Marine

Croaking Science: Portuguese man-o-war and leatherback turtle wash up in Cornwall

November 28, 2023 by Admin

As things calm down after the recent storms, Cornwall has had a number of interesting strandings: in mid-October there were reports of Portuguese Man-O-war jellyfish stranded on beaches near Porthleven.

Froglife Conservation & Science Manager, Andrew Smart, came across them on nearby Loe Bar. “I think we probably saw about 10 gas floats along about 500m of beach; they were still really pink so they’d not been on the shore long; you could see the blue base where the trailing tentacles would have attached.”

The Portuguese man-o-war isn’t actually a jellyfish, but a colonial organism made up of individual ‘zooids’ that have different functions in the colony, such as digestion and stinging tentacles. Recently there have been more regular strandings along the coasts of Cornwall. The gas filled floats are caught by the wind and the man-o-war floats across the ocean following winds and currents, trailing its stinging tentacles behind it.

The oceanic predators of Portuguese man-o-war include the sunfish, which also occurs off Cornwall, and sea turtles, including the UK’s largest reptile, the leatherback turtle. The leatherback is a member of the British Fauna and a UK protected species, with animals in UK waters migrating between the UK and the Caribbean Sea where they nest (see our Croaking Science article here for more information)

Last week, a dead leatherback turtle washed up on Perranporth beach in North Cornwall It was quite badly decomposed and was collected by the Marine Strandings Network and taken away for further analysis. Often leatherbacks die because they swallow floating plastic bags they mistake as jellyfish and investigation of the dead animal will help us understand the extent of this problem.

This animal measured 1.66m, which sounds large, but the largest recorded, washed up in Wales in the 1908s, was measured at 2.9m (9½ ft) long! Its quite late in the year for a leatherback stranding but the sea temperature this year off Cornwall is around 13-15 ͦC, higher than the average for November (11- 12 ͦC) and warmer temperatures may have resulted in more jellyfish and salps for leatherbacks to feed on.

At the start of 2023 there were a high number of strandings of other species, small loggerheads and Kemps ridley’s. Sadly, many of these small turtles die from cold shock because they are not adapted to our colder waters like the leatherback, but if they are found quickly enough they can be nursed back to health and released.

Leatherback turtles are stranded and sighted off our coasts every year:

Year	Strandings & sightings
2018	17
2019	15
2020	9
2021	17
2022	9

Data from Marine Environmental Monitoring Turtle Strandings & Sightings Annual Reports 2018-2022

If you’re out walking our western beaches keep an eye out for stranded turtles. They can be stranded anywhere although mainly on the west and south coasts, as can be seen from this diagram of strandings and sightings over the last 10 years, recorded by R.S. Penrose and M.J.B. Westfield in the May 2023 Marine Environmental Monitoring British & Irish Marine Turtle Strandings & Sightings Annual Report 2022

Turtles in UK waters

July 27, 2023 by Admin

By Andrew Smart, Conservation and Science Senior Manager.

Since it is National Marine Week (22 July to 6 August, organised by the Wildlife Trusts), it is appropriate to return to our only marine reptile species, the marine turtles, last covered by Croaking Science in April 2021: Should we count marine turtles as members of the British fauna? One species, the leatherback turtle (Dermochelys coriacea), is considered to be a member of the British fauna, while the other species, perhaps best described as hard shelled turtles, are vagrants who have moved away from their normal migration paths and, one way or another, end up stranded on UK beaches Turtles stranded on UK beaches after storms send them off course.

These strandings are generally of loggerhead turtles (Caretta caretta) and more recently, Kemp’s ridley, (Lepidochelys kempii). Occasionally green turtle (Chelonia mydas) and very rarely, hawksbill (Eretmochelys imbricata) and olive ridley turtles (Lepidochelys olivacea) (both single records) are washed up on our beaches¹. Loggerheads and Kemp’s ridley originate from the Caribbean, most likely from nesting beaches on the Florida coastline and Gulf of Mexico, from where hatchlings travel across the Atlantic. The hatchlings spend their early years, often called the ‘lost years’, in the North American basin and many move into the North Atlantic gyre², travelling across the ocean from east to west, then follow the current south past the Azores and Canary Islands before travelling westward back towards their nesting beaches as juveniles³.

