January 06, 2021 7 min read

Barometric Pressure and Fishing: How Weather Affects Fish Behavior

There are tons of variables when it comes to picking optimal fishing times. Some anglers believe in fishing by moon phases, and others pay more attention to the seasonal changes. Regardless of how and where you find fish feeding, there's no question that barometric pressure affects fish behavior. 

Anglers and scientists have noted odd scenarios in which schools of fish gather together but do not feed or bite. Then, after a seemingly invisible shift, the fish go into a feeding frenzy. 

What changed? It might have been the air pressure, as barometric pressure and fishing have an exciting relationship. Along with tide, moon phase, water temperature and light levels, atmospheric pressure may affect your fishing trip.

Here's more about how barometric pressure can affect fish behavior. 

What is Atmospheric Pressure?

Barometric (or atmospheric) pressure is a force created by the weight of the air within the Earth's atmosphere. The Earth's surface temperature combined with the atmosphere's movement creates zones of either high or low pressure, which are continually shifting. 

What is Atmospheric Pressure

Most of the time, the barometric pressure at sea-level is 14.7 pounds per square inch, but this figure is an average. In reality, barometric pressure differs across the globe. Additionally, the atmospheric pressure at higher elevations is much lower than the sea level pressure, mainly due to fewer air molecules at high altitudes.  

Barometric Pressure and the Weather

Atmospheric pressure directly affects the weather. As the pressure rises and falls, there is a corresponding and predictable change in the weather. 

When the meteorologist on your local news station describes high and low-pressure systems, they are referring to the effects of atmospheric pressure. 

Just like gravity affects water flowing from the highest to the lowest points, air flows from high-pressure areas to low-pressure areas. This movement intensifies weather conditions in low-pressure areas and pulls air out of high-pressure systems.

Meteorologists often use variances in air pressure to detect storms and track weather patterns. Using a series of data buoys across the oceans, meteorologists from the National Weather Service keep track of tropical storms, monsoons, typhoons and hurricanes. 

A barometer measures shifts in barometric pressure to foretell any drastic changes in the weather. A Torricellian barometer is a transparent glass tube that rests in a pool of mercury. When air pressure pushes on the mercury, it begins to rise up the tube. The higher the mercury goes up the tube, the higher the air pressure. 

How To Measure Barometric Pressure

Serious anglers need to understand how scientists measure barometric pressure in order to comprehend how it affects fish. 

barometer

Atmospheric pressure is measured in a variety of units. For example, meteorologists generally record air pressure in millibars, or mbar. You might also come across hectopascals, or hPa. The World Meteorological Organization uses hectopascals as its official unit of measurement. Luckily, the conversion between mbar and hPa is the same, so 100 mbar equals 100 hPa.

However, the U.S. measures atmospheric pressure in inches of mercury or inHg. If you're using an American weather app on your phone, it might give you air pressure in inHg, but everywhere else, you will probably find it in hPas. 

The standard average pressure across all units of measurement is 1013 hPa or 29.92 inHg. Anything below these numbers is considered low pressure, whereas anything above is high pressure. To put this in perspective, a dip into hurricane-inducing low pressure reads at 27.3 inHg, and a typical high-pressure, cold air, winter front may read as high as 30.7 inHg.

Warm, wet, turbulent weather such as hurricanes, rainstorms and extreme tropical waves results from a low-pressure system. A dip below 28 inHg means gusty, wet weather with winds out of the east or northeast. High barometric pressure usually occurs right after a low-pressure front passes through, which corresponds with the bright, calm days after a storm.

The more significant the difference between the air pressure of two systems, the stronger the wind speed.    

Barometric Pressure and Fish Physiology

Since weather conditions have such a dire effect on fish behavior, atmospheric pressure will have a similar outcome. Much like the mercury in a barometer, fish are incredibly sensitive to barometric pressure. 

Bony fish, as opposed to cartilaginous fish, have an internal gas-filled organ called a swim bladder to help them control their buoyancy and stability. The swim bladder allows them to stay at specific depths without using too much energy swimming. The fish's swim bladder adjusts to the pressure and allows it to ascend or descend. 

Many anglers have experienced being out on the water, seeing tons of fish, but not getting any bites. Although there aren't any conclusive studies, many scientists believe that a change in barometric pressure results in pressure on the fish's sensitive swim bladder, making it feel uncomfortable. 

When the air pressure drops, the fish will feel less pressure on its swim bladder, which will then be able to expand uncomfortably in its body. Fish will move to a lower water column or absorb extra gas into their bladders to make up for this pressure drop.

While they're experiencing the change in air pressure, fish are usually not driven to feed. They're more interested in finding a spot at a low enough depth to relieve the air pressure on their swim bladders. 

