21st January 2020
Welcome to our new and Fun Fact Filled Turtle Tuesdays. As Mem is a marine biologist and a Sea Turtle expert we’d like to share some interesting facts with you about these amazing and wondrous creatures over the following weeks.This will be an ideal opportunity to ask an expert those questions about Sea Turtles you may have had but never got an answer too. Over the weeks we’ll look at their life cycle and some little known but very interesting facts about these fabulous animals.
We thought we would start with some interesting facts about Sea Turtles. They have evolved from their land dwelling cousins the tortoises making them reptiles, in both cases their rib cages have developed to provide a hard exoskeleton to protect them. Sea Turtles shells have become flattened compared to tortoises, allowing them to be more streamlined and move through the water with less resistance. Their front legs have become elongated and flatted and are used to propel them through the water at high speeds, their back legs also have flattened but have not increased much in length, Sea Turtles use their back legs more like rudders to change direction while swimming. This flattening of the shell has meant that they have lost their ability to retract their head and legs into their shell like tortoises. Other than when they lay their eggs Sea Turtles spend their entire lives at Sea, they can be found in almost every ocean basin in the world, they migrate long distances to feed, often crossing entire oceans between feeding and breeding grounds.
As divers we often encounter Turtles in their feeding grounds, we would love to see some of your Turtle photos and hear where they were taken.
I’ll Start, this was a Hawksbill Turtle feeding on a reef in Raja Ampat in Indonesia
30th January 2020
Hello and welcome to another Turtle Fun Fact day this week its Turtle Thursday. With Last weeks post we learned how Turtles are reptiles and how their bodies have adapted from their land dwelling ancestors. This week I’d like to tell you more about their life cycle and really how little is actually known about their early years. As we know Sea Turtles spend their lives at sea and it is only the females that return to the beaches to lay their eggs, many believe that the female will return to the exact beach where she hatched many years previously. This is one of the most highly debated topics in Sea Turtle research, recently with the use of genetic markers scientist have been able to prove that one female logger head actually laid 4 different nests on 4 different beaches off of the Florida Keys…..so which one did she hatch on??? Regardless of the answer the life cycle of Sea Turtles is known for the most part. We know that Sea Turtles actually have different feeding and mating grounds, they will spend most of the year in their preferred feeding ground, adults will migrate to breeding grounds which are located adjacent to nesting beaches, Males will do this annually where as females will only migrate there every 2 or 3 yrs once they are ready to breed. It is such a demanding and strenuous time on the female’s body that they do not lay eggs every year. Depending on the species of Turtle they will become adults and ready to breed between 20-40 years of age, both males and females will congregate in front of the nesting beaches; the males will compete to be the one to mate with a female. The males have special nails/claws on their front fins which are curved to hold on to the females shell while mating, here the female will then swim the 2 of them up to the surface to breath, she will do this for the next 6-7hrs (yes that is correct in hours and not Minutes) that it takes for mating to be completed. After mating it takes 2 weeks before the eggs are ready to be laid and in this time she may well have mated with several males and in fact her clutch may have a number of different Daddies. She may lay 2-4 nests per breeding season with each clutch of eggs varying between 70-120 eggs per nest, the larger the female the larger the clutch of eggs will be.
4th February 2020
Hello and welcome to another Turtle info day, in last weeks post we looked further into Sea Turtles breeding behaviours this week we’re looking at nesting. After mating the females will spend a lot of time resting on the bottom of the sea bed just in front of the nesting beach where after 2 weeks she’ll pull herself out of the water and search for a good spot to lay her eggs, not all nesting exits are successful, if the female isn’t happy with the location or is disturbed before starting to lay her eggs she will return to the water with her clutch still inside her and try again, if she continues to be unsuccessful she will ditch the eggs in the sea. Female turtle have a very special ability to control their stress hormones during breeding, in fact they are able to completely halt responses to stress over the breeding season, they actually stop/reduce the production of hormones released by the hypothalamus in response to stress, unlike the males who at this time of year are very stressed and producing lots of stress hormones. Once a female has decided on the perfect spot for the nest she begins to dig the hole of the nest with her rear fins using them to scoop out the sand. This is done with extreme care as she carefully places each scoop of sand to the side of the nest, once the egg chamber is between 70-100cm deep she begins to lay. Once she’s started laying there is nothing that will deter her from her task at hand, researchers actually use this time to take measurements and recordings of the female that are otherwise very tricky to record on a moving Turtle. The whole process of digging the nest and laying the eggs can take 2-3hrs. Once she has finished laying the eggs she carefully covers over the nest insuring that the last sand dug out the nest is the first sand back into cover the eggs over, this way she is keeping the same temperature and moisture level of sand over the eggs. Once covered she firmly pats down the sand over the eggs chamber and once finished she throws sand around all over to disguise the actual location of the chamber. She’ll then return to the sea where she will rest and start producing the next batch of eggs.
11th February 2020
It’s Turtle Tuesday time folks. Last week we ended with the female Turtle having laid her clutch of eggs and returned to the sea to rest as the next batch develops inside her. . Once the female has laid her eggs that’s her job done and she will never return to check on the nest or meet her hatchlings. It takes between 45-60 days for the eggs to develop and hatch, this time will vary according to the temperature of the sand the eggs have been laid in, the warmer the faster the development. Most females will lay their eggs at least 5m above the high tide line on the beach, with some laying their eggs 50-60m above the high tide line. Like other marine reptiles the sex of each egg is determined by the external temperature that the eggs are developing within, cooler temperatures produce more males and higher temperature more females, the location of the nest in relation to the high tide line has an effect as does our planets ever increasing temperatures. In Turkey we have found that the Loggerhead nests laid on Dalyan Beach are now developing at a 20:80 ratio, 20% male and 80% female where as 20 years ago we were seeing 50:50 sex ratios throughout the nests. Having more females may sound good, more females to lay more nests in the future can’t be a bad thing right? However when you factor in the survival rate of hatchlings developing into adults and continuing the cycle there is a range of estimates from 1 in a 1000 to 1 in 10,000, no matter which, the odds are really stacked against these little cuties and with less males the chances of them surviving to become an adult are extremely low. Turtles combat this with laying as many eggs as they do, as previously mentioned the number of eggs a female will lay in the nest depends on her size but each nest can have 70-120 eggs large clutch sizes help increase the odds of one little hatchling making it to become an adult. Once the nest is ready to hatch the hatchlings use a little sharp notch they have on their beaks to break free of the egg shell. Another amazing fact about Turtles is that when the egg is laid the yolk and embryo will develop in such an orientation that the little hatchling will develop head up so that when it breaks free of the egg it’s head is already orientated to the surface. Once free of the egg shell they work their way to the surface and will spend 3-4 days about 15-20cm below the surface where the weight of the sand will help straighten up their little curved bodies and remove any gunk remaining from the egg, this ‘cleaning’ helps to protect against predators. Once there is a good number of hatchlings ready (20-40) they all co-ordinate and exit the nest at the same time and make their mad dash to the sea where they will frantically swim out to open water avoiding the gauntlet of predators along the way, as the hatchlings are only about the size of a match box there are many creatures both on land and in the sea waiting to pick them off. It can take a few days for the nest to fully hatch. For those that make it out to open sea they enter what is known as the ‘Lost Years’ as its so difficult to tag theses babies and follow where they go we don’t actually know where they spend the next 10yrs or so, evidence points to them hanging out in sea kelp and floating clumps of seaweed until they have developed enough to return inshore and head for feeding grounds.
18th February 2020
Welcome to our next instalment of Turtle Tuesdays, so far we’ve looked at Sea Turtles breeding process and the development of the eggs in the nest. As we’ve discussed the odds of a hatchling Sea Turtle making it adulthood and continuing the cycle are extremely low, we mentioned the gauntlet that the hatchlings have to undergo just to make it out to the open ocean, from the second they emerge from the sand they are at risk of being swallowed up by Foxes, Badgers, Birds, land crabs and even domestic animals such as cats and dogs. Once the hatchlings have left the nest they use the light levels to guide them to the water, often hatching coincides with a full moon which shines brightly over the sea, making the seaward direction lighter than land, unfortunately if there are lights on or behind the beach the poor hatchlings head the wrong way and unless rescued by a passer by they’ll never make it to the ocean before dehydrating, being squashed or gobbled up. Scientists have been able to show their attraction to light by effectively covering the nest with a hut who’s door opens towards to the land, they noted all the hatchlings head out the door and turn 180 degrees and head right for the sea.
Once in the water the threats are still very real, at this small size (about the size of a match box) the hatchlings can only hold their breaths for a few minutes before they need to return to the surface for air making them easy pickings for sea gulls and other marine bird species, large fish, crabs, octopus, morays, well pretty much anything that can grab them takes advantage of these tasty and nutritious little morsels.