Loggerheads are sometimes killed after interactions with boats, caught in longline fisheries⁴, tangled in pot lines or in ‘ghost nets’, but many animals suffer from ‘cold stunning’ when they move out of warm water into colder temperatures (10 – 15^oC) that cause them to effectively ‘shut down’⁵. Turtle hatchlings will die at temperatures below 10^oC⁶. Animals that have been ‘cold stunned’ or died are stranded along European coasts and are collected and examined. Any UK strandings of turtles (or any other marine animal) can be reported to the Marine Strandings Scheme (or in Scotland SMASS). Many stranded dead turtles have been found to have frequently ingested plastics (69% of individuals examined) which they may mistake for food ^{7, 8}; jellyfish and salps. Animals stranded in the UK tend to be juveniles, with a carapace measurement of less than 40 cm, and tend to be stranded in the winter months¹. In the last three decades numbers of loggerhead and Kemp’s ridley turtles have increased, with more than twice the number of animals stranded when compared to the 1980s¹.

Genetic analysis of loggerheads stranded in France indicate that as well as animals from Florida and the Caribbean, some also come from the nesting beach on the Cape Verde Islands, from where animals are occasionally blown north by storms along the Portuguese and Spanish coasts⁹ and into the Bay of Biscay. Loggerheads nesting in the Mediterranean move in and out of the Straits of Gibraltar along with animals from the Caribbean¹⁰, which move inwards through the ‘Straits’ and are sometimes recorded off the coast of Algeria. Mediterranean turtles would be unlikely to move northwards into colder water around the UK. However, recent work suggests that there may be a population of juvenile loggerheads using the Bay of Biscay as feeding grounds during warmer periods¹¹.

Kemp’s ridleys also come from the Gulf of Mexico and are being recorded more frequently as UK strandings in the last three decades. Very occasionally there are strandings of olive ridley, hawksbill and green turtle¹. Green turtles stranded on French coasts have been from African populations not from the Mediterranean¹², where the nesting green turtle populations in the east generally travel along the North African coast to feed before returning to nest in Turkey and Syria¹³.

The leatherback turtle is the largest turtle species; the biggest recorded washed up on a Welsh beach in the 1980s, weighed over 900 kg and was 2.9 m (9 ½ ft) long¹⁴. Leatherbacks feed mainly on jellyfish and other gelatinous plankton, such as salps, and spend a lot of their time feeding because this prey is not very nutritious. Strandings are often linked to plastic ingestion because of the similarity to jellyfish, their main prey species. The animal has a remarkable throat structure with backwards pointing barbs that holds jellyfish in place until it’s swallowed¹⁴.

Leatherbacks are regularly seen off the UK and Irish coasts and these North Atlantic animals have migrated from their nesting sites along the coast of northern South America and some Caribbean islands¹⁵. Females nest at these rookeries, often on a 2 yearly cycle, and animals follow one of three different migration paths based on directions taken by tracked animals. Animals from the North Atlantic population migrate northwards up to the coast of Nova Scotia in Canada, eastwards across the Atlantic towards the Azores and the coast of Africa or north eastwards up to the Atlantic coast of the island of Ireland, the Irish Sea and the Celtic Sea^{16, 17}, where they find jellyfish swarms on which to feed¹⁸. They have been recorded as far north as Norway¹⁴ and can survive in these cold waters because they are able to generate their own body heat and being large, once warm they take longer to cool down. They also have heat conservation and heat exchange mechanisms that enable them to feed actively in waters below 15^oC, temperatures that would cause ‘cold stunning’ to other turtle species. Leatherbacks that are found further north tend to be larger than those off the Spanish and French coasts^{19, 20}.

The continental shelf around Europe and off Canada are ideal sites for their main food, the barrel jellyfish, Rhizostoma pulmo, but they will feed on other gelatinous or jelly-like plankton. Barrel jellyfish can reach 90 cm in diameter and ‘blooms’, large congregations, of jellyfish can occur when conditions are ideal and food (plankton) is plentiful²¹. A leatherback filmed off the Canadian coast²² was found to eat over 50% of their entire annual energy requirement in the 90 days that they spent in northern waters and this is likely to be the case off the UK in the Celtic and Irish seas. Leatherbacks are probably moving into high quality feeding areas where the location of a feeding ‘patch’ will provide them with lots of energy at low cost ^{23, 24}. Unfortunately, some of their foraging areas in the Atlantic align with existing long line fisheries and this has an impact on the population, with estimates in the year 2000, of a leatherback bycatch of between 30,000 and 60,000 animals from both north and south Atlantic populations combined^{4, 25}.

