Sea Turtle of the World

 Sea Turtle of the World

Sea turtles grace our oceans and belong to a unique evolutionary lineage that dates back at least 110 million years. Sea turtles fall into two main subgroups: the unique family Dermochelyidae, which consists of a single species, the leatherback turtle. There are seven species of sea turtle found today that developed from a single, unique group that separated from other turtle species over 100 million years ago. This group then split into two families, Cheloniidae and Dermochelyidae, which represent all sea turtles today. Sea turtles are globally distributed and highly migratory and found in every major ocean basin. They regularly inhabit the Atlantic, Pacific and Indian Oceans, and the Mediterranean Sea. Aside from adult females which periodically come ashore to nest, and occasional on-shore basking by males and females, sea turtles spend their entire lives at sea. They have unique and complex biological traits and life histories that in some cases are not fully understood yet. Their nesting and feeding ground is far away up to thousands of kilometers from coast to coast. Most of the time sea turtle spend in offshore areas. Six of the seven species of marine turtles are classified within the hard-shelled family Cheloniidae and the family Dermochelyidae is represented solely by the unique species, which lacks the hard shell that characterizes other marine turtles. While most species are found primarily in tropical and subtropical waters, individuals have been known to venture as far as the colder waters of the Arctic. Current living sea turtle species are:

 

1.       Lepidochelys olivacea (olive ridley), Eschscholtz, 1829.

2.       Chelonia mydas (Green turtle), Linnaeus, 1758.

3.       Eretmochelys imbricata (hawksbill), Linnaeus, 1766.

4.       Caretta caretta (loggerhead), Linnaeus, 1758.

5.       Lepidochelys kempii(Kemp’s ridley), Garman, 1880.

6.       Natator depressus (flatback), Garman,1880.

7.       Dermochelys coriacea (leatherback), Vandelli, 1761.

 

SEA TURTLE STATUS

Historic and recent published accounts indicate extensive subpopulation declines of sea turtle in all major ocean basins over the last three generations as a result of exploitation of eggs at nesting beaches, juveniles and adults in foraging areas through incidental mortality by marine fisheries and degradation of marine as well as nesting habitats (Eckert, Bjorndal, , Abreu-Grobois and Donnelly, 1999). Six of the seven sea turtle species are classified as threatened with extinction by the IUCN Red List of threatened species. Three species are considered Critically Endangered (hawksbill, leatherback, and Kemp’s ridley), two are considered Endangered (green, and loggerhead), one is considered Vulnerable (olive ridley), and the seventh (flatback) status is not fully known (Data Deficient). The status of sea turtle populations varies greatly on a global scale. Some populations are declining and in some cases near extinction, while others are stable or even increasing. There are five major hazards that endanger sea turtles today, as well as other less significant hazards; all are the result of human actions. The five major hazards are: fisheries impacts, direct take, coastal development, pollution and pathogens and global warming.

 

In Bangladesh marine waters, nesting declined 80 % during last four decades and currently nesting habitat is threatened by tourism (Islam, 2002, 2015). Here turtle conservation started only small scale 20 years back and the outcome of the efforts depends on continuous enhanced long term measures. Four species forage in the Bay of Bengal Bangladesh territory and so far only three of them viz., Olive Ridley (Lepidochelys olivacea), Green turtle (Chelonia mydas) and Hawksbill turtle (Eretmochelys imbricata) recorded with unconfirmed leatherback turtle record (Islam, 2002). Currently only two of them viz., Olive Ridley and Green turtle nest at suitable beaches. In Bangladesh sea turtles are facing dangers from bycatch, egg poaching, predation, beach alteration and disturbances through tourism and artificial lighting. Currently tourism development is the main inland threat along south eastern coast at Cox’s Bazar and St. Martin Island.