For the hatchlings first few weeks they do nothing but focus on getting out to the open ocean, they don’t need to forage for food as they have a reserve of nutrients they absorbed internally from the yolk before they hatch, they can survive on this yolk reserve for up to 2 weeks. Due to their tiny size it has only been recently scientist have been able to attach tiny transponders to the hatchlings and they have finally been able to record that once out of the nest the hatchlings do in fact head to open sea. There they will find shelter in floating kelp masses or Sargassum seaweed clumps where they will feed on plankton and other tiny creatures hanging out in the shelter of the weeds, this time is known as their lost years as we know very little about their time in the open oceans. Over the years they will spending their time feeding and growing, in their first year they’ll grow up to 5cm in length, this is their fastest growth phase, as after 5ys or so they will so down to roughly 1 cm a year. They keep growing their entire lives and we use their shell length as an indicator of their age.
25th February 2020
Welcome to another installment of our Turtle Tuesday info day. Last week we covered the hatchlings leaving the nest and heading out to open sea where they spend the next 10-15yrs growing before they head back closer to the shore and to feeding grounds where they will continue to grow until they are large enough to breed, this time scale varies with different species and it can be between 20 – 40 years before the juveniles have grown and developed enough to begin the cycle and continue it again and again.
All the details and information I’ve given so far has been general for all the different species of Sea Turtle. There are 7 confirmed species of Sea Turtle and one that is still under review as to if it is in fact an 8th species or a sub species. Depending on what you read or what research your looking at you’ll find that some say there are 7 and others will say there are 8 species of Sea Turtle. I personally lean more towards the research that shows there is an 8th species; The Pacific Black Turtle (Chelonia mydas ssp. agassizi). Black sea turtles are unique members of the sea turtle world. While currently classified as the same species as the green sea turtle, the pacific black sea turtle has several features that make it one of a kind! I’ll be looking into each species in more detail over the following weeks.
Illustrated in the 3rd image you can see that each species has different characteristics that we can use to distinguish between each species. To be able to ID effectively you do need some basic Turtle anatomy knowledge, which I’ve covered in the 2nd Image this week. Using these key features we can then identify which species of Sea Turtle we are looking at. This weeks Third Image covers all 8 species and has a great key for all 8 species and you can download the PDF here for future reference. http://www.seaturtle.org/documents/ID_sheet.pdf
10th March 2020
Hello and welcome to another addition of our weekly Sea Turtle installments, 2 weeks ago I introduced you to the 7/8 different Sea Turtle Species, this week I’d like to start looking in more detail into each and every species starting with the largest of all, the Leatherback (Dermochelys coriacea).
Leatherbacks belong to a different taxonomic family than all the other sea turtle species found in the world making they extremely unique. They have existed in their current form since the age of the dinosaurs.
The Leatherback receives its name from its unique shell, which unlike any of the other Sea Turtle species is not hard, in fact their top shell (carapace) is about 1.5 inches thick and consists of leathery, oil-saturated connective tissue overlaying loosely interlocking dermal bones. Their carapace has seven ridges that run along its length and they taper to a blunt point, this helps the Leatherback move more effectively in water. Their front flippers lack claws and scales (again unlike any other Sea Turtle) and are proportionally longer than in other species. Both their ridged carapace and their extra large fins make the Leatherback uniquely equipped for long distance foraging migrations.
Leatherbacks are highly migratory, with some individuals swimming over 10,000 miles a year between nesting and foraging grounds. They are strong swimmers and can dive to depths of approximately 1,200m (nearly 4,000 feet), deeper than any other turtle and most marine mammals; they can stay underwater for up to 85 minutes before needing to surface for air. Leatherbacks have a unique system of blood supply to their bones and cartilage. This enables their body temperature to stay several degrees above the ambient water temperature allowing them to tolerate cold water, much like a mammal.
Once prevalent in every ocean except the Arctic and Antarctic, the Leatherback’s population is rapidly declining in many parts of the world. The populations are divided between the Pacific and Atlantic populations. The Pacific population of Leatherback sea turtles has suffered most over the last twenty years: as few as 2,300 adult females now remain, making the Pacific Leatherback the world’s most endangered marine turtle population. All Leatherback turtle populations are listed as endangered. They face threats on both nesting beaches and at sea. The greatest of these threats worldwide are incidental capture in fishing gear and harvesting of Leatherback eggs and adults for their meat.
Sea turtles have been intentionally killed for their meat and skin for hundreds of years. The primary threat to Leatherback turtle populations worldwide is bycatch in fishing gear. Bycatch primarily occurs in gillnets, longlines, trawls, and trap/pot fisheries. Sea turtles may die after ingesting fishing line, balloons, or plastic bags, plastic pieces, and other plastic debris, which they can mistake for their preferred food, Jellyfish.
Populations numbers are difficult to record due to the adult female Leatherbacks frequently nest on different beaches, making nesting population estimates and trends very difficult to monitor. However, it is estimated that the global population has declined by at least 40% over the past three generations. It is believed there are between 34,000 – 36,000 nesting females worldwide. Females nest at intervals of 2 to 3 years, though recent research has indicated they can nest every year. When they do breed each female can lay between 4 to 7 nests per season, with an average of 10 days between each nest. Female’s lay an average of 80-100 fertilized eggs per nest, the eggs are the size of billiard balls, along with the 80+ fertilized eggs there are usually 20-30 smaller, unfertilised, oddly shaped eggs, in each nest, the reason for this is believed that they are ‘Spacers’ allowing better gas exchange within the nest. Eggs incubate for about 65 days before the hatchlings emerge.
Leatherbacks lack the crushing chewing plates characteristic of other sea turtles that feed on hard-bodied prey. Instead, they have pointed tooth-like cusps and sharp-edged jaws that are perfectly adapted for a diet of soft-bodied Open Ocean prey, such as jellyfish and salps. Their jaws would be damaged by anything other than a diet of soft-bodied animals, so they feed almost exclusively on jellyfish. It is remarkable that this large, active animal can survive on a diet of jellyfish, which are composed mostly of water and appear to be a poor source of nutrients.
Despite the low nutrient content Leatherbacks can grow up to 150 – 200 cm in length, with the largest Leatherback ever recorded at 305 cm (10ft) from the tip of its beak to the tip of its tail and weighed in at 916 kg. On average Leatherbacks weighs 300 – 500 kg. Very little is actually known about their lifespan but its believed they are one of the quickest to mature at 15yrs young and are estimate to live for 30-45 years.
Believe it or not there have been recorded distributions of Leatherbacks off the coast of Britain and Ireland. Present mostly in August and September off the south and west coasts. They have also been recorded off Shetland, the Firth of Forth and in the Humberside. So keep your eyes peeled.
17th March 2020
Hello Folks and welcome to another instalment of our Turtle Tuesdays, last week we found out more about the great ocean traveller, the Leatherback. Keeping with running in size order the second largest of the Sea Turtle species is probably the most famous of all the Sea Turtles, the Green Turtle (Chelonia mydas). Adults are 3 to 4 feet in carapace length (83 – 114 cm). The green turtle is the largest of the Cheloniidae family with the largest green turtle ever found at 5 feet (152 cm) in length and 871 pounds (395 kg). Adults usually weigh between 240 and 420 pounds (110 – 190 kg).
A common misconception is that the Green Turtle receives their name from their diet, which is mainly sea grass and algae; they are the only Sea Turtle species that are for the majority of their lives are vegetarian. They in fact receive the name ‘Green’ as they have green body fat.
Many years ago when sea travel took weeks to months to cross the Oceans, Sailors would catch and store a number of sea Turtles in the ships hold for their meat, you see the turtles could be caught and then stored for months due to the Turtles ability to slow their metabolism, they are able to stay alive for months without any food, this was the beginning of their downfall as this form of meat was in plentiful supply and was the best way for the sailors to keep fresh meat in their diets during long periods at sea.
As with all other species of Sea Turtle the Green Turtle are endangered, however there is some great news for the Greens; in 2016 they went from Critically endangered to Endangered, this is the only Turtle species to show a significant increase in the population numbers, yes they are still endangered and under threat but the population is beginning to make a come back.
Green Sea Turtles have to be one of the most photographed of all the Species, this is due to the fact that their preferred habitat is where divers frequently dive; along the coastlines of temperate sea’s around islands and in bays and protected shores and especially in areas with sea grass beds. Rarely are they observed in the open ocean.
Like other sea turtles, they migrate long distances between feeding grounds and the beaches from where they hatched.
Green Turtles play a vital role in the maintenance of a healthy Sea Grass bed, they act like lawnmowers trimming the grass and keeping it in check. If sea grass beds were left unattended they grow rapidly and become so thick and dense that all water circulation around the bed would actually stop creating a toxic environment. We know sea Grass beds are vital for many juvenile fish, sea horses and other crustaceans.
Green Sea Turtles are easily distinguished from other sea turtles as they have a single pair of prefrontal scales (these are the scales in front of their eyes), rather than two pairs as found on other sea turtles. Their head is small and blunt with a serrated jaw designed for cutting sea grass and algae. The Carapace is bony without ridges and has large, non-overlapping, scutes (scales) present with only 4 or 5 lateral scutes. Their body is nearly oval in shape and their front fins have 1 visible claw. The carapace colour varies from pale to very dark green and plain to very brilliant yellow, brown and green tones with radiating stripes. This too was another downfall for the Greens as this colour and patterning was highly sought after and their shells were used to make a number of different items including jewellery, brushes and souvenirs. The plastron varies from white, dirty white or yellowish in the Atlantic populations to dark grey-bluish-green in the Pacific populations. Green Turtle hatchlings are one of the easiest to identify, as they are dark-brown or nearly black on top with a white underneath and white flipper margins. Greens have been found to be one of the longest lived of all the Sea Turtle Species with estimates of some individuals living for over 120years, generally its believed green Turtles live between 80-100 years.
