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  1. #111
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    Hi Al

    You betcha.

    A 3m croc has moved into the Devil's Elbow reach of the river (about 3 km downstream of city CBD).

    He/she has been exhibiting signs of aggressive behaviour so will probably have to be removed soon.

    Approaching boats (territorial stuff) and stalking dogs having a swim.

    It should be the stupid dog owners in the water. This particular owner was throwing sticks into the water for the dog to retrieve.

    Dog nearly didn't make it back to shore with second stick.

  2. #112
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    Yes makes you wonder what is inside head of some dog owners
    the world is a lot better place if you just smile

  3. #113
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    I've been looking at lure colours in the water and the effect of light absorption and light scattering.

    Some good articles have been written by the likes of Greg Vinall and Steve Starling relating to colours in open ocean situations.

    Light scatter in water has been well documented by people with more degrees after their names than can be found on a thermometer. Hugely informative though.

    However, Greg and Steve's articles only talk about what happens to absorption in clear water. None of the articles talk about what happens in dirty estuary water.

    And that's the reality that we barra/threadfin fishermen face. For us its clarity (turbidity) and for freshwater fishermen you can add water colour itself (eg tannin) with algae thrown in.

    It sure has been a learning curve but will be ready to go pretty soon.

    I've been trying to get a handle on the subject to the stage that I can distill it into simple language that even I can understand easily. Hasn't been easy trying to do that because of all the concurrent interactions that occur. Like trying to pick an end while watching an octopus trying to make love to a set of bagpipes. Where's the start and where's the end?

    So........

    Have a look back through post 102 in relation to lateral lines in the meantime.......and

    Watch this space.
    Last edited by Douglas; 10-02-2018 at 09:23 AM.

  4. #114
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    Last night in the CBD

    Stumpy

    Have seen fish like this before during stocking releases.

    Came from GAWB and we never tagged fish like this on release on the grounds that pro-fishermen would make a federal case out of it if they netted one. Claim that tagging caused the deformity etc....etc...

    Didn't tag and release this one either for same reasons. Their supporters still around.

    Stumpy 70cm.jpg

  5. #115
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    seen a few of those too in fresh as well ,I reckon its also due to over indulgence on good food when young ,way too faster growth for the body to keep up .in boom times in awoonga and mondy when bait was at its peak I saw a few landed with big bodies and small lengths stumpy tails
    the world is a lot better place if you just smile

  6. #116
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    Stocking here has been mainly in the fresh above the barrage.

    This guy probably came down to the salt in the flood last year.

    Mate filleted it and the deformity at the base of the tail was all bone which had formed around the broken backbone.

    Most probably a handling injury at very small size.

    The ones we found when releasing them were about 3-4 per release (500 - 1000). Not a high percentage but apart from the bent stumpy tail the fish were fit and healthy @ 250mm each indicating injury when they were much smaller.

    GAWB didn't like growing them out to 250mm for orders so a guy in Bajool used to buy from GAWB and grow them for supply to southern restaurants. Any deformed ones went to stocking. Injury could have happened at Bajool or Gladstone early in the fish's growth.

    Tasted ok though.

  7. #117
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    Bit about barramundi hearing. Decided to get "hearing" out of the way first as the light issue has a lot of twists and turns.

    We've now done lateral lines and hearing.


    What role does hearing play in barramundi fishing


    No, its not that a fisherman must be able to hear “barra boofs”. It’s how well can barramundi hear.

    Don’t get hearing confused with lateral line operation. Lateral lines deal with low frequency vibrations in the water by objects displacing water as they move around thus sending out waves of energy at low frequencies.

    Hearing is to do with acoustic signals being transmitted through the water. These acoustic signals are frequencies higher than those to which lateral lines are tuned. These are within normal human hearing range. Barramundi are classed as hearing specialists in the piscatorial world.

    Think about the car enthusiast with the $5,000 audio system in his car. Every vehicle stereo enthusiast has to have the biggest and best “woofer” speakers. A “woofer” is a low frequency speaker which produces base sounds.

    A sub-woofer goes even lower in frequency to ranges that we can’t hear (we oldies anyway). But we can feel them in our body well before it becomes evident which ratbag driving past has his volume up (and we don’t even have a lateral line).

    What about hearing then? Barramundi don’t have ears and we do.

    Let’s go diving into the barramundi’s world where sound travels faster (up to 5 times faster than in air) and there’s less absorption. Put your head underwater and note the difference.

