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Unusual Jellyfish blooms affecting fishing activities in the Arabian Sea

Posted on 26 December 2016

Karachi, WWF-Pakistan trained fishermen have reported unprecedented jellyfish blooms in the offshore waters of Pakistan which are affecting fishing activities. During last two weeks, blooms caused by mauve stinger scientifically known as Pelagia noctiluca have been observed in the continental shelf along the Sindh and Balochistan coasts. Large aggregations of this stinging jellyfish which have mauve to magenta colour are reported in offshore waters of Karachi to Swatch Area at the mouth of the River Indus (around 140 KM south of Karachi) and Ormara along Sindh and Balochistan coast. Studies conducted by WWF-Pakistan revealed a population of more than 150 individual per cubic meter which is clogging the nets of the fishermen. Its 8 tentacles are loaded with stinging cells known as cnidocytes. Within these cells are harpoon-like structures full of venom, called nematocysts which shoot out when triggered by touch and can penetrate human skin. Jellyfish is locally known as “Langara” in Sindhi and “Mus” in Balochi.

Pelagia noctiluca is well-known for beautiful luminescence and glittering in the night when disturbed or moved by wave action. Luminescence in sea has been reported by fishermen during last two weeks. Due to the high density of this jellyfish, fishing activities are affected in those areas resulting in clogging of the nets. In addition, handling or removing this jellyfish from the nets can inflict severe and painful stings. Once affected, the pain last for more than 24 hours and results in the inflammation of the skin. Fishermen involved in gillnetting and other fishing operations have decided to move to other areas, mainly shifted their operations to Sonmiani Bay and adjacent waters. Sudden decrease in the catches of some prime fishes is attributed to the jellyfish bloom. One of fishermen, Falak Niaz, trained by WWF-Pakistan pointed out that this luminescent bloom is spread over area of about 250 square kilometres in the offshore waters but currently it is declining. Previously, such blooms in Pakistan were observed to last about 10 to 20 days. This is of no commercial importance of this jellyfish.

In further offshore waters near Swatch Area at the mouth of the River Indus, another bloom of mammoth jellyfish commonly called mushroom jellyfish (scientifically known as Rhopilema hispidium) has been reported. The population of this large jellyfish surged during the second week of December, 2016 and continued till filing of this report. In some of the areas their numbers were so large that fishermen decided to stop their fishing operations. This jellyfish species is very large in size and its disentanglement from the net and throwing back in the sea is a cumbersome process and has to be done carefully due to its painful stings. This jellyfish locally known as “Jungli langara” is of commercial importance. It is harvested in creek areas of Sindh by using set bag nets, surface gillnets and encircling gears.

Jellyfish are also commercially harvested in Pakistan for export purposes. Annually about 2,500 m. tons of dried jellyfish is exported. Rhopilema hispidum and Catostylus perezi are two dominating species which are being processed and exported from Pakistan. Highest jellyfish export was noticed during 2005 to 2007 when annually about 4,000 m. tons of jellyfish products were exported to China and Vietnam. There are about 15 permanent and about 35 part-time or temporary facilities along Pakistan coast. Main processing plants are located in Ibrahim Hyderi, Rehri and Keti Bundar in Sindh and Damb along Balochistan coast. Target harvesting is being done in Damb, Kalmat and creek areas of Sindh whereas large quantities are also harvested through set bag net (“bhulla”) in creek areas and by gillnets in Damb. Jellyfish legs (tentacles) are treated with salt and alum solution and semi dried end product is exported. Jellyfish fisheries in Pakistan support is a source of extra income for small scale fisheries in coastal areas of Pakistan. It is estimated that more than more than 10,000 people are engaged in jellyfish fisheries in Pakistan.

There have been reports of large jellyfish bloom in Pakistan, however, in December 2002, a massive jellyfish bloom occurred all along the coast of Pakistan. Large number of Crambionella orsini  have resulted in decreased catch of commercial fishing operations along the coast of Pakistan. It has resulted in massive clogging of nets and interrupted the operation of the seawater cooling systems of coastal power plants and ships. A number of smaller blooms of jellyfish frequently occur in Pakistan but these do not pose any threat to fishing and other operations.

Muhammad Moazzam Khan, Technical Advisor (Marine Fisheries), WWF-Pakistan pointed that frequency of jellyfish blooms is increasing in Pakistan, like many other part of the world. Such blooms, according to him disrupt the fishing industry by tearing nets and clogging cooling water intakes at power plants, causing power reductions or shutdowns. There are reports that jellyfish blooms can reduce the population of the commercially important fish by eating the zooplankton and consuming their eggs, larvae and juveniles. In 2009, a fishing trawler capsized as the crew tried to pull in nets filled with jellyfish in Japan. Jellyfish sting swimmers, therefore, may discourage tourism in some areas. Khan further pointed out that despite all the circumstantial evidence, scientists acknowledge the need for more research in order to determine conclusively if jellyfish blooms are a function of natural cycles or the result of human impacts on the environment. Jellyfish blooms, according to him feeds on plankton, crustaceans, small fish and fish eggs, therefore, it depletes the food resources of fishes and even larger mammals like whales. He emphasized the need for conducting research on causes of bloom formation by jellyfish.

According to Rab Nawaz, Senior Director Programmes, WWF-Pakistan, the reasons for sudden increase in the population of some jellyfish and forming large blooms are not fully understood. It is generally believed that climate change and resulting warmer sea temperatures favour most jellyfish to increase in massive numbers resulting in blooms spreading in large areas. Overfishing is also believed to favor jellyfish because it eliminates their predators and competitors. Discharge of untreated sewage loads in coastal waters with nutrients may cause eutrophication making available more food for jellyfish polyps and support forming of bloom.

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