The depletion of fish stock in the coastal sea, caused by the rapid warming of the Arabian Sea has triggered tension between the traditional fishermen and trawl boat operators in Kerala. On August 16, traditional fishermen from the Kochi harbour chased and detained two trawl boats alleging they were indulging in illegal fishing. Fishermen gathered in large numbers in front of the fisheries department office and staged a road blockade demanding stringent action against trawl boats.
The traditional fishermen allege that bottom trawling by mechanised boats is destroying the marine habitat, which adversely affects the spawning of fish species. Bottom trawling is the practice of dragging the net through the seafloor. Besides, some boats are found involved in pair trawling where two boats drag the net parallelly catching everything on the surface water. The fishermen were forced to launch the agitation following depletion of fish stocks in the coastal waters, which has started affecting their livelihood. They say popular species like oil sardine and Indian mackerel have disappeared from the coastal waters.
The trawl boats are using banned pelagic fishing nets, which destroy the marine habitat and catch even juvenile fish and eggs. “The fisheries department has ignored our pleas to initiate stringent action against unsustainable fishing practices,” said fishermen union leader Jackson Pollayil. However, trawl boat owners allege that the fishing practice of the traditional fishermen is causing depletion of fish stock. “The ring seine and purse seine nets used by the inboard engine boats of traditional fishermen are destroying the marine habitat. These nets are 1.5 km long and the mesh size is only 10 mm. The government has banned the use of nets with mesh size lesser than 23 mm, said boat owners association leader Joseph Xavier Kalappurackal.
However, researchers say the warming of the Arabian Sea is the key factor that has caused depletion of fish stocks in Kerala’s coastal waters. According to a study, the Arabian Sea is witnessing accelerated warming at the rate of 0.18 degree Celsius per decade, which is much higher than the Pacific and the Atlantic Ocean.
The surface water temperature is a key factor contributing to the survival and breeding of the marine species. For example, the ambient temperature for spawning and recruitment of oil sardine is below 26 degree Celsius. When the temperature exceeds the threshold, it affects the physiology of the species and the ovarian development is disrupted. “There are studies that underscore the co-relation between monsoon rainfall and oil sardine spawning. When the rainfall is deficient, the oil sardine catch will decline,” said researcher and founder vice chancellor of Kerala University of Fisheries and Ocean Studies, Dr B Madhusoodana Kurup.
The second factor is over exploitation of marine resources. The government has introduced a Minimum Legal Size (MLS) for capture of around 60 fish species. If the presence of juvenile fish in the catch is more than 40%, the fisheries department will impose a fine of Rs 2.5 lakh on the fishing boat. However, Dr Madhusoodana Kurup says the criteria to fix the MLS is quite unscientific.
“The MLS for oil sardine has been fixed at 10 cm. But studies prove that the minimum size of maturity for this species is 14-16 cm. So we are catching the juveniles without giving a chance to spawn even once during its life span. By allowing fishermen to exploit juvenile fish we are denying the species the opportunity to attain maturity. This is the reason for depletion of fish stocks,” he explained.
El Nino has also led to the depletion of fish stock in Kerala’s coastal water this year. As the dwelling grounds get warm, the fish species are forced to migrate to deeper waters. The spawning ground of the oil sardine is at a depth of 30 fathoms. When the temperature rises, the intensity of spawning comes down. Pollution and draining of micro plastics into the sea are other reasons.
“The depletion of fish stocks is an inter annual fluctuation and this is a temporary phenomenon,” said Central Marine Fisheries Research Institute director Dr Grinson George. “The inter annual fluctuations were reported even in the pre-independence era.
These are driven by many factors like climate change. The fish stocks of India are at a sustainable level. As per studies, our potential harvestable resource is 5.31 million tonnes and we are catching 3.5 million tonnes a year. The stocks are at biologically sustainable levels. There are many factors that cause depletion of fish stocks, which include extreme climatic events and overfishing,” he said.
According to Dr Grinson George, the fish landing in Kerala reported a decline from the last quarter of 2023 till the first half of the second quarter of 2024 due to the marine heat wave. The warming of the Arabian Sea can affect certain species. But there is only a resource fluctuation, which is temporary and cyclic.
“There have been seasonal fluctuations, which are caused by extreme climatic events like the rise in sea surface temperature. Marine resources and composition have changed and climate change and overfishing can be contributing factors. The annual monsoon trawl ban has helped improve the resources. Now people are demanding to impose a trawl ban during the Northeast monsoon period also, as it is the spawning season of certain species. A fish should be allowed to breed at least once during its lifespan,” he said.