fish finder arches

[dingbat]

Supposedly, the arch you see on the screen come from the difference in density from a fish?s air bladder and it?s body. But what if the fish doesn't have an air bladder? How do you see them then? Are they invisible?

 

[John_S]

Re: fish finder arches

Supposedly, the arch you see on the screen come from the difference in density from a fish?s air bladder and it?s body. But what if the fish doesn't have an air bladder? How do you see them then? Are they invisible?

I thought most of the arch was generated by the fish coming into the cone, peaking at the middle, and then tapering back out of the cone. Wider cone angles produce bigger arches, and S/W can also enhance this. I thought the air bladder was something the fish id algorithms used for the fish symbols and size detection.

 

[dingbat]

Re: fish finder arches

I thought most of the arch was generated by the fish coming into the cone, peaking at the middle, and then tapering back out of the cone. Wider cone angles produce bigger arches, and S/W can also enhance this. I thought the air bladder was something the fish id algorithms used for the fish symbols and size detection.

With a fish finder, you do not "see" the fish at all, what you see is the swim bladder.

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.

You are correct as too why the arch is formed. Can't tell you anything about fish ID, most unit's I've ever operated don't have that silly feature.

Back to the question, how do you see a fish that doesn't have a swim bladder?

 

[bruceb58]

Re: fish finder arches

Back to the question, how do you see a fish that doesn't have a swim bladder?

It must still be a density issue. Same as when you get a reflection from a thermocline. Doesn't take much to disturb the sound wave and cause an echo.

 

[John_S]

Re: fish finder arches

With a fish finder, you do not "see" the fish at all, what you see is the swim bladder.

I disagree, because a fish will reflect some sound waves without the air bladder, like any object in the water. If you need air, explain why weeds, mud, leaves, branches, water disturbance, and just about everything reflects sound. It doesn't make sense that the fishes body would absorb or allow all sound to pass through. It may help and provide more return signal, but invisable without the air bladder, can't see it.

PS: maybe one of the saltwater guys can tell us if sharks show on a ff. no airbladder correct? they got to keep swimming or sink.

 

[dingbat]

Re: fish finder arches

Most objects will return ?some? sound as you say, but??is your transducer and the units detection algorithm sensitive enough to pick up and decipher these returns?

You mentioned weeds. Can you pick up those same weeds in 200? of water? How about a bag of water floating 60 feet under water? Can your sounder "see" that thin film of plastic surrounding the water? How about something like a sea nettle that is an invertebrate and is made up of 95% water. Is your transducer sensitive enough to tell the minute difference in density between the nettle and the surrounding water?

The density of the flesh of a fish is very similar to that of the surrounding water. Unless it has an air bladder, a substantial skeletal structure or a heavily muscled body, the definition/ information you get on the return is minimal. Many fish do not give off good returns simply because there is nothing substantial in their make-up to differentiate its body mass from the surrounding water.

A fish with an air bladder and a heavy skeletal structure give off a very distinct return. While a lean, lightly structured fish tend to give off faint returns. Its very easily to distinguish a large boned fish like a Striper from a leaner, less heavily built, Bluefish by their returns.

Then there are quite a few species of fish where it?s easier to ?see? the disturbed water left by their swimming action than it is to see their bodies. A small, light blue haze right above the bottom is the hot ticket when flounder fishing.

As for the saltwater guy, does thirty-five years experience, ten of it as a pro, qualify for the position?

 

[Capt'n Chris]

Re: fish finder arches

I disagree, because a fish will reflect some sound waves without the air bladder, like any object in the water. If you need air, explain why weeds, mud, leaves, branches, water disturbance, and just about everything reflects sound. It doesn't make sense that the fishes body would absorb or allow all sound to pass through. It may help and provide more return signal, but invisable without the air bladder, can't see it.

PS: maybe one of the saltwater guys can tell us if sharks show on a ff. no airbladder correct? they got to keep swimming or sink.