The greatest threat green Turtles face in this day and age is from the commercial harvest for eggs and food. Other green turtle parts are used for leather and small turtles are sometimes stuffed for ornamental purposes. Incidental catch in commercial shrimp trawling is an increasing source of mortality. It is estimated the current Green Sea Turtle population is between 85,000 and 90,000 nesting females.
It was lovely in our first post to see all your turtle in counters and we’d love to hear and see about any more green turtle experiences you may have had.
24th March 2020
Welcome to another instalment of Aquatron’s Turtle Tuesdays. With everything going on right now we’d like to continue to provide a little distraction in these troubling times.
Last week we looked at the famous green turtle the only turtle species with some success in increasing population numbers, we’ll return to this success story and others like it involving current conservation actions in the following weeks.
This week I’d like to look deeper at the most debated of the sea Turtle species, “The Black Turtle” (Chelonia mydas agassizii). They are a unique member of the sea turtle family, while currently classified as the same species as the Green Sea Turtle (Chelonia mydas), the pacific black sea turtle has several features that makes them rather unique.
Tracing back the history of the black turtle, one important event stands out; between 3 and 20 million years ago Central America rose up out of the sea, this created a land barrier between the Atlantic and the Pacific, isolating two populations of green turtles from each other.
Black turtles are generally found in the eastern t0071a1ropical Pacific, adult’s tend to inhabit bays and protected shorelines from California down the Pacific coastline to Chile. They are not commonly seen in open oceans.
They were initially known as the East Pacific green sea turtle even though there are several differences between them and green turtles, the black sea turtle is smaller and darker in colour than the green’s (hence the name), it has a teardrop shaped carapace rather than oval and their heads are even smaller than those of green sea turtles, however they both share the same serrated jaw not found in any other sea turtle species.
Even though black sea turtles tend to be smaller than greens, they can still weigh up to 300 pounds (136 kg) and reach 4 feet (120cm) in length.
The first of the unique distinction between the black sea turtles and the greens is that they are the only sea turtle known to nest in the Galapagos Islands – black turtle nests also occur in Central America and Mexico. The second unique trait black sea turtles display is that they can been found basking in the sun along some of the Hawaiian Islands beaches, this is a characteristic not found in other sea turtle species, others will bask in the sun while floating at the surface.
There are a number of similarities that lead to the belief that these were in fact green turtles; they have a similar diet of algae, sea grass and mangrove shoots, in addition they both will occasionally eat small fish, jellyfish and other invertebrates.
But is the black turtle a unique species? Studies of skull anatomy suggest the black turtles are indeed different to greens, however DNA analysis shows that there is no genetic distinction between the two and that there is a close genetic relationship between the two types of sea turtle. Based on this evidence, they are classified as the same species. However, due to their differences, some experts consider the black sea turtle to be a sub-species of the green sea turtle, while other experts consider the black sea turtle to be its own species.
Historically, colonies of black sea turtles thrived in Mexico and Central America. The fishing industry and illegal harvest of eggs and turtles for meat has decimated these populations. Today, they are still caught illegally for food and accidentally in many types of fishing nets.
Many conservationists consider a separate species designation as important to saving the black sea turtle, as it would certainly gain additional protection status – since the black sea turtle is more threatened than the green sea turtle.
31st March 2020
Hello and welcome to another instalment of our Turtle Tuesdays, after a little detour with the Black Sea turtle last week, this week we are returning to size order after the green turtle. The next species down in size and is one which holds the biggest place in my heart; the Loggerhead’s (Caretta caretta) this is the species I have had the privilege of working with the most. Loggerheads receive their name due to having the largest head to body size of all the turtle species, their extra large head has developed due to their preferred diet; crabs, hard shelled molluscs and crustaceans. Their muscles they have developed to have the power in their jaws to crush through shells to retrieve the tasty nutritious morsal hidden inside has lead to the development of larger heads.
They are probably one of the most mis identified of all the sea turtles, often mistaken for a green turtle or a hawksbill. Loggerheads range in colour from dark brown, reddish brown too light tan. Their carapace is bony without ridges and has large, non-overlapping rough textured scutes, their carapace is heart shaped and can range in colour like their skin from a reddish brown to dark brown on top and underneath their plastron is a yellowish brown. They have short front fins with 2 short and thick with claws. Often the claws can be used to identify between adult males and females (this is true for all turtle species), the males will have a hooked shaped claw to hold onto the females during mating and the females’s claw will be straight.
Loggerheads typically measure 80 to 110 cm in carapace length (2.5 to 3.5 feet). Adults weigh between 155 and 375 pounds (70 to 170 kg), they are estimated to live between 70-90 years.
As mentioned loggerheads are primarily carnivorous and feed mostly on shellfish that live on the bottom of the sea bed. They eat crabs, lobsters, clams, mussels, and other invertebrates. Their powerful jaw muscles help them easily crush the shellfish. Loggerheads are messy eaters and this has a vital role in the balance of the marine ecosystem, all the crushed shells now provide a calcium source (as well as scraps of food) for many many small creatures that wouldn’t otherwise be able to source this mineral alone.
Loggerheads tend to prefer to feed in coastal bays and estuaries, in the shallow waters along the continental shelves of the Atlantic, Pacific and Indian Oceans as well as along the Mediterranean coast where some areas are feeding grounds and others are nesting sites.
They nest every 2 to 4 years, laying 3 to 6 nests per season, with approximately 12 to 14 days between each nest. Clutches average of between 100 to 130 eggs per nest. The eggs will incubate for 40-60 days.
Loggerheads are listed as venerable with decreasing nest numbers it is feared they will soon have their status changed to endangered.
Their greatest threat is loss of nesting habitat due to coastal development, predation of nests, and human disturbances (such as coastal lighting and housing developments) that cause disorientations during the emergence of hatchlings. Other major threats include incidental capture in longline fishing, shrimp trawling and pollution. Incidental capture in fisheries is thought to have played a significant role in the recent population declines observed for the loggerhead.
It is estimated there are between 40,000 and 50,000 nesting females. It’s important to understand that population estimates on all species of sea turtle are based on the number of nests recorded, this of course won’t include males or juveniles. There are a number of different projects underway with fin tags and satellite tracking, sea turtle research and conservation is a long and slow process partly due to the number of years sea turtles take to reach maturity and reproduce.
7th April 2020
Welcome to our next instalment of Turtle Tuesdays, next in our size order is one of the least studied and most unusual of all the sea turtles, the very unique Flatback Sea Turtle (Natator depressus), often known as the Australian flatback as its native to the northern coast of Australia. It receives its name from (yes you guessed it!) its flat carapace (shell). All other sea turtle species have a curved carapace including the leatherback, however the flatback sea turtle has a more oval carapace lacking in ridges and protuberances, making it appear flat and smooth. Their carapace is grayish-green or olive green in colour with a slight down curve before a distinctive up curve around their outer margins.
Their fins and the rest of the body is a yellowish light green, with their plastrons (the underside of the shell) being pale yellow like most other turtles. These unique features make the flatback one of the easiest turtles to identify.
The flatback has the smallest geographic range of all turtle species (making their lack of research surprising). Their distribution is restricted to tropical regions of the continental shelf and coastal waters of Northern Australia, Southern Indonesia, and Southern Papua New Guinea. They do not have an oceanic phase or undertake long open ocean migrations like other sea turtles, and are usually found in waters less than 60m (200ft) deep and they seldom enter open oceans or venture far from the continental shelf.
Breeding and nesting occur on beaches of the north of Australia, southern Indonesia, and Papua New Guinea. Australia has the largest concentration of females nesting on Crab Island in the NE Gulf of Carpentaria in Queensland.
Some females will lay up to four nests per season with an interval of 13 – 18 days between nests. They breed any time of the year, however breeding increases during the months of June, July and August.
In comparison to other sea turtle species flatbacks lay fewer eggs per nest with an average of just 50 eggs. Despite this their eggs and hatchlings, are proportionally larger than other species. The eggs have a diameter of approximately 2 inches making them slightly smaller than leatherbacks and larger than green turtle eggs. The eggs will hatch around 55 days after the mother has laid them. Once the hatchlings emerge they too are larger than other turtle hatchling, it’s believed their larger size aids the hatchlings in evading predators. You’ll see from the hatchling comparison photos that flatback hatchlings are almost as large as leatherbacks hatchlings.
There are zones close to the Great Barrier Reef that makes up part of their distribution, here there are abundant food sources and an environment full of marine life. However, they tend to prefer to stay in areas with soft sea beds either sandy or covered in marine vegetation, they do not inhabit coral reef systems but mearly visit.
As their carapace is thinner than other turtles, it can be easily damaged by hard substrates, it’s believed they stay away from rocks and rocky seabeds to prevent any injury.
