Hummingbird Fishfinder interpretation

[JAL51974]

I thought I understood how this works but after yesterday I don't know!
this is an older Hummingbird, b/w display, depth, water temp, fish alarms with fish showing as little pics onscreen, etc.

We fished Lake Erie for the first time with this boat, too much waves to go offshore in the deep water for walleyes so hugged the shore for perch. I got a bottom reading around 30' then a secondary dark line at around 15' and at this line the fish suspended maybe 15 or so per page of display. I am confused about how to interpret this data: 1) the secondary line at 15' of water is that thermocline, weedline, what? No weeds to speak of when we retrieved lures though. 2) that suspended fish extended for miles along the shoreline at that approx. depth and despite throwing everything at them including live shiners and worms we couldn't get a bite---any suggestions or interpretations of the data? Bottom was sandy with small rocks all along that shoreline.

Unfortunately for us, the guys that did go offshore in about 50' of water, 5 mi. out limited out on walleyes yesterday. Arggh!

 

[fishmen111]

Re: Hummingbird Fishfinder interpretation

Odds are it was a thermocline. Try setting your sensitivity to a lower setting. At a lower setting, I bet you will see a lot of those "fish" disappear also At a high setting, any debris will show up as a fish and it sounds like it was a rough day out there

 

[jtexas]

Re: Hummingbird Fishfinder interpretation

When you have it set on "fish display", it'll draw a picture of a fish for most any echo return -- vegetation, bubbles, bits of debris drifting in the current, whatever. You'll do better with the fish display turned off, and learn how to interpret the echos yourself.

Were the "fish" behaving like the fish you thought they were? Schooling up, relating to bottom contours or whatever your Lake Erie perch do. Could it have been gar or carp (if ya'll have 'em) or whatever kinda Lake Erie fish don't bite? Or, maybe instead of individual fish, you were marking small schools of bait?

Whenever I'm marking fish that I can't catch, I try downsizing the bait first. Sometimes that works. Otherwise, I just call 'em carp.

 

[Silvertip]

Re: Hummingbird Fishfinder interpretation

Some locators trace a horizontal line at the depth it is interpreting the largest concentration of fish -- in your case at 15 feet. If that horizontal line moves up or down with the fish, that is not a thermocline but just a feature that you can (or should be able to turn on and off).

 

[JAL51974]

Re: Hummingbird Fishfinder interpretation

thanks for the ideas!

I need to correct a part of the information re. temp, the sensor was not connected so that "line" where the fish signs were suspended has nothing to do with thermocline reading on the fishfinder. Yes they were behaving like suspended fish. The sensitivity was one thing I adjusted several times on that trip. from +1, 0, -1 and in all cases that line of signs for fish showed up consistently. Schools of bait do show up on that unit but they are a different type of image. These could have been junk fish which do exist there- gobys and sheepshead but I didn't think those schooled up like that. Although the wave action was 2-3' swells offshore several miles, close in it was more like 1-2' and there was little/no floating debris. When I went swimming late in the day I was surprised how clear the water actually was.

this is a Hummingbird 405sx model, single beam

 

[jtexas]

Re: Hummingbird Fishfinder interpretation

The temp sensor only reads surface temp -- the water actually in contact with the sensor. A thermocline shows up on the screen because that's where tiny creatures congregate -- it's the deepest water where oxygen is at a comfortable level.

 

[JAL51974]

Re: Hummingbird Fishfinder interpretation

thanks for the clarifications!

I think I will play with this a little more without the fishfinder symbols turned on and see if I can get the feel of the unit and information display. Lowrance webpage has a good tutorial too about sonar technology and depth finders which was helpful. I do think that the fish line onscreen was the thermocline image with suspended fish, having reviewed the info on Lowrance site.

Joe