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Seeking Thermal Refuges
Story by "Triton" Mike Bucca

May/June 2005

One of the benefits of being on the water about 200 days a year is being able to actually observe the fish as they move from one seasonal pattern to the next. There are quite a few telltale clues that tip off experienced anglers to the beginning or end of a seasonal transition. Water temperature is one of the most important of these clues.

I believe water temperature is everything when it comes to finding and catching bass consistently, and that a temperature gauge can be the most valuable piece of electronic equipment ever put in a bass boat when it comes to finding active fish. This is especially true during seasonal transitional times, and a temp gauge is always an important tool to help you locate thermal refuges that hold fish.

As a spotted bass guide in the Metro Atlanta area, one of the most frequent questions I get at seminars or guide trips also happens to be the most popular question in all of bass fishing - Where are the fish and how do I find them throughout the year? You can own every lure and have the best of fishing skills and equipment but it won’t help you if you aren’t fishing where the fish are.

To assist in finding fish you need the answers to two basic questions - what time of year and what the current water temperatures are. Water temperature is important because it’s the medium that surrounds the fish and defines its environment. Any change in that medium (water) causes the fish to react. With the knowledge of water temp and season it’s not difficult to eliminate a lot of water and narrow things down to a few basic techniques and bait choices. Under normal circumstances and by knowing the water temperature you can also make assumptions on the activity level of the fish.

Water Temperatures-Bass Activity Level

Bass are a cold-blooded species, meaning that their body temperature is strictly regulated by the temperature of the water, a familiar concept when it comes to fishing. To catch fish in the wintertime, when water temperatures are low, lure presentations must be slow and methodical as cold-blooded fish (bass) are slow moving in those conditions. Likewise, springtime brings increased air and water temperatures and increased fish activity. During these months fishing action may be fast and furious as warm-water fish species such as largemouth bass thrive at their near ideal body temperature and metabolic rate.

The key thing to remember about water temperature and how it relates to bass activity level is that cold-blooded fish are always looking for ideal water and body temperature. They want to be comfortable, or as comfortable as they can get given the conditions that they are given.

Thermal Refuges

I have found that temperature changes are most important during seasonal transitions, spring to summer, summer to fall, etc. In a lot of ways bass are similar to humans when it comes to climate control - when we get cold we turn on the heater, and on those hot summer days we reach for the AC controls. Of course bass don’t have the luxury of flipping on the AC or heat, but they can take advantage of thermal refuges.

Thermal refuges are pockets or layers of water (both hot and cold) that bass seek for comfort depending on the time of the year. For example, the thermocline is one type of thermal refuge – in my area the thermocline is most predictable and productive during summer and early fall. A power plant’s hot water discharge is another type of thermal refuge, one very popular with the bass during the winter.

Sunny Shorelines

Here in North Georgia our water temps seldom go below 38 degrees, so forget the ice out parties. Our winter patterns usually revolve around fishing deeper and fishing slower than a dial-up Internet connection. Obviously, the fish are seeking warm thermal refuges. When you get a bright sunny day during the colder time of the year you’ll find quite a few fish feeding and sunning themselves on riprap, and taking advantage of the warmer water created by the sun’s rays reflecting off the rocks on the riprap.

There are a few keys to remember about shallow thermal refuges during the colder months. Shallow water warms faster than deeper water, there’s less depth for the sun’s rays to penetrate. Muddy/stained water warms faster than clear water as the sun’s rays reflect off the suspended dirt particles in the muddy/stained water which in turn creates heat. Rocks, pea gravel, and ripraps are all good conductors of heat when the sun shines on them. The bigger the riprap or pea gravel flat, the more heat it can hold which makes it a better thermal refuge on most occasions.

In most lakes the northwest shoreline (or southeast facing shorelines) warms up fastest due to the sun’s rays hitting those areas first at sunrise, and most directly during the shortened days. For most of the colder months I start off by fishing shorelines on the northwest side of the lake, preferably those that have riprap (my favorite) and pea gravel, and that are relatively shallow with stained water (if I can find it). Give your area extra bonus points if it’s on a main lake point or secondary point, and is near a deep underwater channel. Being near deeper water makes it easier for the fish to just slip up to feed, and when a cold front comes through all the fish have to do is slip down into the deeper water.

Here’s a little tidbit about fishing during the colder months – a one to two degree temperature variance can be very significant to a bass. Obviously, the greater the temperature variance, the better the chances are that a thermal refuge will hold bass. Even when you can’t find a three to five degree difference, don’t write off a one to two degree variance.

Another factor to keep in mind about winter time fishing is that the wind does funny things to the surface water temperature during the colder months. It’s possible for a strong wind to push colder water to the east side of the lake, leaving the west side of the lake significantly warmer, and that change has nothing to do with the location of feeder creeks. Keep an eye on your temperature gauge to capitalize on those weather generated temperature changes.