The diet of the flatback sea turtle is varied and omnivorous. They prey on species found in shallow waters including mollusks, jellyfish, shrimp, squid, white corals, sea cucumbers, and seagrass. Adults can weigh up to 90 kilos (200lbs) and measure upto 1m in length (3ft).
Adult Flatbacks have a few marine predators; killer whales (Orcinus orca), some species of sharks and saltwater crocodiles. Adult female fallbacks have been observed being attacked by crocs while attempting to nest. On land, they have several natural enemies that eat their eggs or attack the hatchlings such as foxes, dogs and dingos, lizards, sand monitors, birds-including night herons and pelicans, even feral pigs will consume almost their entire nests on some beaches.
Flatbacks have a conservation status of “Data Deficient” in the Red List of the International Union for the Conservation of Nature (IUCN). This classification means that there is not enough information to assess their status as there is no accurate data available on their population numbers and trend. However, estimations believe there to be around 10,000 nesting females.
Other threats to this species include loss and degradation of their habitat, illegal traffic of eggs, direct capture for meat consumption, bycatch, climate change and ocean pollution are some of the greatest threats derived from human activities.
The flatback sea turtles are perhaps one of the least threatened of all sea turtles by bycatch due to their preference to stay in shallow waters where less fishing takes place.
The Flatback is a Turtle I have yet to encounter, have any of you ever seen one?
14th April 2020
Hello and welcome to next instalment of Turtle Tuesdays, this week we’re looking at the Hawksbill Turtle (Eretmochelys imbricata), often viewed as the most beautiful due to their exquisitely patterned and colourful carapace/shell which amazingly can vary in colour depending on whether they are found in cold or warm waters. Hawksbills are relatively small compared to all the other species we have looked at so far, they grow up to 2.5ft – 3ft (70 – 100 cm) in shell length with adults weighing between 45 – 90 kg (100 – 200 lbs).
Their name comes from their narrow heads and sharp, hawks like shaped beak. All other sea turtles have a rounded head with a rounded beak, as you can see in the images, the hawksbills beak is rather pointy in comparison. Their narrow head has 2 pairs of prefrontal scales. Their jaw is not serrated. They have a carapace which is bony without ridges and has large, over-lapping scutes (scales) making this one of the easiest ways to ID them. While young, their carapace is heart shaped, as they mature it elongates and becomes elliptical in shape with a serrated edge. Their front fins have 2 claws each with male hawksbills having longer claws, thicker tails, and somewhat brighter colouring than females.
Hawksbills are found throughout Earth’s midsection in tropical and sub tropical waters of the Atlantic, Pacific, and Indian Oceans. The largest populations occur in the Caribbean Sea, the Seychelles, Indonesia, Mexico, and Australia. They spend the majority of their time in coral reefs but can also be found in rocky areas, lagoons, mangroves, oceanic islands, and shallow coastal areas.
Hawksbills are vital inhabitants of coral reefs and play an important role as ‘Reef Caretakers’. Their special narrow heads and beaks can reach into the cracks and crevices of coral reefs to find their favourite food, sponges which they almost exclusively eat but they will substitute their diet with anemones, squid, shrimp, mollusks, marine algae, crustaceans, sea urchins, fish, and jellyfish.
Hawksbills consumption of sponges, plays a very important role in the reefs ecosystem. Sponges are like weeds of the reef, they are faster growing than corals and if left unmaintained they would suffocate the corals killing the reef. It’s estimated that one turtle can consume over 1,000 pounds of sponges per year.
Hawksbills do a lot of snacking, often break off pieces of the coral reef, which helps other fish access nutrients they otherwise wouldn’t be able to obtain.
Hawksbills are lone travellers and solitary nesters, migrating long distances between feeding and nesting sites, they choosing to nest on small scattered beaches. They mate every couple of years and will lay between 4 – 6 nests with 2 week intervals. Females will lay around 130 to 160 eggs per nest, there have been nests recorded with over 200 eggs! The eggs will incubate and hatch in about 60 days to begin the gauntlet to the sea and survival. Hawksbills live for around 50yrs reaching reproductive age after 15-20yrs
Their hard shells protect them from many predators, but they still fall prey to large fish, sharks, crocodiles, octopuses, and humans.
Hawksbills are considered Critically Endangered around the world by the IUCN Red List. Some researchers believe the Eastern Pacific hawksbill is likely the most endangered sea turtle population worldwide with the worlds population trend decreasing.
Their population has declined more than 80% in the past century, primarily due to the trade of their shell for ‘tortoiseshell’ products, we’ll be returning to this topic in the following weeks. Other threats include coastal development destroying nesting and feeding habitats, pollution and plastic ingestion, boat strikes, entanglement in fishing gear, dynamite fishing and consumption of their eggs and meat.
It’s estimated there are between 20,000 and 23,000 nesting females.
Below is a link to a video of a Hawksbill on a night dive under UV light showing off some amazing biofluorescence.
21st April 2020
It’s Turtle Tuesday time again folks and this week it’s the turn of the Olive Ridley Sea Turtle (Lepidochelys olivacea), they are the second smallest of all sea turtles and it maybe a surprise to hear that they are the most abundant of all. They receive their name from their grey green/olive coloured carapace (shell) which is smooth and almost circular in shape, their head’s are rather small and their carapace is bony, without ridges and has large scutes (scales). Hatchlings are black with greenish sides and juveniles are more charcoal, before as adults becoming its namesakes ‘Olive’ colouring.
Both their front and rear fins have 1 or 2 visible claws. Uniquely there have been some individuals found with an extra claw on their front fins.
Adults measure 2-2.5ft (60-70cm) in carapace length and weighing in between 34-45kg (75-100lbs). Adults reach sexual maturity around the age of 15 years and live for between 45-55 years.
Olive ridley’s occur globally inhabiting the tropical and subtropical waters of the Pacific, Indian and Southern Atlantic Oceans. They are primarily pelagic, spending much of their life in the open oceans. Some inhabit continental shelf areas and venture into bays and estuaries, which is where any sightings take place.
Olive Ridley’s have powerful jaws that allow them to lead an omnivore diet, they eat a variety of prey including crabs, shrimp, lobster, urchins, jellies, tunicates, algae, and fish. They typically forage off shore in surface waters or dive to depths of 500ft (150 m) to feed on bottom dwelling crustaceans.
Olive Ridley’s nest every year and are known for their mass synchronised nesting called arribadas (Spanish for “arrival”). They and the Kemp’s Ridley (which we’ll be covering next week) are the only two sea turtle species to nest this way. Nesting females will nest 2 times a season with an average clutch size of 100-120 eggs which incubate for around 52-58 days.
Main Nesting arribadas occur in Mexico, Nicaragua, Costa Rica, Panama, Australia, and parts of Africa, however they do nest in over 40 countries worldwide where mainly solitary nesting occurs.
The largest arribadas are found in Costa Rica, Mexico, and India. During arribadas, thousands of females will all crawl out on to the beaches together, although arribadas are not well understood, the timing is thought to coincide with weather events or with the lunar and tide cycles. The females congregate in large groups offshore of nesting beaches and then simultaneously come ashore to nest crowding the beaches. It’s unknown why some turtles nest in arribadas and others are solitary nesters, in some cases it has been found that females will use both strategies during a single nesting season, nesting in both groups and alone making any sound theories difficult to prove.
Despite their relative abundance in comparison to other sea turtles, Olive Ridley’s are considered Vulnerable by the IUCN Red List with a decreasing population.
Although they are the most abundant species, their numbers have decreased by approximately 50% since the 1960’s. Unfortunately as olive ridleys congregate in large numbers off of nesting areas, they are prone to mass mortality events and direct harvest of their eggs for human consumption. Other threats include entanglement in fishing, especially shrimping nets and loss of nesting habitat due to coastal development.
There are estimated to be around 800,000 nesting females.
28th April 2020
It’s Turtle Tuesday time again folks, this week we are looking at the last of the sea turtle species and its the smallest and most vulnerable of all; the Kemp’s Ridley Sea Turtle (Lepidochelys kempii), named after Richard Kemp a fisherman from Florida who helped discover and study the species. It’s not clear why they are called ridley, one possibility is due to them having similar nesting behaviours as the olive ridley which we covered last week.
They weigh between 30-50kg (70-108lbs) and grow up to 2 ft long (58-66cm).
Their heads are triangular in shape and a moderate size, they have hooked beaks and strong jaws, their carapace is rounded and bony without ridges and has large, non-overlapping scutes (scales). Their front fins have 1 claw, while the rear fins have 1 or 2 claws. Adults have a dark grey green carapace with a white or yellowish plastron, while the hatchlings are jet black.
They are carnivores and their powerful jaws help them to crush and grind crabs, clams, mussels, and shrimp. They also like to eat fish, sea urchins, squid and jellyfish, however their preferred prey by far is crab. They are found in nearshore shallow areas with sandy or muddy bottoms where their favourite prey is found.
As with the olive Ridleys, the kemp’s ridleys nest in mass arribadas, however kemp’s ridleys will nest mainly during the day making it the only sea turtle to do this. Kemp’s ridleys reach sexual maturity significantly younger than any other turtle species at around 10-15yrs old.
