Sardine population increase, decline linked to monsoon and oceanographic changes: CMFRI study

Kochi, Sep 30 (PTI) The Central Marine Fisheries Research Institute (CMFRI) has said that according to one of its studies climate-driven oceanographic changes have been shaping the population growth and decline cycles of the Indian oil sardines.

It said, in a release, that its study revealed that monsoon rainfall trends caused the sudden surge of juvenile Indian oil sardines along Kerala’s coast in 2024 and the subsequent ecological and economic fallout.

The study, published in Current Science, underscores the urgent need for dynamic fishery forecast models and harvest rules, the release said.

"A lifeline for Kerala’s fishing communities and a major contributor to India’s marine landings, oil sardine had witnessed a steep decline from a record catch of four lakh tonnes in 2012 to just 3,500 tonnes in 2021.

"However, in 2024, an unusual influx of young sardines, averaging 10 cm in size, was reported across Kerala’s coast, with instances of mass beaching in districts like Kozhikode and Thrissur," it said.

With an eco-regional approach, the CMFRI study integrated fisheries biology and oceanographic data from Kochi, Vizhinjam, and Kozhikode, it said.

"According to the study, the phenomenon was triggered by positive monsoon rainfall trends coupled with nutrient-rich upwelling that boosted microplankton growth -- the primary food source for sardine larvae. This spike in microplankton enhanced larval survival, leading to an unprecedented surge in recruitment.

"Later, this condition also increased competition for food resources among the recruits leading to poorly fed fish and lower weight gains for the zero year-class fishes. The economic impact was felt in the massive crash of the market prices for the sardine and led to suspension of fishing for juveniles," U Ganga, Principal Scientist who led the study, is quoted as having said in the release.

The study also pointed out that ecosystem productivity indicators -- especially the microplankton component of chlorophyll-a -- played a stronger role in sardine recruitment than the traditionally emphasized spawning stock biomass, the release said.

The marine heatwaves phenomenon varied in intensity and duration in the three ecoregions and likely affected maturation and distribution trends of oil sardine spawners, it added.

"With climate change intensifying these fluctuations, CMFRI researchers have called for the development of species-specific, short-term fishery forecast models and dynamic local harvest rules to ensure sustainability.

"Within a broader fisheries management framework, dynamic local harvest control approaches for the highly environment driven sardine fishery are also important for safeguarding livelihoods and food security," Ganga said. PTI HMP HMP ROH