THEORY – Fishing the East Johor Straits Part 1
When I first started fishing in 1967, I noticed that some anglers tend to be more successful than others. Although I learned from an early age that knot tying plays an important part in ensuring the hooked fish get landed, and long accurate casts make it better to catch wary fish, I somehow didn’t realise how other factors like tide, wind, structure and transitions etc affect one’s ability to get connected to a fish. Instead, I always attributed the successful angler to be more lucky than me, because I was a “hopeful” angler. That means I casted out and hoped for a fish to come along to take my bait. And if it did, I’d call that my lucky day. It was after knowing my late Sifu Andrew Ling, bless his soul, that my way of fishing changed from a passive participant into that of an active hunter. Hadn’t it been for him, I might have quit the hobby long ago.
Daniel, with a baby Epinephelus lanceolatus on a making tide
And now, after many long hours spent fishing, observing and refining my observations since 1993 I will attempt to put into words, my experiences at the East Johor Straits. This starts off the first part of the theories and conjectures that I had formed. I hope they will be of help to you in catching the fish you had been hoping to catch, and to come back home safely regardless of conditions as it had done for me all these years.
The combined effect of Earth’s rotation, the Sun and the Moon’s gravitational pull cause a cyclical rising and falling of sea levels which we call Tide. During the full and new moons, Spring Tides happen because the moon’s gravitational pull is strongest and in theory, the high tides will be higher than normal, the low tides are also lower than normal. However in practice, Spring Tides are three days after the new and full moons because of the massive size of Earth. Thus the Chinese saying 初三流,十八水。Which describes this phenomena perfectly.
Conversely, the first and third quarter (shaped like a slice of watermelon) moon has the weakest pull, resulting in Neap Tides, where high tide is lower than normal, low tides are higher than normal. In other words, the least difference between high tide and low tides happen during Neap Tides. Keep these in mind, and we shall revisit these later.
Tide Table for Sembawang, Jan 2015 http://tides.mobilegeographics.com
The Moon takes 24 hours 50 minutes to make one orbit around Earth. Because of this, a tide occur every 12 hour 25 minutes. Once when when the Moon is overhead, and once when it is underfoot at the opposite side of Earth. To simplify, we generalise a rule of thumb that the next high tide (HW) is “12.5 hours from the last HW” or the next low tide (LW) is “12.5 hours from the last LW”. Singapore experiences two tides daily, and we call this a semi-diurnal tide. Our tides are mainly generated in the South China Sea and to a lesser extent, the Indian Ocean.
Tide graph for 21 Feb 2015 at Sembawang, showing the slight difference in HW but vast difference in LW within a diurnal day. http://tides.mobilegeographics.com
I’ve noticed that our second tide tend to have a lower range than the first of each day. In the East Johor Straits, the difference in HW within a day may be slight, but the the difference in LW is appreciable. I’ve also noticed, tides tend to be higher at the early and the late months of each year with the lowest HW tides happening around May to August. I guess this is due to the influence of the NE Monsoons causing the higher tides.
Depending on the shape of the sea bed, the high tides can be higher or lower at different locations, e.g. LW is higher at Victoria Dock (Singapore) than at Sembawang (Singapore). HW is higher at Sembawang (Singapore) than at Victoria Dock (Singapore). It even affects the number of tides a place will experience in a day – yes, certain places e.g. Milner Bay at Groote Eylandt in the NT (Australia) may only get one HW and one LW a day!
Although the tide ebbs approximately 6 hours a day and then floods for around 6 hours, the speed at which the tide flows is not constant throughout. The strength or speed of its flow is called its Current. A tidal current that is flowing inland is called the Flooding Tide, Incoming Tide or Rising Tide and a falling tide that is flowing back out to sea is called Ebbing Tide, Outgoing Tide or Falling Tide. It’s important for kayakers to note that the current is stronger for the ebbing tide than the flooding tide and lasts longer.
The maximum HW for Singapore is reckoned to be 3.3m and the minimum height is -0.2m. The difference in height between HW and LW is called the Tidal Range. Therefore, Singapore’s tidal range can be calculated as 3.3m + (-0.2m) = 3.5m or rounded up to 12ft. As mentioned earlier, the Tidal Current is not constant throughout the 6 hours of a tide, neither is it the same for all places at any point in time e.g. when the current is forced to squeeze between a narrow such as at Malang Tiga, Sarimbun Rocks or Sentosa Causeway, the current speeds up a lot. This is important to understand especially for slow or low powered crafts and kayaks.
The tide’s height can be simply estimated by using the Rule of Twelfths as long as you know the timing of HW or LW, their time and depths, as tides rise and fall in the 1 2 3 3 2 1 sequence. (for a full explanation of the Rule of Twelfths, visit http://en.wikipedia.org/wiki/Rule_of_twelfths). Using this sequence, we can understand how the current gradually increases from the first hour after HW or LW till it reaches its maximum, halfway between HW and LW before gradually decreasing to zero again an hour before HW or LW, and the current reverse direction. We call this period where the current stops Slack Tide. It is important to know this because fish are most active when there’s a current moving water around. Except for certain very special conditions, I like to use the peaks of HW and LW to grab a quick hour’s rest as this is the period of slack water.
The direction in which a current is flowing is called the Set of the Current. If a current is ebbing from West to East, it is called a Easterly current. Note that this is the opposite to wind direction. The wind blowing from Northeast to Southwest at the end of each year is called the Northeast Monsoon, from the direction it came from. Knowing the set of the current at any phase of the tide help one to plan for the most efficient use of energy when travelling on the water.
Generally, the set of the current for Sembawang are:
Tidal Streams flow generally West to East for ebbing tide
Tidal Streams flow generally East to West for flooding tide
In some places however, the streams may be deflected by sand banks, rocks awash, jetties and outflows from major rivers or power stations. In such cases, the set of the current may flow contrary to the general direction, especially at the nearshore.
It is interesting to note that ocean currents around Singapore is fed from different locations on different months of the year. We receive water from South China Sea during the NE Monsoon (Nov to March) and the Java Sea during the SW Monsoon (June to Sept). Those who keep this in mind also look forward to the visiting pelagics during these periods. Examples are the eagerly awaited arrival of Queenfish at the year end and Sagai at mid year.
Tarpons, when in season are exhilarating fun on BFS tackle
Tidal streams are too complex to give full details here, but generally, the recorded rates at Tg. Stapa (Punggol) are 6.5km/h ebb and 4.6km/h flood. Knowing this and the prevailing wind direction can help one plan the most appropriate travelling times to save energy and fuel. The further west you go on the East Johor Straits, the weaker the current.
That’s all for part one – a general outline about tides and currents of the East Johor Straits. Stay tuned for the next part when we go into greater detail.
Text and Images © Lawrence Lee
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