Kemp’s ridleys nest more often than many other sea turtles, every 1-2 years on average and they will nest 2-3 times each season. They lay between 90-110 eggs in each nest which incubate for around 55 days.
Nesting is quite a spectacle to witness. Wave upon wave of females come crashing ashore, laying their eggs in broad daylight from April to July on beaches in Mexico, Texas, and Florida. In 1947 an arribada of more than 40,000 Kemp’s ridleys was filmed at Rancho Nuevo, Mexico. In the mid-1980’s a low of around 700 nests were documented on these same beaches.
Hatchlings will head from the beach to open water where they spend the first two years of their lives riding the tides up and down the Atlantic coast, from as far north as Nova Scotia to as far south as Bermuda. After two years of travelling the coast, adolescent Kemp’s ridleys return to the Gulf of Mexico. Here, they forage for crabs and shrimp, rarely diving deeper than 50m (162ft). Adults are mainly limited to the Gulf of Mexico, and are not known to venture far.
By far the greatest threats to the Kemp’s ridleys are due to human activities including harvesting of eggs and adults, as by catch in shrimp trawl nets and pollution. Kemps were on the brink of extinction in the 1960’s and in 1966 it was made illegal to harvest their eggs, and with strict protection laws of their nesting beaches in Mexico the number of eggs harvested has dramatically reduced. Accidental capture in fishing gear, has also been reduced, the shrimp industry is now required to use Turtle Excluder Devices ((TEDs) more details on these in following weeks) in both the U.S. and in Mexico. These devices allow sea turtles to escape through a hatch in the nets, and they have greatly reduced sea turtle mortality from shrimp fishing nets but have a long way to go still to completely eliminate it.
Since the enactment of harvesting laws and commercial fishing regulations, Kemp’s ridleys have been able to recover to a small extent. Current setbacks to their recovery include beach traffic and development, beachfront lighting which attracts hatchlings away from the moonlit ocean and into roads.
Pollution poses another serious threat, Kemp’s ridleys have a hard time distinguishing plastic bags and other litter from food as well as contaminants like oil impacts their survival, following Deepwater Horizon, 600 sea turtles were found dead, 75% of which were Kemp’s ridleys. Unfortunately for Kemp’s ridleys their small distribution makes them particularly vulnerable to localized threats like commercial fishing and oil spills.
Kemp’s ridley sea turtles are listed as Critically Endangered on the IUCN red list.
It is estimated there are between 7,000 and 9,000 nesting females, with an estimated adult population of around 22,000.
5th May 2020
Welcome to another instalment of our Turtle Tuesdays, over the weeks we have covered the life cycle of Sea Turtles and each individual sea turtle species that exists today. Before our modern turtles there were a four different sea turtle families; Toxochelyidae (extinct), Cheloniidae (this family includes all our modern day hard-shelled sea turtles), Protostegidae (extinct), and Dermochelyidae (this family includes our modern day leatherback) as shown in the first image set.
The first turtles appeared during the Triassic period, 245 to 209 million years ago.
Scientists believe that modern sea turtles are derived from marsh-inhabiting ancestors that lived during the Late Triassic period.
Fossil records show that the now-extinct sea turtle Archelon ischyros, which lived 75 to 65 million years ago during the late Cretaceous Period, it belonged to the Protostegidae family. It was one of the largest turtles that ever lived, reaching a length of 4.6 m (15 ft.) and weighing more than 2,700 kg (6,000 lbs.). It was first discovered in 1895 by Dr. G.R.Wieland in South Dakota, he name it Archelon – a name which means “ruling turtle.” Archelon as shown in our second image set lived in the oceans around what is now North America, it was a Carnivore and it’s believed its diet included Squid and Jellyfish.
An interesting fact is not Archelon’s great size but its shell. This turtle didn’t have the same kind of hard shell that modern turtles do today. They had either bony plates or a leather-like covering that stretched over a framework of bones on its back. If it would’ve had a hard shell, then it most likely wouldn’t have been able to stay afloat or swim neutrally buoyant.
Archelon also had flipper-like arms that allowed it to move through the water fairly quickly. Which would’ve been needed considering the kinds of animals it was sharing the ocean with at the time.
Paleontologists believe that Archelon probably had a long lifespan, much like modern turtles do today. Scientists believe that it probably lived around 100 years – on average. They may have lived even longer than that.
The third set of images today are of Protostega gigas is a species of extinct sea turtle from 85 million years ago. They swam in North America’s Cretaceous inland sea, which connected the Gulf of Mexico with the Arctic Ocean. With some individuals over 12 feet long and up to 2,000 pounds. Interestingly there have been fossil records of Protostega in the UK, imagine coming across one of these on a dive!!
It wasn’t long ago that scientists believed the Protostegidae were closely related to modern day sea turtles, however, more recent research suggests they are a completely separate lineage.
Many of the species in the Toxochelyidae and Protostegidae families went extinct during the asteroid event some 66 million-years-ago, it’s believed to have caused the disappearance of the dinosaurs. About three-quarters of the animal and plant life on Earth went extinct during this event. The fact that some turtle species survived this biological catastrophe, including the ancestors of modern sea turtles, is evidence of their adaptability. The few species from Toxochelyidae and Protostegidae families that survived the asteroid eventually became extinct 50 million-years-ago.
But, species from the Cheloniidae and Dermochelyidae families have continued on to the present day.
Scientists are still trying to piece together the sea turtle’s complete and accurate evolutionary history. Their timeline is an ongoing area of research and new discoveries are still being made to fill in their family tree with fossils of new species being discovered as recently as 2019.
12th May 2020
Hello and welcome to our next instalment of Turtle Tuesday’s, this week we’re looking at how turtles have evolved into the turtles that we see in our oceans today. Sea turtles have a complicated evolutionary history, as we mentioned last week. Researchers are still finding new fossils and evidence that are filling in the many gaps and are either confirming or disproving scientific theories. All turtles, tortoises, and terrapins, including sea turtles, are in the Testudine order. It was originally thought that Testudines were closely related to lizards and this was the believed theory for many decades. However in 2014, new DNA sequencing techniques allowed scientists to determine turtles are in fact closely related to Archosaurs, a group that includes birds, crocodiles, and dinosaurs. This new information has led scientists to place the Testudines and Archosaurs into a newly created clade called Archelosauria.(The term “clade” comes from the Greek “klados,” for “branch.” It’s useful to think of a clade as being one branch on the tree of life, where the common ancestor is the place that the branch split from the main trunk).
The following link details the evolutionary history of sea Turtles with some great images and information; https://www.aquarium.co.za/blog/entry/where-did-sea-turtles-come-from
The link above details the evolution of sea Turtles, and I’d like to further elaborate on some other adaptations that turtles have under gone to survive life at sea. All the seven/eight sea turtle species today are part of a group of around 100 living marine reptile species in the world. Sea turtle bodies are hydrodynamic, meaning they’re shaped to minimise drag and resistance when traveling through water. Their shells are streamlined, compact, and flattened. Sea turtles have flippers, which act like big paddles or oars, enabling the turtles to move through the water more like fish rather than lumbering reptiles.
Living in salty water is not easy and sea turtles have special adaptations in order to survive in the excessive salt of their environment. If sea turtles had a salt concentration in their body the same as their saltwater surroundings, it would be lethal. Every living organism needs water to survive and if we were to drink seawater and not freshwater, it would dehydrate us and lead to death. Sea turtles don’t have this problem, they obtain water from their food, and they have developed the ability to metabolise saltwater. They have specialised glands which concentrate and excrete the salt and retain the water. These large glands are located by their eyes, they release salt in higher concentrations than the surrounding ocean water, making them more dense, on land the salt excreation can have an almost jelly like appearance. These salt glands and extreations are why many people who observe sea turtles on land believe that they are crying as shown in the first image set. This adaptation also helps keep sand out of their eyes as they nest.
The leatherback sea turtle has extremely large salt glands compared to other species; their glands are more than twice the size of their brains. They require such large salt glands due to their preferred diet of jellyfish, jellies are mostly composed of seawater, so the leatherback ingests much more salt while feeding than any other sea turtle.
Most sea turtles are ectothermic or “cold blooded,” which means that they cannot regulate their internal body temperature, making their metabolism dependent on the surrounding environment. Being ectothermic has some advantages, it enables them to lower their metabolic rate, so they require less oxygen and can stay submerged for longer periods of time. However, being dependent on the temperature of the environment also has disadvantages. Most sea turtles are limited to tropical and temperate waters. If they encounter cold waters, they can become “cold-stunned” where their body enters into a state of shock and begins slowing down which can lead to turtles becoming stranded or eventually dyeing.
Leatherbacks are uniquely adapted to venture into and stay in colder waters through a variety of behavioural and physiological mechanisms. Leatherbacks possess the unique ability to hold and regulate their body temperature independent of the environmental temperature. This makes them endothermic. Their large size compared to their body surface area allows for a more efficient storage of heat. They use a counter current heating system, this system runs warm blood from their inner bodies out to their extremities next to the cold blood running back inwards. The two blood temperatures participate in heat exchange and, therefore, the cold blood is warmed before re-entering the body core as shown in the second image set.
