Sea Turtles Of The Indian Ocean

Six of the world’s seven species of sea turtles live in the Indian Ocean: the flatback, green, hawksbill, leatherback, loggerhead and olive ridley.  The abundance of each species differs between countries and oceanic areas. While green turtles and hawksbills are abundant in shallow coastal areas, such as in the Maldives and Kenya, the olive ridley turtle occupies more oceanic habitats, migrating towards coastal areas for nesting.

Important Nesting Grounds

Nesting beach on Gaadhoo Island in the Maldives. Image.
Nesting beach on Gaadhoo Island in the Maldives, a green turtle hot spot. © Leanna Crowley.

The Indian Ocean is home to countless sea turtle nesting sites, particularly for those of the olive ridley turtle. Just a handful of mass nesting beaches in the Indian Ocean account for the majority of olive ridley nesting within the region. Three arribada beaches in Odisha, India make up for an estimated 100,000+ nests per year: Gahirmatha, Devi River mouth and Rushikulya.

Other important nesting sites in the Indian Ocean include that of the critically endangered hawksbill. Hawksbills can be found nesting in the Seychelles, Indonesia, Australia and Oman. Considering many populations of hawksbill have been severely depleted, these nesting hotspots are extremely valuable for the future of this species.

Despite leatherback turtles being less common in the Indian Ocean than most other sea turtle species, they do have important nesting grounds in Indonesia, South Africa, Sri Lanka, Mozambique and the Andaman and Nicobar Islands. Meanwhile, the enigmatic flatback turtle predominantly resides in Australian waters, with Crab Island (Queensland, Australia) hosting the largest nesting population.

As well as this, several tens of thousands of female loggerhead turtles can be found nesting around the islands of Masirah (Oman) and Socotra (Yemen), making this population the second largest nesting aggregation of loggerheads in the world!

Epic Migrations

A green turtle swimming in the blue.

Green turtles have recently been recorded migrating just under 4,000km annually within the Indian Ocean, with one individual turtle travelling from Chagos Islands in the Indian Ocean to the coast of Somalia in east Africa!

Like many other species of sea turtle, green turtles frequently migrate between foraging and nesting sites. Nesting sites from green turtles within the region include the Seychelles, Maldives and Oman.

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Sea Turtle FAQ – The Answers to All Your Sea Turtle Questions

Male hawksbill popping head above surface for air, Maldives. Image.
Marvin, male hawksbill, coming up for a breathe, Maldives.

Sea turtles can hold their breath for several hours, depending on their level of activity.

If they are sleeping, they can remain underwater for several hours. In cold water during winter, when they are effectively hibernating, they can hold their breath for up to 7 hours. This involves very little movement.

Although turtles can hold their breath for 45 minutes to one hour during routine activity, they normally dive for 4-5 minutes and surfaces to breathe for a few seconds in between dives.

However, a stressed turtle, entangled in a ghost net for instance, quickly uses up oxygen stored within its body and may drown within minutes if it cannot reach the surface.

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References:

  • Hays GC, Akesson S, Broderick AC, Glen F, Godley BJ, Luschi P, Martin C, Metcalfe JD & Papi F 2001. The diving behaviour of green turtles undertaking oceanic migration to and from Ascension Island: dive durations, dive profiles and depth distribution. Journal of Experimental Biology 204: 4093-4098.
  • Hays GC, Hochscheid S, Broderick AC, Godley BJ & Metcalfe JD 2000. Diving behaviour of green turtles: dive depth, dive duration and activity levels. Marine Ecology Progress Series 208: 297-298.
  • Hochscheid S, Bentivegna F & Hays GC 2005. First records of dive durations for a hibernating sea turtle. Biology Letters 1: 82-86.
  • Lutz PL and Musik JA (eds.) 1996. The Biology of Sea Turtles Volume I. CRC Press.

The actual documentation of a sea turtle’s age in the wild is difficult or nearly impossible. Individual turtles can be tracked for a shorter time of six month to three years with the help of satellite transmitters. Longterm studies rely on capture-recapture principle, just like our turtle photo id project. Each photo of a turtle represents a recapture event documenting that the individual is still alive.

A study of nesting green turtles in Hawaii observed female turtles returning to nest for up to 38 years after they were first identified. Assuming the average age at first nesting activity of 24 years, this would show that green turtles can live to up to at least 62 years.

Similar estimates have been made for loggerhead turtles.

An adult green turtle resting on a reef in Maldives, image
An adult green turtle
Hawksbill turtle resting on the reef, Maldives
An adult hawksbill turtle

References:

  • Dodd C 1988. Synopsis of the biological data on the loggerhead sea turtle. Ecology 88.
  • Humburg IH and Balazs GH 2014. Forty Years of Research: Recovery Records of Green Turtles Observed or Originally Tagged at French Frigate Shoals in Northwestern Hawaiian Islands, 1973-2013. NOAA Technical Memorandum NMFS-PIFSC-40.

When sea turtles are juveniles, it is very difficult to tell their sex by eye as they do not differ externally. However, after reaching sexual maturity male sea turtles develop a long tail, which houses the reproductive organ. The tail may extend past the hind flippers.

