A thermocline is a band of water “in which temperature changes more rapidly with depth than it does in the layers above or below”1. Due to discontinuity in the acoustic impedance of water created by the sudden change in density, thermoclines can reflect active sonar and other acoustic signals. This is realized on fishing sonars and higher end fish finders as a thin band on the monitor2.
Boat fishermen and trollers in particular tend to target the area in or directly above the thermocline as this usually supports the most fish. This early in the year, no thermocline is visible on the sonar or at least it is indistinguishable from the surface clatter in the first 5 feet of surface water.
41 Degree Surface Temp. w/ Uniformly Cold water beneath.
So if you are looking for an early Spring thermocline you might be coming up blank, especially with this cold weather we have been having. As the weather warms though, expect to see a noticeable band on your sonar and expect it to get deeper and deeper as we move toward the summer.