Not All Fish Are the Same

Changes in barometric pressure exert different amounts of force on different fish. Fish with larger swim bladders, such as Trout, Grouper and Snapper, feel these effects more stringently. Fish with smaller bladders, including Barracuda, Kingfish, and Mahi Mahi, are not as affected by minor fluctuations in pressure. Thus, these fish do not change their behavior as much as others.  

Air Pressure and Swim Bladders

Other fish such as sharks, rays and some tuna species do not have swim bladders, making it less likely that barometric pressure will change their swimming and feeding behavior. 

Using Air Pressure to Find Feeding Times

All of this information can help you better your chances of fishing success. If you're a savvy angler, you probably already use water temperature, moon phases and seasonal changes to dictate when and where to fish.

You can add one more discerning factor to your repertoire. In the same way that you equip yourself with performance fishing gear, you can use tools to find your fish by reading the barometric pressure. 

Fish usually prefer to feed during periods of stable high pressure. When a cold front begins to arrive (often preceded by low pressure), the fish sense a drop in barometric pressure and start to feed furiously. 

As the air pressure drops, feeding ebbs and the fish search out the depths to stabilize their internal organs. 

Once the low pressure has moved out, and another high-pressure system is in effect, it will take between 24-48 hours to see another fierce feeding frenzy. 

Adjust Your Techniques

You can adjust your fishing locale to suit the pressure and hopefully find fish. If the barometer dips below 28 inHg, try fishing in deeper waters because the fish may be holding at a deeper level than usual. 

The behavior of the baitfish may also be a factor. A falling barometer may force bait to be less active or to maintain at a deeper level. The fish that feed on those baitfish may follow them to lower depths.

Here are some other weather conditions and how they might affect your favorite fish.

How weather might affect your favorite fish

Extreme High Pressure

Much like low pressure, too much air pressure will decrease your chances of a bite, and bait will stop coming close to the surface. 

Sea and waterbirds are indicators of barometric pressure, too. When the barometer is above 30.0, most birds merely float on top of the water. 

Fish will most likely stay near the bottom and feed halfheartedly. If they're tempted by anything in an extremely high pressure, it'll be dead or cut bait that presents as easy prey. 

High-pressure systems are typically associated with bright, sunny weather. Make sure you pack appropriate sun-protective accessories such as a fishing gaiter, visor and sunglasses to minimize sunburn and glare. 

Extreme Low Pressure

Like very high air pressure levels, most fish won't be too vigorous in extremely low pressures, with a few exceptions.  

mullet fish

Mullet aren't as affected by low pressure as they are by high pressure, and birds will be in the air instead of on top of the water. 

You may spot some fish swimming around, but they will be more nervous and spook easily. Any strikes you get during extremely low pressure will probably be from a distance. 

Rising Pressure

Whenever you have moving pressure systems, you'll have good luck fishing. The fish will sense that the air pressure is rising or falling and feed heavily for the following days. Fish will hit lures in these conditions but may be wary of topwater plugs. 

Anglers have also found that fish may gather in one area the whole day in this type of pressure condition. They are a bit more nervous than usual, so they generally return to the same area if you spook them.

When the barometer gets above 30.2 inHg and you see your strike ratio start to decline, switch to plastics or jerk worms. 

Falling Pressure

A favorite of many anglers, fish in these pressure conditions will engage with topwater lures once again. 

Fish like to move when the pressure falls, and you can sometimes spot schools of fish working their way along a shore or coast.  

During falling pressure systems, you are likely to encounter wet weather, so be sure to outfit yourself with the right fishing gear, including a rain jacket with taped seams and a storm flap to keep out the wind and water. 

Shop Huk Rain Gear

Stable Pressure

When the barometric pressure is stable, you may be able to drift over fish with your boat. Unfortunately, as they aren't interested in eating, you are unlikely to get a strike. 

The good thing about stable pressure is that it never lasts for very long, and it will start to fluctuate soon. Thankfully, the fish's behavior will change along with the pressure.

Fish tail

Final Thoughts

You may have many tools in your figurative tackle box to help you understand the optimal time to fish and where those fish will feed. You can use the lunar phases, water temperature or light levels to make predictions. But, one more weapon in your arsenal is barometric pressure. 

By keeping an eye on your fishing barometer, you can see when the mercury is rising or falling, and this will, in turn, let you know when the fish are liable to be active and hungry. 

Many anglers claim that the best pressure to fish is between 29.95 and 30.05 inHg. To find your ideal spot, bring a barometer when you plan your next fishing expedition. The more you know about your prey, the more luck you'll have hooking them.

Huk makes great gear for anglers by anglers. Explore our range of performance fishing apparel and gear up with high-quality clothes and accessories. 

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