Forty Years of Counting Birds in the Gulf of Mannar: Fifty-Seven Per Cent Are Gone
A long-run survey of India's first marine biosphere reserve finds shorebird abundance collapsing since the late 1980s — with the losses concentrated in long-distance migrants
What happened
Conservation data in India is usually a snapshot, which is why this study is worth knowing: it is a forty-year series, and long series are what allow decline to be distinguished from fluctuation. The more useful finding is not the headline 57 per cent but the composition shift underneath it — long-distance migrants falling while short-distance species hold or rise. That pattern points the causal question away from this coastline and toward the flyway that connects it to Siberia.
Four Survey Windows, One Trend
Gulf of Mannar Shorebirds, 1985–2024
Curlew Sandpiper
Greater Sand Plover
Source: Four-decade shorebird assessment of the Gulf of Mannar (1985–2024)
The Gulf of Mannar is a shallow bay of the Laccadive Sea lying between south-eastern India and western Sri Lanka, roughly 160 km long and 130 to 275 km wide.
●It is bounded to the north-east by Rameswaram Island, Adam's Bridge and Mannar Island, and connects to Palk Bay through the Palk Strait; the Thamirabarani drains into it on the Indian side and the Aruvi on the Sri Lankan, with Thoothukudi as the principal Indian port.
●It holds three distinct coastal ecosystems in close proximity — coral reefs, seagrass beds and mangroves — across a chain of 21 islands, and supports more than 4,223 recorded species, including 117 species of hard coral, dugongs, sea turtles, sharks and dolphins.
●It was declared a Marine National Park in 1986 and a Biosphere Reserve in 1989, making it the first marine biosphere reserve in India and South Asia.
●For migratory shorebirds it is a wintering and staging ground on the Central Asian Flyway, one of the world's major migratory bird routes, for which India adopted a National Action Plan for Conservation of Migratory Birds.
●The new four-decade assessment (1985–2024, four survey periods, 40 species) records an approximately 57 per cent decline in overall shorebird abundance, with the sharpest reduction beginning after 1987–88.
The composition shift is the diagnostic signal — long-distance migrants such as the Curlew Sandpiper falling while shorter-distance species rise points to pressure along the flyway, not only at the wintering site.
◎ In Simple Words
The Gulf of Mannar is a shallow sea between Tamil Nadu and Sri Lanka, full of coral reefs and small islands. Every winter, birds fly there from as far away as Siberia to feed on its mudflats before returning north to breed. Scientists have counted these birds on and off since 1985. Comparing the counts, they found that only about four in every ten birds remain compared with the 1980s. Interestingly, the birds that travel the farthest have declined the most, while some shorter-distance species have actually increased — which suggests the problem may lie along their long journey, not only here.
Factual Pointers
Practice · 2 questions
With reference to the Gulf of Mannar, consider the following statements:
1. It lies between south-eastern India and western Sri Lanka and connects to Palk Bay through the Palk Strait.
2. It was declared India's first marine Biosphere Reserve.
3. It contains coral reefs, seagrass beds and mangroves.
Which of the statements given above are correct?
The 'Central Asian Flyway', often mentioned in the context of migratory bird conservation in India, refers to:
Mains Practice Questions
"Protected area status secures a wintering ground and nothing more." Examine the limits of site-based conservation for migratory species, with reference to the Central Asian Flyway. (250 words, GS3)
Long-run monitoring series are disproportionately valuable in ecology. Discuss with reference to shorebird decline in the Gulf of Mannar. (250 words, GS3)
Explain why the Gulf of Mannar is ecologically significant, and identify the principal pressures on it. (150 words, GS3)
Frequently Asked
· People also askWhat did the Gulf of Mannar shorebird study find?
It found an approximately 57 per cent decline in overall shorebird abundance across four decades. The assessment used four survey periods between 1985 and 2024 — 1985–88, 2005–07, 2018–19 and 2021–24 — recorded 40 species, and identified a marked reduction beginning after 1987–88.
GS3 · EnvironmentStandardised peak seasonal counts were analysed using a hierarchical generalised linear mixed model, which is what allows a genuine trend to be separated from the large year-to-year fluctuation typical of migratory populations.
SOURCE Four-decade shorebird assessment, Gulf of Mannar
Which species declined and which increased?
Historically abundant long-distance migrants declined significantly — notably the Siberian Sand Plover and the Curlew Sandpiper — while the Kentish Plover and Greater Sand Plover increased in recent years. The pattern is a shift in community composition rather than uniform depletion.
GS3 · EnvironmentThat asymmetry is diagnostic: if the pressure were purely local habitat loss, declines would be broadly similar across species using the same mudflats. Long-distance migrants falling points to conditions along the Central Asian Flyway.
SOURCE Four-decade shorebird assessment, Gulf of Mannar
Why is the Gulf of Mannar ecologically important?
It holds three coastal ecosystems in close proximity — coral reefs, seagrass beds and mangroves — across a chain of 21 islands, and supports more than 4,223 recorded species including 117 hard coral species, dugongs, sea turtles, sharks and dolphins.
Prelims · GS3It was declared a Marine National Park in 1986 and a Biosphere Reserve in 1989, making it the first marine biosphere reserve in India and South Asia.
SOURCE Gulf of Mannar Biosphere Reserve Trust
Where exactly is the Gulf of Mannar?
It is a shallow bay of the Laccadive Sea between south-eastern India and western Sri Lanka, about 160 km long and 130 to 275 km wide. It is bounded to the north-east by Rameswaram Island, Adam's Bridge and Mannar Island, and connects to Palk Bay through the Palk Strait.
Prelims · GeographyThe Thamirabarani drains into it on the Indian side and the Aruvi on the Sri Lankan side; Thoothukudi is the principal Indian port on the bay.
SOURCE Survey of India
What is the Central Asian Flyway?
It is one of the world's major migratory bird routes, linking breeding grounds in Siberia and northern Eurasia with wintering grounds in South Asia and the Indian Ocean region. India has adopted a National Action Plan for Conservation of Migratory Birds along this flyway.
GS3 · IRIndia is party to the Convention on Migratory Species and hosted its Conference of the Parties in 2020 — but flyway conservation depends on other range states protecting staging habitat, which domestic protection cannot substitute for.
SOURCE Convention on Migratory Species; Ministry of Environment, Forest and Climate Change
Why can't protected area status alone save these birds?
Because migratory species depend on an entire chain of sites. India can manage the Gulf of Mannar well and still lose its Curlew Sandpipers if intertidal staging habitat is reclaimed elsewhere along the route or if Arctic breeding conditions shift.
GS3 · EnvironmentThe parallel is the East Asian–Australasian Flyway, where reclamation of Yellow Sea mudflats crashed populations wintering thousands of kilometres away — the clearest demonstration that one broken link breaks the chain.
SOURCE Convention on Migratory Species