorSmall-scale fisheries are an important source of food, income and cultural identity to millions of people worldwide. Despite many fisher people observing declining catches, a lack of data remains a barrier to understanding the status of small-scale fisheries and their effective management in many places. Where data exist, complex analyses and stock assessments are often beyond the capacity and budgets of local managers. Working with small-scale fisheries in western Madagascar, we analyze landings data to provide a description of the fishery and evaluate the top twenty most commonly caught species for evidence of overfishing. Using length composition data, we use Froese’s three simple rules: Let them spawn, let them grow and let the mega-spawners live, as well as Cope and Punt’s decision tree to infer if spawning biomass is less than target reference points. We then use length-based parameters to calculate fishing mortality and compare with published estimates of natural mortality to assess overfishing (F > M). Over 17,000 fishing trips were registered over a 2-year period (2010–2012), landing just short of 2 million individual fish. Length data were recorded for a sample of over 120,000 individuals. Fish comprised 95% of landings, with the remainder comprised of other groups including crustaceans (mostly shrimp, crab, and lobster), cephalopods, and holothurians. We provide some of the first evidence that fish species caught in the small-scale fisheries of the Menabe region of Madagascar are experiencing overfishing. The most notable result is that for 13 of the 20 most common species, fishing mortality exceeds natural mortality. Many species had a large proportion of individuals (in some cases 100%) being caught before they reached maturity. Very few species were fished at their optimal size, and there were low numbers of large individuals (mega-spawners) in catches. Overfishing in western Madagascar presents a serious threat to the income, food security and well-being of some of the most vulnerable people in the world. The results of this paper support the call for improved management. However, management approaches should take account of overlapping fisheries and be inclusive to ensure the impacts of management do not undermine the rights of small-scale fishers. Further data are needed to better understand the trends and to improve management but should not hinder pragmatic action.European Union’s Regional Coastal Management Programme of the Indian Ocean Countrie

Determinate or indeterminate growth? Revisiting the growth strategy of sea turtles

This is the author's accepted manuscript.The final version is available from Inter Research via the DOI in this record.Traditionally, growth can be either determinate, ceasing during the natural lifespan of individuals, or indeterminate, persisting throughout life. Although indeterminate growth is a widely accepted strategy and believed to be ubiquitous among long-lived species, it may not be as common as previously thought. Sea turtles are believed to be indeterminate growers despite the paucity of long-term studies into post-maturity growth. In this study, we provide the first temporal analysis of post-maturity growth rates in wild living sea turtles, using 26 yr of data on individual measurements of females nesting in Cyprus. We used generalised additive/linear mixed models to incorporate multiple growth measurements for each female and model post-maturity growth over time. We found post-maturity growth to persist in green Chelonia mydas and loggerhead Caretta caretta turtles, with growth decreasing for approximately 14 yr before plateauing around zero for a further decade solely in green turtles. We also found growth to be independent of size at sexual maturity in both species. Additionally, although annual growth and compound annual growth rates were higher in green turtles than in loggerhead turtles, this difference was not statistically significant. While indeterminate growth is believed to be a key life-history trait of ectothermic vertebrates, here, we provide evidence of determinate growth in green and loggerhead turtles and suggest that determinate growth is a life-history trait shared by cheloniid species. Our results highlight the need for long-term studies to refine life-history models and further our understanding of ageing and longevity of wild sea turtles for conservation and management.Fieldwork was supported by the British Associate of Tortoise Keepers, British Chelonia Group, British High Commission in Cyprus, British Residents Society, Carnegie Trust for the Universities of Scotland, Darwin Initiative, Erwin Warth Foundation, Friends of SPOT, Glasgow Uni versity Court, Kuzey Kıbrıs Turkcell, MEDASSET UK, and Natural Environment Research Council

Phenotype-environment matching in sand fleas

This is the final version of the article. Available from the publisher via the DOI in this record.Camouflage is perhaps the most widespread anti-predator strategy in nature, found in numerous animal groups. A long-standing prediction is that individuals should have camouflage tuned to the visual backgrounds where they live. However, while several studies have demonstrated phenotype-environment associations, few have directly shown that this confers an improvement in camouflage, particularly with respect to predator vision. Here, we show that an intertidal crustacean, the sand flea (Hippa testudinaria), has coloration tuned to the different substrates on which it occurs when viewed by potential avian predators. Individual sand fleas from a small, oceanic island (Ascension) matched the colour and luminance of their own beaches more closely than neighbouring beaches to a model of avian vision. Based on past work, this phenotype-environment matching is likely to be driven through ontogenetic changes rather than genetic adaptation. Our work provides some of the first direct evidence that animal coloration is tuned to provide camouflage to prospective predators against a range of visual backgrounds, in a population of animals occurring over a small geographical range.M.S., A.E.L. and J.T.: Biotechnology and Biological Sciences Research Council (BB/G022887/1). Fieldwork was funded by the Darwin Initiative (Project no. 19-026)