A layer of fat under the carapace insulates the turtle’s insides from the cool water, and the oils in its body store heat. Diving deeper than other sea turtles. Leatherbacks have a higher number of red blood cells and higher concentrations of myoglobin in their muscles, enabling them to carry more oxygen and stay submerged for longer periods of time.
19th May 2020
It’s Turtle Tuesday time again folks, this week and next we’re looking at Turtle’s senses. Sea Turtles have all the same senses as us which are adapted to help them survive a life under the sea. In addition to the regular senses sea turtles have some additional ones that we’ll cover next week. This week we’ll cover sight, sound, touch and taste.
Sight
Turtles have developed a great sense of sight, spending most of their lives below the waves they have excellent underwater vision. Sea turtles spend significant amounts of time at the surface when breathing, or as hatchlings and nesting females also spend time, however brief, on the beach. Therefore, sea turtles have eyes adapted to see in both air and water and they can easily adapt their vision between the two. However, their eyes are best adapted for excellent vision underwater.
Humans eyes have a curved cornea that refracts light and helps us to see/focus in air. Corneas lose all ability to refract light when submerged in water, this causes the blurred view we see when we open our eyes underwater, hence why we use a mask to create the air space for our eyes to focus.
Fish have a cornea merely as a protective barrier, all the refractive power of a fish’s eye is contained in their lens giving them underwater sight. Turtles have eyes that combine these two eye types, they have flat corneas and a nearly spherical lens, consequently, they are a little nearsighted on land but perfectly suited to seeing underwater.
Sea turtles can see in colour, this ability helps them to avoid predators and distinguish what foods they are going to eat. They are able to distinguish pattern and shape differences. Despite being able to see well enough to detect patterns, turtles don’t have peripheral vision.
Turtles spend time at a variety of depths in the ocean with varying light levels. In the eye, cells called rods detect movement in dim light conditions and cells called cones detect coloured light. Animals that see well in the dark have more rods than cones. Another trait that equips animals to see well in dim light are large eyes with large pupils.
Sea turtles have fairly evenly distributed rods and cones and their eyes are small in comparison to their body size. These traits equip sea turtles to see best in bright light. So, how do sea turtles see when they feed at depth or at night? The answer may lie in their ability to see bioluminescence. The pupil of a sea turtle’s eye is sufficiently big enough to detect the point-source light of bioluminescent prey. This glow is all they need to locate their meal.
Hearing
Turtle’s ears are much smaller than ours and though not visible on the outside of their head, their ears allow them to hear vibrations in the water. Their ears are covered by a protective layer of skin called the tympanum. Underneath the tympanum is a layer of fat unique to sea turtles. Scientists believe this layer may act similarly to the way a toothed whale’s fatty tissue can channel low-frequency sounds into the inner ear.
In 2014 a study showed that both hatchling and juvenile loggerhead sea turtles hear and respond to low-frequency sounds. This observation suggests that, like some whales, sea turtles are low-frequency specialists.
Interestingly it has also been found that even though Turtle’s ears are lacking an eardrum and other organs, the organs they do have within their ears help them to feel changes in water pressure that can warn them of the presence of predators not in their line of sight. More research needs to be done to further understand how and what sea turtles are hearing.
Touch
Turtles can’t feel touch in the same way as we do, while their skin is leathery, it is still very sensitive. Even the hard bony shell of a sea turtle can actually sense when something touches it. There are a series of thin nerves running along the shell and detect pressure changes associated with touch (a compassion would be like our nail’s, you can feel when something touches them but can’t feel detail like our finger tips). The nerves do not contain pain receptors so scientists do not think sea turtles feel pain when touched on the shell. In addition, researchers and scuba divers have observed sea turtles responding to the stimulation of being touched on the skin of their head, neck and shell. Whist working for a rescue centre we had one patient who actually loved a neck tickle and would swim over from the other side of her rehab pool towards you and stretch her neck out waiting for a tickle. I have also personally found that wild turtles who have a lot of algae growth on their shells and have signs that they have been scratching their shells on rocks, often love a good shell scratch. I’ve even seen hawksbills and green turtles wedging themselves under rocks and rocking back and forth to scratch their shell.
Taste
Sea turtles have taste buds giving them the ability to taste their food, which raises the question of how they deal with jellyfish venom. Interestingly there are fresh water turtles, like the snapping turtle which do not have taste buds, it’s believed to help them eat food/prey that would otherwise be perceived as poisonous. For Sea Turtles they can eat both non-poisonous and poisonous jellyfish. Sea Turtles actually have special adaptations to protect them from sea jelly venom called papillae. Papillae are spiny projections pointing inwards towards the throat, they line the turtle’s oesophagus from the opening of their mouth all the way to the stomach. They are made out of the same protein found in our hair and nails; keratin. Not only do they protect the turtle’s throat and mouth from jellyfish stings, they also help break down the food and expel excess salt water. There is one unfortunate disadvantage to having papillae and that is they only allow passage in one direction, so in the case of a mis-identified jellyfish, plastic bags can not be regurgitated, we’ll be coving more on this in future weeks.
26th May 2020
Welcome to another Turtle Tuesday, this week we’re continuing with senses and starting with smell.
Smell
Most researchers believe that sea turtles have an acute sense of smell in the water and on land. The two holes above their mouths are nares and are part of the turtle’s nose, they don’t have nostrils as such but can open and close their nares.
There have been a number of different experiments testing if turtles do have a sense of smell, a study a few years ago revealed that loggerheads may locate their prey with smell. A follow-up study found that the turtles are particularly attracted to a smell similar to that of boiling cabbage.
Researchers placed young loggerheads in tanks, and wafted different scents over the tanks – lemon, cinnamon, jasmine, and a cabbagey smell produced by a compound known as dimethyl sulphide. In the oceans, it’s released by algae when they’re being consumed. The turtles were indifferent to the other smells, but spent twice as long sniffing air that was dosed with dimethyl sulphide.
In the open ocean, that smell is common in areas of upwelling. Cold, nutrient-rich waters from the deep rise to the surface, spawning massive blooms of algae. The blooms attract creatures that dine on the algae, including jellyfish. So if a loggerhead smells the aroma of boiling cabbage, it’s a good bet that there’s a plentiful supply of jellyfish – a feast that helps the loggerhead keep going in its long-range journey through the sea. Other experiments also showed that loggerhead hatchlings react to the scent of shrimp and other shellfish. It’s believed turtles use both sight and smell to locate prey and rely more on smell in reduced visibility.
A sea turtle opens its mouth slightly and draws in water through the nose and passes over the olfactory gland. It then immediately empties the water out again through the mouth. Pulsating movements of the throat are thought to be associated with smelling the water.
Sea turtles use their sense of smell during mating season to pick up on the pheromones coming from female turtles.
Smell is also believed to contribute to how female sea turtles find their way back to their home beach to nest.
Magnetic sense
Sea turtles have an internal compass, which they use to orientate themselves to the Earth’s magnetic field and navigate the open oceans. This internal compass uses an additional sense that enables them to detect and utilise the Earth’s magnetic field as a guide/map, although scientists do not fully understand how their magnetic sensitivity works. In one study hatchling loggerhead sea turtles were placed in a large pool of water in a controlled laboratory setting. Researchers varied the magnetic orientation of the pool to observe the hatchlings behaviour. When the sea turtles were exposed to simulated magnetic conditions that placed them either north or south of their normal migratory pathway, they reacted by swimming in the direction that put them back on their normal migratory course. This remarkable magnetic sense provides sea turtles directional information, the same way we use a compass, as well as an accurate sense of their location and position on the Earth, helping them orient as they travel vast distances across the oceans to arrive in their desired location.
Natal homing
Female sea turtles migrate thousands of miles, sometimes to the same beach where they were born, in order to nest. This phenomenon is called natal homing. There are two main hypotheses for how sea turtles are able to do this. The first is that sea turtles use the Earth’s magnetic field to distinguish their global position by latitude and longitude. Navigating by this internal compass would enable a sea turtle to return to the specific location she remembers from when she first entered the sea as a hatchling. Another possibility is that sea turtles can imprint or distinctly remember certain characteristics of their home beach, such as a distinctive sights and smells. Scientists think that sea turtles use a combination of these two techniques to find their way back to their birth beach. The use of the magnetic field would get them to the right area of the globe, while the imprinting would help them identify the exact beach. Research has been conducted where female turtles have had magnets attached to their shells to disrupt the magnetic field around them, they still found their way back to the beach, they have even put little blindfolds on females and again they still find the beach. One set of research went even further where they inhibited the females from smelling (they covered their nares) and again the females returned to the beach. No research has been conducted where all the above senses are tested at the same time and no research has yet confirmed the use of any one sense in explaining how females turtles return to the same beaches year after year, amazing!!!
2nd June 2020
Welcome to our next instalment of Turtle Tuesday, this week we will be focusing on sea turtle behaviours. Many of us who have been lucky enough to encounter a sea turtle on a dive have the rare privilege to observe their behaviour underwater, in earlier posts we had videos shared showing some of the behaviours we as divers witness: feeding, sleeping, surfacing for air, investigating divers and surroundings. Divers little realise that often what they may be witnessing is something Marine Biologist, Zoologists, and Sea Turtle researchers rarely get to see. Turtles are generally solitary creatures that remain submerged for much of their time at sea, making them extremely difficult to study leaving many unknowns about their behaviour. The main areas of turtle behaviour researchers have been able to study are those easier to witness, such as migrations (with the use of satellite tags) and behaviours shown during courtship, mating and nesting.