    I can recall somebody on a fishing DVD with a black box and underwater microphone listening to underwater sounds one rainy night on the Fitzroy.

    You’ll hear an outboard motor underwater long before you hear it with your head out (and louder too). So, can barramundi match our hearing? Yep, sure can. Their hearing (without ears) is just as sensitive as ours and occupies the bottom section of our audible frequency range.

    Barramundi have a hearing threshold of 70db of signal pressure while a diver has a threshold of about 67db of pressure wave. Forget the technical figures. It just means they can hear about the same as us.
    Barra also have a lateral line, so they’re streets ahead of us already.

    But where are their ears? They don’t have ears that we would recognise but they have bony things called otoliths and they work in conjunction with their gas bladder to “hear”.

    Now we’re starting to get into the subject of rattles. Rattles don’t work very well on lateral lines but they do on barra hearing if they produce noise between 100 hz and about 1,000hz (1 khz). Above 1 khz barra start going deaf. Steel ball bearings hitting together inside a lure produce sounds towards the upper limit of barra hearing. Lead bearings would produce lower frequency noise being denser but probably need lure design to overcome weight problem. Wooden balls would produce lower frequency noise but of a lower level.

    To produce the rattle noise though, there'd need to be stabbing retrieves to get the balls to hit together or against the walls of the rattle chamber in the lure. A straight slow retrieve wouldn't produce any rattle noise.

    We’re also into the area of boat, anchor chain, items dropped, walking around in boat etc….Anything that produces a noise. Trebles rattling around on split-rings during stabbing retrieves produce noise.

    Remember the warnings in pet shops about not tapping on glass of aquariums? The close-up loud noise produced scares the hell out of the fish.

  8. #118
    Grand Slam
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    I know from personal experience that that they can hear you walk up over gravelly shores to the water's edge, can hear a car stop, can hear a car drive over a bridge overhead, can hear talking people and doors close on cars, so they do have accute sound awareness/hearing.
    Now, I'm not saying we should invoke capital punishment for Stupidity, but how about we just take all the warning labels off everything and let nature sort itself out?

  9. #119
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    Some people think they can hear the sounder frequencies working away on their boat. They can't.

    What they're actually hearing is the audible sound of the sharp rise time of the pulse hitting the membrane of the sounder face. Put your hand over the transducer while its operating and you'll see what I'm referring to. A sounder sends out so many of these pulses in a second. Sometimes these pulses are called "pings" if you watch submarine movies.

    Frequencies of 50khz, 83khz, 200 kHz, 300khz, 455 kHz, 800 kHz or 1200 kHz are the frequencies transmitted by the transducer depending on what type of sounder you've got (fish cannot hear these frequencies).

    The rate at which the sounder sends these pulses out depends on the depth of water. If deep water, then it takes longer for the pulse to travel there and back so the longer the sounder needs to "listen" for the echo. That dictates that the rate of pulses being sent out is slower. That rate is called the Pulse Repetition Frequency (PRF). War movie buffs will know it as the ping speed.

    It shows up as a low level "clicking" sound which can be heard by fish and humans. It sounds like the ticking of an electric fence which operates on a similar principle except the fence sends its pulse along the wire while a sounder sends its pulse out into the water.

    It is a low level and low frequency rate between 5 and 30 times per sec. Some sounders allow the operator to "fiddle" with the PRF (or "ping" for the movie watchers) but most change the rates automatically on selection of depth or frequency selected by the operator. There is usually an adjustment for scroll speed to keep up with increased pulse rates when travelling fast. When travelling fast, more pulses are needed per sec to get some detailed echos onto the screen.

    I found out last night that there has been a "underwater duck caller" on the market (and in use) by anglers for some time.

    Apparently this "fish/duck caller" is marketed under the name of Hydrowave. It plays audio sounds into the water of a variety of sounds of fish activities designed to attract fish to the vicinity of the boat.

    Is it a successful "fish caller"? Anybody got one?
    Last edited by Douglas; 07-03-2018 at 02:17 PM.

  10. #120
    Legendary Angler
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    Anyone know if Rocky has had much rain/flow down the fitz
    Cheers
    Gazza

    IF MEN ARE FROM MARS AND WOMEN ARE FROM VENUS, THEN POLITICIANS MUST BE FROM URANUS

 

 
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