Turbidity and bass feeding

Bass are visual predators. Fishing shallow is usually the best approach in muddy water, but bass located in deep, muddy water can still be caught.
Bass are visual predators. Fishing shallow is usually the best approach in muddy water, but bass located in deep, muddy water can still be caught.

Study may help you do better in muddy water

Muddy water seriously shakes my confidence when it comes to catching fish. A few years back, I asked a couple of bass pros and a successful fishing guide to keep fishing logs of water clarity and catch.

The significant finding was that bass were caught shallower in turbid water. That makes sense; bass are primarily sight feeders, so you might expect them to feed (and strike baits) higher in the water column, where presumably, they can see better.

A recent study on smallmouth bass adds some support to a shallower bite in turbid water. Canadian researchers found smallmouth bass foraged more on prey in the shallow-water zone where rooted aquatic plants grow and ate a wider diversity of prey as turbidity increased.

But an experience on Pickwick early this spring made me rethink this simple reasoning. The water temperature was in the 50s, and in an effort to learn some new ways to catch bass, I decided to give a tube bait a try. The water was also muddy — about six inches of visibility — and flowing from more than a week of heavy rain. I marked some fish on the bottom in 20 feet of water on a bluff point with my electronics. The only thing I had on deck that would reach those fish was a rod rigged with small tube, so I tossed it to the marked fish. Six casts produced four fish. Tubes are a silent bait. How did the bass find such a small bait in a presumably dark environment?

The scientists say

Catching bass when the water turns muddy can be challenging. To up your odds, fish around cover where you’re likely to find bluegill.
Catching bass when the water turns muddy can be challenging. To up your odds, fish around cover where you’re likely to find bluegill.

Searching fish-biology literature led me to a recent study by Oklahoma State University fisheries scientists that coupled controlled laboratory and field studies to better understand how turbidity affects bass foraging.

Laboratory trials measured the consumption of bluegills and gizzard shad by 9- to 14-inch largemouth bass in 6-foot diameter tanks at turbidities varying from 3 inches to 13 inches of visibility. Consumption rates of both bluegill and shad declined rapidly with increasing turbidity. Conclusion: increasing turbidity reduces feeding — or at least feeding success. Interestingly, over half the bass did not eat during the 24-hour test period when visibility was less than 6 inches. The bass were held in clear water until 24 hours before the trial began. Possibly, a sudden decrease in water clarity simply shut down feeding for a brief period for some fish.

The field study measured the diets of largemouth bass collected from three lakes under varied water clarity (6 to 34 inches). Their predominant diet items were crayfish, sunfish and gizzard shad. Diets varied widely between lakes, but the overall trend was increased sunfish consumption or, in one lake, sunfish and shad consumption and decreased crayfish consumption as turbidity increased. The bass also tended to eat a wider variety of forage fish as turbidity increased. Total weight of forage consumed was not significantly related to turbidity.

The field study results indicate forage consumption changes little with declining water clarity, but prey selection does. Explanation of the field study results is complicated, because what bass eat is a function of the habitats they select — which may change with turbidity — and the habitats the prey uses, which also may change with turbidity. Dissimilarity of habitat types could explain the lake-to-lake variation observed. But the take-home message for me from the field studies is fish where a bass would eat sunfish when the water gets muddy. Depending on what lake you are fishing, that may be near shallow vegetation, brush piles or docks.

About Hal Schramm 138 Articles
Hal Schramm is an avid angler and veteran fisheries biologist.