30 December 2009

Why are there so many dead fish on Pasir Ris?

Are there REALLY "more than 1,000 dead fish" on Pasir Ris as reported recently in the press?
Today, a small team checked out Pasir Ris to find out.

Well there were a LOT of dead groupers. Which didn't seem to bother the beach users much.
They were all about the same size and probably are the "tiger garoupas from nearby fish farms" referred to in the media. Strewn throughout the shoreline, it is entirely possible that "more than 1,000 fishes" washed up on Saturday. And continue washing up as those we saw today looked freshly dead. I wonder why the fish farms are allowed to just release dead fishes into the waters like this.

Several 'pairs' of these fishes were seen in this state, mouths locked. I have no idea how this happened.
We came across a pile of the fishes!
There was even a BIG fish on the high high shore, probably dragged up there by beach users.
What is particularly worrisome is that a wide variety of wild fishes were also seen among the dead fishes. So many kinds that I've done a separate post of what I saw. It's not just the fish farm fishes that died.

What is going on?

Well, the water quality at Pasir Ris has been rated poor for some time.

I got some hints from this person who went out to castnet in deeper water but returned soon after. I chatted with him when he got back to the high shore.
He said the water was 'red' further out from the shore. And there were no fish at all in the red zone. He has been fishing on this shore for 20 years and he has never seen anything like this before.

Could this be 'red tide'? Red tide is a situation where there is a large concentration of tiny harmful organisms in the sea such as microscopic, single-celled algae called dinoflagellates. These tinge the water red, but also other colours. A bloom can be dangerous because the tiny algae produce toxins. Filter-feeding animals such as bivalves concentrate these toxins. The toxins do not harm the bivalves, but can be fatal to humans. The toxins are not destroyed by cooking. Crabs and other marine creatures can also concentrate these toxins.

The fisherman decided to throw back the few fishes he caught (they were still alive) rather than risk eating them. He also told some young fishermen just setting up on the shore to reconsider catching fish until the situation improves.

Indeed, from a distance, there does seem to be a change in the water colour. On the horizon is Pulau Ubin, with Chek Jawa at the tip of the dark mass before the lighter mountains of Johor in the distance.
According to the media report, the Agri-Food and Veterinary Authority (AVA) said the fish deaths were probably "due to high levels of plankton, the result of heavy rain. Decomposing plankton can lead to oxygen starvation in the water".

Indeed, massive 'dead zones' of water covering thousands of kilometres develop in other parts of the world in response to excessive fertilisers and other imbalances in the ecosystems. Called hypoxia, such dead zones occur when there is a massive bloom of algae, fed by nitrates and phosphates (usually from fertilisers) . When the algae die and fall to the bottom, microbes feeding on the dead algae use up oxygen from the bottom up. A body of water without oxygen forms, killing fishes and other marine life. It is said that there are more than 250 hypoxic areas in U.S. waters alone. More links to dead zones:

Do the fish farms have a role in this event?

I don't know. But there are a lot of fish farms in the area, and I have no idea what kind of environmental controls are in place at these farms. Here's more about our fish farms and plans to hugely expand the number of fish farms in Singapore.

Is it just due to heavy rainfall recently?

The shores of Pasir Ris (and Chek Jawa and Changi) lie at the mouth of the huge Johor River which would bring lots of freshwater if there is excessive rainfall in Johor.
Freshwater alone can have an effect on marine life. The mass deaths of 2007 at Chek Jawa is believed to be related to excessive rainfall.

Besides a lot of dead fishes, there doesn't seem to be too many other dead animals. There was one dead cuttlefish, and the rest saw a dead octopus.
There were a few washed up Sandstars (Astropecten sp.), and many skeletons of sea urchins. But this is not unusual.
In fact, I saw one large happy Biscuit sea star (Goniodiscater scaber). And Kok Sheng and James saw sea cucumbers. In 2007, many sea stars and sea cucumbers died at Chek Jawa.
And we saw many Haddon's carpet anemones (Stichodactyla haddoni) which looked normal. In 2007, many of the carpet anemones on Chek Jawa turned yellow or white, bloated up, exploded and died.
Kok Sheng shared more about living marine life encountered today. So probably it isn't exactly the same situation as in 2007. But something is not right.

Fortunately, in the mangroves, the mudskippers were still skipping very healthily.
The seagrasses at Pasir Ris were doing well.
Here, Spoon seagrass (Halophila ovalis) grows lush with huge leaves quite clean of scummy epiphytes.
Which is great for Eugene who is conducting a vital experiment on this shore to learn more about what affects the growth of our seagrass meadows. I can see his experimental set up is still in place.
Unfortunately, this shore is impacted by more than just dodgy water. There is massive on-going work to rebuild the seawalls which started in Nov 09 and will go on until May 10. Although on this portion, there are orange sausage-like things that seem to be silt traps.
Nevertheless, the big excavator romped right along the shore to get to the next seawall! I have no idea why it can't move on the high ground.
And it only mucked up the shore to get up to the high shore and do more excavating from the high shore. Sigh.
Another perpetual issue on all our recreational beaches is the massive unending amount of litter.
Most of the litter clearly come from beach users.
Pasir Ris has interesting marine life as past posts on this blog and other blogs show. Hopefully, the situation will eventually improve.

This is why I feel it is important to regularly monitor all our shores.

Other posts about this trip

Related media reports


Related Posts with Thumbnails