THEORY – Fishing the East Johor Straits Part 5 Atmospheric Conditions

THEORY – Fishing the East Johor Straits Part 5 Atmospheric Conditions

In part 3, we learn of the best tides to fish, the best phases of the tides as well as where to fish. In this part, we see how atmospheric conditions can affect the bite rate.

Looking back on my younger days, 10 of us would pool $300 to charter a Tekong ferry boat from Changi Creek for a day’s fishing. Oh how we would look forward to that appointed day, while we make preparations, packed our bags and tied our rigs in anticipation of that big fish. And the night before the trip, I’d not be able to sleep a wink!

At that time, we had no theory in fishing except to watch the boatman. If he drops a line to fish, it’s time to fish diligently. If he stops to take a nap, it’s time to take our lunch since he knows the fish are not expected to bite. At the end of a day’s fishing, we mostly go home dejected, with a packet each of unfinished live prawns to cook with our instant noodles, and the apologetic excuse from the boatman that “water was cold this trip, better luck next time”. At that time, I often wondered what he meant by cold water when I was being roasted alive under the hot sun…

When water turn colder, catfish comes on the menu

Somebody once joked that Singapore has two seasons — we have the hot season and the hotter season. It’s understandable, since the Equator lives a few doors down of us, and the East Johor Straits is only 1.3º to 1.4º north of that imaginary “hot” line. But even so, very slight variations in temperature makes its effect known known to anglers by lock jawed fish or a sudden frenzy of reckless bites.

Most fish feed active actively when the temperature is within their range. Being cold blooded creatures, fish tend to become sluggish and stay close to the bottom when the temperature is colder than their preferred range. But when the temperature gets higher than their range of tolerance e.g. when a pond dries up under the scorching sun, fish can be found gasping at the surface as high temperatures cause water to lose density and they find it hard to breathe.

The Thermocline
When my late sifu Andrew Ling tutored me in game fishing, he explained a strange concept called a Thermocline. A Thermocline is a band of water that is distinctly different in temperature from the surrounding water above and below. If you went swimming in a lake at midday and tried to swim down to reach the bottom, you will surely have felt the warm surface water suddenly turn cold at a certain depth as you swam deeper. You had just passed the thermocline at that point.

He said that fish tend to hang out at the thermocline since it is the most ideal temperature for them, and it contains more oxygen than at the upper layer. He would find the thermocline by increasing the “gain” on his echo sounder till he is getting two bottom readings, and only then, by reading all the bounced signals and noise, almost the same way a shaman looks at tea leaves, will he pronounce “the thermocline is at such to such depth”. On hindsight, I wish I had paid more attention then. But at that time, I only wanted to set my gear up and let a bait down as quick as I could, so I have paid scant attention to his lesson.

The Thermocline is still very much applicable in today’s fishing. But with advances in electronics, the thermocline can easily be seen as a line or band on the colour screen of a fish finder, somewhere between the surface and the bottom. No more upping the gain to read reflected pings. Simply zoom in to that line to see the full range of the thermocline! At at the East Johor Straits, the Thermocline is most noticeable after 10pm to just before 8am. During the daytime, there’s probably too much traffic to allow a Thermocline to form.

I’m sure you can see that Cleon was cold and wet when he jigged up this Glassfish on Jackall Mameta.

Water too Cold
Before I had a fish finder to tell me water temperature, I learned to tell the water temperature by relative feel. I can only do this at night or on a rainy day when there is no sun to make me feel hot. Here’s how I do it:

After settling down at the spot, setting up my gear, getting my eyes accustomed to the darkness, and cooling down from the exertion, I cast out my lure and start working it. After a few casts, I hold the lure in the palm of my hand after retrieving it through the water. If the lure feels cold, then water at the swimming level of the lure is too cold. It’s time to change the depth of the lure to find the right temperature, or to take a break and catch up with the kakis.

Similarly, on a cold and rainy day, if you step into the water and feel it is warmer than out on land, or your lure comes back feeling warmer, you have hit the right depth or temperature for fish to turn on the bites — fish hard at the chance!