LEGAL STATUS OF SEA TURTLE

Because of sea turtles highly migratory nature, effective conservation requires international and sometimes intercontinental cooperation. Sea turtle populations have been seriously reduced in all range countries through a number of human influences. For these reasons all species of sea turtle are protected internationally, considered threatened and protected all over the world. Trade of sea turtle and their products is prohibited under the Convention on International Trade in Endangered Species (CITES), which lists sea turtles in Appendix-1. Sea turtles are protected by many national laws and by regional agreements such as “Indian Ocean–South-East Asian Marine Turtle Memorandum of Understanding (IOSEA-MoU)”, the “Inter-American Convention (IAC)” for the Protection and Conservation of Sea Turtles and the MoU Concerning Conservation Measures for Marine Turtles of the Atlantic Coast of Africa. In Bangladesh after a long time sea turtle finally enlisted in protected list of Bangladesh Wildlife (Preservation & Protection) Act, in 2012. Briefly, the laws state that: “No person may take, harass, harm, pursue, hunt, shoot, wound, kill, trap, capture or attempt to engage in any such conduct to sea turtles, turtle nests, and/or turtle eggs.” Any person who knowingly violates any provision of the ACT may be assessed civil penalties and/or up to a certain year imprisonment. Bangladesh Government also signed IOSEA-MoU. This MoU puts in place a framework through which states of the Indian ocean and South East Asia region as other concerned states and partners can work together to conserve and replenish depleted sea turtle population and habitats for which they share responsibility. It acknowledges a wide range of threats to sea turtles, including habitat destruction, direct harvesting and trade, fisheries by-catch, pollution and other man-induced sources of mortality. A special, Year of the Turtle, has been celebrated throughout the Indian Ocean and South East Asian region in 2006, focusing on core themes: celebrating sea turtles, taking measures to ensure long time survival, conserving habitat, reducing accidental capture in fishing operations.

 

 

 

   

SEA TURTLE SPECIES OF THE WORLD

Green turtle (Chelonia mydas)

Status:  Endangered

 

Basic Info:  Green turtle has the most numerous and widely dispersed nesting sites of the seven species, and was once highly sought after for its body fat, a key ingredient in the popular delicacy, ‘green turtle soup.’ Although it has become illegal to trade those in many parts of the world, green turtles and their eggs continue to be consumed. There are two deferent coloration of green turtle, the adult is dark greenish or dark texture bluish (top) and the sub-adult remains mostly reddish and reddish brown (2^nd from top)in color. The hatchlings of green turtle are quiet black with white bordering throughout the body and the plastron is brilliantly white.

 

Distribution: Nesting throughout tropical regions are often on islands and coral atolls in addition to mainland beaches; Non-nesting range extends to temperate regions during immature stages.

Size: Adults: Length 80-120 cm; mass up to 300 kg; Hatchlings: Length 30-40 mm; mass 25-30 g.

 

Diet: For immature stages, soft-bodied invertebrates such as jellies and jelly-like organisms. For later immature stages and adults, mainly herbivorous, but also sessile invertebrates such as sea pens and other soft corals.

 

Reproduction: Every 2-4 years, Lay 2-5 clutches of eggs per season, Lay 80-120 eggs per clutch, ping-pong ball size eggs weigh approximately 40-50 grams, Incubation period approximately 60 days long. Can take 20-40 years to reach sexual maturity.

 

Facts: Green turtles were important for European explorers to the New World; they provided an essential source of food, and they helped crews navigate around islands at night by the increased volume of their aggregated breathing.  The former abundance of green turtles in the Caribbean is estimated to have been as high as 500 million individuals. Eastern Pacific green turtles are termed ‘black turtles’ because of their darker coloration. They tend to be smaller and to lay fewer eggs than green turtles elsewhere. Green turtles nest in highly diverse types of habitats, including archipelagoes, isolated coral atolls, mainland beaches, in all tropical and sub-tropical oceans. Bangladesh Green turtle have been recorded from Sandwip Island, Sonadia, fewer spots of Teknaf peninsula and St. Martin Island (Islam, at. el.1998, Islam, 2002, Rashid & Islam, 2005).  

Olive ridley turtle (Lepidochelys olivacea)

Status: Vulnerable

 

Basic Info: One of nature’s greatest spectacles known as arribadas, the Spanish word for “arrival” known for olive ridleys, they come ashore simultaneously by the hundreds and thousands to nest. Though they are the most abundant of sea turtles, olive ridleys are increasingly threatened by trawling and coastal development.

