I have heard some of the Pros say that once you locate some fish, a school, some good structure you should turn off your depthfinder. The sonar signal is easily detected by fish and it can spook them or shut them down. I know a TM can sure alert them, but is the depthfinder really a problem?

I've also read that the sonor ping can spook the fish, however I think they would have to be exceptionally sensitive for sonor to effect them detrimentally. Just my opponion.

I use a low power unit (Eagle Cuda) most of the year for this reason. I think it makes a difference at times. When I fish deeper water I go to a more powerful unit Eagle 480 since I don't think it matters as much in deep water. If I don't need them to catch the fish I turn them off.

I run Lowrance units and turn them off when I'm up fishing shallow water. Not sure if it makes a difference, but I always do it just to be safe.

interesting stuff guys. I honestly never heard this before.

I fish a lot of deeper, off-shore structures in a clear reservoir for smallmouth bass. I find that shutting off the sonar can get you a few more bites. Especially if you've taken one or two off that structure and released them right away. The way I look at it, it certainly can't hurt to shut it off!

I never turn mine off

The only time mine are off is when the boat is not on the water (I forget that sometimes).

According to Lowrance a fishings ear is not capable of hearing sounds in the frequency range that sonars use so they can't hear it.

But I know a lot of good anglers that swear by turning them off when fishing shallow and/or in weeds.