After feeding through the summer the leatherbacks head back south-westerly and generally follow a straight line migration path back to their nesting beaches²⁶. Scientists have been able to track animals leaving nesting beaches and also animals that have been caught in fishing gear off the UK coast and found that when they’re feeding in northern waters they tend to stay close to the surface, feeding in localised patches, suggesting feeding in jellyfish swarms in the surface waters^{21, 27, 28, 29}. Tracking results indicate that when they travel to and from their nesting beaches they swim much faster and tend to be more prepared to undertake deeper dives to find food^{29, 30}.

How has this leatherback migration pattern developed? One suggestion is that leatherback hatchlings drift out of the gyre, get caught up in the North Atlantic current and drift northwards during the so-called hatchling/juvenile ‘lost years’, finding areas where foraging is high-quality¹⁷. Having returned to nesting grounds, they are able to find these sites again as adults, using some form of navigation system¹⁵. Whatever the process they use, as long as we have our existing ocean currents, and large jellyfish blooms, we are lucky enough to provide an important feeding area for these migratory turtles, the most widely distributed reptile species in the world.

Published work referred to in this article:

¹Botterell ZLR, Penrose R, Witt MJ, Godley BJ (2020) Longterm insights into marine turtle sightings, strandings and captures around the UK and Ireland (1910-2018). Journal of the Marine Biological Association of the United Kingdom 100:869-877

²Putman NF, Seney EE, Verley P, Shaver DJ, López-Castro MC, Cook M, Guzmán V and others (2020) Predicted distributions and abundances of the sea turtle ‘lost years’ in the western North Atlantic Ocean. Ecography 43:506-517

³Monzo´n-Argu¨ello C., Dell’Amico F,. Morinie`re P,. Marco, A Lo´pez-Jurado L. F.,. Hays G C, Scott R, Marsh R and Lee P, (2012) Lost at sea: genetic, oceanographic and meteorological evidence for storm-forced dispersal Journal of the Royal Society Interface 9, 1725–1732

⁴Lewison RL,. Freeman S A and. Crowder L B (2004) Quantifying the effects of fisheries on threatened species: the impact of pelagic longlines on loggerhead and leatherback sea turtles Ecology Letters, 7: 221–231

⁵Bellido J, Castillo J, Pinto F, Marti’n J, Mons J, Ba’ez J and Real R (2010) Differential geographical trends for loggerhead turtles stranding dead or alive along the Andalusian coast, southern Spain Journal of the Marine Biological Association of the United Kingdom, 90(2), 225–231.

⁶Kettemer L, Biastoch A, Wagner P,. Coombs E J, Penrose R, and Scott R, (2022) Oceanic drivers of juvenile sea turtle strandings in the UK Endangered Species Research 48: 15–29

⁷Darmon, G.; Schulz, M.; Matiddi, M.; Liria Loza, A.; Tom, J.; Camedda, A.; Chaieb, O.; El Hili, H.A.; Bradai, M.N.; Bray, L.; et al. (2022) Drivers of litter ingestion by sea turtles: Three decades of empirical data collected in Atlantic Europe and the Mediterranean. Marine Pollution Bulletin , 185, 114364

⁸Sala B, Balasch, A, Eljarrat E, Cardona L (2021) First study on the presence of plastic additives in loggerhead sea turtles (Caretta caretta) from the Mediterranean Sea Environmental Pollution 283 117108

⁹Nicolau, L., Ferreira, M., Santos, J. et al. (2016). Sea turtle strandings along the Portuguese mainland coast: spatio-temporal occurrence and main threats. Marine Biology 163, 21 https://doi.org/10.1007/s00227-015-2783-9

¹⁰Garofalo L., Mastrogiacomo A., Casale P., Carlini R., Eleni C., Freggi D., Gelli D. Et al. (2013). Genetic characterization of central Mediterranean stocks of the loggerhead turtle (Caretta caretta) using mitochondrial and nuclear markers, and conservation implications. Aquatic Conservation: Marine and Freshwater Ecosystems, 23: 868–884.

