The weekend of April 16 and 17, 2016, is the perfect scenario to discuss how high and low air pressure affects fishing. Prior to this weekend, the crappie bite was phenomenal. This weekend, to put it mildly, just stunk. You couldn’t buy a bite. Well, how can it be? They were biting like crazy last weekend and now it is sunny and blue skies, when people want to get out and fish, and it has all changed.

Enter the barometer. Barometric pressure has a ton (pun intended) to do with how fish will bite. Now I’m not going to get all Mr. Science on you and explain millibars and post frontal, yada yada. I will put it in the simplest way I can to shed some light, though. High and low pressure systems are pretty easy to pick out. Blue-bird sunny skies almost always equal high pressure. Overcast and cloudy days, or a storm approaching, most always equal low pressure.

High pressure means exactly that: there is high atmospheric air pressure pushing down on everything. Humans have adapted over the millennia and are denser and don’t notice that. Fish, on the other hand, do. There are many ways in which atmospheric pressure affects fish. The most important one is their swim bladder. Imagine a balloon not completely filled with air. Take your hands and squeeze it. This has the same effect on a fish’s swim bladder. The expanding swim bladder causes them discomfort and forces them to find deeper water to stabilize their condition. This, in turn, shuts down their feeding mechanism.Low pressure, on the other hand, allows fish to swim more freely in the water column and makes them more likely to chase bait into shallow water.

High and low pressure has an effect on just about every living organism in the water, even zooplankton. The smaller bait fish feed off them and the larger fish feed off the baitfish. With high pressure in place, the zooplankton sinks to the bottom, and with low pressure, it floats higher in the water column. And thus the feeding buffet begins. So a slow day can turn into a memorable outing the very next day. And vice versa.

Now does that mean that a prolonged high pressure system lasting a week or so means stay home? Not exactly. Over an extended period, the fish will eventually stabilize and become accustomed to the pressure and will bite here and there. It will just not be as predictable where or when. It also should be noted that larger fish don’t feel the effects of pressure as much as smaller fish do. We have all heard stories about how there wasn’t a thing biting all day and then I got this trophy. So next time, pay a little attention to the barometer when you go out. Make a mental note: Hey I had a really good day, what was the barometer reading? Or the same with a bad day. Jerry’s Outdoors Show heard Friday mornings on KWPC AM 860 and 95.1 FM.

Contributed by Jerry Purviance