I was told by a prominent guide long ago that salmon & steelhead are often bothered by stronger sonar waves emitting from fish finders: particularly in shallower areas of rivers & bays. That made sense to me and ever since I have used my Fish Finder sparingly and on low power. Now, just this afternoon, I read in Field & Stream about a small study where divers observed fish behavior under varying strengths of sonar signals. They first noticed that the sonar was audible to them as "pinging" sound. So they figured that the more sensative fish's lateral lines would pick it up stronger. And indeed, they observed that under more intense FF sonar waves that many fish would be bothered to move a distance away. So this now confirms to me that my suspicion of multiple sonar emittions coming from a number of boats in areas of heavy usage, such as at the mouth of the Wind R. is one of the factors that cause the bite to just shuts off many times. Of course there are other factors for that, but they are mostly out of our control. There are also exceptions to this syndrome; such as the bumperboat meat hole by the N. F. Lewis hatchery where many boats cram over stacked up springers in 30' to 40' of water. For fishing sal./steel. in 5' to 20' feet of water I think that FF's more often function as a depth sounder than a true fish locator. In the shallower areas of rivers most fish tend to swim around the noise of the OB motor and FF, rather than swim right under the narrow band of the transducer anyway. So I would like to get some feedback opinions here as to what you think dozens of FF's buzzing the fish in an otherwise productive area does to affect the bite. And what can be done about it? I don't think anyone cares to stand up to yell thru a bullhorn for everyone to shut off their FF's instead of just leave them on. Media education of anglers? - Steve

[This message has been edited by Reel Truth (edited 05-16-2000).]

Interesting post, RT.
FYI, it is almost certain that sound from transducers is detected in the inner ear, not in the lateral line. The lateral line detects pressure gradients caused by water movement, not sound waves. For a fish to detect the output from a transducer in its lateral line it would have to be very close to the transducer, probably within an inch or two at high power. Beyond that transducers won't move water, that type of energy dissapates very quickly.
People have tried to use sound to repel fish before, with varying degrees of success. Most of the success has been with members of the herring family. No one has had any success with salmon that I'm aware of. The Field & Stream article is interesting but seems pretty weak to me to base any conclusions on. I think the more likely explanation of why the fish at the Wind get put down is all of the boat motors. Motors emit both sound and energy enough to be detected by both the lateral line and the inner ear. Motors put out a lower frequency noise than transducers, which both travels farther and is more easily detected by fishes hearing systems. The noise from the motors and the hulls slapping the water probably dwarfs transducer noise. Then again, maybe the fish get put down by all the cussin' going on. Cheers

Just my two cents worth. I have always fished from a drift boat and do not have a fish finder. I like sneaking up on my fish. I have been on say the N fork of the lewis along with many power boats. One day I was fishing a hole that many boats just pass up. I was haveing a very good day untill a power boat went by than the bite went off. I moved in to a lower hole that was empty of other boats got a fish in that hole also. Once again a power boat moved in and the bite was gone. Please believe that I have nothing against power boats (we all need to fish) But I do believe that noise has alot to do with the bite. KEEP THE RIVERS CLEAN!!!

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dank

I have no direct experience with the use of fish finders in rivers, but have fished many of the various "meat holes" on several rivers. My impression is that both the commotion of fishing pressure (boat motors, oars, all those lines) and fighting fish in the water are the primary determinants of how active or put off the fish are going to be.

In most terminal areas, the bite tends to be in flurries with dead time in between, rather than a steady bite all day. I think this is due to the fish being spooked into not biting or moving to a different area. The fish, however, have short memories and after a quiet period will get active again or move back into the hole because of its good holding water qualities (after all, we anglers don't fish bad water!?!).

I also think this short memory contributes to an acclimation affect, in which the fish just gets used to all the commotion. Thats why the fish come back rather than vacate permanently.

I've also noticed that a struggling fish on a line can sometimes antagonize other fish into hitting. How many times have you observed two or three fish hooked one right after the other. But this aggressive behavior eventually switches to fear and the remaining fish either temporarily vacate or or just quit hitting for a time.

Related to this is the 'moving fish is always most aggressive' theory. When fish arrive in a new area, its most aggressive and will pick up. This goes for fish migrating in from downstream or fish that have been spooked from one part of the hole to another.

Add to this such intangibles as barometric pressure, water clarity, sunshine, etc., affecting the bite and you're bound to get this on and off activity at any high pressure spot.

Specifically regarding sonar detection, I think like any other disturbance, if its not severe enough to make the fish beat fins to the next hole, they'll get acclimated to it and eventually engage in suicidal behavior again.

Or I could be 150% wrong.

[This message has been edited by obsessed (edited 05-17-2000).]

Interesting topic!

In smaller, confined areas like you mention it seems like a reasonable possibility that FF's can disrupt a bite. I have no experience with FF's in a river situation but I do in the ocean and estuaries such as Buoy 10, Grays Harbor and Willapa Bay. Based on my experience in these larger bodies of water I think their effects are minimal to non-existent. In all of these fisheries, we have the fishfinder/depth finder on contiuously. More often than not, we are hooking fish directly under or very close to the boat. What seems to influence the bite here (more than anything) is the time of tide and strength of tide. We've also had some very hot bites in water 10-15 deep at times in these areas so I don't know that a FF has been a detriment us.

I would be curious to know if there is any science other than the magazine article to back up the topic. Intersting stuff.

The Field & Stream piece is in the Feb. 2000 issue. It is in a short subjects section (can't remember the page). I agree that it seemed more like a one observation experiment than being good science. That's why I wanted to get a consensus of opinion to help figure if they might be a detriment in some situations. I do think it certainly can't hurt for us fishermen to use them only where helpful & keep the FF's on the lowest intensity setting needed. - Steve