Cooler coastal waters of Kerala may have led to Sardine Rush, say researchers

Researchers study the 'Sardine Rush' phenomenon in Kerala, linking cooler waters and environmental factors to massive sardine aggregations.

The search for cooler waters could have forced the Sardine Rush, the sudden rush of Indian oil sardines (IOS) to coastal waters in huge numbers, in Kerala, according to researchers.

The Kerala coast had been witnessing the unique event of shoals of IOS rushing to the shallow waters in large numbers. In some instances, a large number of fishes could be seen splashing in the water and often throwing themselves on to the shores. Researchers have termed the “ephemeral dense IOS aggregation events” as Sardine Run.

As many as 14 such events were reported in various coastal areas of Kerala during the last three years, with the last one being reported from Vypeen on May 1, 2023.

The relatively lower sea surface temperature (SST) conditions in the regions could be one of the critical factors supporting the events. The coast-ward sea surface current and wind could have complemented the propagation of shoals toward the beach, according to a scientific paper published in Environmental Science and Pollution Research.

A team of oceanographers from the Indian National Centre for Ocean Information Services (INCOIS), Telangana, the Indian Institute of Technology, Bombay, Berhampur University, and Kerala University of Fisheries and Ocean Studies (Kufos), Kochi, led by T. M. Balakrishnan Nair, the Group Director of INCOIS, carried out the study as part of the efforts to give a “plausible scientific basis for the ephemeral non-periodic mass Indian oil sardine beaching events.”

The SST in the Arabian Sea during a majority of events was in the range of 26 degrees Celsius to 29 degrees Celsius. A marginal lowering of SST as a result of precipitation before most of the events might have attracted IOS towards the near-coastal waters. The availability of a phytoplankton diet and probable hypoxic conditions that degrade the IOS habitat could also have led to aggregation events.

The shifting or expanding feeding grounds due to climate change, predation pressure due overexploitation, and mismatches in blooming and breeding seasons due to human interventions could also have contributed to the extreme events, they noted.