Pune: A large increase in fishing pressure, coupled with climate-related changes, could seriously impact sardine numbers off the country’s south-west coast.Researchers from the Indian Institute of Tropical Meteorology (IITM) and the National Center for Ocean Information Services (INCOIS) have warned thousands of coastal families dependent on India’s sardine fishing after studying more than five decades of fishing data off India’s west coast. The team found that large-scale climate change has affected the winds and ocean conditions that determine food availability and breeding conditions for sardines.India is one of the largest marine fish producers in the world. Sardines constitute a large part of the country’s catch.The researchers said moderate changes could be absorbed, but warned that overfishing could lead to drastic declines in sardine numbers. The study led by IITM scientist Vinu Valsala has been published in the journal “Ecological Modeling”. This is the first model of its kind developed for the Indian coast. Other scientists involved in the study include Inaconda Veera Ganga Bhavani and Faseela Hamza.The researchers reached the conclusion after building a climate-driven population model for the Indian oil sardine (Sardinella longiceps), called BIOFIM. When run against real landings data from 1965 to 2017, the model reproduced real-world swings in sardine catches, including a well-known crash in sardine counts between 1980 and 2000 and subsequent recovery.Oil sardines are not just a food source. They are a vital link in the marine food chain – what scientists call “forage species” – feeding on the plankton at the bottom of the chain and, in turn, feeding larger fish, sea birds and marine mammals.One discovery that surprised researchers was what most affected the numbers of sardines. “We examined the role of sea surface temperature, air temperature and atmospheric pressure and found that atmospheric pressure emerged as the strongest factor associated with year-to-year variation in sardine numbers,” Valsala said.The researchers said this link probably works through winds and ocean conditions. “Changes in atmospheric pressure affect wind patterns and ocean currents off the southwest coast of India. These, in turn, affect coastal upwelling – a process that brings cool, nutrient-rich water to the surface and helps support marine food chains,” Valsala said.The study also found that sardines grow best within a relatively narrow temperature range of the upper 75 meters of the ocean, averaging 25.5–26.5°C. During hot periods, when temperatures rise beyond that limit, feeding conditions become less favorable. The researchers observed that periods of low sardine biomass, including 1980-84, 1996-98 and 2014-17, coincided with temperatures above 26.5 degrees Celsius, which they say could provide clues about how future ocean warming might impact the fishery.Valsala said, “We found that the fishery remained relatively stable with small changes, but a sharp decline in sardine numbers is projected if fishing pressure increased by 40-50%. We also found that when both fishing and natural mortality increased simultaneously, fish populations declined significantly, which shows how environmental stress and fishing can affect long-term sustainability.”Oil sardines have a lifespan of approximately two and a half years, making them vulnerable to disruptions in reproduction and survival.