Luftdruck und Angeln

Air pressure is the weight of the air above us. It is measured in hectopascals (hPa) and usually lies between 980 and 1040 hPa. High pressure tends to mean calm, clear weather, low pressure windy and unsettled weather. For fishing it is rarely the level that matters, but how the pressure changes.

Why would fish notice the pressure?

Many fish have a swim bladder, a gas-filled bladder that keeps them afloat. When the air pressure changes, the pressure in the water changes slightly and the fish has to adjust. The change is small compared with what a fish experiences when it moves a few metres up or down, so how much the pressure itself matters is debated. What is more certain is that the pressure follows the weather: falling pressure comes ahead of a front with wind, cloud and rain, and those are changes fish do respond to.

Rules of thumb many anglers stick to

• Steady pressure for a couple of days often gives even, predictable fishing. The fish have settled and follow their habits.
• Falling pressure ahead of a change in the weather can give a short spell of hard biting, especially for predators such as pike.
• Quickly rising pressure after a front, with clear skies and colder air, is often felt to be slow. The fish move to deeper water or cover.

Pressure and depth

A fish a few metres down is affected more by its own depth than by the air pressure, so the swings in pressure are felt most in shallow water. After a change with rising pressure and clear skies, fish often go deeper, and it can pay to follow: fish the edges where the shallows drop into deep water, and slow down.

Different species, different moods

Pike have a reputation for biting well as the pressure falls and the weather turns. Perch are often felt to be most reliable after a few days of settled weather. Trout and grayling in running water seem to care less about pressure and more about flow and temperature. These are experiences rather than laws, and they differ between waters.

Keeping an eye on the pressure

Look at the pressure in the fishing weather, and above all at how it has changed over the last day. A pressure curve says more than a single figure. The pressure is also saved with the weather whenever you log a catch or a fishing day. Over time you can see how your own water responds, and that is worth more than any rule of thumb.