Tides of Change
  |  First Published: March 2010

I had always kept a diary of fishing trips to help work out patterns that turn the fish on and off and have found that my little diary entries were invaluable to making the most of my time on the water. Things stepped up a notch when I moved away from the familiar waters of South East Queensland and made Cape York home. I had to start all over again.

I had the common cry of mates from down south telling me all the locations that they had caught fish on trips to the north and many of these suggestions failed dismally. It was a matter of getting on the water as often as I could and document every detail possible about these trips to work out my options.

After 12 months and many fishing expeditions, I have started to get a handle on this place and to my surprise, the biggest single factor that now influences my fishing up here is tide height. What I am interested in more than anything is the height of the water. I don’t care about what time high tide is and I don’t want to fish an hour before or after the low, it is all about the height of the water.

Before I get into how water height effects my fishing, I should give you a rundown on exactly what tide height is all about.

Tidal Datum Points

Tide heights are measured in metres from a common datum point. Generally speaking, a datum point can be anything from a scientific measurement to a line on a rock or a mark on a stick but it is common practice for all tide measurement to be measured from a datum point of the lowest astronomical tide or LAT.

The LAT is the lowest the tide would be expected to reach in that area with normal atmospheric conditions. A 0.8m low tide is 0.8m above the LAT and the high of 1.6m is 1.6m above the LAT – simple.

In Fig.1, there is a 0.8m difference between high and low water. To work out the tide heights at various stages of the tide, we need to understand how the tide flows throughout this single, low to high period. If our low tide of 0.8m occurred at midday and our high was due at 6pm, I would allow 5% of the total rise to have occurred in the first hour, 20% to occur in the second, 50% in the third, 80% by the fourth, 95% by the fifth and all in by the sixth. This first half of the tide cycle is reversed for the second half. In the chart, this has been broken down into actual figures which make a lot more sense.

This example will give you a ball park figure on what the height of the tide will be doing. It is possible to get hourly tide heights for some regions that will take the guess work out. Some locations have plot charts available that give a wavy line on a graph that depicts the tide heights at the various times of the day and these are another easy way of working out tide heights at various times.

Changing tide heights

Variables that effect tides are the positions of the sun, moon, planets, and weather.

When the weather is bad enough to make big differences in tide height, then we need to ask ourselves why the hell we are out there fishing. Planets don’t have enough influence on tides to worry about them so let’s look at the sun and moon.

We all know that we have bigger tides when the moon is full and also during a new moon. This is because the sun also has a gradational effect on the earth’s water and during new and full moons, the sun and moon are aligned and both working together. These larger tides in a monthly cycle are known as spring tides; the high tides are higher and the lows are lower.

When we see a half moon the sun is at the side of the moon, which is why only one side is lit. The sun is pulling water one way while the moon pulls that water the other, therefore they are not working together so the tides are smaller and known as neap tides. Neap tides have less variation between high and low tide so instead of a 0.8m variation we may only get a 0.4m so the tides may be from 0.6-1m, giving us a higher low tide but a lower high tide.

The only other technical bit that I need to add, and it will be the last so keep paying attention, is that summer and winter sees a variation in tides from day to night. In summer, tides during the day are greater and night tides are smaller. Winter sees the opposite effect purely because when the sun is in the southern hemisphere, our summer, it has a greater effect during the day time high but at night the sun is actually in the northern hemisphere, pulling water away from us and there for decreasing our tides.

That is a very basic rundown on tide heights and how they come about but just how this all effects the fishing is what we all want to know.

Fishing Tide

Moving to Cape York in the middle of summer was an issue for me. I had been north on previous fishing trips but only in winter when the dry season allows vehicle access to the Cape so being here in summer with the bigger day tides caught me by surprise.

I was all pumped for catching big barramundi and casting at the mangrove fringes, I could hear the odd barra smashing schools of mullet deep in the mangroves. Yep, the barra were there alright and it soon became obvious that the big tides flooded the mangrove roots with a good metre of water, pushing the bait well back into the thick mangroves with the barra chasing them. If I was able to cast a lure through the thick layer of mangroves I would be able to catch fish but that wasn’t possible. Realising my mistake, I started to motor around looking for steep banks that had very narrow sections of mangroves so the fish were not able to hide. Problem was that the narrow runs of mangroves didn’t have any bait on them so the barra weren’t about to hang around either. My last thought was to wait for the tide to be at a level where the bait was either leaving the mangroves due to a falling tide or was about to enter the mangroves.

My next trip had me on the water at sunrise and fishing a very active patch of mangroves on a falling tide. Plenty of action was happening deep in the mangroves but it was not until around 10am that my first barra came out and smashed the lure. A neat little 70cm fish but after a week of casting lures at the mangroves and trying various locations, I was thrilled to have finally landed one.

Ninety minutes after my first fish came on board, I had a tally of seven barra with one edging 90cm and two that found the roots of the red mangroves and disappeared with my lure still attached. The tide continued to fall and the fishing slowed down and the regular boofs of feeding barra had stopped.

Heading home, I checked the tide times and found that when the tide touched the 1.8m mark, the fish came on and when it got below 1.5m, the bites stopped. The high tide for that day was a 2.4m high which gave the fish close to a metre of water to chase bait in before they had to leave the shallowing mangroves. I suddenly had a new plan which was to sit at home waiting for the tide to hit the magical 1.8m mark and fish it hard for a couple of hours before heading back home to catch the start of the cricket.

I have since added a stack of similar stories and my fishing diary confirms that tide heights are a major factor in where and when I fish. Tides in some locations can have a variation of 7m or more and thankfully my home waters have an average tide of less then 2m but knowing how your local tides influence fish behaviour can be as vital to your fishing as it was to mine.

Far from Familiar

Having spent most of my life fishing southern Queensland and NSW waters, I know bread and butter fish like flathead and whiting were incredibly sensitive to tide variations but all for very different reasons.

Flathead were a very fickle fish that wanted a combination of clear, cool water that was loaded with baitfish. The clear water was often found on a rising tide in summer. A falling tide would often be too warm so raising was best and then it was a case of working out what tide height would bring bait out of the creeks, drains and banks to fire the fish up. It was a real jigsaw puzzle that started and often ended in a good hard look at tide times and heights.

Bream and whiting on surface poppers was a favourite summer pursuit and the best place to chase them was around the weed on the sand flats. Tide heights gave me access to the flats, and would also have to be considered to insure I was able to get out of there. The fish would also really fire up when they first got enough water to get up onto the flats. This was generally a little less than a metre above LAT and a lot of run that would be found around the spring tides would fire them up.

I can’t think of a single saltwater species that does not have a feeding pattern that is influenced by tides in some way. Whether it is marlin or garfish that you are chasing, tides are just another tool for the serious anglers’ belt.


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