A day in the Fitzroy

[Douglas]

Greetings all.

Brother went down to the Fitzroy mouth today for round 2 of his battle with "big things".

Was cleaned up several times last week on 150lb handline without turning a scale. Got some other things but not what was cleaning him up.

This time armed himself with venetian blind cord on a hand spool and some 250 lb (110 kg) stainless steel leader. Hooks approaching 2/3 size of a can of 4x gold.

Whacked on a live 3kg GT and waited.

20 mins later it was on for young and old.

His hands took a beating and eventually the stainless steel leader failed in the middle.

Skin off his hands and swollen bruised fingers.

At times he had 3 wraps around a stern cleat with boat being pulled around. Thought of that classic Jaws saying by Roy Schieder " I think we need a bigger boat".

No success. He is convinced that one of his fingers is broken when it got caught up.

Retrieved what was left of his handline and put it away. Didn't want another round although he still had 2 more tackleshop made leader rigs left.

Wants me to go with him on Wednesday for round 3.

Luckily, I'm going unintentional barra scouting and cant make it.

Some big strong mothers at the mouth of the Fitzroy. Possibly groper or big cod.


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[Douglas]

Bit more news from the Fitzroy.

A couple of months ago a 5.2m croc was found dead (shot) in fresh water above barrage.

Latest news.........

Caught.

https://www.themorningbulletin.com.au/n ... c/3296952/

Looks like coppers extracted bullet, tested it, combined it with other info and found the rifle that fired the projectile at a local property.

[gunna]

3kg live bait. What a hoot.

[Douglas]

Went down to the Fitzroy mouth Wednesday (outside MacKenzie I.

3 x unintentional barra up to 790mm, 1 x king threadfin of 840mm, grunter, bream, blue salmon & couple of gold spot cod. Bit of variety & all on lures.

On the mudflats past MacKenzie there were thousands of threadfin fingerlings. Thousands. Trying to follow a bunch of prawns, mate was getting 30 - 40 threadfin about 2 inches long each cast.

Gave up on the prawns as we didn't want to kill baby threadfin in the process.

On the way back up came across a beam trawler anchored up. There are about 7-8 beam trawler licensees who operate in the lower Fitzroy still.

We never learn.

We stopped the nets killing an average of 11 tonnes of threadfin parents but still allow these beamies to kill the kids as tonnes and tonnes of bycatch each year.

[Douglas]

Fitzroy mouth GE image

[Douglas]

As you know, I target wild barramundi and king threadfin. Fitzroy is a notoriously dirty water river and I've been looking at what I could find about barra and king eyesight and lateral line sensors.

Barra have always been a bit of a mystery with their pinky/red eyes. Some believe its infrared sight.

Its not infrared but simply the result of colour given off as light is reflected back through the eye twice.

Barra do this to make up for the effects of dirty water or other low light conditions.

But that only works when they can actually get within visible range which is usually very close in this river.

So there must be another mechanism that gets them within vision range.

It has to be the result of lateral line data sent to the brain.

The more I searched for info on lateral lines, I began to understand how predator fish rely on lateral lines.

The sensors in the lateral lines (called neuromasts) process incoming vibrations in the water and tell the brain the direction of the source.

A bit like a "steer left or right" signal which allows the fish to home in on food that produces vibrations in the water.

The steering direction brings the fish into vision range to the point where the eyes then take over for the strike.

That explained a few things to me like barra preference for live bait (fish or prawns) because they produce vibrations by movement which the lateral lines pick up. Very seldom do you catch a barra on a dead prawn or dead fish bait. No movement therefore no vibrations unless you provide some movement. I'll come back to that.

That meant that attracting a barra strike was a two stage process. The lateral line role and then the eyesight role.

I've had a bit of a play around with what I consider to be those two processes over the last few weeks.

Anybody had a look at this subject at all?

[Funchy]

As you know, I target wild barramundi and king threadfin. Fitzroy is a notoriously dirty water river and I've been looking at what I could find about barra and king eyesight and lateral line sensors.

Barra have always been a bit of a mystery with their pinky/red eyes. Some believe its infrared sight.

Its not infrared but simply the result of colour given off as light is reflected back through the eye twice.

Barra do this to make up for the effects of dirty water or other low light conditions.

But that only works when they can actually get within visible range which is usually very close in this river.

So there must be another mechanism that gets them within vision range.

It has to be the result of lateral line data sent to the brain.

The more I searched for info on lateral lines, I began to understand how predator fish rely on lateral lines.

The sensors in the lateral lines (called neuromasts) process incoming vibrations in the water and tell the brain the direction of the source.

A bit like a "steer left or right" signal which allows the fish to home in on food that produces vibrations in the water.

The steering direction brings the fish into vision range to the point where the eyes then take over for the strike.

That explained a few things to me like barra preference for live bait (fish or prawns) because they produce vibrations by movement which the lateral lines pick up. Very seldom do you catch a barra on a dead prawn or dead fish bait. No movement therefore no vibrations unless you provide some movement. I'll come back to that.

That meant that attracting a barra strike was a two stage process. The lateral line role and then the eyesight role.

I've had a bit of a play around with what I consider to be those two processes over the last few weeks.

Anybody had a look at this subject at all?

G'Day Douglas

Must admit it is not an area of expertise for me but I want to thankyou you for the info. Like you say it explains alot. Makes sense why trolling lures up north in muddy waters is successful.

[3Macks]

Not my area either but some lure makers are looking at their lures under UV light as they consider that that is how fish see in muddy water. Came across it on FB when sent a post from Big John (Jigs). He had a series of photos of how the colours changed if under white or UV light. As I say not my area but I am sure John would be happy to discuss.

[tackle_buster]

I put this link up some time ago in relation to another thread, but applies to this one as well, I think

https://en.wikipedia.org/wiki/Lateral_line

[Douglas]

Thanks Gazza.

I had a good look at that page over the last couple of weeks. Plus others.

What I was trying to work out was if the differential in signal characteristics between the side facing towards the signal source and the side facing away from the signal source gave the fish's brain a steering signal telling the fish to go left or right until it homed in on the source. Bit like the Doppler system used on EPIRBs, it only works if the fish keeps moving (the satellite) or if the source keeps moving (the epirb). Or both.

As long as there's movement relative to each other, then a homing path can be calculated.

You'll see a somewhat similar effect on a GPS. If the boat is stationary, then the compass heading wont change.

However, I'm starting to lean towards another mechanism.

The other way that lateral lines can produce a useable output is if the minute hairs in the nueromasts contained in the lateral line bend away from the direction of the source. That gives a directional signal (opposite to the direction of bend) from the side of the fish facing the source.

Following that up by observing barramundi in a fish tank, it became obvious that the fish liked to remain stationary in the water column fanning it 3 rudder fins (broad tail and anal and upper fins) in such a way that it turned its body to face the direction of a new vibration into the tank.

The air pump and filter pumps set up 2 fixed sources of vibration which the fish took a little while to become accustomed to. Bit like a steady level of "background noise" to which the fish became used to hearing.

But introduce a new/different vibration and the fish knew immediately.

Took a little while and patience to work out what was happening.

But having worked it out (or so I think), I've started into looking at lures and the vibrations that they introduce.

I've also had a look at lure colours in respect of barra eyes. Some interesting conclusions when you realise that a barra doesn't see in colour. So what is it that catches their attention vision-wise?

The one thing about barra behaviour is that just as you think you've got something worked, the bloody fish does something completely different and you're back to square one.