Chilika Lake emerges as single largest habitat of Irrawaddy dolphins in the world

The Chilika Lake in Odisha has emerged as the “single largest habitat of Irrawaddy dolphins in the world”, following a fresh monitoring survey that pegs the number of individuals of the endangered species at 155.

Chilika is Asia’s largest brackish-water lagoon with an estuarine character, and one of India’s first Ramsar Convention sites (wetlands of international importance). Straddling three Odisha districts, Chilika, the part marine, part brackish and part freshwater lagoon, dotted with islands, is bordered by hills and hillocks of the Eastern Ghats.

Infused with fresh water from inland rivers and injected with saline water from Bay of Bengal, the lagoon supports rich biodiversity, including some rare, endangered and vulnerable species such as the Irrawaddy dolphin, which is also known as snubfin dolphin (Orcaella brevirostris), the limbless skink belonging to the Barakudia genus among others, and is a haven for migratory birds.

According to the 2017 TEEB India report, the diverse and dynamic “assemblage of fish, invertebrate and crustacean species provides the basis of rich fishery, which generates over six per cent of the state’s foreign exchange earnings and supports livelihoods of 0.2 million fisher-folk who live in and around the lake.”

A landmark ecological restoration effort

Considered as a dying water body in the 1990s, Chilika scripted history with the success of its landmark ecological restoration model.

The dolphins in Chilika –a prime tourist attraction – were under stress due to shrinking habitat, rampant use of fishing gear like gill nets, mechanised boats and widespread illegal commercial prawn culture.

A pen culture is an aquaculture system where a specially designed enclosure of bamboo (or other material), encircled by zero mesh nets, is constructed in a water body for rearing fish/prawn. The structure is enclosed on all sides except at the bottom where the construction touches the bottom of the lake or sea. Zero mesh nets are fine-mesh nylon nets which can capture virtually all fish encountering it; even very small fish seedlings and post-larval prawns can’t escape them.

In February this year, officials sighted 155 Irrawaddy dolphins in the pear-shaped lagoon while executing the first annual monitoring survey conducted by the Chilika Development Authority (CDA). The survey’s aim was to map the number and extent of the lagoon’s flagship species and to study the hydrological impacts of removal of pen culture, locally known as gherries.

The number is more compared to last year’s census count of around 100 dolphins. The range of population is believed to be between 145 and 160. They are classed as Schedule-I animal under the Wildlife Protection Act, 1972.

The discovery of the shy mammals inhabiting pockets of the lagoon where they were not sighted before has brought cheer to wildlife officials. This habitat extension is attributed to weeding out migration barriers like the use of gill nets and the presence of gherries.

Susanta Nanda, chief executive of CDA, told Mongabay-India that the dolphins were earlier confined mainly to the outer channel and were unable to move across the lake because of obstructions. Now, Nanda says, the dolphins have colonised new areas mainly in the southern and central sector of the lake, which were once invaded by illegal aquaculture systems.

Illegal pen cultures deal a blow to the lake ecosystem

“Pen cultures occupy mainly the shores which are the finest habitat for fish spawning. Because of such illegal encroachments-the fishing area is reduced, nursery ground for recruitment of fish is destroyed, the lake is silted up at a faster pace, the water is polluted and the hydrology is severely affected. The seagrass bed is also seriously compromised. This destroys the ecosystem of the lake,” Nanda observed.

Despite a decline in the rampant use of zero mesh nets, the nets still pose the maximum threat to the ecosystem of the lake as they hasten siltation. Besides, unscientific laying of the khandas (trap nets) is also hindering the migratory path of the juveniles and is adding to siltation of the lake, Nanda explained.

Trap nets or ‘net boxes’ form a maze-like chamber into which fish can easily enter, but once inside, they cannot easily escape.

Ritesh Kumar, Conservation Programme Manager, Wetlands International South Asia, says illegal aquaculture in Chilika has persisted for over two decades, nearly taking up the highly productive fringes in central and southern sectors of the lagoon, and along its outer channel.

