Jellyfish bloom on Sindh's coast a threat to other fish species: experts

Prof Dr Mukhtiar Ahmed Mahar Director Centre for Coastal and Deltaic Studies University of Sindh Campus Thatta and Dr Baradi Waryani a Postdoc Scholar in Evolutionary Biology from Institute of Zoology Chinese Academy of Sciences Beijing visited few areas of Khai creek and Pettiani creek in coastal belt of Sindh to study the population dynamics and occurrence of Jellyfish.
Its population is not recorded or compared in summer season in creeks. The fishing community is involved in catching edible species Catyostylus prezi from deep sea about 50 to 100 km into Arabian Sea. Actually the Jellyfish populations around the world have increased in recent years, and several very large jellyfish blooms have been reported since the early 2000.The cause of these, and general population increase, has remained somewhat unclear until now though. Is it simply observation bias? Cycling population change? Warming waters? Changing currents?
Presently, the new research of the world's institutes has given the clear picture of jellyfish blooms that the primary cause is overfishing and with it the decline of many ecological important species. It has been observed that, the predators of jellyfish, such as tuna and sea turtles have seen their numbers plummet in recent years as a result of overfishing.
And with their decline, jellyfish have begun to see their populations grow. But perhaps far more important than its decline, though, is the overfishing of small pelagic fish, such as sardines and herring, which are the main competitors of jellyfish.
However, jellyfish are primarily taking advantage of the overfishing of small pelagic fish. Just like these cnidarians, sardines, herring, anchovies and more feed off zooplankton. 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.
Jellyfish blooms are still not fully understood in Pakistan. It is believed that climate change and sea temperature is going warmer which are supporting factors of most jellyfish blooms spreading in large areas. Overfishing is also considered to favor jellyfish because it removes 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.
Thus, the negative impact has been observed of these cnidarians, herring sardines, anchovies, which feeds on zooplankton. Therefore, they are presenting their food competition. The fishing ground of these fishes caught free up an ecological niche. The cnidarians now have free bridle and can thrive. Moreover, it has been observed that small fishes eat the eggs and larvae of jellyfish. Consequently, under normal circumstances, they regulate the population. In their absenteeism, there is nothing to stop the propagation of these gelatinous creatures.
The jellyfish blooms are of frequent occurrence estuaries and creeks along the coast. In the past decades, dramatically spatial rises and temporal changes in jellyfish dispersion in sea waters have been noticed all around the world. Such changes are associated with ecological consequences such as biogeochemical pathway and food web alterations.
The Sindh coastal fisheries are affected by the unprecedented jellyfish blooms in the offshore waters. "It has been learnt from the on line literature that large aggregations of this stinging jellyfish have been reported in the offshore waters of Karachi to Swatch Area at the mouth of the River Indus (around 140km south of Karachi) and Ormara along Sindh and Balochistan coast," said adviser on marine fisheries at the WWF-P Mohammad Moazzam Khan.