‘Unprecedented disaster’ for Hong Kong fish farmers: deadly red tide kills 36 tonnes of stock

A surge in a rare but harmful species of fish-killing red tides has devastated stocks in Hong Kong waters this winter in what is described as an unprecedented disaster for fish farmers.

Virtually all reports of the algal bloom involved the karenia papilionacea or karenia mikimotoi species, both of which are harmful to fish, with the latter a proven killer due to its effects on the gill tissues of fish and their breathing systems.

A Post review of statistics on the Agricultural, Fisheries and Conservation Department’s Red Tide Database from last November to the end of January indicate that most red tide reports were concentrated around Tolo Harbour and Long Harbour in the eastern New Territories.

The red tides have been linked to a massive fish kill in the area. Since late December, more than 36 tonnes of fish have died off mariculture zones in Kau Lau Wan, Yim Tin Tsai, Sham Wan, Yung Shue Au, Lo Fu Wat and Tap Mun.

Red tides, or algal blooms, are areas of seawater discoloured – brown, pink or red – by large concentrations of microorganisms that may deplete levels of dissolved oxygen. Sightings usually peak in the spring.

While there were more reports of red tides in the same period of 2014-15, distribution was more or less evenly spread, with just as many sightings around Lantau Island, Lamma Island and Tung Wan. But the red tides that winter were nearly all formedby the noctiluca scintillans species, which is non-toxic and commonly found in Hong Kong waters.

The situation has been serious enough to prompt the government to launch an emergency relief fund for mariculturists affected.

“I’ve lost about four tonnes of fish so far,” said Yim Tin Tsai fish farmer Lee Muk-kan, one of 222 applicants to the fund so far. “Yesterday I looked and I had two fish left.”

READ MORE: Mainland sewage fuelling Hong Kong’s ‘red tides’

The vice-chairman of the New Territories Fishermen Fraternity Association, Chan Mei-tak, said the scale and severity of the fish deaths was unlike anything he had ever seen and possibly on par with the disaster in 1998, when a red tide killed 80 per cent of the stock at fish farms across Hong Kong.

“It is an unprecedented and unnatural disaster,” he said. “The issue isn’t about the dead fish now, it’s about fish farms closing.”

Chan estimated the mariculture industry had suffered losses of “more than HK$100 million” in just a month.

An ecotoxicologist at the Hong Kong Institute of Education, Professor Rudolph Wu Shiu-sun, said it was hard to explain why the harmful algae blooms were forming this year, but red tides were formed under precise conditions. Variables included the ratio of nitrates and phosphates, commonly found in wastewater, and the sea temperature.

READ MORE: Hong Kong’s algal blooms - red alerts from nature

An expert in aquatic toxicology at Chinese University, Professor Chan King-ming, said it was possible the species may have been “transferred” to the Tolo area by marine vessels from Yantian port further north in Shenzhen.

Tai Po district councillor Wong Yung-kan, a former lawmaker for the fisheries sector, said the mass deaths began a few weeks after a massive bluish-green discharge was found in the Shing Mun River in Sha Tin in December. He believed there was a link between the two events. He believed there was a link between the two events.

"In 1998, red tides killed fish everywhere, but this time it's all happening in the Tolo Harbour area," he said. "Something is not right."

Since November there have been multiple reports of dead fish in the river. But the government has ruled out any connection between river pollution and red tides.

Food and health chief Dr Ko Wing-man said red tides were a “natural phenomenon” and there were “no measures to prevent the occurrence or spread”. He did however agree that there was room for the red tide alert and monitoring mechanism to be improved.

The Environmental Protection Department said it would keep up surveillance of planktonic algae in the river with preliminary results of a new batch of samples expected for release this week. Previous tests have found no toxic algae or "suspicious sources" in the watercourse.

The Agriculture, Fisheries and Conservation Department said it would step up real-time monitoring of water quality at all 26 fish culture zones.