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

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

The importance of passive integrated transponder (PIT) tags for measuring life-history traits of sea turtles

This is the final version. Available from the publisher via the DOI in this record.Capture-mark-recapture studies rely on the identification of individuals through time, using markers or tags, which are assumed to be retained. This assumption, however, may be violated, having implications for population models. In sea turtles, individual identification is typically based on external flipper tags, which can be combined with internal passive integrated transponder (PIT) tags. Despite the extensive use of flipper tags, few studies have modelled tag loss using continuous functions. Using a 26-year dataset for sympatrically nesting green (Chelonia mydas) and loggerhead (Caretta caretta) turtles, this study aims to assess how PIT tag use increases the accuracy of estimates of life-history traits. The addition of PIT tags improved female identification: between 2000 and 2017, 53% of green turtles and 29% of loggerhead turtles were identified from PIT tags alone. We found flipper and PIT tag losses were best described by decreasing logistic curves with lower asymptotes. Excluding PIT tags from our dataset led to underestimation of flipper tag loss, reproductive periodicity, reproductive longevity and annual survival, and overestimation of female abundance and recruitment for both species. This shows the importance of PIT tags in improving the accuracy of estimates of life-history traits. Thus, estimates where tag loss has not been corrected for should be interpreted with caution and could bias IUCN Red List assessments. As such, long-term population monitoring programmes should aim to estimate tag loss and assess the impact of loss on life-history estimates, to provide robust estimates without which population models and stock assessments cannot be derived accuratel

Assessing the Effects of Banana Pingers as a Bycatch Mitigation Device for Harbour Porpoises (Phocoena phocoena)

This is the final version. Available on open access from Frontiers Media via the DOI in this recordData Availability Statement: The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation, to any qualified researcher.Bycatch is a significant cause of population declines of marine megafauna globally. While numerous bycatch mitigation strategies exist, acoustic alarms, or pingers, are the most widely adopted strategy for small cetaceans. Although pingers have been shown to be an effective measure for numerous species, there are some concerns about their long-term use. Bycatch is recognized as a persistent problem in waters around Cornwall, United Kingdom, where several cetacean species are resident, with harbour porpoises (Phocoena phocoena) being the most-commonly sighted. In this study, we assessed the effects of a Banana Pinger (Fishtek Marine Limited) on harbour porpoises in Cornwall between August 2012 and March 2013. Two passive acoustic loggers (C-PODs; Chelonia Limited) were deployed 100 m apart to record cetacean activity during cycles of active and inactive pinger periods. Harbour porpoises were 37% less likely to be detected at the C-POD near the pinger when the pinger was active, while they were only 9% less likely to be detected 100 m further away. The effect of the pinger was constant over the study period at both C-PODs despite the temporal variation in harbour porpoise detections. In addition, we found no evidence of reduced pinger effect with changing environmental conditions. Furthermore, harbour porpoise detections at the C-POD near the pinger did not depend on the time elapsed since the pinger turned off, with harbour porpoises returning to the ensonified area with no delay. Together these results suggest that (1) harbour porpoises did not habituate to the pinger over an 8-month period, (2) the pinger effect is very localized, and (3) pinger use did not lead to harbour porpoise displacement over the study period, suggesting an absence of long-term behavioral effects. We suggest that the deployment of pingers on fishing nets would likely reduce net-porpoise interactions, thereby mitigating bycatch of harbour porpoises and potentially other cetacean species. As the small-scale fishery dominates in United Kingdom waters, there is an acute need for cost-effective mitigation strategies with concurrent monitoring to be implemented rapidly in order to address the problem of harbour porpoise, and more generally, cetacean bycatch.Whale and Dolphin ConservationFishtek Marine Limite

Investigating the presence of microplastics in demersal sharks of the North-East Atlantic

