Upon asking a serious angler whether barometric pressure influences angling success, most will reply with an emphatic, “absolutely”. All information should be taken with a grain of salt and I am continuously reminded how trendy and naïve people can be with information, and trust me, after working at the Musky Shop, I’ve heard it all. If I believed half the things I’ve heard in the shop, I’d be fishing with my hat on sideways, one shoe untied, a lure with magic dust on it, and all with just the right amount of sun-block on at midnight. The things people say can be absolutely comical and some things downright disturbing. Don’t get me wrong, information can be extremely valuable, i.e. location and technique, but it’s important not to be a sucker.
A heavily accepted piece of fishing information that everyone seems to agree on is that when the barometric pressure is dropping or rising, the fish bite the best. At a glance, this theory seems to make sense because fish have a swim bladder that is filled with gas, and it regulates that amount of gas based on the surrounding pressures to match the environment. Therefore, anglers assume that when air pressure changes, the fish’s body changes, and their feeding habits change. Or people simply take the theory at face value without this bit of knowledge.
However, when this theory is dissected more, it becomes obvious that the pressure changes happening above the water surface cannot possibly be noticed by the fish, and the improved fishing conditions associated with a drop in mercury is more likely a result of the changing weather conditions associated with barometric pressure shifts, such as increased cloud cover or wind.
Let me explain. Pressure is expressed by scientists in terms of ‘atmospheres’, whether it is in the air or water. And atmospheric pressure is often called barometric pressure because it can be measured by inches of mercury in a barometer, typically around 30. When there is an extreme weather event such as a strong thunderstorm the barometric pressure can be as low as 28 inches, and during a high pressure system, as high as 30.7 inches. The difference in pressure therefore, can be about 2.7 inches, which equals about .09 atmospheres, from one extreme to the other.
In water, the pressure increases very rapidly, and at 32.8 feet beneath the surface the pressure is equal to double the pressure above the surface, or two atmospheres. Consequently, in the underwater world, moving up or down 1/10th of an atmosphere is equal to 3.28 feet. And 0.1 atmospheres is more change than the barometric pressure difference can yield between its two extremes of high and low pressure.
This means that when a fish moves up or down just 3.28 feet in the water, it is experiencing more pressure effect than it would from any amount of pressure fluctuations occurring above the surface. It is also important to understand that it takes hours for a typical cold front to change the barometric pressure, and that pressure difference is easily matched in just a few seconds by a fish simply moving up or down a couple of feet in the water.
It’s always fun to think the ultimate key to unlocking angling immortality lies with the mercury levels upon your wall, but the truth is that your barometer is a better indicator of the weather outside, not a secret devise that tells you when fish suddenly feel the need to eat.