A fish finder with a temperature sensor, can easily be set to sound an alarm when the temperature gets within the optimum range. I find that fish are most willing to bite at 78.8º F (26ºC) to 82.4º F (28ºC). However, since the temperature is read from the sensor at the transducer, I am only getting the water temperature at the very surface layer, which may not be an accurate reading especially when fishing deep, still waters at midday. So even though I have such a device, I usually prefer to trust my feelings most of the time.

So what to do if water is cold? When the water is turning colder, you’ll find more eels and catfish taking your bait. As temperature continue to drop, baits get eaten up by sea lice. Your Tamban comes back a skeleton. When this happen, it’s either time to pack up and move, or to go take a break till the current starts flowing to warm the water again.

If you decide to move, where should you move to? Try looking for places where drains or water pipes empty into the sea. If it had been a hot day all day, the heat from the ground will get transferred into the water that flows through the drains. This warmed fresh water will attract micro-organisms which in turn attract prawns and small fish which in turn attract the larger fish. But if it had been raining all day, don’t bother going to these places; you’ll probably be better off going home. Haha!

Water too Hot
If you are fishing a still creek, or a disused prawn farm on a hot day, the surface waters can get superheated by the sun. When that happens, water loses density and oxygen becomes less available to the fish. Without oxygen life is not possible for fish, so they either move away to the shade or go deep where it’s cooler.

I remember a time in the early 90s when an island was being reclaimed in front of the Changi Cargo Complex. They had surrounded the sea with a row of caged rocks, then slowly filled in the lagoon that was formed. When the mouth of the lagoon was closed off and the lagoon was filled in, fish that was trapped in the lake was driven to beach themselves when the water got too hot from the sun. On one afternoon, we saw this phenomenon. We were gaffing fish and big rays off the shallow, crystal clear, hot water till our arms ached. That day, we had red snappers, stingrays, jewfish and threadfin without wetting a line!

When the water gets too hot, (it feels like someone turned on the hot shower), target deep for fish. If that pond is shallower than 7 feet, you can forget about fishing there for the moment as fish will have left the pond or are comatose at the bottom. When fishing on a hot day, cast into the shadow areas as fish will be cooling off their fins there.

The impending storm whipped the surface into furry waves and the normally cautious Tarpons threw all caution to the wind, landing Cleon his first Tarpon.

Atmospheric Pressure
The lowest possible tide levels recorded at a tidal station over a span of many years is collated to become the Chart Datum, which is the depths shown on the contours of a marine chart. Theoretically, water depths are calculated based on Chart Datum + the predicted tidal height. So to know the depth of the water at say, high tide, at the tidal station, you simply add the predicted tidal height to the chart datum depth to determine the true depth of water. It is a bit more complicated if you want to compute the depth of water at any other point on the map and at any other time other than high and low tides. In such a situation you need to apply the Rule of Twelfths. But for the purpose of this lesson, the details here presented should suffice.

However, the calculations are based on the assumption of an average Mean Sea Level Pressure of 1013.2hPa, and that there are no storm surges, both of which can affect the actual water depth. The average Mean Sea Level Pressure (MSL) is 1013.2 hPa (For those curious to know what hPa stand for, it’s hecto-Pascal. In the past, it’s read as millibars, but since ISO standardisation, it is renamed hPa).

Roughly, if the atmospheric pressure should increase by one hPa, the sea level will be shallower by 1cm; and a pressure reading of 1047 hPa means the sea is 1 foot shallower. Under storm conditions, a reading of 925hPa translates to seas being almost a metre higher! Changes in sea level is even greater if it’s caused by strong offshore winds or storm surges. These happen surreptitiously. The wind may already have changed direction, but the swells they had created continue to travel a great distance and that’s when it can get dangerous especially if you are setting up anchor in a nice quiet bay for the night. In short, a high barometer reading tends to lower sea level and a low barometer raises it.

But why tell me all these? You say, since you don’t have a boat and with a kayak, you need not worry about water depth. Well let me tell you as a person who had made the mistakes before, so you need not make them for yourself.

They say, knowledge is good. But knowing a little can kill you, and it almost did to me. In the old days, there wasn’t animosity between boaters and anglers, and the term terrorist was confined to someone at Ireland or somewhere far away. So there was no rule restricting boaters to stay a distance from popular fishing piers, and fishing there was never considered a security risk, so we could take our Coleman Scanoe under piers to fish.