You are correct!

 

[Capt'n Chris]

Re: fish finder arches

Most objects will return ?some? sound as you say, but??is your transducer and the units detection algorithm sensitive enough to pick up and decipher these returns?

You mentioned weeds. Can you pick up those same weeds in 200? of water? How about a bag of water floating 60 feet under water? Can your sounder "see" that thin film of plastic surrounding the water? How about something like a sea nettle that is an invertebrate and is made up of 95% water. Is your transducer sensitive enough to tell the minute difference in density between the nettle and the surrounding water?

The density of the flesh of a fish is very similar to that of the surrounding water. Unless it has an air bladder, a substantial skeletal structure or a heavily muscled body, the definition/ information you get on the return is minimal. Many fish do not give off good returns simply because there is nothing substantial in their make-up to differentiate its body mass from the surrounding water.

A fish with an air bladder and a heavy skeletal structure give off a very distinct return. While a lean, lightly structured fish tend to give off faint returns. Its very easily to distinguish a large boned fish like a Striper from a leaner, less heavily built, Bluefish by their returns.

Then there are quite a few species of fish where it?s easier to ?see? the disturbed water left by their swimming action than it is to see their bodies. A small, light blue haze right above the bottom is the hot ticket when flounder fishing.

As for the saltwater guy, does thirty-five years experience, ten of it as a pro, qualify for the position?

You are also correct!

 

[John_S]

Re: fish finder arches

Most objects will return ?some? sound as you say, but??is your transducer and the units detection algorithm sensitive enough to pick up and decipher these returns?

I fish freshwater lakes, and for the most part, focus in 50' or less water. For the most part, the unit will display what it returns, minus any filtering, or sensitivity, etc setting. "Decipher" might be more appropriate to fish symbols.

You mentioned weeds. Can you pick up those same weeds in 200? of water? How about a bag of water floating 60 feet under water? Can your sounder "see" that thin film of plastic surrounding the water? How about something like a sea nettle that is an invertebrate and is made up of 95% water. Is your transducer sensitive enough to tell the minute difference in density between the nettle and the surrounding water?

Weeds stop growing in the 30-40' range in our clear lakes, and short season. Yes, I can see them. I fish allot of rivers, and have hooked numerous plastic bags verticle jigging. The bag does provide a return.

The density of the flesh of a fish is very similar to that of the surrounding water. Unless it has an air bladder, a substantial skeletal structure or a heavily muscled body, the definition/ information you get on the return is minimal. Many fish do not give off good returns simply because there is nothing substantial in their make-up to differentiate its body mass from the surrounding water.

I am not sure it is a density only thing, no more than just an air bladder thing. Somethings you have mentioned are probably a factor. The fish profile as seen from above, but others like skin or scales, would seem to have factors as well.

A fish with an air bladder and a heavy skeletal structure give off a very distinct return. While a lean, lightly structured fish tend to give off faint returns. Its very easily to distinguish a large boned fish like a Striper from a leaner, less heavily built, Bluefish by their returns.

I don't disagree that different fish with different profiles give off different returns. Where they are in the cone and where they are relative to the overall depth, changes how it appears as well.

Then there are quite a few species of fish where it?s easier to ?see? the disturbed water left by their swimming action than it is to see their bodies. A small, light blue haze right above the bottom is the hot ticket when flounder fishing.

So, it is sensitive enough to see the disturbance in water that has the same density, and no mass or material difference, but not enough for a fish body that has a different density, different surface, etc?

As for the saltwater guy, does thirty-five years experience, ten of it as a pro, qualify for the position?

From a freshwater only guy, does that mean sharks and rays are totally invisable on your ff, being no air bladder or bones?

Do squid have air bladders? If not, I did see a documentary on them, where they were being seen on a ff. They were using a ff to locate them for filming. I believe they mentioned that some modification was done to them, so they would display them better, though.