The first contact sea turtles have with each other is when they hatch in the nest. As we’ve already covered; hatchlings will emerge from the nest in groups, they instinctively time their exit from the nest and collectively look for the sea. Once they have achieved the objective, they separate and do not socialise with other turtles until they are mature enough to start mating.
The only other times outside of mating seasons that turtle have been found together are in cases where there are high concentrations of algae or marine plants that attract a number of turtles to feed at the same time, once they have finished eating, they return to their solitary life. This can often be witnessed on dive site with sea grass beds where there may be several green turtles grazing at the same time.
Sea turtles do not have a permanent social structure; each turtle lives alone and confronts the dangers found in their marine habitat this way. They are not aggressive and share habitat with a large diversity of species without claiming territory or showing signs of aggressiveness to other marine creatures.
Males do not represent any social hierarchy or have any ranking. Several of them mate with a single female, and there is not any status order since she is the one who decides whether she wants to mate with a certain individual or not.
Sea turtles are polygamous, which means that both males and females may mate with many partners. Sea turtles don’t only have many partners in a lifetime, but they will have many partners in each nesting season as we mentioned in our earlier posts which can mean a clutch of turtle eggs within any one nest may be the product of many fathers.
Females choose who they mate with. If they are approached by a partner that is not suitable, she will frequently cover her cloaca (the hole where waste is excreted and where copulation takes place) with her back flippers and settle on the ocean bottom until the male goes away or until she needs to surface to breathe. Mating is not a fun task for adult turtles. Males will often bite females on their neck and flippers, leaving open wounds that heal slowly, often taking weeks to do so. Males will compete to mate with the female, so if one male is mating with a female, another male will frequently approach and try to pry the male off, or bite his head, flippers, or even his tail.
Turtles rarely interact with one another outside of courtship and mating.
But even when large numbers of turtles do gather on feeding grounds or during migration, there is little behavioural exchange between individuals.
Sea turtles are known to feed and rest off and on during a typical day, they can sleep at the surface while in deep water or on the bottom wedged under rocks in nearshore waters. Many divers have seen green turtles and hawksbills sleeping under ledges in reefs and rocks. Hatchlings typically sleep floating on the surface, and they usually have their front fins folded back over the top of their backs, it is not known why they do this. While working for a turtle rescue centre I witnessed a number of adult turtles still exhibiting this behaviour while others would sleep with their fins to their sides, other had their fins tucked under their plastrons (bellies).
It was while working for the rescue centre that I really got to see how different each and every individual was and each would exhibit different behaviours and characters.
We saw timid turtles who where very nervous and jumpy at anything new where others were more bold and inquisitive. Unfortunately for some of the inquisitive ones it had led to the injuries that had bought them to the centre in the first place. Two in particular spring to mind, Nuri and Simge, they were two loggerheads that were bought to the centre (at different times but both from the same area) with damage to their shells caused by boat propellors and in both cases they had lost one of their fins due to entanglement in fishing line. Both Nuri and Simge were not afraid of humans and both unfortunately had learnt that humans to them meant food, the area that they were rescued from is known for feeding turtles crabs by hand, and both would swim over to any one at the side of their rehab tank in hope of a tasty morsel. The large image is of Nuri having a closer look at the camera, I’m sure to see if it is edible!!!
The reason both Nuri and Simge come to mind is that both were repeat visitors to the centre and after release returned to the area they were rescued from, it became clear that these learned behaviours needed to be ‘un-learned’ and we began a new feeding regime where Nuri and Simge were only fed live prey dropped into the tank when no human was visible, we did see them activity look less for food from humans when they were around their tank and after their 2nd release they have not returned to the centre. It shows just how capable turtles are to learn behaviours and just how little we do really know about them.
9th June 2020
Hello and welcome to another instalment of Turtle Tuesdays, over the past weeks we’ve looked at the life cycle of sea turtles and in turn at each of the different turtle species. For each we’ve mentioned some of the key threats that impact their survival. This week we will begin to look more in depth at the human caused impacts threatening the survival of sea turtles and the conservation efforts that are underway to help reduce these threats.
The following link shows the IUCN Red List’s listing for the 7 Species of Sea Turtle (the Black turtle is not included on the list as it is not classified as a separate species from the green turtle)
In brief the hawksbill and Kemp’s ridley are listed as critically endangered, with green turtles as endangered (a few years ago they were listed as critically endangered, a positive for the greens) and the loggerheads, leatherbacks and olive ridley’s are all listed as vulnerable, unfortunately for the flatback sea turtles there is not enough population information and they remain listed as data deficient. Notedly one of the most important things the list shows is that for each species the population trend is decreasing, meaning each year the number of individuals is on the decline and it is the reasons behind this decline that we will be looking at further. There are considered to be five major threats to sea turtle populations; Fisheries as by-catch, coastal development, pollution and pathogens, direct take and climate change. We’ll be covering the different threats over the next few weeks.
Loss of significant numbers of sea turtles affects their valuable ecological role in the helping maintain the marine environment, all efforts made to reduce the loss of sea turtles is part of the link in the chain of marine life that needs to be there to maintain the balance within the marine ecosystem.
The first area of human impact on turtle populations we’ll cover this week is that of the affects the fishing industry. It’s estimated that the industry contributes to the death of tens of thousands of sea turtles each year. A study in 2010 estimated that as many as 1.5 million sea turtles had been caught in fisheries around the world over an 18 year period. Turtles that become trapped in longlines, gill nets and trawls are thrown away as by-catch and there is no system in place that records numbers of each species caught as by-catch making any actual counts impossible. It’s through finding dead individuals either at sea or washed ashore that provide the evidence that fishing activities were the cause of their death.
Fisheries not specifically targeting sea turtles as their target catch play a major role in their dwindling populations (sea turtles can be a target species in some countries and we’ll be covering this in later weeks). Sea turtles often congregate in the same areas as commercially valuable fish and can be prone to becoming by-catch. National Oceanic and Atmospheric Association (NOAA) developed TurtleWatch and new software called EcoCast. TurtleWatch provides current oceanic conditions to map where sea turtles may prefer so that fishing vessels can make more informed decisions for where and when to fish and reduce the chance of sea turtles becoming by-catch.
Trawls, longlines, drift-nets, gill-nets, pots, and traps have all been responsible for the incidental capture or entanglement of sea turtles for decades.
Longlines, containing thousands of baited hooks on lines which can be tens of miles long, hook and entangle many animals and fish that aren’t intended to be caught. Sea turtles, particularly greens, loggerheads, olive ridley’s, and leatherbacks, are attracted not only to the bait but often the green lights on the line used to lure in fish, this is especially the case for the leatherbacks and unfortunately they become caught on the hooks or become entangled in the lines and drown, long lines are the main threat attributed to the decline in leatherback numbers over the past few decades.
Even if rescued, a released turtle will often have a hook left behind in its jaw, throat, or stomach and in many cases this can still cause their death even months later. The largest sea turtle ever weighed was a 2,000 pound male leatherback that washed up dead on the Welsh coast, it died after becoming entangled in fishing lines.
Efforts are underway to find solutions to by-catch issues effecting sea turtles. Practical solutions include changing the size or shape of hooks so a turtle can’t get its mouth around it (from a j-shaped hook to a circle hook), and the use of turtle-excluder devices (TEDs). TEDs are attachments to trawling nets that allow sea turtles to escape through a trap-door system while still capturing the desired catch. These devices have developed over the years and there are now a number of different systems in operation, the two main types work in different ways, for shrimp nets the TED relys on the turtle’s weight to push the door down in order to leave the net. Shrimp are too light to activate the door and so remain within the confines of the net. The other system (as shown in the picture and it’s the system thats proven to be the most effective) has a set of bars attached in the net allowing the desired catch to pass through and directs turtles towards an escape flap
Current TED designs have been shown by NOAA to be 97% effective in excluding turtles from shrimp trawls. In the US all shrimp trawlers are required by law to have TED’s in all their nets, however this is not regulated worldwide. There is still away to go before by-catch can be eliminated as a threat to sea turtles by we defineantly think TED’s are a great step in the right direction and deserve a high 5!
16th June 2020
It’s Turtle Tuesday time again folks and with today being the 16th of June its the lesser known World Sea Turtle day, this day differs from world turtle day in May as world SEA turtle day is the birthday of Dr Archie Carr known as “the father of sea turtle biology” he devoted his entire career to sea turtle research and conservation and a lot of his conservation efforts are at play here this instalment of Turtle Tuesdays. Continuing on from last week where we began to look at the threats to sea turtle we looked at TED’s and some of the other ways the fishing industry is working to reduce the threat it poses on the survival of sea turtles.
