A fishing barometer is a tool that measures barometric pressure in the atmosphere. Anglers use them to help predict the times when fish might be biting. Studies seem to show that barometric pressure has a direct impact on the feeding habits of most fish, though the impact seems to be more pronounced in shallow water. This is believed to be because the pressure of water volume in very deep water probably outweighs the significance of barometric pressure in the air above the water.
Based on studies that measured the feeding activities of fish during various barometric readings, the optimum conditions for catching fish seemed to be when the fishing barometer has a reading of low, and the weather conditions indicate an approaching storm front. During this time, many fish are actively seeking food. Some fishermen advise speeding up lures, and using surface or shallow water lures during periods of low barometric pressure.
Fishing during stormy weather is generally not considered a good idea. Not only is it a safety concern, but fish behave differently during storms and they are usually not feeding. They can sense the changes in the atmosphere above the water, and they react accordingly. Some of the fish will flee shallow water during storms, so for fishing enthusiasts who insist on fishing during bad weather, they will probably have more luck fishing in deeper waters.
When a fishing barometer shows high pressure, and the weather is clear, fish generally are not as interested in feeding. Sometimes the fishing barometer will show a reading of normal, and during this time, fishing is generally normal, which is to say, chances of catching a fish are probably about even. This is not an ideal time for fishing, but it is probably better than periods with a high barometric reading.
The fishing barometer may be a useful tool, but barometric pressure is by no means the only thing that can influence the feeding habits of fish. Other factors play an important role, such as water disturbances, water temperature, and the cleanliness and clarity of the water. In addition, freshwater fish seem to be more affected by barometric pressure than saltwater fish.
Barometric readings seem to affect all animals to a certain extent. One theory suggests that during times when barometric pressure is low, there is slightly less available oxygen. This theory was the result of studies conducted on mice to measure their reactions to different atmospheric conditions.