April 7, 2015

Why Trout Seek Deep Holes


Knowing why speckled trout seek deep water is key to successfully catching them during all times of the year.

I love talking fish behavior because it dictates everything else. I have spent many a fishing trip contemplating why they do what they do.

This story is one of those fishing trips:

I have been sitting on the bow of my boat cross-legged, staring at the water. I have a rod in my hand, but the line is reeled in.

Behind me on the deck are several speckled trout, flopping around as I had just pulled them from their marine environ. As I stare into the turbid water of the Biloxi Marsh, it’s almost as if I can see it.

The visual taking place in my head most closely matches what is actually happening underwater. I make a note to myself before starting the motor and pulling up the anchor.

As the bow begins slicing fog I contemplate what happened back there.

The spot I was fishing had water that was 24 feet deep. It was in a bayou that served as a main artery of the surrounding marsh and I had caught thousands of trout there over the years.

The key feature that separated this spot from others is the deep “hole” it possesses.

Why do trout like this feature? Below are my theories.

1. Stable Temperature

If you have ever been diving then you know the deeper you go the more cold water becomes. It may not be gradual but could be sudden in the form of a thermocline.

Initially, it doesn’t make sense for a trout to seek colder water when it is trying to survive during winter months, but consider how much more fluid air is than water.

Cold air can move in at the blink of an eye and make us reach for a jacket. But water doesn't change temperature as fast. Yes, a few degrees is a big difference for a fish, but they can't reach for warming layers, either.

With trout, it’s not really so much the cold temperature that could kill them, but a sudden change in temperature. At the bottom of these deep holes lies water unaffected by drastic temperature changes.

This water is “safe” because it is stable. Think of deep holes as a “bunker” trout can seek refuge in during bad weather.

A deep water fallacy?

I have had heard anglers use the explanation that trout seek deep holes because the ground at the bottom keeps them warm. Essentially, the trout is attracted to the geothermal radiation of the earth.

I respectfully disagree with this.

Consider these points:

  • There is ground at the bottom of shallow water, too. Does that earth not warm the water as well?
  • Warm water originating from deep holes would "turn over" the water column as it rises above colder water. We see this happen in still-water, but not in our tidal marshes.

2. Stable Salinity

Saltwater is denser then fresh water, causing fresh water to float on top.

Now lets take it one step further: some saltwater is saltier than other saltwater, and the saltiest of saltwater will be pulled to the bottom by gravity.

How is this relevant? We know that speckled trout like clean and salty water.

Salty water readily provides a stable environment for trout to reside in.

When trout are hiding out from bad weather and battling cold temperature, salty water gives them an edge they can use to survive.

Two Ideas of Salty vs Fresh:

  • What if slightly warmer saltwater is heavier than slightly colder freshwater? This could create a layer of warm water at the bottom of a deep hole.
  • Another angler used this analogy: saltwater is like cold wood and freshwater is like cold steel. Which would you rather have touch your skin?

Winter is not the only season trout relax in deep water.

This “stable environment” idea lends credence to observations of trout behavior during the summer.

Summer time is hot and speckled trout seek cooler temperatures, preferably in the shade.

It comes as no surprise that trout, when not actively feeding, would get away from hotter water at the surface to chill out in the cooler water at the bottom.

3. Security Needs

I cannot be certain this is a factor or not, but it is something I have contemplated.

While speckled trout are somewhat apex predators, they are still easy meals for animals higher in the food chain.

Consider that baits we use are being “skylined” when viewed from the bottom of the water column, making them easy targets.

Their silhouettes give away their position and leave them vulnerable. It is easily understood why trout want to avoid putting themselves in this predicament.

When trout hold to the bottom of a deep hole, there is no way they can be skylined.

4. Hydrodynamic Efficiency (Holding to the Bottom)

It would also seem to me that it would be easier to hold in one place if water isn’t flowing around one side of the trout body, but I could be wrong.

This is a guess on my part.

I know when I go diving that holding to the bottom is easier than being fully exposed to the current.

5. Warming Areas and Nearby Baitfish

Almost all deep holes I fish during winter have a nearby shallow water area.

Some are oyster reefs, others are ledges.

Trout will leave the protection of their deep holes to feed in the shallow water and catch the warming rays of the sun.

If I don’t catch fish in deep water, I will move to the nearby shallow water. Often I will catch trout in shallow water while people fishing the associated deep water don’t catch anything.

This has also happened first thing in the morning.

This limit of trout and a redfish were caught before 8am on a very cold December morning. They were caught in water about 3-4 ft deep adjacent to a canal about 12ft deep. A weak cold front had cleared the skies and the water temps were in the mid 40s.

The Takeaway

What can we take from this to apply to our fishing trips? What key elements make good winter spots “good”?

  • deep water
  • nearby shallow water
  • moving water

Moving water is important. Trout love moving water and seem to hate it when it's not.

Moving water brings bait to them. Slack water does not. For a speckled trout, it is time to rest when water is slack.

Check out this link to see what good moving water looks like.

Additional Details

I have noticed large schools of trout do not prefer locations consisting of small bodies of water.

They instead prefer areas where there is a lot of water, areas like main bayous, mouths of bayous, and structure in bays like oyster beds and underwater "humps".

That's not to say I have not caught loads of trout in "small" water that are suitable for 1-3 man limits, but I generally find the larger schools suitable for 4-6 man limits in "bigger" water.

Biloxi Marsh

Oyster beds have done very well for me. Rather than cover that topic again, you should read this simple article about oyster beds.

Conclusion I left that spot with a better understanding of why trout prefer to seek these deep safe havens.

I went on later that day to find more trout at similar locations.

Maybe this article satiated your curiosity. Perhaps it will help you in your fishing endeavors and you will Fish Smarter!

Captain Devin

About the Author

Devin is a veteran of the Iraq War and former fishing guide. He founded Louisiana Fishing Blog in 2012 to share his ideas as a charter captain and still writes in it today. Since then he's created a fishing university — LAFB Elite — where he teaches inshore anglers how to safely navigate Louisiana's coast and catch more fish.

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  • Hey Ronald, thanks for commenting. I have no experience fishing Virginia and can’t give you a definitive answer. However, speckled trout are speckled trout and I think you’d serve yourself well to take what you can from here and test that knowledge on your own waters.

    Good luck out there, and tight lines!

  • You are absolutely correct that a fish in moving water can use less energy by staying on the bottom. The reason is because the current speed next to the bottom is up to 90% less than the fastest portion of that current. This is called. ‘Laminar Flow’ within the field of Hydrology.

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