This week I spotted the largest school of fish I have ever seen in Hong Kong. The grey mullets (Mugil cephalus) were attracted to a submarine seawater cooling outflow pipe that was discharging a grey liquid into the sea in western Kowloon. Each of the fish in the video below is 30-50 cm in length and I estimate there were at least 1000 of them.
I often see large mullets in that area. They regularly leap several feet into the air which is quite a spectacular sight. I have also seen an old angler at the Central ferry piers catching a 40cm mullet to the raucous applause of about 30 onlookers. The thing is the fish wasn’t hooked through the mouth but through the fin (quite a skill!) because it was swimming at the surface gasping and dying…
The behaviour of leaping out of the water according to some sources is a method mullets use to get more oxygen by storing air in their bodies so they can dive down into anoxic or low-oxygen water layers to catch prey others can’t. Grey mullets are known to be hypoxia-tolerant meaning they can tolerate low-oxygen environments better than other fish.
And here is another video of a large mullet just meters from Discovery Bay beach. The way it is gasping at the surface while swimming in its side is just how the fish was behaving which I saw caught at Central ferry pier.
So what does it mean if there is a large aggregation of fish which are known to be tolerant of low-oxygen environments and which are exhibiting low-oxygen behaviour? It’s a pretty good sign of a lack of oxygen – duh! What causes low oxygen in the sea? Nearly always eutrophication – the process whereby excess nutrients from normally man-made sources cause microscopic algae known as phytoplankton to grow into large blooms (and sometimes red tides). When these inevitably die off the mass of dead material on the seabed decomposes using up oxygen until there is so little that the seabed and lower depths become so-called dead zones (anoxic zone) where very few hardy species can survive.
So I suspected illegal waste-water discharge and made a report to the EPD (Environmental Protection Department) online including the above video (you can also report pollution via the government telephone hotline 1823).
Say what you want about the HK government, the civil service works! They followed up with a site visit to test the water and issued an order to the building management to repair their outflow pipe. Apparently the pipe was seawater cooling air conditioning outflow, but was discharging wastewater as well. Two days later after the problem was fixed and the fish were gone!
(Note: grey mullet is a very popular food fish in southern China and you will see it even in most supermarkets. But the vast majority is farmed – in case you were worried about your fish being from sewage outfalls!)
So what have HATS got to do with it?
HATS stands for the Harbour Area Treatment Scheme, a large sewage and wastewater treatment scheme designed to clean up HK’s notoriously filthy harbour. Setup in 2 phases, the first phase was successful enough to reduce the concentration of sewage to levels acceptable enough to allow the return of the New Year’s Cross Harbour Swim event. The annual event sees swimmers cross 1.89km from Lei Yu Mun’s Sam Ka Tsuen pier to Quarry Bay Park pier. First held in 1911 the event was stopped in 1978 because of health concerns.
However, in 2011 the EPD announced that water quality in the harbor, particularly in the eastern section where the race took place, had “shown significant improvement” and E. coli levels had decreased by 95 percent since 2001. Yet, the data from the EPD Shortly before the restarted race revealed that E. coli levels in the harbor were still twice the maximum acceptable level at Hong Kong bathing beaches. But it was still a big improvement.
The sewage levels are evaluated by measuring the concentration of the common gut bacteria Escheria coli(E. coli) in the samples as a proxy for all the other gut inhabiting and potentially dangerous bacteria and viruses in sewage.
However,the planned second phase of Hong Kong’s Harbour Area Treatment Scheme (HATS) has recently been put on indefinite hold. The upgrade would have boosted the capacity of the treatment works to remove nutrients such as phosphates from effluent. This would have reduce eutrophication and helped rehabilitate the dead zones. Excess phosphates are also linked to increases of toxic algal blooms.
Officials said the current chemical-based treatment system was enough to meet most water quality objectives and stressed the upgrade to biological treatment was not “critical” at this stage. The planned upgrade would deliver “only marginal improvements” to water quality in western Victoria Harbour and bring little benefit to near-shore pollution. Their priority was to cut off improperly connected pipes and crack down on unlawful discharges into the harbour off Central and Wan Chai.
When I first read that I was highly sceptical and thought the government was just trying to save money. But having seen illegal discharge from a major shopping mall and office complex directly into the Harbour I now think they actually have a very good point!
Denying the scheme was declared dead, assistant director of environmental protection Amy Yuen Wai-yin said that in terms of E coli levels close to the harbour’s shores, the upgrade was “not an answer”, citing water quality modelling results. The cost of the upgrade, according to the latest estimate based on 2012 prices, has almost tripled from the 2004 estimate of HK$11 billion to up to HK$30 billion. Perhaps then they are right to concentrate on cleaning up the illegal and accidental discharges of wastewater before tackling the finer points of more advanced clean up.
Jonathan Wong Woon-chung, another council member, said officials should clarify to what extent illegal discharges and improperly connected pipes contributed to water pollution. He also questioned whether the upgrade would have the intended effect, as improvements might be offset by cross-border pollution.
As a side note, the Kai Tak nullah, has been renamed Kai Tak river and has seen the return of grey mullets. This drainage channel in the old airport area is a catchment for several rivulets from the foothills of the Kowloon mountains, but was surrounded by rapidly growing factories and homes from the 1960’s to the late 1980’s which discharged all their effluent into it. It was so badly polluted and foul smelling that at one point there was a plan to completely cover it up and make it subterranean! Luckily science prevailed in the planning and there is now a scheme to remediate and green the area and especially the river. Obviously this wi take years, but the effort seems to already be beating fruits. See the project website here for more details.