How Does Weather Affect Fish Behavior?

Fish can be mystifying creatures but they do have reasons for how they behave.
One of these is the change in the weather.
Different species of fish react differently to certain kinds of weather or air pressure.

If you like to fish, knowing their habits will assist you in knowing what kind of fish to try for, when to try, and sometimes even what kind of bait to use.

Fishing in Rainy Weather  -  Windy Weather  -  Hot Sunny Days  - Cold Winter Weather - Barometric Pressure

Fishing in Rainy Weather.

Fish are just like people in that they prefer certain kinds of weather conditions over others.
Some fish hate the rain and wind and will go deeper under water.
Others such as bass, trout and sunfish are insect-eating fish.
When it rains, insects get knocked into the water, so these fish will be biting more and staying close to the surface in a downpour.

Fishing in Windy Weather.

Fish like large mouth bass will come closer to the banks if it is windy. This is because small bait fish such as sunfish will be pushed toward the bank with the wind, or will follow insects blown to the bank. The bass eat the small fish that are in turn eating the insects. On large lakes a Constant wind can stack up water on the banks the wind is blowing too causing a change in depth and temperature.

Fish Behavior on Hot Sunny Days

Contrary to popular belief, nice weather is not always the best fishing weather.
On hot days, fish can become listless.
Since there are not as many insects buzzing the water because of the heat, fish usually go deeper into cooler waters.
This is one of the reasons why people tend to fish early in the morning or early in the evening during the summer.
When a cold front is coming in and begins to displace the heat, fish will bite more than any other time.

Fish Behavior in Winter Weather.

Fish feed in cold weather, being cold blooded their metabolism slows and they tend to feed less.
Fish will go after slower and smaller baits.
Bass tend to stay to the top more because they like to follow moving food.
All fish are more sluggish in the cold, so they follow slower trolling baits and bite less often.

Barometric Pressure.
Many fishermen believe good or poor fishing can be determined by the level of barometric pressure.
At any given time, barometric pressure is either stable,  rising or falling.

One of the least-understood factors affecting fish and fishing is barometric pressure.
It may get a little ink or lip service now and then, but few people do more than scratch the surface of this important piece of the fish-behavior puzzle.

Changing barometric pressure stirs up fish in their habitat by changing the buoyancy of low-level food items such as plankton.
Small fish follow the plankton, larger fish follow the smaller fish.

Compared with changes in hydrostatic pressure (water pressure up or down within the water column) barometric pressure changes are very slight and not likely to be felt directly by the fish.

Experts say fish likely are not reacting to barometric pressure changes but rather the effects of weather on the water.

Weather following a change in barometric pressure can change light levels, water temperature and other factors affecting fish behavior.

Fisheries biologist and tournament angler Roger Hugill says, "An extended period of stable weather allows fish to find their comfort zone---a balance of the right water temperature, oxygen, light penetration and other factors---and fuels a nice, steady bite."

A guide to how barometric pressure affects fish and fishing

Have you ever caught fish like an all-star one day and bombed the next, even though you were using the same tactics and fishing the same area?
You're not alone. It's a common and often frustrating fact of fishing.

What makes a red-hot bite turn to ice?

Many factors may contribute to the fact fish quit biting.
Fishing pressure, boat traffic and weather-related changes in water conditions can all cause forage species and predators to alter their locations and behavior, causing a productive fishing pattern to fall apart faster than you can say,
"Should have been here yesterday."
But change doesn't have to be a bad thing, especially if you understand what's going on in that mysterious, watery realm beneath the surface.

"Everything in the water either sinks, floats to the surface or suspends," says Fisheries biologist Roger Hugill
"Few anglers give it much thought, but a change in barometric pressure is to a small degree like a change in gravity."

Because objects weigh less in the water, the affect of a pressure change is far more pronounced beneath the surface than above.

Here's how it works. In simple terms, barometric pressure - or atmospheric pressure - is the weight of the air pressing down upon us.
 
