Why Did the Fish Die in Masan Bay, Changwon-si? ... Aquatic Animal Research Center: "Suffocated Due to Oxygen Deficiency"

On October 1, 2022, fish are surfacing in groups to breathe in the sea near Haeyang Nuri Park, Masanhappo-gu, Changwon-si, Gyeongnam. / Photo by Jonggu Song jgsong@

[Asia Economy Yeongnam Reporting Headquarters Reporter Lee Seryeong] The cause of the mass fish deaths in the Masan Bay area of Changwon City, Gyeongnam, which occurred from the 1st until recently, has been revealed to be a lack of oxygen in the seawater.

On the 18th, the National Institute of Fisheries Science under the Ministry of Oceans and Fisheries announced that after investigating items such as on-site surveys, biological analysis, marine environment, marine physics, red tides, and fluctuations in fishery resources from the 2nd to the 7th, they reached this conclusion.

The National Institute of Fisheries Science stated, “Among the dead fish confirmed during the on-site investigation, many individuals were found dead with their mouths open,” adding, “Most were sardines measuring 14 cm to 16 cm, and although anchovies, sea bream, and other species were present, they accounted for only 0.1%.”

They explained, “At the Masanhappo-gu Marine Nuri Park and the northern waters of Jindong-myeon, where mass deaths occurred, oxygen-deficient water masses with dissolved oxygen concentrations below 3 mg/L were observed from the 4-meter depth layer to the bottom layer during the on-site investigation.”

According to the institute, water masses with dissolved oxygen concentrations below 3 mg/L are called hypoxic water masses, which interfere with the respiratory activities of fish and shellfish.

The institute analyzed that the phenomenon occurred because, as summer water temperatures rose, a density gradient layer formed between the upper and lower layers of seawater due to differences in density, preventing the seawater from mixing.

They stated that as oxygen supply from the upper layer was cut off, dissolved oxygen in the lower layer was depleted, causing the fish to suffocate and die.

The institute emphasized, “No pathogens capable of causing mass sardine deaths were detected in the biological analysis,” adding, “Some pathogens commonly found in natural waters were detected in some carcasses, but the possibility of mass deaths caused by them is low.”

They added, “The concentration of heavy metals in the muscles of the fish was also below the permissible limits for food, indicating a safe level.”

Furthermore, “No harmful red tide organisms were found in the marine environment survey, and trace metal concentrations in seawater were also good,” they said, dismissing concerns by stating, “Although the pollution levels of organic matter and sulfides in seabed sediments were relatively high, they were not at a level to cause mass fish deaths.”

They also noted that when backtracking the movement of floating carcasses using a seawater flow prediction system, the deaths occurred inside the bay, making it unlikely that they were caused by inflow from outside.

The institute reported that the private advisory group, which also participated in analyzing the cause of the mass deaths, agreed with the opinion that suffocation due to oxygen deficiency was the cause.

It is estimated that the reason for the large number of sardines appearing in domestic waters is due to increased inflow of individuals spawned off the eastern coast of the South Sea and the eastern waters of Jeju.

Director Woo Dongsik said, “We will strengthen fishery environment monitoring to identify environments that can cause mass deaths of aquatic organisms.”

This content was produced with the assistance of AI translation services.