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Ecologically or Biologically Significant Areas (EBSAs)

  published: 10 Jul 2017

Olive Ridley Sea Turtle Migratory Corridor in the Bay of Bengal

General Information
The coast of the Indian state of Odisha is the world's largest nesting site for olive ridley turtles. The mouths of the Devi, Rushikulya and Bhitarkanika rivers hold the world's largest nesting congregation of this species. Satellite telemetry studies have demonstrated that the majority of turtles migrate north-south∕south-north to and from Sri Lanka. However, beyond this point no pattern has been established. The congregation and nesting of the olive ridley turtles within the Indian EEZ are protected by the environmental laws/acts of the country, however, the corridors in which they move for feeding and mating are unprotected. A major segment of the olive ridley population visiting the Odisha coast is from southern Sri Lanka. Genetic studies confirmed the results from tagging and satellite telemetry studies and showed that there is no genetic difference between nesting populations in each of the mass nesting beaches. More significantly, the results revealed the distinctiveness of the population on the east coast of India and Sri Lanka, and suggested that this population is the ancestral source of contemporary global populations of olive ridley sea turtles.

The coast of the Indian state of Odisha hosts the world's largest breeding area for olive ridley sea turtles (Lepidochelys olivacea) near the  mouths of the Rushikulya, Devi and Gahiramatha rivers. Besides Odisha, a few olive ridley sea turtles nest in northern Andhra Pradesh, Tamil Nadu, and the Andaman and Nicobar islands on the east coast and in Gujarat, Maharashtra, Goa, Kerala and Lakshadweep on the west coast (Tripathy and Choudhary, 2003; Bhupathy, S. and Saravanan, 2002; Andrews, et al. 2001). They are known to breed between October and May. They migrate en masse from the Indian Ocean south of Sri Lanka with the onset of winter. Based on evidence from tagging studies, the migration of breeding olive ridley turtles takes a northerly course through the coastal waters off Tamil Nadu and Andhra Pradesh prior to the arrival of the turtles in Odisha (Das and Kar, 1990; Pandav and Choudhury, 2000), where they spend a considerable amount of time in the shallow waters off the continental shelf of Odisha. Large concentrations of olive ridley sea turtles have been reported in the coastal waters of Sri Lanka, migrating northwards during September and November (Etnoyer et al. 2006).

In a recent study by the Wildlife Institute of India (unpublished data), of the 68 tagged turtles (63 females and 5 males), most of the tracks suggest north-south movement (Figure 1). Despite a significant quantity of work on the biological behaviour of olive ridley sea turtles (Tripathy et. al., 2008; IOSEA, 2014) a major gap still exists in the knowledge  of what happens and where all these turtles move to once they reach Sri Lanka. In the past all the ridleys tagged at all the three mass nesting beaches as well as in the coastal waters off Gahirmatha have been recaptured from Sri Lanka (Pandav and Choudhury, 2000). This clearly indicates the movement of the olive ridley sea turtles through the Bay of Bengal. The nesting and nearshore feeding areas are protected as national parks and sanctuaries under the Wildlife Protection Act of India (1972).

The areas beyond national jurisdiction that are used by migratory olive ridleys have not, however, been well studied for the biological or oceanographical setting of this species. The area described here, which is entirely beyond national jurisdiction, recognizes the significance of this migratory corridor for olive ridley sea turtles.

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Description of the location
North-East Indian Ocean

The area is located beyond national jurisdiction, in the Bay of Bengal

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Area Details

Mishra et al. (2011) studied the movement of olive ridley sea turtles in coastal regions and their nesting behaviour in India between 2003 and 2007, and related them to oceanographic parameters. The impact of oceanographic parameters, including potential environmental influences on their movements and nesting, was compared on the west and east coasts with remotely sensed variables, including sea surface temperature (SST), sea surface current (SSC), surface chlorophyll  concentration (Chl-a), sea surface height (SSH) and mixed layer depth (MLD). The movement has been observed on the east coast, including the oceanic migration for pelagic and mass nesting that increased gradually southward from the west coast and then northward, with mass nesting on the east coast of Odisha.  The movement results from the potential mean surface Chl-a concentration of 3 mgm-3 with threshold limitation of mean surface temperature at 250C off the east coast of Odisha. Although the mean surface Chl-a and SST were maintained on the west coast, there was a distinct variation in MLD, WSC with SSH characteristics. The study revealed the favourable oceanographic condition for mass nesting of olive ridley turtles on the east coast of Odisha. The data provided by Brewer et al (2015) clearly suggests that for much of the year, high productivity only occurs near the coast and off the mouths of rivers. In the area described as meeting the EBSA criteria, however, high productivity was noted for a very limited period from January to April each year, which is also peak olive ridley migratory period and consistent with the findings of Mishra et al. (2011) and BOBLME (2012).