Hot Water Discharge

There are literally thousands of hot water discharges generated by power plants and large manufacturing plants, and they’re dotted all over our lakes here in the United States. The only thing to remember about hot water discharges in the winter time is that they are fish magnets! The fishing can be fast and furious, even during the coldest months of the year. You can actually fish for spawning fish in January in many places due to the vast temperature variances in the discharge areas.

Your main lake temperatures may be in the 40’s, while at the discharge you might have 70-80 degree water temperatures - that 40-degree difference causes a serious migration of fish to the area for their comfort. The one danger about fishing a hot water discharge is fog, dense fog - when 30-degree air temperatures mix with 70-degree water it creates a fog wall so thick you may not even be able to see the steering wheel in front of you. That can cause some serious boating accidents if everyone is not carefully practicing safe boating.

Thermal Stratification

Once post-spawn is complete and you move toward summer time patterns, the fish start seeking cooler thermal refuges vs. warm thermal refuges. The thermocline (also known as the metalimnion) is one of the most well-known types of thermal available to the bass during the hot summer months. The thermocline is defined as a layer in a large body of water that sharply separates layers of water differing in temperature, so that the temperature gradient across the layer is abrupt.

In most areas the thermocline starts to develop in the early parts of the summer. A big misconception is that most people believe the thermocline starts developing in deeper water. The thermocline actually starts to develop at the surface, and the cooler, denser water slowly sinks deeper as the season progresses into late summer and early fall.

There are three layers to thermal stratification. The upper portion is known as the Epilimnion, the middle layer is the thermocline (located within the Metalimnion), and the bottom layer is the Hypolimnion.

As you look at the temperature graph to the right of the figure above notice the near constant temperatures in the Epilimnion (top layer) and the hypolimnion (the bottom layer). The thermocline is where you have the greatest temperature change. You also have an increase in dissolved oxygen compared to the other levels, which is another reason why fish seek the thermocline level during the stratification period.

The thermocline can easily be found by using a drop down temperature probe such as the Pro Catch Plus, available at Bass Pro Shops. This temperature probe eliminates the guess work on what depth levels to concentrate your efforts. The only thing to do is to find the concentrations of fish within the thermocline level.

Inflow Refuges

Another summer thermal refuge is what I call an inflow refuge. Now we’re getting down to the real nitty-gritty, the holy grail of honey holes and one of my prized secrets for catching fish during the heat of summer, without risking molestation by the crotch rocket traffic. I grew up in South Mississippi and fishing inflow thermal refuges brings back some of my childhood memories about creek heads, beaver sloughs, and swamps off the Pearl River.

In a nutshell inflow refuges are where cooler water enters the main lake via creek heads. I consider creek heads to be creeks where you can travel all the way upstream to the point where you can go no farther. What you are looking for in the creek heads is a temperature variance compared to the rest of the lake.

Most mountain lakes are known for having multiple inflow refuges, and where natural springs and running streams enter the main lake is typically a dynamite area during the summertime. Such streams/springs are normally quite a bit cooler that the general lake temps where they empty into the creek head. Many times you can narrow down which creek heads have the best inflow thermal refuges by looking at a contour map.

Creeks that show that they have steep sides above the creek head (contour lines close together), are usually spring fed (cooler water) and will be worth the boat ride to give them a try. Another good indicator is a state map, if one is available, that shows all the trout streams in your state. If any of those creeks empty into your lake there is a good chance that creek head will qualify as a good spot to try. Most trout can’t handle temperatures above 55 degrees, so that qualifies a trout creek as a spring-fed creek.

Creek heads vary widely in size, from the size of a large river down to a small trickle that you can barely push pole your way into. There can even be waterfalls or drainage pipes emptying into a creek head, and beaver dams create excellent inflow refuges. Obviously the greater the temperature variance the better, and the smaller the thermal refuge in size, the more concentrated the fish will be.

Fish found in a creek head are usually sitting in a current break or eddy, waiting for an easy meal. You will find that the current, no matter how slight, will make a tremendous difference in the action of the bass. Current offers both elevated oxygen levels and cooler temperatures - you will usually find that where there is current, the bass stay shallow.

Not only is the flowing water cooler, but it also creates a natural ambush point for bass awaiting an easy meal. Those fish are normally fairly active and don’t require a lot of coaxing to bite, that is, until you educate the ones that are there when you set the hook on a few of their friends. As a side note, inflow refuges usually replenish themselves with fish fairly quickly. So if you catch a few fish in such an area, go back in a few hours and you can usually catch a few more to finish out your limit.

