Thread: Two Questions

Pretty good assessment Lowepro. I would just point out that most of what you describe is a direct result of a lack of dissolved oxygen. This is what you are seeing on sonar, the water is denser where the dissolved oxygen levels are the lowest, thus the harder return. The surface temp of a body of water will always be warmer than below the surface regardless of ambient temperature, seasons, etc., because heat rises. As Slade pointed out, there wont be much of a difference from surface temp to bottom temp in the Winter, so the oxygen will be more evenly distributed throughout the water column, allowing the fish to move more freely as weather patterns dictate. As the surface temps get warmer, the temps below the surface continue to drop. At some point, usually the point that sunlight stops to penetrate, the temps begin to drop at a much faster rate than the water above and below it. This is the thermocline. Water clarity plays a huge part in where the thermocline starts. The water above continues to be replenished with oxygen, while the water below continues to be depleted. This is why fish can be caught in as little as 6" of water when the water temp is pushing 100*. Oxygen levels can be so low in the main body of water, including rivers that haven't had much flow for an extended period of time, that the only place with sufficient oxygen is on a shallow bank or a large dock that has been pounded with waves.