Olive ridley sea turtles, like other species of sea turtles, act as navigators and travel long distances, from hundreds to thousands of kilometres, between their feeding and nesting habitats (Akesson 1996). They frequently travel in open sea areas, where the sea currents are likely to favour their movement patterns (Nichols et al, 2000). The navigational pattern indicates that this is linked to certain oceanographic parameters, like SST and SSC, and hence they perform in response to geomagnetic cues (Luschi et al, 2003).

Fitzsimmons and Limpus (2014) note the considerable progress that has been made to define population boundaries and migratory behaviour of marine turtles within the Indo-Pacific. They identify the relative size of rookeries and identify the olive ridley population on the east coast of India and northern Sri Lanka as a discrete genetic stock.

The eleventh meeting of the Conference of the Parties to the Convention on Migratory Species, in Quito, Peru stated that habitats for migratory species are becoming increasingly fragmented across terrestrial, freshwater and marine biomes and recognized the need for transboundary area-based conservation measures for animals that migrate for long distances across or outside national jurisdictional boundaries.

The results of recent surveys to investigate the Cetacean Community Ecology in the Waters of Sri Lanka and the Bay of Bengal site (Baumgartner 2014), should provide substantial additional information regarding the ecological and biological significance of this area.

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The area is located within the Bay of Bengal Abyssal Province (Brewer et al., 2015), which is characterized as a low productivity pelagic zone, where seasonal monsoon events, combined with the high sediment load from the Ganges and Bengal Fan, create seasonal variation in this unique province among deep-ocean abyssal systems. It is a stable, extremely deep-water offshore area and a major component of the Bay of Bengal biogeography.