The effect of thermal variance on the phenotype of marine turtle offspring.

PublishedJournal ArticleTemperature can have a profound effect on the phenotype of reptilian offspring, yet the bulk of current research considers the effects of constant incubation temperatures on offspring morphology, with few studies examining the natural thermal variance that occurs in the wild. Over two consecutive nesting seasons, we placed temperature data loggers in 57 naturally incubating clutches of loggerhead sea turtles Caretta caretta and found that greater diel thermal variance during incubation significantly reduced offspring mass, potentially reducing survival of hatchlings during their journey from the nest to offshore waters and beyond. With predicted scenarios of climate change, behavioral plasticity in nest site selection may be key for the survival of ectothermic species, particularly those with temperature-dependent sex determination.We thank all the volunteers of the Marine Turtle Conservation Project (northern Cyprus) who aided in data collection during the 2011/2012 nesting seasons. This work would not have been possible without the Society for the Protection of Turtles (SPOT) and the Department for Environmental Protection. For their continued support we thank the British Chelonia Group, the British High Commission, the British Resident’s Society, Ektam Kıbrıs, Erwin Warth Foundation, Friends of SPOT, Gemini Dataloggers (UK), and Kuzey Kıbrıs Turkcell

A global review of marine turtle entanglement in anthropogenic debris: a baseline for further action

Entanglement in anthropogenic debris poses a threat to marine wildlife. Although this is recognised as a cause of marine turtle mortality, there remain quantitative knowledge gaps on entanglement rates and population implications. We provide a global summary of this issue in this taxon using a mixed methods approach, including a literature review and expert opinions from conservation scientists and practitioners worldwide. The literature review yielded 23 reports of marine turtle entanglement in anthropogenic debris, which included records for 6 species, in all ocean basins. Our experts reported the occurrence of marine turtles found entangled across all species, life stages and ocean basins, with suggestions of particular vulnerability in pelagic juvenile life stages. Numbers of stranded turtles encountered by our 106 respondents were in the thousands per year, with 5.5% of turtles encountered entangled; 90.6% of these dead. Of our experts questioned, 84% consider that this issue could be causing population level effects in some areas. Lost or discarded fishing materials, known as ‘ghost gear’, contributed to the majority of reported entanglements with debris from land-based sources in the distinct minority. Surveyed experts rated entanglement a greater threat to marine turtles than oil pollution, climate change and direct exploitation but less of a threat than plastic ingestion and fisheries bycatch. The challenges, research needs and priority actions facing marine turtle entanglement are discussed as pathways to begin to resolve and further understand the issue. Collaboration among stakeholder groups such as strandings networks, the fisheries sector and the scientific community will facilitate the development of mitigating actions

Defining conservation units with enhanced molecular tools to reveal fine scale structuring among Mediterranean green turtle rookeries

This is the final version. Available on open access from Elsevier via the DOI in this recordData accessibility: the data associated with this article is avaiable in the Dryad Digital Repository: https://datadryad.org/stash/dataset/doi:10.5061/dryad.7db01Understanding the connectivity among populations is a key research priority for species of conservation concern. Genetic tools are widely used for this purpose, but the results can be limited by the resolution of the genetic markers in relation to the species and geographic scale. Here, we investigated natal philopatry in green turtles (Chelonia mydas) from four rookeries within close geographic proximity (~200 km) on the Mediterranean island of Cyprus. We genotyped hypervariable mtSTRs, a mtDNA control region sequence (CR) and 13 microsatellite loci to genetically characterise 479 green turtles using markers with different modes of inheritance. We demonstrated matrilineal stock structure for the first time among Mediterranean green turtle rookeries. This result contradicts previous regional assessments and supports a growing body of evidence that green turtles exhibit a more precise level of natal site fidelity than has commonly been recognised. The microsatellites detected weak male philopatry with significant stock structure among three of the six pairwise comparisons. The absence of Atlantic CR haplotypes and mtSTRs amongst these robust sample sizes reaffirms the reproductive isolation of Mediterranean green turtles and supports their status as a subpopulation. A power analysis effectively demonstrated that the mtDNA genetic markers previously employed to evaluate regional stock identity were confounded by an insufficient resolution considering the recent colonisation of this region. These findings improve the regional understanding of stock connectivity and illustrate the importance of using suitable genetic markers to define appropriate units for management and conservation.Natural Environment Research Council (NERC)Ministerio de Economía y Competitividad, Spai