As a guide, a good temperature variance for an inflow refuge in the dead of summer is usually four to ten degrees less than the warmer main lake temperatures. Of course not all creek heads are productive - use your trusty temperature gauge as your guide and look for big temperature variances. Every little trickle, no matter how small or how big, deserves a shot with your temperature probe before you write it off as unproductive. (run Bucca 1 print here)

One drawback to fishing inflow refuges is that they are usually spread out and almost always at the extreme back end of the creeks – with gas at today’s prices you may need to apply for a bank loan to fish them all. But by far, inflow refuges are my favorite spots in the summer. Most anglers don’t put forth the effort to get to these out-of-the way places, possibly the reason why they are as good as they are.

In the back of the creeks on weekends you’ll usually be away from most pleasure boaters and jet skis, so you normally won’t have to doodle a four-inch worm in 20 feet of water just to get bit. Fast-moving reaction baits will work - Lucky Craft flash minnow 95 and 110 jerkbaits, CB 200 cranks, and spinnerbaits are a few of my favorite lures for these areas. I usually work my way to the back of the creek using a fast presentation, and then on the way back out I slow down and fish a weightless Senko or pitch a Fat Ika or 7X Kut-Tail worm to pick off any stragglers that I missed on the way in.

After fishing inflow refuges for over 20 years I’m still surprised at how small a creek can harbor some very big bass. Turn the dog days of summer into the hawg days of summer by giving some of those inflow refuges a try.

Shade Refuges

When I was growing up (my wife thinks I haven’t quite made it yet) my friend had a waterslide on his dock at the local lake. On those hot summer days it felt so good to take a slide off into the lake. That dock with the slide on it had a covered boat slip with a stepladder inside the boat slip. I remember the water in the shaded boat slip was several degrees cooler than the un-shaded water only a few feet away.

On a few occasions, I have actually seen bass in shallow ponds relate to the thin shade provided by a power line that casts its shadow across the pond. Several bass were actually lining themselves up horizontally with the power line shadow to take advantage of the cooler water in that narrow area. These are both great examples of what anglers call the shade pattern during the summer months of the year.

Shade refuges come in many different forms - boat houses, piers, stumps and laydowns are probably the most common forms of shade makers. A stump, for example, only offers a limited area of shade in midday, but a big laydown tree or a boat house offers gobs of shade, no matter what the angle of the sun happens to be. For that reason it’s no surprise that they are very productive, fish holding areas during the summer months.

Grass and lily pads are also a major form of a thermal refuge. The covered boat slip example is the same theory as why grass beds and heavy pads are great fish producers during the dawg days of summer. I’ve lived near Lake Guntersville near Huntsville, Alabama for several years, where the shade grass pattern doesn’t really start until the grass gets matted thickly on the surface. And the hotter the air temps and the more $%*!%$ gnats you have, the better the fishing gets. On Guntersville it’s a given that the fish are relating to the grass in some shape or form. The absolute key to catching fish in the grass is to find out which grass beds are holding the best concentrations of fish.

My home lake is somewhat of a mini canyon-type lake, with quite a few steep bluff walls. If your lake doesn’t have grass, or is surrounded by Corps of Engineer land and/or a Wildlife Management Area which allow very few if any houses or piers, you’ll need to find other sources of shade. I often rely on the shade lines at the base of the bluff walls. If you have several rows of bluff walls facing different directions, you can fish the shaded bluff wall pattern all day long. Once the sun rises to the point where the shade is gone on one particular bluff wall, just crank up and find another wall on the opposite side of the lake and fish the shaded areas there.

Here is what I’ve done to refine the bluff wall pattern even further. Bluff walls are known for holding fish 365 days a year due to their proximity to deep water. In the morning a big bluff wall will typically have a huge shaded area. As the morning progresses, I look for a bluff wall where the shade hugs close to the bank. What I look for is a bluff wall with a shade line that is maybe five feet wide, or less.

When you have a big shaded area, 15 feet wide or more, all of those fish are swimming around in that 15-foot zone. As the sun rises the shaded area gets smaller and smaller. What this does is concentrates the fish into that smaller shaded area, which in turn makes it easier for me to get my bait into the strike zone, maximizing my efficiency and chances of getting bit. Another key to fishing this shaded bluff wall pattern is to find out what time of day each bluff wall has the thinnest amount of shade in front of it and plan your tournament attack on those specific walls based on those peak “shade times”.

Regardless of the season, water temperature is everything to a bass, and plays a major part in not only how to fish for them, but most importantly where to fish for them. Throughout the year I make detailed notes on not only when the transitions start, but also when they start tapering off.

The yearly life cycle of a bass is repetitious and when certain key water temps are achieved, fish patterns repeat themselves over and over, just like clockwork. The tips in this article are the rules of thumb I use to put my clients on fish on a consistent basis. Water surrounds a fish on every square inch of its body. If the fish isn’t comfortable it will seek out thermal refuges. Catching fish is easy, finding them can be the hard part. I hope I’ve made the hard part a little easier.

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