The cause of mass fish deaths in the Central region

Wastewater from the shore has decomposed strongly, depleting oxygen in deep water; cyanide used in fishing... may be the reasons for the mass death of marine fish along four central provinces.

Dr. Vu Thanh Ca, Department of International Cooperation and Science and Technology (General Department of Sea and Islands) said that according to incomplete statistics, since the beginning of the year, there have been more than 30 cases of mass fish deaths in the world, mainly related to the marine environment. There are many reasons for this, such as:sudden changes in temperature, leaks of pollutants, outbreaks of toxic algae due to eutrophication, oxygen depletion due to decomposition of organic matter in deep water, epidemics caused by bacteria, viruses or parasites...

For shallow sea areas, organic pollutants discharged from the shore will not be diluted quickly. If the seawater temperature increases sharply, the decomposition of organic matter will occur quickly, and the oxygen consumption will be large. The surface heating will create a very strong stratification of seawater density. If the wind is not strong, the surface waves will not be enough to create water disturbance, which will cause the water in the subsurface layers to be depleted of oxygen, killing the fish.

The dead fish in the coastal areas of North Central Vietnam on April 14-18 were hot and sunny days, and the sea was quite calm, so the wind blowing from the shore was not enough to create strong disturbances in the seawater. "Therefore, the reason for the mass death of marine fish could be because the wastewater from the shore had decomposed strongly, causing oxygen depletion in the subsurface water layers," said Mr. Ca..

Sharing the same opinion, Dr. Nguyen Huu Dung, who used to work at the Vietnam Association of Seafood Processors and Exporters, pointed out more clearly that the source of waste causing sudden changes in the marine environment is likely to originate from the Vung Ang industrial park (Ha Tinh). "The toxic substances flow into the sea through the water, then spread to other sea areas through the ocean currents," Mr. Dung said.This is the first time Vietnam has recorded such a large number of deep-sea fish dying..

Mass fish deaths have left many people in the Central region panicking. Photo: Duc Hung.

According to aquatic expert Bui Quang Te, normally polluted marine environments cause algae to "bloom", taking up all the oxygen and killing fish. ButIn the central coastal area, algae cannot even grow, which proves that the pollution level is too serious. In 2001-2002, in the coastal area of ​​Ninh Thuan and Binh Thuan, there was a red tide phenomenon, also known as algae "bloom" due to pollution in a range of 25 km long and 5 km wide, causing mass deaths of fish and shrimp in cages. After that, many other coastal areas also had this phenomenon.

Meanwhile, a marine resources expert recommended that the authorities check whether the fish contain cyanide. This is a poison used as a fishing tool by affecting the nervous system of fish and as a sedative to make fishing easier. The Philippines had previously asked China not to use this substance to catch fish.

"In my experience, the fish on the reefs and corals are very healthy and I think the poison like cyanide killed them," he said.

Several other causes have been suggested by scientists, including waste from a drilling rig that China previously placed at the mouth of the bay.

Despite many hypotheses about the cause of the fish deaths, experts in fisheries and marine environment still believe that in order to clarify the incident, authorities need to take water samples from different layers at many locations and analyze them to determine the level and composition of pollutants. In addition, authorities must inspect production facilities and residential centers on shore that are likely to discharge waste, causing seawater pollution.

The first fish deaths were recorded in sea cages near the Vung Ang Economic Zone (Ky Anh town, Ha Tinh) in early April. Then, wild sea fish, cage-raised fish and coastal lake fish in Ha Tinh, Quang Binh, Quang Tri, and Thua Thien - Hue died en masse. Every day, fishermen in coastal communes collect tons of dead fish, each weighing from a few ounces to 50 kg.

According to VNE