An “upwelling” of cold, saturated seawater from the bottom of Manila Bay likely caused the recent fish kill in the waters off the Baseco area in Tondo, Manila, the Bureau of Fisheries and Aquatic Resources (BFAR) said on Saturday, September 19.
The Department of Environment and Natural Resources (DENR) earlier denied the “fish mortality” was caused by the dolomite sand the government laid over a portion of the Manila Bay shoreline along Roxas Boulevard.
“It is highly possible that an oceanographic phenomenon called upwelling or overturn caused the depletion of dissolved oxygen, causing fish mortality of estimated 10 kilograms of fish on September 15, 2020 in Manila Bay, particularly in the Baseco area,” BFAR said in a statement.
“Upwelling” or “overturn” happens when phenomena such as a “rainfall event” cause cold water from the deeper part of the sea to rise, replacing the lighter, warmer water near the surface. The upwelling water draws up sediments from the seafloor and “organic load” – minuscule organisms that compete with fish for dissolved oxygen.
With dissolved oxygen in the seawater depleted, the fish “easily succumbed to choking,” the BFAR said.
The BFAR said water quality testing in the Baseco area indicated a “very low level” of dissolved oxygen at 0.11 milligrams per liter. The “acceptable level” of dissolved oxygen in seawater is 5 milligrams per liter.
Residents earlier reported seeing different kinds of fish – biya, kanduli, asohos, and tilapia – “gasping for air” following heavy rains. These are bottom and midwater species, the BFAR said.
Photos of the dead fish went viral on social media last week, raising questions on whether the Manila Bay white sand project caused it. The DENR on Thursday, September 17, brushed off such claims, citing the breakwater that separates Baseco from the project site, among other details.
The project to lay dolomite to simulate a white sand beach on a stretch of the Manila Bay shoreline has drawn much criticism. Environment advocates warned about the potentially adverse impact the introduction of a foreign material would have on the ecosystem. Other critics questioned the timing of the project – why spend public funds on a cosmetic project in the middle of the COVID-19 pandemic, which remains unabated?
The government said the project was meant to give Manila’s poor a place for leisure, since they could not afford trips to real white sand beaches like Boracay in Aklan province. – Rappler.com