Telling size of fish with electronics

[Gordon Fothergill]

A recent publication had an article that talked about guessing/telling size of fish with your electronics. In a nutshell it said you cannot judge size, echo strength is determined by position in cone. I don't believe. What do you guys think.

[Guest]

In the summertime with my Vex I can tell the average size of fish in a school by the signals and the way they are grouped. (Crappies)

Upon catching one fish in the winter I can tell there after if the next approaching fish will be of nicer size or of smaller size.

Keep in mind that your jig will be in the center of the cone, and in order for the fish to strike it, it must also be in the center of the cone. At that point is where you have common variables and can then do comparison.

PCG

[Guest]

I saw that too, i believe you cant tell on a flasher. A flasher relays its targets by signal and echo strength. I fished with a guy once who kept telling me the size of the crappies down his hole by the bars on his Zercom. Three bars was a 11 inch crappie. I bumped his gain up and his jig was three bars. We never did get any crappies that day over 10 inches.

I do believe you can certainly tell the size on a LCR graph. The pixels fill in the screen by target size. That article from what i remember didnt specify flashers vs LCR's.

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[Ice Hole]

LOL ...of COURSE you can tell the size...if you know the fish is interested and in the center of the cone, you can determine the size by how "thick" or "strong" the signal is. There is a mininum and a maximum reading for each fish, dependant on size. The maximum size of that signal occurs when the fish is in the middle of you cone(obviously) and the mininum when the fish is on the edge of the cone(obviously). When you KNOW that signal is at its maximun, it WILL coralate DIRRECTLY to the size of the fish. One other note, a 3 lb crappie will appear smaller than, say a 3lb walleye. Think of how much area there is from a top view of the fish. That is what gives you that signal, and the bigger the area that fish takes up, the bigger signal. That article is talk...unless using a flasher in open water, trolling. Because you can never know when that fish is in the center of the cone.

[Guest]

You can tell no doubt about it.

[Ice Hole]

Too add to this, you can tell the size of your lure, and weather or not your lure has bait by the size of the signal you get back from your flasher. A #10 glow demon will look smaller than a 4" jigging rap.

[Ice Hole]

D-man what makes you think a LCR graph gets its signal any different than a flasher. Still the same concept bro.

[This message has been edited by Ice Hole (edited 01-10-2003).]

[This message has been edited by Ice Hole (edited 01-10-2003).]

[Guest]

Nice point.

When you TURNED UP THE GAIN and his lure read three bars then fish signal probably went to 5 or 6

Very true, you can not change settings in the middle of things...It just does not work.

Fish up higher will read stronger. But my strike zone typically stays the same. So the fish signal will be comeing from the same general depth.

PCG

[Guest]

Ice Hole , not the same concept Bro.. The concept of sending an echo is the same, its what the unit uses to display the information is what is different. A flasher displays its information from its receiver and uses flashing lights(thus the term "flasher") heres some info taken from Richard Christman a former Vexilar engineer
"How We See Fish"
Sound waves are reflected by physical discontinuities (places where the speed of sound suddenly changes). The flesh of a fish is mostly water, and the difference between the speed of sound in water and in the gas of a swim bladder is so great that much of the energy that strikes it is reflected back. The swim bladder enables a fish to remain at a chosen depth without having to swim constantly to keep from rising or falling. With depth sounders, you do not "see" the fish at all, what you see is the swim bladder.

Like a bell or a column of air in an organ pipe, each gas-filled swim bladder has a natural frequency. When the impinging sound waves are at that same frequency, the swim bladder resonates and the reflection is several times stronger than other wise. The target "looks" much bigger than it actually is. To complicate matters further, the tone at which the swim bladders resonate is determined by water pressure, the size and shape of the swim bladder and the physical constraints within the fish itself. These factors change as the fish moves vertically through different pressures.

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[This message has been edited by D-man (edited 01-10-2003).]

[Poutmaster]

All science and facts aside, I know I can tell the difference between a 4 inch perch and a 10 inch crappies on my flasher. You can tell when a "bigger" fish is right on your lure.

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Love them 'Pout!

[Guest]

Would'nt a bigger fish have a bigger bladder to discontinue the sonar signals?
I may not be able to tell the differance between a 4 inch crappie and an eight inch crappie. But when a big northern moves in the marks are noticably larger.

[Ice Hole]

Exactly my point D-Man ...Your graph does the same exact thing, except shows a history of what you saw by using lcd pixels and shades and what-not. The leading edge of your graph, where the bottom and fish appear is simular to the depth scale on the flasher, except in a circle instead of vertical. Being able to tell the size of fish has nothing to do with what is displaying the information, whether it be a graph or a flasher. You can do it with either.

[Guest]

But you are comparing two totally different concepts on sonar. If a 32 inch walleye came into my cone would it fill my entire dial of my flasher? Why doesnt the red bars get much bigger than 1/2 of an inch? Why? because there are over 500 lines on a Vex dial. Each line represents less then half of an inch, thus giving you the "up to" 1/2 target seperation. I got my first Micronar in 1985. Its the same concept. What you are seeing is the fish entering the center of the cone like you explained.