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References

Akesson, S (1996). Geomagnetic map used for long-distance navigation? Trends Ecol Evol 11:398-399.
Andrews, H.V., Krishnan, S., Biswas, P., (2001). The Status and Distribution of Marine Turtles around the Andaman and Nicobar Archipelago, Madras Crocodile Bank Trust, Tamil Nadu, India.
Abreu-Grobois, A & Plotkin, P. (IUCN SSC Marine Turtle Specialist Group) (2008). Lepidochelys olivacea. The IUCN Red List of Threatened Species. Version 2014.3. www.iucnredlist.org Downloaded on 25 March 2015.
Baumgartner, M. 2014. Cetacean Community Ecology in the Waters of Sri Lanka and the Bay of Bengal. Woods Hole Oceanographic Institution, Biology Department, Woods Hole, MA.
Bhupathy, S. and Saravanan, S. (2002). Status Survey of Sea Turtles along the Tamil Nadu Coast. Kachhapa 7, 7-13
BOBLME (2012). Transboundary Diagnostic Analysis (TDA) Confirmation Workshop held in Phuket Thailand from 13 to 14 February 2012, Vol 2, pp. 108.
Das, M.C., and Kar, C.S. (1990). The Turtle Paradise-Gahiramatha. Interprint, New Delhi.
Deraniyagala, P.E.P. (1953), A coloured atlas of some vertebrates from Ceylon. Vol. 2. Tetrapod  Reptilia, Ceylon National Museum Publication. 101pp.
Brewer, D., Hayes, D., Lyne, V., Donovan, A., Skewes, T., Milton, D. and N. Murphy (2015). An Ecosystem Characterisation of the Bay of Bengal. Report for the Bay of Bengal Large Marine Ecosystem Project. CSIRO, Australia, ISBN: 978-1-4863-0521-6. 288 pp.
Etnoyer, P., Canny, D., Mate, B.R., Morgan, L.E., Ortega-Ortiz, J.G and Nichols, W.J (2006). Sea surface temperature gradients across Blue Whale and sea turtle foraging trajectories off the Baja California Peninsula, Mexico. Deep-Sea Res II 53:340-358.
Fitzsimmons, N.N. and Limpus, C.J. (2014). Marine turtle genetic stocks of the Indo-Pacific: Identifying boundaries and knowledge gaps. Indian Ocean Turtle Newsletter No. 20: 2-18.
IOSEA (2015) Bibliography. Available online at: http://www.ioseturtles.org/bibliography.php [Accessed 26.3.15]
Luschi, P, Hays G.C and Papi F (2003). A review of long distance movement by marine turtles, and the possible role of ocean currents. Oikos 103:293-302.
Mishra, R. K., S. M. Marale, S. Mishra, and S. Naik (2011). Olive Ridley Sea Turtle Movement in Relation to Oceanographic Parameters in India. IJEP Vol.1 No. 3, pp 49-54.
Nichols, W.J, Resendiz, A, Seminoff, J.A, Resendiz B. (2000). Transpacific migration of loggerhead turtle monitored by satellite telemetry. Bull Mar Science, 67:937-947.Tripathy, B., R. S. Kumar, B. C. Choudhury, K. Sivakumar & A. K. Nayak. 2008. Compilation of Research Information on Biological and Behavioural Aspects of Olive Ridley Turtles along the Orissa Coast of India ninsula, Mexico. Deep-Sea Res II 53:340-358.p. Areas of Research. Wildlife Institute of India, Dehra Dun.
Tripathy, B., Shanker, K. & Choudhury, B.C. (2003) Important nesting habitats of olive ridley turtles along the Andhra Pradesh coast of eastern India. Oryx 37: 454 – 463.
Valverde, R.A., Gates, C.E., 1999. Population surveys on mass nesting beaches. In: Eckert, K.L., Bjorndal, K.A., Abreu-Grobois, F.A., Donnelly, M. (Eds), Research and Management Techniques for Conservation of Sea Turtles. Publication No-4. IUCN/Marine Turtle Specialist Group, pp.56-60.
Tripathy, B. and Rajasekhar, P.S. (2009). Natural and anthropogenic threats to olive ridley sea turtles (Lepidochelys olivacea) at the Rushikulya rookery off Orissa coast, India. Indian Journal of Marine Sciences, Vol 38 (4), pp. 439-443.

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Status of submission
Areas described as meeting EBSA criteria that were considered by the Conference of the Parties
  • dec-COP-13-DEC-12
Assessment of the area against CBD EBSA criteria
C1: Uniqueness or rarity High

The annual mass movement of olive ridley turtles for nesting and their return through  the area is just one of two such occurrences in the world and also the largest (Tripathy and Choudhary, 2003; Bhupathy, S. and Saravanan, 2002; Andrews et al. 2001).

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C2: Special importance for life-history stages of species High

This area is very important for the life cycle of the olive ridley sea turtle. The mass movement of the adult turtles through the area beyond national jurisdiction of the Bay of Bengal is an important part of their life cycle, as they appear to disperse after reaching the seas off the Sri Lankan coast (Das and Kar, 1990, Pandav and Choudhury, 2000).

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C3: Importance for threatened, endangered or declining species and/or habitats High

Olive ridley turtles are listed as vulnerable on the IUCN Red List (Abreu-Grobois, A & Plotkin, 2008).

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C4: Vulnerability, fragility, sensitivity, or slow recovery High

Olive ridley sea turtles are highly vulnerable in near shore-breeding congregation areas. Eggs and young hatchlings are vulnerable to predation, while nesting sites are vulnerable to shore plantations, armoring and beach illumination (Tripathy and Rajasekhar, 2009).  However, the degree of vulnerability is unknown during movement through this area.

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C5: Biological productivity No information

No information available.

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C6: Biological diversity Low

The biodiversity of the area beyond national jurisdiction in the Bay of Bengal is relatively low (Mishra et al. 2011; BOBLME 2012; and Brewer et al. 2015).

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C7: Naturalness Medium

Area beyond national jurisdiction with limited shipping lanes and industrial fishing.

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