This is the final version. Available from Nature Research via the DOI in this record. Data is available from the British Oceanographic Centre (Marine).Microplastic pollution is ubiquitous in the marine environment and is ingested by numerous marine species. Sharks are an understudied group regarding their susceptibility to microplastic ingestion. Here, we provide evidence of ingestion of microplastic and other anthropogenic fibres in four demersal sharks species found in the waters of the United Kingdom and investigate whether body burdens of contamination vary according to species, sex or size. Sharks were collected from the North-East Atlantic. Stomachs and digestive tracts of 46 sharks of 4 species were examined and 67% of samples contained at least one contaminant particle. Although we acknowledge modest sample size, estimated particle burden increased with body size but did not vary systematically with sex or species. A total of 379 particles were identified, leading to median estimates ranging from 2 to 7.5 ingested contaminants per animal for the 4 species. The majority were fibrous in nature (95%) and blue (88%) or black (9%) in colour. A subsample of contaminants (N = 62) were subject to FT-IR spectroscopy and polymers identified as: synthetic cellulose (33.3%), polypropylene (25%), polyacrylamides (10%) and polyester (8.3%). The level of risk posed to shark species by this level of contamination is unknown. Nevertheless, this study presents the first empirical evidence and an important baseline for ingestion of microplastics and other anthropogenic fibres in native UK shark species and highlights the pervasive nature of these pollutants.Natural Environment Research Council (NERC

Efficacy of a novel shark bycatch mitigation device in a tuna longline fishery

This is the final version. Available on open access from Cell Press via the DOI in this recordElasmobranchs (sharks, rays, and skates) are caught throughout fisheries globally, leading to over one-third of species being threatened with extinction1. Oceanic shark populations have undergone an average 71% decline over the last half century, owing to an 18-fold increase in relative fishing pressure2. Incidental capture or 'bycatch' is a primary driver of population declines, and poses an important challenge for species conservation3. This threat necessitates mitigation strategies that exist for sharks but are often focussed on haul-back and post-capture effects for longline fishing. We trialled a novel shark bycatch mitigation device ("SharkGuard") in a commercial longline fishery targeting bluefin tuna (Thunnus thynnus), where bycatch consists largely of blue sharks (Prionace glauca) and pelagic stingrays (Pteroplatytrygon violacea).Innovate U

Dietary analysis of two sympatric marine turtle species in the eastern Mediterranean

This is the final version. Available from Springer via the DOI in this record. Data and any available visuals, such as figures and tables, will be provided upon reasonable request to the corresponding author. Any codes created to assist in data analysis and/or any software application utilised in the current study will be provided upon reasonable request submitted to the corresponding author.Dietary studies provide key insights into threats and changes within ecosystems and subsequent impacts on focal species. Diet is particularly challenging to study within marine environments and therefore is often poorly understood. Here, we examined the diet of stranded and bycaught loggerhead (Caretta caretta) and green turtles (Chelonia mydas) in North Cyprus (35.33° N, 33.47° E) between 2011 and 2019. A total of 129 taxa were recorded in the diet of loggerhead turtles (n = 45), which were predominantly carnivorous (on average 72.1% of dietary biomass), foraging on a large variety of invertebrates, macroalgae, seagrasses and bony fish in low frequencies. Despite this opportunistic foraging strategy, one species was particularly dominant, the sponge Chondrosia reniformis (21.5%). Consumption of this sponge decreased with increasing turtle size. A greater degree of herbivory was found in green turtles (n = 40) which predominantly consumed seagrasses and macroalgae (88.8%) with a total of 101 taxa recorded. The most dominant species was a Lessepsian invasive seagrass, Halophila stipulacea (31.1%). This is the highest percentage recorded for this species in green turtle diet in the Mediterranean thus far. With increasing turtle size, the percentage of seagrass consumed increased with a concomitant decrease in macroalgae. Seagrass was consumed year-round. Omnivory occurred in all green turtle size classes but reduced in larger turtles (> 75 cm CCL) suggesting a slow ontogenetic dietary shift. Macroplastic ingestion was more common in green (31.6% of individuals) than loggerhead turtles (5.7%). This study provides the most complete dietary list for marine turtles in the eastern Mediterranean.European CommissionErwin Warth FoundationKarşıyaka Turtle WatchAngela WadsworthMaureen and Tony HutchinsonKuzey Kıbrıs TurkcellMAVA FoundationNatural Environment Research Council (NERC)University of Exete

Diet-related selectivity of macroplastic ingestion in green turtles (Chelonia mydas) in the eastern Mediterranean

