Unconventional fish species, a warm Arabian Sea change community patterns in Indian fisheries

Thiruvananthapuram: The Arabian Sea, situated between the Arabian Peninsula and the Indian subcontinent, is witnessing the invasion of unconventional fish species like jellyfish, puffer fish, and leather jacket fish, threatening its conventional fish distribution.

According to marine scientists, the sea, located in the northwestern part of the Indian Ocean, is also witnessing rising temperatures and frequent weather events, which are impacting the livelihood of the fishermen community.

They said the Arabian Sea, which has always had a temperature below 28 degrees Celsius, is warming up faster due to climate change.

Due to these reasons, some non-conventional, non-commercial species are now becoming part of the fisheries, the scientists insist.

"Jellyfish, puffer fish, and leather jacket fish crowd the nets of our fishermen these days. There are changes in the community structure," Dr Grinson George, principal scientist at the Central Marine Fisheries Research Institute, told PTI.

He said there has been a steady rise in the landings of these species of fish.

"From zero tonne in 2007, the catch of jellyfish on the South West coast has gone up to 10 tonnes in 2021; the catch of puffer fish from zero tonne in 2007 to 20 tonne in 2022, and the catch of leather jacket fish from half a tonne in 2007 to over 25 tonnes in 2022", the scientist said.

When the Arabian Sea is warming up, the thermal-saline circulations have a shift in their patterns, forcing a change in conventional fish distribution in the sea.

"Some of these species were initially thought to be of a menace, but now they (the fishermen) know they are fetching some export value. So they are catching them and exporting them," George said.

Experts also said when the Arabian Sea is churning out more cyclones and pushing higher amounts of moisture into the atmosphere, the total number of days for fishing is coming down, and the monsoon is getting affected.

All these factors are going to cause a huge financial deficit in the Indian economy. The situation is all set to get worse as there is a strong El Nino (sea temperature cycle) happening, and it is not affecting the Pacific or Atlantic oceans but the Northern Indian Ocean, they said.

The temperature rise in the Arabian Sea is not just affecting the fish community pattern but also effectively reducing the number of days of fishing, causing a major economic impact.

"If the ocean temperatures are above 28 degrees Celsius, it supports strong weather activities, like cyclones. Until recently, the Arabian Sea temperatures were below 28 degrees Celsius, but now they are up by more than 1 degree Celsius. It supports more cyclonic formations," Dr Roxy Mathew Koll, a scientist at Indian Institute of Tropical Meteorology, told PTI.

The Arabian Sea is now supporting cyclonic formations even close to the monsoon seasons, and the cyclone durations are also increasing, he said.

More cyclones and cyclone warnings mean fewer days at sea for fishermen.

According to the Fisheries Annual Report 2022–23, Indian fisheries recorded a revenue of Rs 1,37,716 crore.

So one day less fishing could bring in a loss of Rs 377.3 crore to the Gross Value Added (GVA).

The ocean warming is also changing the pH levels of the water, and the water is getting more acidic.

According to George, there has been a phenomenal rise in cases of Harmful Algal Blooms (HBAs), a challenging water pollution problem, in the Arabian Sea, increasing the fish mortality rate.

It is also causing coral bleaching, effectively reducing the nutrient habitat for fish populations.

Ocean acidification is also badly affecting the shellfish varieties as calcium carbonate formation is impacted due to the acidic nature of the water.

"Temperatures have risen across the Indian Ocean. In the Bay of Bengal also, the temperatures have gone up. The Bay of Bengal has always had a higher temperature, supporting cyclone formation. The Arabian Sea, it was not." Roxy said.

He said unlike the Pacific or Atlantic, which are open in the north, the Indian Ocean is landlocked in the north with the South Asian subcontinent. So there is no vent to flush out the additional heat, so the northern part of the Indian Ocean is warming faster. As a result, the monsoon winds also get weaker, leading to an erratic monsoon pattern.

Arabian Sea warming is going to have a cascading effect on the variability of the monsoon, atmospheric character, and weather and adversely impact the Indian agriculture sector.

"There is a clear shift in the monsoon pattern," Roxy said. He added there will be short spells of heavy rains as the warmer Arabian Sea pushes more moisture into the clouds, pushing up the relative humidity during the summer months and also increasing the incidents of extreme rain events.

"All impacts will be translated by monsoon variability. Effects on the coastal community from ocean warming are one thing, but what is more worrying is how the monsoon would be affected by these changes," Dr Vimal Mishra, climate scientist and professor at the Indian Institute of Technology, Gandhinagar said.

He said over the years, the number of rainy days in the monsoon has drastically declined, but in some areas, the total amount of rainfall has gone up.

"Most of the rain is occurring in terms of heavy rains.

That is not good for agriculture, it is not good for groundwater recharge, and it is not good for anything. These things will continue, and this will add up to more variability in the monsoon. Both monsoon onset and departure could be affected," he added.