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[This message has been edited by D-man (edited 01-10-2003).]

[Steve Foss]

If your lure is in the center of the cone and there's a line under your lure that gets wider and wider, at it's widest point it's probably in the center of the cone, too. So it's possible to believe the wider the red line that stops under your lure, the bigger the fish. Actual pound estimates? That's dreamland, for sure.

[Guest]

My only point is that it is possible to compare the size of a fish by the signal once it has entered the center of the cone.

Exact weight..No. But telling if the next fish will be bigger then the last one..Yes, providing the difference in size is more then a few inches.

[This message has been edited by Pro Crappie Guide (edited 01-10-2003).]

[Mr. Pike1]

Simple answere to your question. No, you can not tell the size of the fish on your Vex. There are many variables that determine the strength of the signal displayed however none of those variables is the size of fish. You can use all the false logic you like to try to assertain this to be true however it is false. The answer is no and do not be fooled by anyone who trys to tell you different.No, No, No...

[Guest]

OK, SO why is it you an see the temp change?
There isn't any thing there but water(at a different temp) no air bladder.
I do feel that i can tell the size difference in fish. How much? I think that comes along with the amount of time you spend with your flasher.
racer

[This message has been edited by racer (edited 01-10-2003).]

[Guest]

Ok I am wrong...No matter what I have proved in the past, no matter how many have witnessed it.... I am wrong.

Asertain thinking? whatever

PCG

[This message has been edited by Pro Crappie Guide (edited 01-10-2003).]

[Surface Tension]

How can a LED get wider, It cant. It can change color thats it. You can only get so much info from an LED. Thats why a graph or video sounder is my first choice.

Theremoclines show up because of the change in water density.

[Mr. Pike1]

If you would like confirmation of the "fact" that sonar flasher units can not determine fish size simply contact Vexlar direct. They are located in Bloomington. You can speak to one of the engineers who designed the unit and they can give you a physics lesson on the reasons why this is not possible with this type of technology. Your signal will be weak or strong based on the location of the target in the projectory of the cone when it is struck by the sonar.

[Mr. Pike1]

Thankfully there is technology out there that will allow you to not only determine the size of the fish in question but also the species. This technology became available at a somewhat reasonalbe price in the early 90's. It is called an underwater camera. I won't bore you with the physics behind how this devise captures data from the depths of your favorite ice hole and actually transmits this into a viewable image for he human eye. So to recap if you truely wish to know the size and species of what lie below the ice purchase an underwater viewing system. If you wish to know if a target/fish of some size and unknown species lies below the ice use a vex sonar device. If the belief that you have the abilty to determine the size of a fish with technology that does not have the capability to do this makes your fishing experience more enjoyable then I salute you.

[Guest]

Even with all the technical info supporting the fact that a person cannot tell the size of a fish I'd have to disagree. You can tell the difference in the size and/or species of a fish. (mainly when the fish is looking at your bait directly under the transducer at the same depth as you caught the last one) It may not be as precise as being able to say this is a six inch gill or this is a nine inch gill, but there is a difference. The size of the blip isn't necessarily the best way to tell what's down there. There are other factors that can help you tell based on the different characteristics of different species of fish and the mood that the fish are in. It varies on from lake to lake and day to day, but you can make some overall generalizations. One quick example could be the smaller gills today would dart around and flicker more. They'd come up look and go right back down or they would pop it quick and try to go back down. Where as the bigger gills would slowly come up, stare for a while, and then either suck it in or leave the screen. I'd be interested to hear more on how that swim bladder frequency thing works, but you would think that if a 1/4 oz spoon gives off a better echo than a 1/64 oz jig, a 4" swim bladder would reflect more than a 1" swim bladder. (once again at the same depth directly under the transducer)

[This message has been edited by flyingfish (edited 01-10-2003).]

[Guest]

Lots of good points here. There are a few variables that were not mentioned in the first post by Gordon Fathergill, one of the few, on a very short list of EXCELLENT fisherman that I know.

A vexilar is not able to tell you the difference is size of a fish of a specific species. If you are fishing one species or another, a vexilar will certaily be able to tell you if a different species had entered the cone if you familiar with how each species reacts. For example, while crappie fishing you may see a fish enter the cone that appears a little different. This fish gives off a "double signal". Experience has shown that this fish is a catfish. Now, to an untrained eye, it may be a crappie. There are a lot of finite rules when it comes to reading vexilar signals. I think the person that posed this question knows the exact answer,as he is a GREAT fisherman. This is one of those subjects that could be determined a different way depending on the context of the situation. Good one GF! Scott Steil

[Guest]

I can tell the difference between a 4" Crappie and a 11" Crappie on my Vex when the fish are in the center of the cone.

I know the fish are in the center of the cone because I catch them. In order for me to catch them they have to inhale my jig. My jig just happens to be coincidentally in the center of the cone as well.

I should now contact Vexilar and tell them mine is defective.

PCG

[This message has been edited by Pro Crappie Guide (edited 01-11-2003).]

[Guest]

Pro Crappie.. Tell how you can tell?