A 1 - inch-square column of air, measured from sea level to the top of the atmosphere, would weigh about 14.7 pounds.
Multiply that by the surface of your favorite fishing hole and you've got serious pressure.
So much for lighter than air.

Fish, anglers and other living creatures are created to handle this pressure. But changes in pressure can ignite major shifts in fish behavior.
Understanding all the dynamics is the key to playing this wild card to your advantage.

One is fish react to pressure changes more than most fishermen realize.

"Fish are extremely in tune with their environment,"  Hugill explains. "They have an incredible array of pressure-sensing systems such as the lateral line - that key them in to changes in barometric pressure, which in turn could signal feeding opportunities or foretell the arrival of a major weather change."
How game-fish react depends on what affect variations in pressure (and accompanying factors such as fluctuations in water temperature due to a warm or cold front are having on their food supply and the world around them.

For example, a drop in pressure can cause tiny particles of sediment and other material to float off bottom or rise higher in the water column than they normally suspend - particularly when currents are involved - slightly reducing water clarity.

But more importantly, it can affect tiny creatures such as zooplankton and phytoplankton - the building blocks of any respectable aquatic food chain.

"These organisms need to move up and down in the water column in response to changes in light intensity and other factors, so they have built-in mechanisms for maintaining buoyancy," says Hugill.

Some have tiny air bladders. Others possess the ability to retain air as a means to regulate their position in the water. "They're generally able to adjust to variations in barometric pressure, but a fast change can catch them off guard, making them slightly unstable."

This can push algae, phytoplankton or zooplankton out of its comfort zone and make it more vulnerable to predators. In some cases, gamefish such as crappies may move in to feed on zooplankton, but often a parade of forage species ranging from bloaters to shiners and dace - depending on the fishery - may also show up to feast on destabilized prey.
Larger predators follow to sample the baitfish buffet.

Most catchable-size fish aren't phased by the change in pressure. If anything, they're stoked by it. "The physical affect on bigger fish is less pronounced," Hugill explains. "Bass, walleyes, pike and other larger fish are built to handle it, and the changes in pressure are small compared to their overall size, mass and ability to swim."

Plus, these fish are used to adjusting to pressure at depth - related pressure changes as they travel up and down in the water column.
If you've ever jumped into a lake or pool and had your ears "pop," you know that pressure is greater the deeper you go.

"If a fish is neutrally buoyant three feet beneath the surface, then swims down to 10 feet it won't suspend anymore - it will sink - so it has to adjust, "'Hugill says.
Compared to these depth-related pressure changes, a slight rise or fall in the barometer is easy for a bass or walleye to handle.

All of this helps explain why a rising or falling barometer often signals good fishing.
Now is the time to be on the water, fishing known feeding areas with aggressive tactics.


It's worth noting that fish and other creatures living in shallow water are more susceptible to the affects of changes in atmospheric pressure than their deep - water counterparts.
So a bluegill holding in five feet of water is more susceptible to changes than a Striped Bass 60 feet down.

The Down Side

Right now every experienced angler reading this is probably thinking, "If a rise or fall in barometric pressure heats up the fishing, why does the action go south when a low-pressure system - especially a dreaded cold front - passes through?"

That's a good question.

The answer has more to do with the after - effects of the weather system than changes in pressure.
"Falling barometric pressure makes tiny aquatic creatures unstable - which can make baitfish more active and trigger a flurry of activity in the entire food chain. It also alerts fish to the approach of a weather change,"
says Hugill.
"Bass, walleyes and other gamefish often react by feeding before the rain or storm arrives.


"But once the weather changes, its effects trump lingering variations in atmospheric pressure," he continues. "For example, in the spring, when a cold front arrives and air temperatures drop, strong winds can push cold surface water into a warm bay where fish are active. The water temperature will drop and fish become less active."

Indeed, fish may pull out of chilled shallows to sulk along the nearest drop-off or in the closest deep hole.
After the front passes and the water begins to warm again, they will move back in and become more active.