¹¹Chambault P, Gaspar P and Dell’Amico F (2021) Ecological Trap or Favorable Habitat? First Evidence That Immature Sea Turtles May Survive at Their Range-Limits in the North-East Atlantic. Frontiers in Marine Science. 8:736604. doi: 10.3389/fmars.2021.736604

¹²Avens L and Amico FD (2018) Evaluating viability of sea turtle foraging populations at high latitudes: age and growth of juveniles along the French Atlantic coast. Endangered Species Research 37, 25–36

¹³Clusa, M., Carreras, C., Pascual, M. et al. (2014). Fine-scale distribution of juvenile Atlantic and Mediterranean loggerhead turtles (Caretta caretta) in the Mediterranean Sea. Marine Biology 161, 509–519 https://doi.org/10.1007/s00227-013-2353-y

¹⁴Beebee, T.J.C. & Griffiths, R.A. (2000) Amphibians and Reptiles. A Natural History of the British Herpetofauna. Harper Collins Publishers, London, UK

¹⁵Dodge KL, Galuardi B, Lutcavage ME. (2015) Orientation behaviour of leatherback sea turtles within the North Atlantic subtropical gyre. Proceedings of the Royal Society B 282: 20143129. http://dx.doi.org/10.1098/rspb.2014.3129

¹⁶Fossette S, Hobson V J., Girard C, Calmettes B , Gaspar P, Georges J-Y ,. Hays G C (2010) Spatio-temporal foraging patterns of a giant zooplanktivore, the leatherback turtle Journal of Marine Systems 81 225–234

¹⁷Fossette S, Girard C, Lo´pez-Mendilaharsu M, Miller P, Domingo A, et al. (2010) Atlantic Leatherback Migratory Paths and Temporary Residence Areas. PLoS ONE 5(11): e13908. doi:10.1371/journal.pone.0013908

¹⁸Bailey H, Fossette S, Bograd SJ, Shillinger GL, Swithenbank AM, et al. (2012) Movement Patterns for a Critically Endangered Species, the Leatherback Turtle (Dermochelys coriacea), Linked to Foraging Success and Population Status. PLoS ONE 7(5): e36401. doi:10.1371/journal.pone.0036401

¹⁹Eckert S A. 2002 Distribution of juvenile leatherback sea turtle Dermochelys coriacea sightings Marine Ecology Progress Series 230: 289–293,

²⁰Witt MJ, Penrose R, Godley BJ (2006) Spatio-temporal patterns of juvenile marine turtle occurrence in waters of the European continental shelf. Marine Biology 151:873-885

²¹Houghton J.D.R., Doyle T.K., Wilson M.W., Davenport J., Hays G.C. (2006) Jellyfish Aggregations and Leatherback Turtle Foraging Patterns in a Temperate Coastal Environment. Ecology.;87:1967–1972. doi: 10.1890/0012-9658(2006)87[1967:JAALTF]2.0.CO;2. – DOI – PubMed

²²Wallace, B.P., Zolkewitz, M. & James, M.C. (2018) Discrete, high-latitude foraging areas are important to energy budgets and population dynamics of migratory leatherback turtles. Science Reports 8, 11017. https://doi.org/10.1038/s41598-018-29106-1

²³Eckert Scott A. (2006) High-use oceanic areas for Atlantic leatherback sea turtles (Dermochelys coriacea) as identified using satellite telemetered location and dive information Marine Biology 149: 1257–1267

²⁴Chambault P, Roquet F, Benhamou S, Baudena A, Pauthenet E, de Thoisy B, et al. (2017). The Gulf Stream frontal system: A key oceanographic feature in the habitat selection of the leatherback turtle? Deep Sea Research Part I: Oceanographic Research Papers, 123: 35–47.