Understanding the drivers of key interactions between marine vertebrates and plastic pollution is now considered a research priority. Sea turtles are primarily visual predators, with the ability to discriminate according to colour and shape; therefore these factors play a role in feeding choices. Classifcation methodologies of ingested plastic currently do not record these variables, however here, refned protocols allow us to test the hypothesis that plastic is selectively ingested when it resembles the food items of green turtles (Chelonia mydas). Turtles in the eastern Mediterranean displayed strong diet-related selectivity towards certain types (sheet and threadlike), colours (black, clear and green) and shapes (linear items strongly preferred) of plastic when compared to the environmental baseline of plastic beach debris. There was a signifcant negative relationship between size of turtle (curved carapace length) and number/mass of plastic pieces ingested, which may be explained through naivety and/or ontogenetic shifts in diet. Further investigation in other species and sites are needed to more fully ascertain the role of selectivity in plastic ingestion in this marine vertebrate group

Cayman Islands Sea Turtle Nesting Population Increases Over 22 Years of Monitoring

This is the final version. Available on open access from Frontiers Media via the DOI in this recordData Availability Statement: The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.Given differing trajectories of sea turtle populations worldwide, there is a need to assess and report long-term population trends and determine which conservation strategies are effective. In this study, we report on sea turtle nest monitoring in the Cayman Islands over a 22-year period. We found that green (Chelonia mydas) and loggerhead (Caretta caretta) nest numbers increased significantly across the three islands since monitoring began in 1998, but that hawksbill nest numbers remained low with a maximum of 13 nests recorded in a season. Comparing the first 5 years of nest numbers to the most recent 5 years, the greatest percentage increase in green turtle nests was in Grand Cayman from 82 to 1,005 nests (1,126%), whereas the greatest percentage increase for loggerhead turtle nests was in Little Cayman from 10 to 290 nests (3,800%). A captive breeding operation contributed to the increase in the Grand Cayman green turtle population, however, loggerhead turtles were never captive-bred, and these populations began to increase after a legal traditional turtle fishery became inactive in 2008. Although both species have shown significant signs of recovery, populations remain at a fragment of their historical level and are vulnerable to threats. Illegal harvesting occurs to this day, with multiple females taken from nesting beaches each year. For nests and hatchlings, threats include artificial lighting on nesting beaches, causing hatchlings to misorient away from the sea, and inundation of nests by seawater reducing hatch success. The impacts of lighting were found to increase over the monitoring period. Spatial data on nest distribution was used to identify critical nesting habitat for green and loggerhead turtles and is used by the Cayman Islands Department of Environment to facilitate remediation of threats related to beachside development and for targeted future management efforts.Cayman Islands Department of Environment (DoE)Foreign and Commonwealth OfficeTurtles in the Overseas Territories (TCOT project)Turtles in the UK Overseas Territories Project (TUKOT)Cayman Islands Governor’s FundDarwin Initiativ

Interactions between marine megafauna and plastic pollution in Southeast Asia

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record Southeast (SE) Asia is a highly biodiverse region, yet it is also estimated to cumulatively contribute a third of the total global marine plastic pollution. This threat is known to have adverse impacts on marine megafauna, however, understanding of its impacts has recently been highlighted as a priority for research in the region. To address this knowledge gap, a structured literature review was conducted for species of cartilaginous fishes, marine mammals, marine reptiles, and seabirds present in SE Asia, collating cases on a global scale to allow for comparison, coupled with a regional expert elicitation to gather additional published and grey literature cases which would have been omitted during the structured literature review. Of the 380 marine megafauna species present in SE Asia, but also studied elsewhere, we found that 9.1 % and 4.5 % of all publications documenting plastic entanglement (n = 55) and ingestion (n = 291) were conducted in SE Asian countries. At the species level, published cases of entanglement from SE Asian countries were available for 10 % or less of species within each taxonomic group. Additionally, published ingestion cases were available primarily for marine mammals and were lacking entirely for seabirds in the region. The regional expert elicitation led to entanglement and ingestion cases from SE Asian countries being documented in 10 and 15 additional species respectively, highlighting the utility of a broader approach to data synthesis. While the scale of the plastic pollution in SE Asia is of particular concern for marine ecosystems, knowledge of its interactions and impacts on marine megafauna lags behind other areas of the world, even after the inclusion of a regional expert elicitation. Additional funding to help collate baseline data are critically needed to inform policy and solutions towards limiting the interactions of marine megafauna and plastic pollution in SE Asia.National Research Foundation, Prime Minister’s Office (Singapore) and the Natural Environment Research Council (United Kingdom)National Research Foundation, Prime Minister’s Office (Singapore) and the Natural Environment Research Council (United Kingdom