Recently, a huge stock of dead fish like Mullet was found at a section of Karachi beach and fear prevails that the visiting people may use it for food or animals.
Talking to Business Recorder, fisheries scientists said that every year more than one hundred tonnes of different kinds of seafood such as 'Mullet' could be poisonous due to 'Red Tide and Harmful Algal Blooms' (HABs). They called red tides as natural phenomenon.
The fisheries scientists said the reason behind the dead fish was the Red tide, local fishermen call it as 'Bad Aab' (polluted water).
Some people believe that deep-sea trawlers throw unwanted dead fish back into the sea, as it is not fit for the export.
But deep-sea fishing industry spokesman said: "we do not catch the small fish like Mullet. We do not dump the dead fish in the sea."
"It is nothing but allegation to destroy the deep-sea industry by some so-called fisheries' experts."
They said that the Mullet could be found in the shallow water (near the coast). They said certain fisheries experts did not know actual causes of the dead fish and alleging the deep-sea fishing industry for dumping unwanted fish.
They said that deep-sea fishing trawlers had been given licenses for catching fish between 12 to 35 nautical miles and they did not catch near the coastline. Mullet could be found near the coast, they added.
Apart from this, the deep-sea fishing trawlers have been stopped at Korangi Fish Harbour since the October and the question regarding their operation nowadays was unacceptable.
In this connection when contacted, the Marine Fisheries Department (MFD) official confirmed that the deep-sea vessels were not operating for more than one month, hence allegations regarding dumping dead fish is not correct.
Fisheries scientists also requested to the higher authorities that the 'Mullet' should not be used for fishmeal industry. Because the dead fish is poisonous and if the dead fish was used in fishmeal industry, it may damage the human life as well as animals.
Replaying to another question regarding the red tide, fisheries scientists said that harmful algae are microscopic, single-celled plants that live in the sea. Most species of algae or phytoplankton (plant plankton) are not harmful and serve as the energy producers at the base of the food web, without which higher life on this planet would not exist.
Phytoplanktons are believed to generate as much as 80 percent of the world's oxygen supply. They absorb nutrients and carbon dioxide from the water and produce oxygen through photosynthesis. The two most common types of marine phytoplankton are diatoms and dinoflagellates.
Occasionally, the algae grow very fast and accumulate into dense, visible patches near the surface of the water.
"Red-tide" is a common name for such a phenomenon where certain phytoplankton species contain reddish pigments and "bloom" and the water appears to be coloured red.
The term "red-tide" is thus a misnomer because they are not associated with tides; they are usually not harmful; and those species that are harmful may never reach the densities required to discolour the water. During these blooms, most of the phytoplankton eventually die and sink to the bottom, where they decomposed by bacteria.
They said, at night when photosynthesis stopped algae and other aquatic plants produce carbon dioxide and consume oxygen. These processes deplete the dissolved oxygen necessary for the survival of fish and other organisms.
Scientists further said that unfortunately, a small number of species also produce potent neurotoxins that can be transferred through the food web where they affect and even kill the higher forms of life such as zooplankton, shell fish, fish, birds, marine mammals and even humans that feed it either directly or indirectly.
Scientists now prefer the term HAB to refer to bloom phenomenon that contains toxins that causes negative impacts.
People are exposed principally to the toxins produced by harmful algae through the consumption of contaminated seafood products. Scientists said dinoflagellate algae blooms create red tides, which could release strong neurotoxins, such as saxitoxin, that can be ingested by shellfish and passed on to humans who eat the infected shellfish.
They further said that the most significant public health problems caused by harmful algae are: Amnesic Shellfish Poisoning (ASP), Ciguatera Fish Poisoning (CFP), Diarrhetic Shellfish Poisoning (DSP), Neurotoxic Shellfish Poisoning (NSP) and Paralytic Shellfish Poisoning (PSP).
Fisheries scientists said that each of these types of health problems is caused by different species of toxic algae which occur in various coastal waters of the world.
They said that in the last few years there had been several reported instances of mass deaths of birds and marine mammals associated with the diotom Pseudonitzschia and domoic acid, which was produced by Pseudonitzschia. The cause was traced to domoic acid found in anchovies, which is the birds' food source.
They said that more recently, domoic acid was identified as the cause of death of many sea lions throughout central and southern California.