25 Fossette S, Witt, M. J. et al. (2014) Pan-Atlantic analysis of the overlap of a highly migratory species, the leatherback turtle, with pelagic longline fisheries. Proceedings of the Royal Society B 281: 20133065. http://dx.doi.org/10.1098/rspb.2013.3065

²⁶Dodge KL, Galuardi B, Lutcavage ME. (2015) Orientation behaviour of leatherback sea turtles within the North Atlantic subtropical gyre. Proceedings of the Royal Society B 282: 20143129. http://dx.doi.org/10.1098/rspb.2014.3129

²⁷Doyle TK, Houghton, JD O’Súilleabháin, PF Hobson, VJ Marnell, F Davenport, J Hays, GC and Hobson V (2008) Leatherback turtles satellite-tagged in European waters Endangered Species Research: 4, Pages: 23 – 31,

²⁸Hays GC Farquhar MR, Luschi P, Steven L.H., Tierney T,. Thys M (2009) Vertical niche overlap by two ocean giants with similar diets: Ocean sunfish and leatherback turtles Journal of Experimental Marine Biology and Ecology 370 134–143

²⁹Dodge KL, Galuardi B, Miller TJ, Lutcavage ME (2014) Leatherback Turtle Movements, Dive Behavior, and Habitat Characteristics in Ecoregions of the Northwest Atlantic Ocean. PLoS ONE 9(3): e91726. doi:10.1371/journal.pone.0091726

³⁰Hays, G.C. ; Houghton, J; Myers, A.E. (2004) Endanqered species – Pan-Atlantic leatherback turtle movements. Nature. 429(6991). pp. 522-522

National Marine Week

June 27, 2023 by Admin

Written by Ellia Cobb, Transforming Lives Trainee.

Did you know that oceans are home to more than half of the world’s wildlife with over 30,000 species of marine plants and animals found here in the UK, ranging from seahorse to orcas? National Marine Week is an opportunity to celebrate and appreciate the wonderful wildlife we have here in our seas. We have only explored 5% of our oceans, so who knows what other marine life is out there yet to be discovered!

The world’s seas and oceans hold the largest ecosystems and biodiversity. It is estimated 50-80% of the world’s oxygen is produced by the oceans of which marine plants and animals contribute to, it is so important that we do our best to conserve our oceans and marine life.

National Marine Week, held by The Wildlife Trust from 22nd July- 6th August, gives people the opportunity to explore the shorelines of local beaches to try and spot some of the incredibly diverse marine life we have here in the UK. Taking advantage of the low tides, this helps encourage people to better understand and protect these species.

It is a great opportunity to learn about marine life and how we can help protect it. There are many different activities being held such as exploring rock pools, snorkeling and beach clean-ups for all ages to get involved with.

Take the opportunity this upcoming National Marine Week to learn more about our marine wildlife, how we as Individuals can help protect them and why it is so important. There are so many beautiful, diverse, and interesting creatures to learn about.

Should we count marine turtles as members of the British fauna?

March 25, 2021 by Admin

In August 2020, the media outlet Wales On-line reported that a five-foot long marine turtle had surfaced beside a small fishing boat off the north coast and swum alongside it for an extended period before diving out of sight. The excited boat owner said that he had fished those waters for over 20 years, and never seen a turtle before. Was this an exceptional sighting? The fisherman was certainly lucky. Over the last century or so, the average number of leatherback turtles (the species observed) seen in British waters each year is around 15. However, this is bound to be a vast underestimate of the turtle numbers actually present in British waters. This is due to them being incredibly difficult to locate as they rarely emerge from the depths to breath, nor do they nest on British beaches; so the chances of actually spotting one in the huge expanses of our coastal waters are very slim.

Botterell et al. (2020) have published an analysis of marine turtle sightings, strandings (usually found dead washed up on shore) and captures (by-catch in fishing nets) since 1910. Of 1997 records, 84% are of leatherbacks; 12% of loggerheads, and 3% of Kemp’s ridleys. The remaining 13 records concern tiny numbers of three more species. Until 1980, records were small in number for all species, with substantial increases from the 1990s onwards. Mapping of the records shows that most are predominantly from the western side, including the English Channel, all around Ireland and north to the Orkneys and Shetlands. Leatherbacks and loggerheads have been recorded at all times of the year, with peaks in June-October (leatherbacks) and November-March (loggerheads). Kemp’s ridleys have only been seen from October-February. Measurements on body size, mostly from strandings and captures, suggest that most leatherbacks in British waters are adults, while loggerheads and Kemp’s ridleys are juveniles.

Although they may seem like an exotic species, these data clearly show that we should regard leatherback turtles as normal members of the migratory fauna that inhabits our surrounding seas. Adult leatherbacks manage this by generating enough heat that their body temperature is above ambient, allowing them to remain active in the cold waters of the North Atlantic; even juveniles can raise their body temperature above cold water temperatures by activity and reduction of heat loss (Bostrom et al., 2010). For loggerheads and Kemp’s ridleys, the majority of records in British waters are strandings of juveniles in winter: these are most likely animals cold-stunned as water temperature declines. What is unknown is the number which venture into our waters, but manage to travel south and survive.