Now piers are wonderful, fertile and comfortable hunting grounds to a canoeist who fish. I think now-a-days they call themselves yakkers but I digress… Under the pier, you are shielded from the hot sun and the rain. You have a huge fish aggregating device right below you, and by simply moving from pillar to pillar is akin to moving to a new spot. So instead of paddling to Ubin or Tekong, we’d be fishing the piers at mainland and having a great time.

Almost Tragedy
Now there was this fateful trip, a day after a new moon. We had planned on fishing till two hours before high water, and go home. By our calculations, we will have enough headroom to go back. But by fate, a low pressure hit us. It started to storm, while we were sitting under the pier, cool, dry and best of all, having a frenzy of snappers and groupers. Now when it pours heavily outside, the wind tends to die down and the sea was flat, lulling us to a false sense of safety. Then a series of slow swells lifted the Scanoe, and bashed our heads against the underside of the pier which woke us to reality.

Suddenly, our boat was crushing us up against the underside of the pier. The entrance that we got in from was almost covered with water and we were in peril of getting crushed between our Scanoe and under the pier. With each incoming swell, the tide seemed to rise at an alarmingly fast rate, and we couldn’t sit upright anymore but were lying within the Scanoe. By divine providence, we managed to slip overboard while we could, then we scooped water to fill the Scanoe till she was low in the water. Then by some determined kicking and dragging, we managed to pull her under the overhanging pier wall out into the open. She popped right up and with some scooping, we managed to drain her enough to climb on board. We had lost most of our catch, some gear and water had flooded all our remaining gear. But at least we were safe and a lesson learned to share with you all.

Muddy Affair
On another trip, we launched from the Charcoal Port at the mouth of Sungei Serangoon on the rising of a neap tide. Our plan was to fish up river following the tide, then fish back downstream as the water ebbs. Being a neap tide, we knew there’d be around foot of water left for us to float over the mud when we got back. We quietly congratulated ourselves in having a light boat with a shallow draft of a few inches which affords us liberty to fish many such places.

We drifted slowly upstream with the tide, casting at the mangrove roots growing out of the banks and at the mouth of streams emptying into the river. I remember the barra were keen to bite a pink/purplish Yozuri Ailemagnet lure that day! We drifted to where they had just completed the TPE bridge over the river. Under the bridge, there was an outflow of fresh water into the eastern bank of the river and baitfish tended to hang out there.

Under the shade of the bridge, we saw a school of Tarpons rolling just a bit upstream. We paddled upriver to chase them. It was a huge school that turned the water a patch of black the size of half a tennis court! We fished upstream past a colony of floating Orang Seletar houses hidden in the bend of the river, at the confluence of Sungei Pinang and Sungei Tengah where today, the Buangkok East Drive bridge crosses the river. Fascinated, we explored upstream.

We came to a sluice gate that controls the waters from Lorong Teck Hock and Paya Lebar Air Base. Here, the river had become a canal, and Hougang Ave 7 was at the western bank. We were hitting juvenile barra at the drain outlets, and people seated at the orange and cream-coloured bus stop watched our antics with interest.

It was fine weather with a fresh breeze keeping things cool. We forgot about the tide and when we had drifted back to our landing point, we found to our horror, the tide was lower than expected. We had to wade through mud for a stretch only 20ft long. But wading in knee deep mud is tiring and slow. What would normally take 10 minutes, we took half an hour and got out cut and blackened in smelly mud and we had no water to wash off!

After the rains left us, this barra demonstrated some spectacular topwater attacks when it sucked down Keith’s Tetraworks Poco Poco.

The Barometer and Fishing
I hope I have your attention now, to talk about the barometer and fishing. I used to have a Thommen Altimeter, a leftover gadget from my climbing days that I took to fishing trips with me. It was not very useful. Next I got me a new-fangled Humminbird Fishfinder with sidescan sonar technology, GPS, temperature and barometric readouts. Well, to be honest, that was not too useful to me too. It got too bulky in my little bathtub-sized Portabote and so I thought of getting one of those Casio triple sensor watches when I found that Android phones have a barometer sensor all along…

I’m sure by now, you would have heard the saying that a rise or fall in barometric pressure triggers fish to feed. From the records I’ve collected of my catches through the years, I’ve found that at 1009 hPa and lower, fish was holed up at the bottom and fishing was generally poorer. But if the mercury climbs a mere millibar to 1010 hPa, the fish were feeding at all depths.