Female turtles have a short tail, which generally doesn’t extend more than 10 cm (4 inches) past the edge of the carapace. Male sea turtles (except leatherbacks) have elongated, curved claws on their front flippers to help them grasp the female when mating.

The sex of a sea turtle embryo is determined by the temperature of the sand: warm temperatures result in more females while cooler temperatures result in more males.

Male green turtle tail
Male green turtle tail
Female green turtle tail
Female green turtle tail

The olive and Kemp’s ridley sea turtles are the smallest species, growing only to about 70 cm (just over 2 feet) in shell length and weighing up to 45 kg (100 lbs). Leatherbacks are the largest sea turtles. On average leatherbacks measure 1.5 – 2m (4-6 ft) long and weigh 300 – 500 kg (660 to 1,100 lbs). The largest leatherback ever recorded was 2,56 m (8.4 ft) long and weighed 916 kg (2,019 lbs) !

Kemp’s Ridley

Nesting female kemp's ridley turtle, nicknamed
Nesting female kemp’s ridley turtle, nicknamed “Mij”, laying 116 eggs on Galveston’s East Beach. ©Ron Wooten, Wildscreen Exchange.

55.6-66.0 cm carapace length, weight range of 25-54 kg for nesting females.

References:

  • Marquez-M R 1994. Synopsis of Biological Data on the Kemp’s Ridley Turtle, Lepidochelys kempi (Garman, 1880). NOAA Technical Memorandum NMFS-SEFSC-343.

Olive Ridley

Female Oliver ridley turtle nesting on the beach during arribada
Nesting female olive ridley turtle ©Susie Gibson.

Curved carapace length 52.5-80.0 cm, weight less than 50 kg (average 35.7 kg) for nesting females.

References:

  • Qureshi M 2006. Sea turtles in Pakistan. In: Shanker K and Choudhury BC (Eds.). Marine Turtles of the Indian Sub- continent. Heydarabad: India Universities Press, pp. 217–224.Reichart HA 1993.
  • Reichart HA 1993. Synopsis of biological data on the olive ridley sea turtle Lepidochelys olivacea (Eschscholtz 1829) in the western Atlantic. NOAA Technical Memorandum NMFS-SEFSC-336.

Hawksbills

Adult male hawksbill turtle swimming in the blue, Maldives. Image
Adult male hawksbill, Maldives.

Nesting females reported between 53.3 and 95.5 cm carapace length, with weight between 27.2 and 86.2 kg.

References:

  • Witzell WN 1983. Synopsis of biological data on the hawksbill turtle, Eretmochelys imbricata (Linnaeus, 1766). No. 137. Food & Agriculture Org.

Green turtles

Adult green turtles mating, Malsdives. Image.
Adult green turtles mating, Maldives.

Nesting green females reported curved carapace length 75-134 cm, weight (after egg deposition) 45-250 kg (!).

References:

  • Hirth HF 1997. Synopsis of the Biological Data on the Green Turtle Chelonia mydas (Linnaeus, 1758). Vol. 2. Fish and Wildlife Service, US Department of the Interior.

Flatbacks

Nesting flatback sea turtle ©Lyndie Malan / CC BY-SA.

Ones study (Ref. 1) found nesting females have a mean curved carapace length 86.3 cm, and mean weight of 67.4 kg. Another study (Ref. 2) found flatbacks to be between 87.5-96.5 cm.

References:

  • Schäuble C, Kennett R and Winderlich S 2006. Flatback Turtle (Natator depressus) nesting at Field Island, Kakadu National Park, Northern Territory, Australia, 1990-2001. Chelonian Conservation and Biology 5: 188-194.
  • Limpus CJ 1971. The Flatback Turtle, Chelonia depressa Garman in Southeast Queensland, Australia. Herpetologica 27: 431-446.

Loggerheads

Adult female loggerhead, Oman.

Adult loggerhead turtles measure between 65 and 115 cm in curved carapace length and typically weigh between 40 and 180 kg. The largest recorded loggerhead weighed 545 kg and measured 213 cm in presumed total body length. On average, nesting, and therefore adult, female loggerheads have a curved carapace length of 65.1-114.9 cm and weigh between 40.0 and 180.7 kg. Males fall into the same size range (79.0-104.0 cm curved carapace length).

References:

  • Brongersma LD 1972. European Atlantic turtles. Zoologische Verhandlingen 121, Leiden.
  • Dodd C 1988. Synopsis of the biological data on the loggerhead sea turtle. Ecology 88: 1-119.
  • Ernst CH and Lovich JE 2009. Turtles of the United States and Canada, 2nd edition. John Hopkins University Press.

Leatherbacks

Leatherback Turtle, Claudia Lombard, USFWS
Adult leatherback turtle ©Claudia Lombard, USFWS.

143.8-169.5 cm curved carapace length, weight 259-506 kg recorded for nesting females all around the world. Largest ever recorded specimen was found dead on a beach on the coast of Wales. The adult male turtle weighed 916 kg and its shell was 256.5 cm long. An autopsy revealed that it had drowned.