Marine turtles display what are known as cosmopolitan ranges, meaning that they are near-ubiquitous in waters globally. This has led to their incorporation into indigenous cultures around the world, with their size and habits having led to mythological status in many places. In an ecological context, the extensive migrations they undertake between foraging and nesting grounds (which often span entire oceans) are important for connecting ecosystems globally. The three species commonly found in British waters have distinct breeding and foraging grounds, with much information recently derived from satellite tracking of tagged adult females following capture at nesting sites (Fossette et al., 2014). For example, Atlantic leatherbacks consist of two separate populations. South Atlantic turtles breed either along the coast of Brazil or of West Africa, especially Gabon. Foraging takes them across the ocean and southwards, but not into the North Atlantic. The North Atlantic population breeds on the beaches of southern Florida, the islands of the Caribbean and the Guianas. They forage east and north, as far as British waters, as we have seen. Adult females return to nesting beaches every 2-4 years and lay up to 7 clutches, each 60 – 110 eggs, over several months.

*Female leatherback turtle nesting on a beach in Tobago.*

The males wait near the approaches to the beaches and attempt to mate with any females that turn up; however, they do not come onto land and instead spend their entire lives at sea. Leatherback females show moderately high nesting site fidelity, with all their nests in a season being laid on the same beach which they were born on or ones in close proximity. Hatchlings disperse into the sea and travel east towards open ocean to develop into juveniles. Kemp’s ridleys nest in the Caribbean, nearly all on one 16- mile Mexican beach; juveniles extend across the North Atlantic. Loggerheads are highly cosmopolitan with three distinct Atlantic populations. In the West Atlantic, they nest on beaches as far north as New Jersey and south to Parana in Brazil. Juveniles forage very widely. The Gulf Stream (also called the North Atlantic Gyre) was thought to be the primary determinant of juvenile distribution, as it carries developing individuals into east Atlantic waters. However, active dispersal has been recently documented in loggerhead, green and Kemp’s ridley turtles which suggests a more selective use of habitat than previously thought (Mansfield et al., 2014).

Sources of nutrition are a key determinant of marine turtle distribution. In other words, they go where the food is. The abundance of jellyfish in eastern Atlantic waters brings adult turtles, including loggerhead and Kemp ridley’s, but especially leatherbacks to UK and Irish coasts. As well as helping to predict the position of leatherbacks, the presence of jellyfish affects the depth at which the turtles swim. Jellyfish display a diurnal pattern of vertical migration, following their plankton prey up and down the water column. Plankton move to the water’s surface at night, when they are less visible to potential predators, and are closely followed by the jellyfish and, in turn, the turtles. Leatherbacks are so committed to pursuing their translucent prey that one intrepid individual was found swimming over 1000 metres underneath the surface during a foraging mission. This feat put leatherbacks into the top three diving animals on the planet alongside beaked whales and sperm whales. Their dedication to pursuing cnidarians was also shown by a 12,000 mile foraging journey from Indonesia to the US, which shows the determination present in their feeding habits.

It is these same feeding habits that have become a source of harm in recent times. Ingestion of marine litter, especially plastic bags, is a leading cause of turtle mortality. Particularly affected are leatherback turtles, due to their specialised diet of jellyfish which closely resemble partially degraded plastic bags hanging in the water column. One study analysed historical autopsy records spanning 123 years (1885-2007) and found plastic to be present in the digestive tracts of 34% of the dissected turtles (Mrosovsky et al., 2009). Plastic ingestion has a range of detrimental consequences, including reduced nutritional intake and asphyxiation.

There is a considerable worldwide effort to conserve marine turtle populations. One measure of this is the regularly updated IUCN Red List. Since the 1980s, there has been a large reduction in leatherback numbers which has led to a ‘vulnerable’ classification by the IUCN. However, there are subpopulations that are doing even worse, such as those of the northwest Atlantic subpopulation who were reclassified from Least Concern to Endangered in 2019. Another case was a subpopulation based in the South China Sea that produced 10,000 yearly nests on the beaches of Malaysia. However, from the 1960s the population dwindled to the point where only two nests were laid in 2008, both of which were infertile (WWF, on-line). This decrease in numbers was partly made worse by misled conservation efforts, which collected and artificially incubated eggs at excessive temperatures, scrambling the sex determination process. As in many other reptile species, sex is determined by the temperature of incubation of the eggs. This shows the need for in depth research when developing conservation measures to deal with anthropogenic threats.