 

Distribution: Circumglobal; nesting areas in tropical regions, non-nesting range extends to temperate regions. It is the widely distributed and major species of sea turtle almost found all nesting beaches so far recorded. It is also most vulnerable species in marine fisheries bycatch.

 

Size: Adults: Length 60-70 cm; mass up to 70 kg; Hatchlings: approximately 25 mm; weight mass 15-20 gm.

 

Diet: For all life stages, mostly benthic invertebrates (crabs, other crustaceans, and mollusks) and occasionally jelly fishes.

Reproduction: Reproduce every 1-3 years, Lay 1-3 clutches of eggs per season, Lay 90-130 eggs per clutch, eggs smaller than green turtle eggs weigh approximately 30 grams each, Incubation period approximately 60 days long.

 

Facts: Olive ridleys are thought to be the most abundant sea turtle species globally, Along with Kemp’s ridleys, olive ridleys are the only sea turtles species to exhibit synchronous mass nesting, termed arribadas. During the arribadas, the Spanish word for ‘arrivals,’ tens of thousands of female turtles nest during the same 3-7 day period once a month. Along with Kemp’s ridleys, and, to a lesser extent, flatbacks, olive ridleys are the only sea turtle species to commonly nest during the day. During the last 30 years monitoring and incidental surveys Olive ridleys have been recorded at St. Martin Island, Shahporirdwip, Teknaf, Inani, Pechardwip, Cox’s Bazar and Najirartek and all Teknaf peninsular spots, Sonadia, Kaladia, Laldia, Haser Char (Dhalghata), Matarbari, Kutubdia, Gohira, Parki, Sandwip Island, Sonar char, Kuakata, Dublar char and nesting beaches along large mangrove forest Sundarban (Islam, at. el.1998, Islam, 2002, Rashid & Islam, 2005, Marinelife Alliance, 2013). 

 

 

Hawksbill turtle (Eretmochelys imbricata)

Status: Critically Endangered

 

Basic Info: Named for its sharp, pointed beak, the hawksbill feeds primarily on reef sponges, invertebrate organisms whose bodies contain tiny indigestible glass needles. The hawksbill has a beautiful, translucent shell, which has long been exploited for use in tortoiseshell jewelry. Though international trade of tortoiseshell has been prohibited, illegal trafficking continues.

 

Distribution: Circumglobal; nesting areas in tropics, non-nesting range is generally restricted to tropical regions, although during immature stages it extends to sub-tropical regions.

 

Size: Adults: Length 75-90 cm; mass up to 150 kg; Hatchlings: Length approximately 30 mm; mass approximately 5 g.

 

Diet: Large juveniles and adults predominantly eat sponges and other sessile invertebrates associated with coral reefs and rocky reefs.

 

Reproduction: Reproduce every 2-4 years; Lay 2-5 clutches of eggs per season; Lay 120-200 eggs per clutch; Ping-pong ball size eggs with approximately 25-30; Incubation period is approximately 60 days long.

 

Facts: Hawksbills are the only marine consumer whose diet predominantly comprises sponges and thus play a significant role in tropical coral reef ecosystems; Hawksbills commonly nest within beach vegetation on secluded, low-energy beaches; Hawksbills in the Eastern Pacific are probably the most endangered sea turtle population in the world. In our regional water, Hawksbill nest in Sri Lanka, Myanmar, and the Andaman Islands. In Bangladesh, only habitat for adult hawksbill is St. Martin Island, and due to the severe degradation of coral habitat, this species may no longer travel up here. The last nesting was recorded at St. Martin Island in 1998 (Islam, 2002). Foraging juveniles and subadults have been recorded along the Teknaf peninsular coast and Sonadia Island those stranded in ghost nets are also trapped in beach seine. Since the carapace of Hawksbill is spiny, it is likely to entangle far easier than other species. Stranded hawksbill found to have been injured by gear and sick or starved for a long time. Three individuals have been released healthy after rehabilitation at Marinelife Center, Cox’s Bazar.

