Changes in pressure disrupt normal feeding habits. When the barometric pressure drops, trout feel less pressure on their swim bladders. This causes the bladders to expand, and trout become less hungry unless they move to deeper water for more pressure. As the pressure rises, more pressure is applied, so they look to relieve it.
As anglers, we know the weather affects our chances of catching fish. We may need help understanding the direct impacts, but different weather means different types of bites. Rain, clouds, sun, and wind impact how trout feed, but barometric pressure is a lesser-known factor. As the weather changes, the barometric pressure changes.
What is Barometric Pressure?
Barometric pressure is weight pressing down on the earth. At sea level, the barometric pressure is 14.7 pounds per square inch. As you gain elevation, barometric pressure lowers.
Our ears have ground-level air trapped inside, and as we change elevation, our ears pop to adapt to and equalize the pressure around us.
Not only does elevation determine the amount of barometric pressure, but weather also significantly impacts it. Warm air, increased humidity, or rising air causes low-pressure systems, which usually bring inclement weather.
High winds, precipitation, and cloud cover result from low-pressure systems. Low-pressure systems often bring in cool air once it passes through.
Cool air, less humidity, and sinking air create high-pressure systems. They bring sunshine and slightly warmer temperatures and tend to be consistent in their weather.
All of these changes in pressure impact how fish feed.
Barometric Pressure and Trout’s Swim Bladders
As barometric pressure changes, trout struggle to regulate their swim bladders. They move up and down in the water column to find a pressure that alleviates any extra pressure on their bladders.
If a low-pressure system is moving in, trout move to deeper water because there’s less pressure on their water bladders, and it expands. They’ll move deeper and stop feeding as much until the pressure regulates.
The opposite is true with a high-pressure system. The trout’s swim bladders feel the effects when the system changes from low to high pressure. The more pressure on their bladders, the shallower the trout move to try to get comfortable.
Trout know when barometric/atmospheric pressure will change, so they often feed as soon as it begins because they don’t immediately feel the effects on their swim bladders. Timing these changes isn’t always easy, but when you do, it’s an excellent time to fish.
Barometric Pressure and Food Sources
Small food sources like nymphs and larvae feel the effects when barometric pressure drops. They often have air bladders that keep them stuck to the bottom of a lake or river, but a sudden change can cause them to float up higher in the water column.
When this small drop happens, trout move into a feeding frenzy. They have easy access to food and know the pressure is changing.
Even if the pressure increases, fish move shallow to try and catch insects and other smaller prey that can’t adapt quickly enough off guard. The larger trout have an easier time feeding during the sudden changes because they don’t have to fight the pressure changes as much.
Fishing During Pressure Changes
A trout’s willingness to feed is difficult to predict in even the most consistent pressure systems. Take the pressure off to figure out when the fish might feed, but understand that the barometric pressure does impact their feeding habits.
High-Pressure Fishing
Trout feed differently in a consistent high-pressure system than when the system changes from low to high pressure. As a low-pressure system (precipitation, wind, clouds) leaves and a high-pressure system enters, the trout bite improves.
Trout move out of the deeper water into the shallower water and are more willing to feed in all levels of the water column. The low-pressure system isn’t keeping them down deep to regulate their swim bladders.
They don’t always feed immediately after a low-pressure system passes, but the bite usually improves within 24 hours. As the pressure changes from low to high, fish slower with smaller flies.
Give the fish time to adapt and work up their appetites. Usually, a change in pressure from low to high signifies a hatch is on the way.
If there’s been a consistent high-pressure system, the fish appreciate it. The fewer changes they have to endure, the better. However, high-pressure systems can come with consistently high temperatures and bright sunshine.
These high temperatures can heat the water, cause fish to become uncomfortable, and cause them to retreat to deep and cool water even though their bladders can’t handle it.
Wait for a low-pressure system to move to you, and then fish the change.
Low-Pressure Fishing
When the pressure switches from high to low, that’s usually when feeding is best. Sediment from the bottom of lakes, rivers, ponds, and streams stirs up, and insects get exposed. Fish large streamers and nymphs in an aggressive fashion.
Trout know a low-pressure system is coming, and once it hits, they hunker down and stop feeding for a while.
However, in that transition, you’ll find that trout feed aggressively. They don’t shy away from any of the larger baits you may throw their way.
Once that low-pressure system settles in, the fishing might be challenging. Precipitation, wind, and clouds already present enough challenges. Fish deeper, slower, and smaller.
Drift smaller nymphs and dead drift streamers. Avoid creating too much action. You should prioritize keeping your flies and lures looking natural.
During these times, the fish are uncomfortable and less willing to go after a large, appetizing meal.
Once these low-pressure systems start to pass, the fishing picks up again. For example, suppose you’re fishing a trout river in the Western United States. In that case, the low-pressure system may have dropped the surface water temperature a few degrees, making it far more comfortable for the trout to cover all levels of the water column.
Fishing in low-pressure systems presents challenges, but fishing before and after them is often a blast.
Frequently Asked Questions
Is Fishing Better with High or Low Barometric Pressure?
Usually, the transition from a high-pressure to a low-pressure system is the best time to fish. Trout know inclement weather is coming and their swim bladders will be affected, so they want to feed as much as possible.
How Does Weather Affect Trout Fishing?
The weather has a major impact on trout fishing. Because consistency is best, trout’s feeding habits change when the weather changes. Be prepared to switch up your methods, flies, and spots you usually fish.
When the weather changes, trout’s normal routines change, so it becomes more of a guessing game.
Even small changes in water temperature can trigger a feeding frenzy. A slight drop might make conditions more comfortable, whereas an increase can shut things down.
What Flies Should I Use in Low-Pressure Systems?
In low-pressure systems, use flies like Pheasant Tail Nymphs, Midge Nymphs, RS2s, Prince Nymphs, Hare’s Ear Nymphs, and Pat’s Rubber Legs. Smaller nymphs and streamers usually work better when the fish aren’t willing to feed.
What Flies Should I Use in High-Pressure Systems?
In high-pressure systems, you have more freedom with your fly choices. Usually, you can fish all levels of the water column, but you should stay higher. Dry flies like Elk Hair Caddis, Parachute Adams, and Chubby Chernobyls work well.
Also, suspended nymphs and non-weighted streamers like Woolly Buggers, Pat’s Rubber Legs, and unweighted Pheasant Tails do well.
Is it Safe to Fish in a Low-Pressure System?
If you’re not fishing in lightning or putting yourself at risk of flash floods, you can fish in a low-pressure system. It’s a good experience to learn how the fish react to these changes in conditions.
Conclusion
As trout anglers, we want every advantage we can get. Understanding barometric pressure and its impacts on fish is a slight edge we can gain on the fish. Remember, transitions from high-pressure systems to low-pressure systems are your best bet. Also, consistent pressure systems lend themselves to solid fishing. Stay aware, and you’ll have a good chance at landing trout.