"On the other hand," he notes, "a cold front in August can trigger an increase in fish activity.
I've seen sluggish walleyes on mid-lake reefs come alive when a cool front lowered the surface temperature by even a few degrees."

Some fisheries are more vulnerable than others to rapid water temperature changes.
"Rivers can really change a lot, up to 8 or 9 degrees a day," Hugill points out. "Small feeder streams can change even more."

Other factors besides water temperature can be involved, of course.

Light intensity

Due to wave action, cloud cover or water clarity - can have a huge impact on the feeding behavior of species like bass and walleyes.

The amount of light passing through the water can also affect how baitfish and predators position themselves in relation to cover or structure. "When conditions are right (such as when the water is clear and warm), cloud cover can pull fish into the shallows," Hugill says.

"In the end, the key to success is figuring out what the weather is doing to the area of a lake or river you're fishing, then alter your fishing tactics accordingly. A drop in water temperature may call for smaller baits and slower presentations, or seeking out areas where the fish are less affected."

Stable Pressure

We've talked much about the effects of change, but some of the most consistent fishing times comes when the barometer is steady, especially for several days or more.

"An extended period of stable weather allows fish to find their comfort zone - a balance of the right water temperature, oxygen, light penetration and other factors - and fuels a nice, steady bite," Hugill grins. "And that's something we all like to see."

How fish react to fishing pressure, a new study on brown trout offers clues.

To gauge different responses to angling pressure between heavily fished and relatively untouched populations, biologists measured the catch rates and various behaviors of brown trout in two backcountry New Zealand rivers.

The Ugly River is a wilderness stream accessible only by hiking 10 hours through untracked and difficult terrain.

The second site was the Owen River, which is easily accessed by road and has high fishing pressure for a backcountry river. Both are 50 to 100 feet wide, provide the same habitat, and have similar densities and size structures of brown trout.

Teams of guides and experienced fly anglers methodically fished similar stretches of each river on four three-day trips.

In 12 days, 157 browns were caught on the Ugly River, 51 on the Owen. The fish represented 43 percent of the Ugly River's estimated population of browns and 11 percent of the Owen's population. Fish in both rivers averaged about 3.8 pounds.

Both the number of trout seen and hooked declined on successive days of each three - day trip on the Ugly, presumably because fishing pressure pushed the browns tight into cover. Researchers allowed two to four weeks to elapse between each three-day fishing trip, and noted that trout sightings and catches returned to high levels on the first day of each trip.

 In other words, fish responded to angling immediately, but the effects on trout behavior disappeared after two weeks.

On the more pressured Owen River, the numbers of fish seen and hooked were much lower on the first day and did not change during successive days of each trip.

Also, the trout in the Ugly River were less likely to be spooked, more likely to be caught on the first cast, and overall required fewer presentations. Fish in the Owen that did not spook were more likely to remain at their feeding station while anglers cast to them.

What It Means
Relatively un-fished brown trout are less angler-shy and more vulnerable to capture. But the "virgin waters" effect is short-lived. As was apparent in the Ugly River, a single capture drastically changes a fish's behavior.

Whether this response is learned or has a physiological basis - such as elevated levels of stress hormones or the depletion of energy reserves after capture - is not easily determined, but the effect lasts several days.

There was also a "chronic" effect of fishing in the Owen's browns. The trout were less visible and less catchable. And, while fish occupying visible feeding stations were less likely to spook, they were also less likely to take a fly.

Do these findings apply only to brown trout in New Zealand streams? I doubt it. Fish in small, clear streams are highly vulnerable, but dozens of anglers fishing even a large lake or reservoir day after day can "educate" a lot of fish.

I commonly hear fisheries management biologist who try to maintain large populations of quality fish lament the effect of "increasingly skilled anglers" and how technology has raised angler efficiency.

There is little doubt that angler skill and efficiency is increasing, but we may be wrong in assuming that the fish don't change, too.


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