Signals from the sea: why jellyfish and sardines are washing ashore in record numbers

From Kerala’s "Chakara" festivals to mysterious blue swarms on city beaches, scientists are decoding the environmental messages behind mass marine strandings.

Along the sun-drenched coasts of Kerala, Karnataka, and Goa, a recurring phenomenon known as "Chakara" has long been a cause for local celebration. For generations, fishermen have viewed these massive aggregations of Indian oil sardines—where fish appear in such density that they wash ashore—as a seasonal blessing. However, as these events become more frequent and unpredictable, marine experts are looking past the windfall to identify the deeper, often troubling, signals hidden within the tides.

The Warming Ocean Connection

Researchers at the Indian National Centre for Ocean Information Services (INCOIS) in Hyderabad have begun mapping these events using satellite data, identifying a complex web of environmental triggers. At the heart of the disruption is the El Niño-Southern Oscillation (ENSO). When El Niño conditions drive Sea Surface Temperatures (SST) beyond the optimal tolerance range for sardines, the fish experience severe physiological stress. In their search for cooler, oxygen-rich refuge, they are often pushed toward the coast. While these nearshore microhabitats—enriched by rainfall and localized upwelling—offer temporary relief, the fish often find themselves trapped, eventually washing ashore as currents and tidal forces intensify.

A Wider Pattern of Marine Distress

The trend is not limited to the west coast or to fish alone. Across the country, the east coast has witnessed its own set of biological anomalies, most notably the mass beaching of jellyfish. Following Cyclone Mocha in May 2023, hundreds of jellyfish were deposited along the Puri coast. Investigations revealed that persistent marine heatwaves in the Bay of Bengal had accelerated their metabolism and boosted reproduction rates. These jellyfish, along with the "blue button" jellies (Porpita porpita) frequently spotted on Mumbai’s Juhu beach, act as living barometers of a changing ocean environment.

Why These Events Matter

The surge in these gelatinous blooms is rarely the result of a single factor. While natural rhythms like currents, tides, and seasonal upwelling play a standard role in moving marine life, they are being amplified by human-induced stressors. Overfishing, which depletes natural predators like sea turtles and tuna, allows jellyfish populations to thrive unchecked. Simultaneously, coastal pollution creates low-oxygen "dead zones" where more sensitive fish struggle to survive, while resilient jellyfish species multiply.

Lessons from the Shoreline

The global nature of these events underscores a mounting ecological shift. Observations from citizen scientists, such as those documenting "by-the-wind sailor" jellies washing ashore in the millions across North American beaches, mirror the findings in Indian waters. Whether through the sudden arrival of glowing blue organisms or the mass stranding of economically vital fish, these occurrences serve as clear signals that our oceans are drifting out of balance. For coastal communities, the transition from seeing these events as mere curiosities to understanding them as indicators of climate change remains a critical challenge for future resilience and governance.