 

Loggerhead turtle (Caretta caretta)

Status: Endangered

 

Basic Info: Loggerheads are named for their large heads, with jaws powerful enough to crush an adult queen conch. Like most sea turtles, loggerheads are famed for their vast migrations. As a species that may travel thousands of miles across ocean basins, loggerheads are in grave danger due to worldwide habitat loss and incidental capture by fishermen.

 

Distribution: Circumglobal. Nesting areas in tropical to sub-tropical regions Non-nesting range extends to temperate regions. 

 

Size: Adults: Length 70-100 cm; mass up to 200 kg; Hatchlings: Length approximately 25 mm; mass 15-20 gm.

 

Diet:  For all life stages, mostly benthic invertebrates (crabs, other crustaceans, and mollusks) and occasionally jellyfish.

 

Reproduction: Reproduce every 2-4 years; Lay 2-5 clutches of eggs per season; Lay 80-120 eggs per clutch; Large ping-pong ball size ; eggs weigh 30-40 grams; Incubation period approximately 60 days long; Can take 20-30 years to reach sexual maturity.

 

Facts: Loggerheads exhibit trans-oceanic developmental migrations from nesting beaches to immature foraging areas on opposite sides of the ocean; A large juvenile loggerhead named Adelita was the first sea turtle to be tracked by satellite across an entire ocean basin; Her approximately 10,400 km journey from feeding areas off Baja California, Mexico, to coastal regions off her natal Japan corroborated the link across the North Pacific Ocean established by genetic studies. There was no record of Loggerhead nesting in Bangladesh or dead washed ashore. The matter was emphasized after the start of sea turtle conservation in 1996, and we have no idea about previous occurrences. The nearest nesting habitat is in Myanmar and Andaman Island. A significant concentration of nesting in Myanmar currently occurs on Thamihla Kyun (Diamond Island), where about 7,000-15,000 loggerhead eggs are laid annually. However, there appears to be some confusion regarding the discrimination between loggerhead and olive ridley turtles, and some of the reported loggerhead turtle eggs may, in fact, be those of the olive ridley turtle since there is no thorough monitoring in Myanmar (Thorbjarnarson et al 2000).

Leatherback turtle (Dermochelys coriacea)

Status: Critically Endangered globally.

 

Basic Info: Largest of sea turtles, the leatherback can reach over 1.8m (6 ft) in length and 680 kg (1,500 lb) in weight. During their long migrations, leatherbacks regularly dive to depths greater than 1,000m (3,281ft) in search of gelatinous zooplankton to eat. The leatherback is rapidly declining in many areas of the world.

 

Distribution: Circumglobally, present in all the world’s oceans except the Arctic and Antarctic; nesting areas are in the tropics, non-nesting range extends to sub-polar regions

 

Size: Adult: Length 140-160 cm; mass 300-1000 kg; Hatchling: Length approximately 50 mm; mass 40-50 g.

 

Diet: For all life stages, gelatinous zooplankton (jellies and jelly-like organisms).

Reproduction:  Reproduce every 2-4 years; Lay 4-7 clutches of eggs per season; Lay 50-90 eggs per clutch; Billiard ball size eggs weigh roughly 80 grams; Incubation period is approximately 60 days long

 

Facts: The leatherback is the only remaining member of its taxonomic family (Dermochelyidae); Leatherbacks rely on a unique suite of adaptations, including large body size, changes in activity and metabolic rate, peripheral insulation (i.e. fat), and adjustments in blood flow to maintain stable core body temperatures in varying water temperatures from temperate to tropical latitudes; The largest leatherback ever reported was an adult male found in Wales. It was greater than 2 meters (6.6 feet) long and 916 kg (2,019 lbs) in mass; the longest recorded leatherback migration was 20,800 kms one way.  In Bangladesh the only suitable nesting habitat was St. Martin Island according to local elders. There were 3 dead records during the last 20 years of monitoring since 1996 at St. Martin Island (CCL 138 cm) and Cox’s Bazar (Islam, at. el.1998, Islam, 2002). The only stranded record was in May 2005, accidentally turtle entered into the Bakkhali river of Cox’s Bazar and finally died before attempts taken for rescue (Islam, 2002, 2006). There was one unconfirmed record of Leatherback nesting according to local observer at south of Shil Baniar Gula, St. Martin Island during 2000-01 season under the St. Martin Pilot Project (NCSIP-1) and here misidentification is a big issue although the site is very suitable for leatherback nesting. In addition few elders claimed to have witnessed leatherback nesting or emergence at south west corner, St. Martin Island, before the during six decades back (Islam, 2002). Offshore fisher’s those travel far from the coast and deeper water claimed to see leatherback swimming in Bangladesh marine territory.