But I can’t in my mind, rationalise how such a slight change in pressure, can change fish feeding behaviour. Let’s look at it this way. Disclaimer: I’m no good with Math and I never quite know how much change I’m supposed to get back when I buy things. But there’s this thing called Google and it helps me with stuff such as this but I digress…

So, fish live in the sea, under the water. Water is 800 times denser than air, so hydrostatic pressure will rise at a faster rate than barometric pressure. The sea has tides, and a typical spring tide at the East Johor Straits at high water is 3m or higher. The weight of seawater is 64 lbs/ft³ or 0.44psi. A 3m High Tide is 9.8ft deeper than Chart Datum, and will exert 4.3 psi more pressure on the fish. 4.3 psi is 296.5 hPa.

The average weight of the air at sea level is called One Atmosphere (1 atm) which is 1013.2 hPa. The eye of a typhoon is the spot of lowest pressure. In 2013, Super Typhoon Haiyan, the deadliest typhoon to hit Philippines in modern times, had an estimated 895 hPa reading or a drop of 118.2 hPa.

The worst storm at the East Johor Straits will never come near that of Typhoon Haiyan. Yet if we compare the numbers from a typical tidal change (296.5 hPa) to that caused by Typhoon Haiyan (118.2 hPa), one can conclude that fish will experience far greater changes in pressure from high tide to low tide than would a typhoon. Not to mention that they constantly feel the changing pressure of waves 1ft (30.3 hPa) or greater.

As the rains weakened to a drizzle and the last rays of the setting sun peeped out to warm our cold bones, Notti boy got his barra on a Maria Fakebait 90mm

Maybe I’m just theorising too much, but these numbers just tell me that the commonly held theory that fish feed aggressively to rises or falls in barometric pressure is untrue. Fish at sea simply won’t be affected much by barometer changes. However, I recall from my sailing theory lessons that the faster the barometer falls, the faster the storm is gaining on you and vice versa. It also means that the weather is changing, when the barometer reading has risen or fallen. We all know that fish tend to feed at transitions (see Part 3), and changing weather is a transition, as is changing day to night and night to day.

One last observation about rain. Rains after a long drought, tend to be bad news as algae blooms usually show up soon after. When the algae blooms, it takes up the oxygen from the water at night and fish die off.

Chermin love nothing more than to forage at the waters which had been stirred by wind created waves and are a lot of fun on Keith’s Kistler UL tackle.

Winds can be the blessing or the bane of anglers. Wind knots are something that is not appreciated by egg beater reel users. Baitcast anglers will see their distance hampered by a headwind blowing against them. But there’s more to winds than just casting.

The strength, direction and duration of winds can have great impact on sea level. When a strong onshore wind is blowing against a shallow beach, the wind will raise the level of the sea which is called “wind setup”. Offshore winds (those blowing from the land to the sea) will have the opposite effect, lowering the tide level. The NE Monsoon is an Onshore Wind. Because of this, high tides in Singapore tend to be higher at the early (Jan, Feb) and the late months (Oct to Dec) of each year with the lowest high tides happening around August. I guess this is due to the strong surge from the NE Monsoons causing the higher tides.

From an angling viewpoint, a more important effect of the wind is the creation of waves. In shallow water, waves stir up the sea bed, uprooting seaweed and dislodging animals from the sea bed and clinging to the seaweed. Fish often come inshore to feed on these dead or injured creatures and it is during the period, or after storms, that good catches can be expected. Onshore winds also create waves that oxygenate the foreshore and muddy the water. In highly oxygenated, muddy waters, fish are more willing to bite a lure as they are less wary. Conversely, during the SW Monsoon, the offshore wind tend to lead to still, clear waters especially on a neap tide. Fish are more wary to bite a lure and finesse tackle need to be employed, or you need the cover of night to tempt them to bite.

This instalment on the East Johor Straits had been a dry, technical and boring piece. I apologise for that. If it had been any consolation to you, I also struggled, referring to my notes over and over to coax this piece out. But I hope you will find its usefulness in proportion to the tedium of reading it.

Till my next instalment, tight lines, be safe and I hope to see you on the water!


Text and Images © Lawrence Lee
All Rights Reserved
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