How Barometric Pressure Affects Trout Behavior

     When it comes to fishing, most people don't give the weather a thought other than for their own comfort. But, the same weather that makes us miserable also makes fish uncomfortable and therefore, knowing both the recent and present Barometric Pressure in your locale can help you to pick a good day to go fishing. The reason this information is helpful has to do with the atmospheric pressure and the fish’s air bladder (buoyancy compensator). The amount of pressure that the Earth’s atmosphere exerts as it presses down on the Earth’s surface is measured either in units called millibars (Mb) or inches of Mercury (inHg). Thus, as a general guideline for the continental United States, think of 30 inHg (1016 Mb) to be a normal level with 30.5 inHg as an extreme high and 28.5 inHg as an extreme low. Thus, because a higher or lower barometric pressure creates more or less pressure respectively upon the surface of the water, fish feel these changes in their swim bladder and it makes them uncomfortable. Consequently, a slight change +/- of just 0.02 inHg is enough to positively or adversely affect a fish’s feeding habits. Therefore, it is very important for a fly angler to be aware of the Barometric Pressure in their locale and how it affects both the weather and the fish’s habits and to use that knowledge to their advantage.

Affects of Change in Barometric Pressure