Flatback turtle (Natator depressus)

Status: Data Deficient

 

Basic Info: The flatback is the least studied of the sea turtles and has one of the smallest geographic ranges. The only endemic sea turtle species, flatbacks nest solely along the northern coast of Australia, and live solely on the continental shelf between Australia, southern Indonesia, and Papua New Guinea.

 

Distribution: Nesting only on northern coast of Australia; all life stages occur on continental shelf north of Australian continent.

 

Size: Adults: Length 80-95 cm; mass up to 100 kg; Hatchlings: Length approximately 45 mm; mass approximately 40 gm.

 

Diet: For all life stages, mostly benthic invertebrates (crabs, other crustaceans, and mollusks) and sometimes jellies.

 

Reproduction: Reproduce every 2-4 years; Lay 2-3 clutches of eggs per season; Lay 50-70 eggs per clutch. Billiard ball-sized eggs weigh 70-80 grams; Incubation period is approximately 60 days long.

 

Facts: For a long time, flatbacks were thought to be a type of green turtle, but were finally described as a separate species in 1988; Flatbacks have the most giant eggs and hatchlings relative to their adult body size of all sea turtles; Flatbacks have a unique physiology that allows them to stay active underwater for more extended periods than most other species; Over much of their nesting range they are predated upon by saltwater crocodiles, which have also been known to attack human beings. Because of this, there are virtually no underwater photos of adults in the wild.

Kemp’s ridley turtle (Lepidochelys kempii)

Status: Critically Endangered.

 

Basic Info: The Kemp’s ridley is the smallest of the sea turtles and has a highly restricted range, nesting only along the Caribbean shores of northern Mexico and Texas, U.S.A. Fifty years ago, the Kemp’s ridley was near extinction. Although this species now shows signs of recovery, fishing nets, and coastal development continue to threaten the species, and much work remains to be done before it can be considered safe.

 

Distribution: Most restricted geographic range of all sea turtle species. Only nesting areas in Rancho Nuevo, Tamaulipas, Mexico, and Texas, the U.S. Non-nesting range extends between the Northwest Atlantic Ocean, the Gulf of Mexico, and the Caribbean.

 

Size: Adults: Length 60-70 cm; mass up to 60 kgs; Hatchlings: Length approximately 25 mm; mass 15 to 20 gm.

Diet: For all life stages, mostly benthic invertebrates (crabs, other crustaceans, and mollusks) and some jellies.

 

Reproduction: Reproduce every 1-3 years; Lay 1-3 clutches of eggs per season; Lay 90-130 eggs per clutch; Ping-pong ball size eggs weigh approximately 30 grams each; Incubation period is about 60 days long; Takes 10-15 years to reach sexual maturity

 

Facts:  Along with olive ridleys, Kemp’s ridleys are the only sea turtle species to exhibit synchronous mass nesting, termed arribadas; During the arribadas, the Spanish word for ‘arrivals,’ tens of thousands of female turtles nest during the same 3-7 day period once a month; Along with olive ridleys, and, to a lesser extent, Flatbacks, Kemp’s ridleys are the only sea turtle species to commonly nest during the day; An incredible bi-national effort has been made to save Kemp’s ridleys from extinction by translocating eggs from beaches in Mexico to beaches in Texas, and by ‘head-starting’ juvenile Kemp’s ridleys, whereby hatchling turtles are grown in captivity to larger sizes before being released in an attempt to mitigate predation effects.