There is a wide range of barriers to the recovery of turtle numbers, with pressures both natural and anthropogenic. Among the natural threats faced by marine turtles is the impact of climate change on temperature-dependent sex determination, which disrupts reproduction and has knock-on effects on population demographics and dynamics. Another prominent challenge to successful reproduction is the predation of eggs and juveniles, which make for easy pickings for a diverse array of coastal predators.

*A group of black vultures patrol a nesting beach looking for hatchlings to prey on.*

Conservation efforts and scientific surveys are often based around these issues, when the turtles are onshore and accessible for data collection. Studies focused on the reproductive stage of turtle life are very valuable to the implementation of management strategies and can provide a range of insights into their life histories. The Exploration Society operating out of the University of Glasgow has run many research projects along these lines, based in the Caribbean islands of Trinidad and Tobago. These studies have contributed analyses of egg temperatures, tagging efforts to track distribution and last year uncovered a novel female behaviour for nest protection: after burying the eggs, females create a ‘decoy trail’ aimed at misleading predators over the location of the nest (Burns et al., 2020). All of these contributions are helpful to maintaining healthy populations of turtles, but there is still a large gap in the knowledge of turtle life out in the open ocean.

*Leatherback hatchlings burst from a concealed nest, heading to the sea to begin their life of roaming the oceans of the world.*

Marine turtles spend most of their lives navigating the oceans, across a massive geographic range and at various depths. This makes them pretty tough to track throughout their development from hatchling to mature adult, and even between nesting events. However, as we have seen, the use of satellite tracking has revealed much about adult migrations. In addition to this, the missing pieces of the puzzle can be cleared up with the help of sighting and stranding data collected from coastlines within their range, which can be acquired through citizen science projects and compiled into databases to map distributions at different stages of development. Stranded carcasses can also be inspected to gain an insight into the causes of death, and the larger scale threats to their survival. For example, carcasses with scars on their shells can show the impact of high densities of fishing vessels. The number of sightings can also be used as an indicator of population trends, as was shown by Botterell et al. (2020), summarised above. Tracking sightings and strandings off the British and Irish coasts, the study was able to attribute dips in numbers to major environmental events such as the Deepwater Horizon oil spill in 2010 and link population increases to successful conservation programmes. This shows that despite the challenges facing this fascinating group of reptiles, we can make use of the full range of analysis tools available to more fully understand their life history; from hatching through juvenile to nesting adult. From this, effective conservation strategies can be developed to protect marine turtles throughout their cosmopolitan range.

References

Bostrom, B.L. et al. (2010). Behaviour and physiology: the thermal strategy of leatherback turtles. PLoS ONE 5(11), e13925.

Botterell, Z.R.L. et al. (2020). Long-term insights into marine turtle sightings, strandings and captures around the UK and Ireland (1910-2018). Journal of the Marine Biological Association of the United Kingdom 100, 869-877.

Burns, T.J. et al. (2020). Buried treasure- marine turtles do not ‘disguise’ or ‘camouflage’ their nests but avoid them and create a decoy trail. Royal Society Open Science 7, 200327.

Fossette, S. et al. (2014). Pan-Atlantic analysis of the overlap of a highly migratory species, the leatherback turtle, with pelagic long-line fisheries. Proceedings of the Royal Society B 281, 20133065.

Mrosovsky, N. et al. (2009) Leatherback turtles: The menace of plastic. Marine Pollution Bulletin 58, 287-289.

Mansfield, K.L. et al. (2014) First satellite tracks of neonate sea turtles redefine the ‘lost years’ oceanic niche. Proceedings of the Royal Society B: Biological Sciences 281, 20133039.

WWF on-line. Search at https://www.wwf.org.my/?25625/Marine-Turtles-Malaysias-National-Heritage

Cameron Boyle, Roger Downie and Jack Rawlinson

Photos generously provided by Jack Rawlinson

University of Glasgow

Marine

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