Red tide causes mass marine mortality along Clifton
KARACHI: Tens of thousands of small size dead fish, comprising Tiger tooth croaker, John croaker, mullets, terapons, scat, seabreams and other small fish, washed ashore on the Clifton beach. World Wildlife fund for Nature estimates that around 100 metric tonnes of fish died in the current spell of marine disaster.
The dead fish have been coming in at the beaches since Saturday evening. These dead fish are small in size and inhabited the open coastal waters along Clifton.
It is the second spell of marine mortality along Karachi coast this month. On August 5, mass mortality of fish, mainly consisting of grey mullets, occurred within the Karachi Port, extending between Baba Island and Chinna Creek. The fish started dying after factory effluents, dumped in Lyari and Malir Rivers, were flushed into the sea because of torrential monsoon rains and floods.
The marine experts attributed the mortality to pollution, and said that highly toxic chemicals brought in by rainwater flowing through Sindh Industrial Trading Estate (SITE) entered Karachi Harbour.
Some experts of WWF-Pakistan are attributing the current mortality to red tide, a phenomenon which occurs due to abrupt and immense growth of small sized plants found in the sea. The reason for inducing sudden increase in this toxic plant (collectively known as phytoplankton) is not well understood.
WWF-Pakistan Director Rab Nawaz has said that the recurrent mortality of natural fish stocks may affect the livelihood of fishermen along the coastal area.
"Mortality on account of toxic phytoplankton can be widespread and direct or indirect consumption of such dead fish can be harmful for human beings as well," he said, adding that WWF-Pakistan has collected the samples of fish and will get them analysed to identify the species of phytoplankton which caused fish mortality.
WWF-Pakistan Technical Advisor Marine Fisheries Muhammad Moazaam Khan informed that abrupt and immense growth of phytoplankton is known as "Harmful Algal Bloom" (HAB) or "Red tide". Phytoplankton is algae, and not harmful to human beings and marine animals. However, because of a number of reasons some of which are still not well understood, these microscopic algae grow in millions resulting in change in colour of the water, which may range from green to blood red. Locally known as “mara paani” (in Sindhi) and “bad aab” (in Balochi), this phenomenon is a regular occurrence in Pakistan, and sometimes results in marine mortality.
Co-Principal Investigator Khalid Mahmood and WWF - Pakistan Data Enumerator Saba Ayub, who surveyed the area pointed out that mortality of fish is widespread along entire Clifton coast mainly in Do Darya and Sea View, but the quantities are not large. Most of the dead fish have already been collected for fish meal processors.
On the other hand, Khan showed concern on use of dead fish for fish meal, that when consumed can lead to serious health concerns, on account of toxic bloom. He further informed out that WWF-Pakistan is working with National Institute of Oceanography to identify the species of phytoplankton responsible for fish mortality.
He further pointed out that red tides are known to occur in Pakistan since long, and the first such record dates back to the 13th Century. An event of red tide in 1906 resulted in elimination of the entire stock of oysters from waters in Sindh.
Nawaz has urged research organisations to keep a vigil on the appearance of harmful algal blooms and establish a regular system of monitoring as some toxins may lead to serious health related issues including death.