“Removal of prawn enclosure through a continuous operation during the last six months taken by CDA in collaboration with enforcement agencies is also a landmark. Given the fact that CDA does not have any regulatory powers of its own, the organisation’s ability to convene the state apparatus to enforce the Supreme Court’s decision is commendable. This also indicates political support to the wetlands restoration,” Ritesh Kumar told Mongabay-India.

Winged visitors

Apart from the dolphins, the survey has also shed light on the status of the 0.9 million birds, including migratory species, congregating in the lake, the largest wintering ground for migratory waterfowl found anywhere on the Indian sub-continent.

Flocks of migratory waterfowl arrive from as far as the Caspian Sea, Lake Baikal, remote parts of Russia, Mongolia, central and south-east Asia, Ladakh and the Himalayas to feed and breed in its waters.

The Nalabana Island, a submersible island with extensive mudflats that stretch over 15.53 square km, is exposed only during the dry season from December to May. During these five to six months, the little island attracts over 300,000 waterbirds. The island supports the largest concentrations of waders in the lake, and a few thousand flamingos.

Although no new species were identified during the monitoring, it was observed that the birds, mainly the migratory ducks, have started settling in new areas that were earlier encroached upon by pen culture.

Noted ornithologist S. Balachandran, deputy director, Bombay Natural History Society, says migratory waterbirds connect continents and countries and are therefore excellent environmental indicators at both global and local scales. Arrival patterns of migratory birds have undergone a change due to climate change and development activities in the wetlands, he points out.

Reviving a dynamic ecosystem

Fed by 52 rivers and rivulets, the lagoon–popular in Odisha folklore –is connected to the Bay of Bengal by a narrow sea mouth.  It has a water-spread ranging from 1165 square km in the rainy season to 906 square km in the dry season.

In 1981, Chilika was one of the first wetlands to be designated as a Wetland of International Importance – a Ramsar Site under the Convention on Wetlands –  by the Indian government.

With the lake reeling under pressures of increasing silt load, declining fisheries and expansion of shrimp aquaculture, the Odisha government in 1991 constituted the CDA to address the challenges. In a one of a kind model, this authority is chaired by the chief minister of the Odisha government.

During 1950 to 2000, the TEEB India report says, increasing siltation from catchments and a variety of anthropogenic activities, choked the lagoon’s connection with the Bay of Bengal, sounding the death knell for the water body. In 1993, Chilika was ultimately placed under the Ramsar Convention’s Montreux Record (a list of wetlands facing adverse threats).

Giving it a fresh lease of life, in 2000, a new mouth to the Bay of Bengal was cut open by dredging of the outer channel which connects the lake to the sea, to let sea water in. In 2002, Chilika became the first Asian site to be removed from Montreux Record.

Maintained fish yield levels, a stable (rather increasing) population of flagship Irrawaddy Dolphin, diversification of habitat use by various species notably waterbirds, is an indicator of ecosystem resilience and effectiveness of management, Kumar noted.

The latest annual monitoring survey also highlighted an increase in sea grass bed indicating improved hydrological condition of the lake.

“One must note that these trends come after a conspicuous shock induced by cyclone Phailin in October 2013, wherein the lagoon switched to a predominantly freshwater stage for a prolonged period. The cyclone caused a near complete destruction of sea-grass beds, and changes in composition of fish species. The outcomes of current monitoring are an indicator that the Chilika ecosystem is highly resilient, even in the face of ecological shocks,” Kumar stressed.

Improvement of Chilika habitat, in particular the increase in dolphins, has led to a resurgence of wetland tourism. The annual number of tourists visiting the wetland during 2000 – 2014 averaged 0.3 million – an increase of over 60 percent as compared to arrivals during 1994 – 1999, as per the TEEB India report.

Nanda says although the presence of dolphins in different sectors of the lake has raised hopes of eco-tourism, a “high degree of caution is necessary to preserve them by taking up responsible tourism.”

Ritesh Kumar agrees. “Safeguards needs to be put in place to prevent mass tourism within a fragile ecosystem as Chilika. Increasing urbanisation and intensification of agriculture would also increase pollution loading in the wetland,” he said.