References:

  • Eckert KL and Luginbuhl C 1988. Death of a Giant. Marine Turtle Newsletter 43: 2-3.
  • Eckert KL, Wallace BP, Frazier JG, Eckert SA and Pritchard PCH 2012. Synopsis of the Biological Data on the Leatherback Sea Turtle (Dermochelys coriacea). Biological Technical Publication BTP-R4015-2012, US Fish & Wildlife Service.

Each sea turtle species feeds on a specific diet and all lack teeth:

  • Flatbacks are mainly carnivorous turtle feeding in shallow waters on soft bottoms.
  • Green turtles are vegetarian and prefer sea grasses, sea weeds and algae as adults, however, green turtle hatchlings are omnivorous, eating jellyfish, snails, crabs, and shrimp.
  • Hawksbills have a bird-like beak that is used to cut through soft coral, anemones and sea sponges.
  • Kemp’s ridleys are omnivores at the beginning of their lives, feeding on seaweed and small creatures like crabs and snails. As adults, Kemp’s ridleys look for food on the seabed, feeding on crustaceans, fish, molluscs, squids and jellyfish.
  • Leatherbacks feed mostly on jellyfish.
  • Loggerheads feed mainly on hard-shelled organisms such as lobsters, crustaceans, and fish.
  • Olive ridleys are omnivorous, mostly eating jellyfish, snails, crabs, and shrimp but they will occasionally eat algae and seaweed as well.

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Enroll Today And Learn More About Sea Turtles:
Free Online Courses

Free

e-Turtle School – All About Sea Turtles

Everything you have ever wanted to know about sea turtles, from evolution to conservation. Suitable for all sea turtles lovers and those who want to learn more about these fascinating creatures.
Free

Sea Turtle Science & Conservation

Deep dive into sea turtle science and conservation. Suitable for budding conservationists and those with an interest in the science surrounding turtles, their biology and conservation.

References:

  • Briscoe, D.K., Parker, D.M., Bograd, S., Hazen, E., Scales, K., Balazs, G.H., Kurita, M., Saito, T., Okamoto, H., Rice, M. and Polovina, J.J., 2016. Multi-year tracking reveals extensive pelagic phase of juvenile loggerhead sea turtles in the North Pacific. Movement ecology, 4(1), pp.1-12.
  • Conant, T.A., Dutton, P.H., Eguchi, T., Epperly, S.P., Fahy, C.C., Godfrey, M.H., MacPherson, S.L., Possardt, E.E., Schroeder, B.A., Seminoff, J.A. and Snover, M.L., 2009. Loggerhead sea turtle (Caretta caretta) 2009 status review under the US Endangered Species Act. Report of the loggerhead biological review Team to the National Marine Fisheries Service, 222, pp.5-2.
  • Hays, G.C., Mortimer, J.A., Ierodiaconou, D. and Esteban, N., 2014. Use of long‐distance migration patterns of an endangered species to inform conservation planning for the world’s largest marine protected area. Conservation Biology, 28(6), pp.1636-1644.
  • Karl, S.A. and Bowen, B.W., 1999. Evolutionary significant units versus geopolitical taxonomy: molecular systematics of an endangered sea turtle (genus Chelonia). Conservation biology, 13(5), pp.990-999.
  • Limpus, C.J., Couper, P.J. and Couper, K.L.D., 1993. Crab Island revisited: reassessment of the world’s largest flatback turtle rookery after twelve years. Memoirs of the Queensland Museum. Brisbane, 33(1), pp.277-289.
  • Pritchard, P.C., 1999. Status of the black turtle. Conservation Biology, pp.1000-1003.
  • Mast, R.B., Hutchinson, B.J. and Hutchinson, A.H. eds., 2008. Proceedings of the Twenty-fourth Annual Symposium on Sea Turtle Biology and Conservation: 22 to 29 February 2004, San José, Costa Rica (Vol. 567). National Marine Fisheries Service, Southeast Fisheries Science Center.
  • Mortimer, J.A. and Carr, A., 1987. Reproduction and migrations of the Ascension Island green turtle (Chelonia mydas). Copeia, pp.103-113.
  • National Marine Fisheries Service and US Fish and Wildlife Service (NMFS and USFWS), 2020. Endangered Species Act status review of the leatherback turtle (Dermochelys coriacea).
  • US Fish and Wildlife Service, 2007. Hawksbill Sea Turtle (Eretmochelys imbricata). 5-Year Review: Summary and Evaluation. 
  • US Fish and Wildlife Service, 2014. Olive Ridley Sea Turtle (Lepidochelys Olivacea) 5-Year Review : Summary and Evaluation
  • Witt, M.J., Augowet Bonguno, E., Broderick, A.C., Coyne, M.S., Formia, A., Gibudi, A., Mounguengui Mounguengui, G.A., Moussounda, C., NSafou, M., Nougessono, S. and Parnell, R.J., 2011. Tracking leatherback turtles from the world’s largest rookery: assessing threats across the South Atlantic. Proceedings of the Royal Society B: Biological Sciences, 278(1716), pp.2338-2347.

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