This week we’re looking at the second of the five major threats, and that’s coastal development. When you initially think of costal development you think of buildings along the shoreline, however coastal development is a very broad category which includes an array of human activities including beachfront construction of homes, hotels, restaurants, roads and promenades. It includes things like beach renourishment, seawall construction, marina development, jetties and piers, nearshore dredging and oil platform construction as well as boat and marine traffic.
Humans have been making alterations to coastlines for centuries, however these changes are becoming more and more common place in recent years with over 40% of the worlds population living within 60 miles of the coast. Increased coastal populations result in increased development, increased beach recreational activities, increased pollutants and increased marine vessel activity, all of which can have catastrophic effects on sea turtle nesting beaches and feeding grounds.
With the development of coastlines the natural run off from the land changes. Increased coastal population increases pollutant runoff and wastewater discharge into the sea are polluting and damaging turtle habitats. We’ll be covering more on pollutants next Tuesday.
A developed beach will present a nesting female with many barriers, these can be physical such as sea walls, jetties, and sandbag structures aimed at preventing beach erosion. These can block nesting sea turtles from being able to move above the high tide line to nest. If the nest is laid too close to the high tide line, it runs the risk of being flooded before the eggs hatch drowning the hatchlings within. Other physical obstacles can include sun beds, tables and chairs, beach huts, windbreakers etc, all making it difficult for a female to navigate to find a good spot to lay her eggs and will often result in a false crawl (a crawl from the sea where females don’t nest or lay eggs).
Other non physical barriers include beach renourishment, this is the practice of filling in beaches with sand from another site to help reduce erosion. Sometimes this sand is taken from offshore, and has different characteristics to the normal sand found on natural beaches. This in turn can lead to problems with egg incubation, if the new sand causes differences in nest temperature, gas exchange, or water content it will all effect the development of the eggs within the nest. Beach renourishment can also affect the ability of a female to successfully dig a nest as the composition of the sand can vary greatly.
One conservation effort underway that will benefit the sea turtles is the implementation of living shorelines instead of hardened structures such as sea walls and jetties to help prevent beach erosion. Living shorelines incorporate as many natural elements as possible which create more effective buffers in absorbing wave energy and protecting against shoreline erosion, this natural barrier allows sea turtles access to their home beaches without the physical concrete barrier. Oyster beds and salt marshes are examples of living shorelines that feature natural structures which absorb incoming wave energy and act as protective barriers during storms. Living shorelines have other benefits as well, such as improving water quality, storing carbon, and increasing biodiversity.
Even if a beach is not eroded and barrier-free, coastal development can still harm the hatchlings chances of survival. Upon hatching and digging their way out of the nest, the hatchlings must find the sea. As we have covered, hatchlings generally find their way to the sea by heading towards brightest light, in natural circumstances this would be the moonlight reflecting off the sea’s surface. However when artificial light sources are present on land, it disorients the hatchlings, leading them away from the sea towards roads and buildings where they can fall victim to domestic predators, vehicles, or become trapped by obstacles and become exposed to the elements. Even if they realise their mistake and turn back to the sea, the longer time period spent on land means a longer time period of vulnerability to predators, desiccation, dehydration and exhaustion.
Beachfront lighting not only affect hatchlings but can also disorient nesting females and may result in failed nesting attempts.
We are becoming more aware throughout the world that protecting nesting beaches is a vital key in the conservation of sea turtles, the more nests, the more eggs, the more hatchlings giving them a better chance at survival. Turtle friendly lighting (a red light the turtles can’t see) is being implemented in nesting sites in the US and Europe. Coastal residents are informed about shading their windows at night and turning lights away from the beach during nesting seasons or to replace the lights with a red ‘turtle friendly light’. These actions are helping to reduce hatchling disorientation and mortality rate due to crawling in the wrong direction.
There is a lot of working taking place to help protect nesting beaches around the world and there is some great working going on, we will be returning to this in more detail in later weeks.
Boats and personal watercraft are responsible for large numbers of sea turtle injuries and deaths each year. As coastal populations increase, boating activities increase and collisions with sea turtles that must surface to breathe, are inevitable. In Florida, most sea turtle strandings are the result of collisions with boats with the worst injuries caused by the propellors.
In many important sea turtle hotspots around the world, tourism development has hurt conservation efforts more than they have helped.
The demand for a beachfront hotel and watersports is higher than the demand to protect sea turtles. Another success in helping protect turtles is the development of propellor cages/guards to help prevent sea turtle injuries. I have worked in an area in Turkey where the majority of the boats had these propellor guards in place and they have been effective in reducing the number of turtle injuries caused by props. Unfortunately propellor guards are not a requirement by law which is such a shame as with the right design they do not impact the boats performance and they have been proven to help reduce injuries not only to sea turtles but other marine mammals as well like manatees and river dolphins.
23rd June 2020
Hello everyone, it’s turtle Tuesday again and today we begin to look at the next threat to sea turtles; pollution and pathogens, we’ll be covering this topic over the next few weeks.
Pollution can have serious impacts on both sea turtles, and the food they eat. Sea turtles are vulnerable to ocean pollution at all stages of their life cycle, from eggs through to adults. Pollutants may cause immediate harm to them through direct contact or it can build up in their tissues over time leading to immunosuppression resulting in disease, chronically ill turtles are more vulnerable to predation and collisions with boats increasing likelyhood of death.
Pollutants include toxic metals, pcb’s (polychlorinated biphenyl’s), petroleum products, agricultural and industrial runoff contaminants such as fertilisers, chemicals, nutrients, untreated waste and of course plastic. We’ll return to the topic of plastics in next weeks instalment and pathogens the following week.
All species of sea turtles are affected by marine pollution and unfortuneately some are impacted more than others.
Sea turtle habitats overlap with areas most likely to be affected by offshore oil exploration and production. Oil from spills far offshore concentrate along convergence zones (where currents meet) these areas are important for juvenile turtle development. The 2010 Gulf oil spill was one of the largest marine oil spills in history. NOAA reported that the spill released 134 million gallons of oil into the Gulf of Mexico. NOAA scientists released figures indicating that tens of thousands of sea turtles were killed by the spill and many more were injured. During the spill of the dead that washed ashore, 75 percent were found to be the critically endangered Kemp’s ridley, a species who only nests in and around the Gulf of Mexico. Sea turtle habitats and breeding grounds were heavily contaminated during and after the spill, degrading nesting habitats, and impacting nests, nesting females, and hatchlings making their way to the sea. The thickest oil concentrations after the spill were found in the convergence zones of the Gulf, hence the highest number of turtles killed or injured by the spill were juveniles.
Sea turtles are also affected by ingesting food contaminated by oil or tar balls. Tar balls form when crude oil floating in the water degrades. A large percentage of dead hatchlings found over the years were found to have stomach contents containing toxic tar balls.
PCB’s are a group of manmade chemicals that are very stable organic mixtures, they are resistant to extreme temperature and pressure. PCBs were used widely in electrical equipment like capacitors and transformers. They were found to be environmentally toxic and classified as a ‘persistent organic pollutant’ and their production was banned by the Stockholm Convention in 2001. Despite the ban on production PCB’s are still found in the environment, and in materials produced prior to the ban. Organisms that ingest these chemicals may suffer from suppressed immune systems, illness, disease, and impaired reproduction. Researchers have found PCB’s in sea turtle eggs. Unfortunately with the length of time it takes turtles to reach maturity we may still yet have to see the true effects PCB’s may have had on turtle reproduction.
Degradation of sea turtle habitat from pollution also poses a threat and can occur over large areas and fertilisers are often to blame. Fertilisers runoff from the land and causes eutrophication from the extra nutrients. Eutrophication is an explosion of algal blooms that can deplete the water’s oxygen and suffocate marine life. Eutrophication has created enormous dead zones in many parts of the world. Improper sewage disposal is another factor that causes eutrophication.
As the ocean is so large, many assume that pollutants will be diluted and dispersed to safe levels, but in reality they create havoc with the oceans’ natural balance. Some toxins even become more concentrated as they break down and enter the food chain. Sea turtles are affected by pollution in more ways than one; they do not have to directly ingest a tar ball, for example, to be affected by it. Small marine animals, on the lower levels in the food chain, like plankton, absorb these chemicals as they feed. The chemicals then accumulate in these animals’ bodies, which makes the toxins much more concentrated than in the surrounding water. These small animals are then consumed by larger animals, like sea turtles, which continues to increase concentration levels of chemicals and pollutants which all intern have adverse effects on the sea turtles health.
As the importance of protecting our marine environment is becoming ever more understood more and more alternatives are being found that are less damaging to our oceans. We can help by following local regulations enforcing fertiliser bans near waterways. By using less chemical fertilisers in our gardens and opting for natural compost, opting to buying organically produced food and products. By reducing oil consumption by carpooling, using public transportation or buying energy-efficient vehicles. By speaking out against off shore drilling and supporting green alternatives such as wind and solar. By being informed about local waste disposal to ensure that untreated waste water isn’t introduced to natural waterways and oceans.
There is still along way to go, education is important to solving marine pollution. With more regulations being put in place and with more awareness of the damage being done to our oceans the more each of us becomes aware and makes changes the less the threat of pollution on sea turtles will become.
Watch this space for weekly turtle posts from our very own Mem.