Shelf life: Neritic habitat use of a turtle population highly threatened by fisheries

This is the final version. Available on open access from Wiley via the DOI in this recordAim: It is difficult to mitigate threats to marine vertebrates until their habitat use is understood. We report on a decade of satellite tracking loggerhead turtles (Caretta caretta) from an important nesting site to determine priority habitats for their protection in a region where they are known to be heavily impacted by fisheries. Location: Cyprus, Eastern Mediterranean. Method: We tracked 27 adult female loggerheads between 2001 and 2012 from North Cyprus nesting beaches. To eliminate potential biases, we included females nesting on all coasts of our study area, at different periods of the nesting season and from a range of size classes. Results: Foraging sites were distributed over the continental shelf of Cyprus, the Levant and North Africa, up to a maximum distance of 2100 km from nesting sites. Foraging sites were clustered in (1) near-shore waters of Cyprus and Syria, (2) offshore waters of Egypt and (3) offshore and near-shore regions of Libya and Tunisia. The North Cyprus and west Egypt/east Libyan coasts are important areas for loggerhead turtles during migration. Movement patterns within foraging sites strongly suggest benthic feeding in discrete areas. Early nesters visited other rookeries in Turkey, Syria and Israel where they likely laid further clutches. Tracking suggests minimum annual mortality of 11%, comparable to other fishery-impacted loggerhead populations. Main conclusions: This work further highlights the importance of neritic habitats of Libya and Tunisia as areas likely used by loggerhead turtles from many of the Mediterranean rookeries and where the threat of fisheries bycatch is high. Our tracking data also suggest that anthropogenic mortalities may have occurred in North Cyprus, Syria and Egypt; all within near-shore marine areas where small-scale fisheries operate. Protection of this species across many geopolitical units is a major challenge and documenting their distribution is an important first step.Peoples Trust for Endangered SpeciesBritish Chelonia GroupUnited States Agency for International DevelopmentBP EgyptApacheNatural Environment Research Council (NERC)Erwin Warth FoundationKuzey Kıbrıs TurkcellEktam KıbrısSEATURTLE.orgMEDASSETDarwin InitiativeBritish High Commission in CyprusBritish Residents Society of North CyprusMarine Turtle Conservation ProjectMarine Turtle Research GroupSociety for the Protection of Turtles in North Cyprus (SPOT)North Cyprus Department of Environmental Protectio

No evidence of fine scale thermal adaptation in green turtles

This is the final version. Available on open access from Elsevier via the DOI in this recordData availability: Data are stored in the Ascension Island Government Conservation Department database. Data are available on figshare, under embargo until publication. Beach data: https://figshare.com/s/dc16fbd027a59560ce1d; Lab data: https://figshare.com/s/24788e81a4140547b38b.Adaptation to increasing temperatures may enable species to mitigate the long-term impacts of climate change. Sea turtles have temperature dependent sex determination (TSD) and variation in the thermal reaction norm, which influences offspring sex ratio, has been suggested as a potential adaptive mechanism to rising global temperatures. Here, we investigate the sex ratio of green turtle Chelonia mydas offspring from nests on beaches with notable differences in their thermal properties, to look for evidence of localised adaptation. We compared pivotal temperatures and hatch success in both the laboratory and in situ using eggs laid on two nesting beaches (dark vs. pale sand) at Ascension Island that represent the extremes of the range of incubation temperatures experienced by this population. We found no effect of beach of origin on pivotal temperatures, hatch success, or hatchling size in the laboratory or the wild. This suggests that turtles from the same rookery are not locally adapted to different thermal conditions experienced during incubation. Under predicted climate change scenarios, this will result in reduced hatch success and an increased proportion of female offspring unless temporal or spatial range shifts occur