MTN 83:10-12 An Update on the Mortality of the Olive Ridley Sea Turtles in Orissa, India

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An Update on the Mortality of the Olive Ridley Sea Turtles in Orissa, India

Bivash Pandav & B.C. Choudhury

Wildlife Institute of India, P.O.Box # 18, Chandrabani, Dehradun 248 001, Uttar Pradesh, INDIA. (E-mail: pandavb@hotmail.com)

Olive ridley turtles (Lepidochelys olivacea) nest in low densities all along the eastern coast of India. However, the most important nesting beaches are in Orissa, where three of the few remaining mass nesting or "arribada" sites in the world are found (Gahirmatha, Robert Island and Rushikulya; Pandav & Choudhury 1998). A significant portion of the world's olive ridley turtle population nest at these three rookeries and they have received considerable attention in recent times due to the large scale mortality of adults, mostly due to drowning in illegally operated trawl fisheries. Fishing in the coastal waters off Gahirmatha became restricted in 1993 and was completely banned in this area in 1997, when Gahirmatha was given the status of a Marine Sanctuary.

Uncontrolled mechanised fishing in areas of high sea turtle concentration has resulted in large-scale mortality of adult sea turtles during the last two decades in Orissa (James et al. 1989; Dash & Kar 1990; Pandav et al. 1994; Pandav et al. 1997). Dash and Kar (1990) report the stranding of 4,682 adult olive ridley turtles at Gahirmatha rookery between September 1978 and May 1985. James et al. (1989) document the stranding of more than 8,000 individuals between 1983 and 1987.

Figure 1. Dead turtles stranded at Orissa (1993-1998, n=33,617).

Since November 1993, records of marine turtle strandings on the coast of Orissa have been kept as a part of the ongoing sea turtle research programme of the Wildlife Institute of India. The entire Orissa coast, stretching over 480 km has been divided into eight survey sectors (Pandav et al. 1994) and each of these sectors is walked once every two weeks during the breeding season (November-April). Dead turtles washed ashore are measured, sexed and marked with white paint on their carapace to avoid repeat counts during subsequent surveys. In the 1993/94 season, 5,282 dead olive ridley turtles were recorded (Pandav et al. 1994; Pandav et al. 1997). Since then we have documented the stranding of more than 30,000 olive ridley turtles in Orissa (Figure 1). Near shore mechanised fishing, specifically shrimp trawling, is thought to be the major cause of this high mortality. Mortality due to such illegal trawling has been increasing each year and reached a record high of 13,575 ridleys in the 1997/1998 season (Figure 2). This figure is thought to be a minimum estimate. The majority (89.6%) of the recorded strandings occurred on the coast near Gahirmatha, Paradeep, Kujang and Devi (Pandav et al. 1994). The coastal waters of these four sectors are subjected to the highest levels of shrimp trawling in Orissa.

Figure 2. Seasonal stranding at Orissa (November 1997- April 1998, n=13,575).

Shrimp trawling has been identified as one of the greatest causes of sea turtle mortality throughout the world (Hillstad 1981; Ruckdeschel & Zug 1982; Henwood & Stunz 1987; Ehrhart 1987; Magnuson et al. 1990; Robins 1995). Despite the wide acceptance of this fact, the Government of Orissa and the Orissa State Fisheries Department appear reluctant to accept this large scale mortality is a result of incidental capture of turtles in fishing nets. They speculate that disease, migration fatigue, and marine pollution (as cited in many Indian newspapers) are the causes of these deaths. To counteract these arguments quantitative information on observed captures of sea turtles and the rate of mortality of these individuals during offshore fishing operations is absolutely essential. In the interim, strict enforcement of Orissa Marine Fishing Regulation (OMFR) Act 1982 and Rules 1983, which prohibit any kind of mechanised fishing within five km of the shore along the Orissa coast, is needed. A blanket ban on near shore mechanised fishing should significantly reduce the turtle mortality. A second step towards minimizing this mortality would be the mandatory use of Turtle Excluder Devices (TEDs) in trawl nets. Currently none of the 3,000 odd trawlers operating off the Orissa coast use TEDs in their nets.

However, the use of TEDs alone will not eliminate turtle mortality resulting from fisheries. Additional factors which must be considered are that in areas of high fishing intensity, turtles that are captured and released several times may die and turtles are also caught and drowned in gill nets. Therefore strict enforcement of the existing law, prohibiting near shore mechanised fishing seems to be the best short term solution to reduce turtle mortality.

The number of nesting females at Gahirmatha has declined in recent years. Although intense offshore fishing activities may have played a role, it is also thought that this may be due in part to unsuitable beach conditions. The beach width has been severely reduced due to erosion processes. A third possibility is that artificial illumination created by construction work at the nearby missile testing range at the Outer Wheeler Island, has caused disturbance. Notwithstanding, the high levels of marine turtle mortality in the area are a matter of utmost concern and urgently need to be addressed. DASH, M.C. & C.S. KAR. 1990. The turtle paradise - Gahirmatha. Interprint, NewDelhi, 295 pp.

EHRHART, L.M. 1987. Marine turtle mortality in the vicinity of Port Canaveral, Florida1977-84. In: Ecology of east Florida sea turtles. W.N. Witzell (Ed.). Proceeding of theCape Canaveral, Florida Sea Turtle Workshop, Miami, Florida, Feb. 26-27, 1985, pp.1-20.

HENWOOD, T.A. & W.E. STUNZ. 1987. Analysis of sea turtle captures and mortalities during commercial shrimp trawling. Fisheries Bulletin, 85: 813-817.

HILLESTAD, H., J. RICHARDSON, C. MCVEA & J. WATSON. 1981. Worldwide incidental capture of sea turtles. In: K. A. Bjorndal (Ed.). Biology and conservation of sea turtles. Smithsonian Institute Press, Washington D.C., pp. 489-495.

MAGNUSON, J.J., K.A. BJORNDAL, W.D. DUPAUL, G.L. GRAHAM, D.W. OWENS, C.H. PETERSON, P.C.H. PRITCHARD, J.I. RICHARDSON, G.E. SAUL & C.W. WEST. 1990. Decline of the sea turtles: Causes and Prevention. National Academy Press, Washington D.C., 259 pp.

JAMES, P.S. R.B., M. RAJGOPALAN, S.S. DAN, A. BASTIAN FERNANDO & V. SELVARAJ. 1989.On the mortality and stranding of marine mammals and turtles at Gahirmatha, Orissa from 1983 to 1987. Journal Marine Biological Association, India. 31: 28-35.

PANDAV, B. & B.C. CHOUDHURY 1998. Olive ridley tagged in Orissa recovered in the coastal waters of East Sri Lanka. Marine Turtle Newsletter 82: 9-10.

PANDAV, B., B.C. CHOUDHURY & C.S. KAR. 1994. A status survey of olive ridley sea turtle (Lepidochelys olivacea) and their nesting beaches along the Orissa coast, India. Unpublished Report. Wildlife Institute of India, Dehradun. 48pp.

PANDAV, B., B.C. CHOUDHURY & C.S. KAR. 1997. Mortality of olive ridley sea turtle (Lepidochelys olivacea) due to incidental capture in fishing nets along Orissa coast, India. Oryx. 31(1): 32-36.

ROBINS, J.B. 1995. Estimated catch and mortality of sea turtles from the east coast otter trawl fishery of Queensland, Australia. Biological Conservation. 74: 157-167.