The ups and downs of drawdowns

Spring drawdowns can have a dramatic effect on reservoir bass populations, but is it good or bad?

Jerry Farmer has seen the worst example of water management and its effect on a reservoir’s bass population. As a guide and tournament angler on several east Tennessee lakes, he spends countless days on reservoirs such as South Holston, Boone, Watauga and other notable bass waters.

“We had an unusually large rain in April a couple of years ago and Boone Lake went way up,” he recalls. “The water stayed up for about a week and the bass went to the shallows and spawned. Then they dropped the water real fast the next week.”

Over the course of that week, Farmer watched a smallmouth bed go dry as the water dropped. The last time he saw the female, she was hugging the shore under her nest, which was a foot out of water.

Such an example is rare, and it’s one that can’t always be avoided, but countless anglers who spend the bulk of their time on Tennessee Valley Authority and Corps of Engineers lakes have seen similar examples of poorly timed drawdowns. Most lakes managed by these government agencies serve as a flood control mechanism, an electrical generating plant, or both, so recreational fishing and the health of a lake’s fishery are usually secondary. But Farmer wondered why they couldn’t drop the water sooner or keep the lake up another week until the eggs had a chance to hatch. It’s a question to which he couldn’t get an answer.

According to Tennessee Wildlife Resources Agency biologist Todd St. John, the TVA does consider fish and wildlife when it raises and lowers lake levels, but says the primary goal of these highland reservoirs is to provide flood control and electricity.

“We meet with the TVA annually to discuss the needs of the resource and they often take them into consideration,” he says. “For example, they will maintain river flows during the sauger spawning run on rivers below their dams and they typically don’t drop lake levels during the peak spawning period.”

When major spring drawdowns do occur, such as the one Farmer experienced, entire year-classes of fish can be wiped out and the age structure of a lake’s bass population can become skewed.

“Anglers typically won’t notice any effect until three or four years after a catastrophic occurrence,” explains Virginia Department of Game and Inland Fisheries biologist John Odenkirk. “That’s when bass grow large enough to be considered catchable or desirable, and when you lose a year-class, there’s a gap in the size structure of the lake. Anglers stop catching those quality bass because they aren’t there.”

Despite such incidents, dropping and raising lake levels can actually benefit a fishery when done properly.

“Seasonal drawdowns can really benefit a fishery in a number of ways and they can be used to actually improve a fishery,” says Odenkirk.

Spend a winter day on any highland reservoir and you’ll get a firsthand look at a drawdown. Some are lowered 20 feet or more and kept that way through the winter in anticipation of heavy winter and spring rains. It’s a precautionary measure that serves a vital purpose for the residents that live below these reservoirs.

“Winter drawdowns help concentrate forage which gives gamefish easy access to more food,” explains Odenkirk. “That helps reduce forage fish, which can overpopulate a reservoir quickly, and it increases the average size of predator fish such as bass, crappie and even sunfish.”

Winter drawdowns also allow for maintenance on dams and boat ramps and, says Odenkirk, they help control nuisance aquatic vegetation by exposing the plants to freeze-thaw cycles. Too much aquatic vegetation can hinder a fishery and create a wide variety of problems. Late summer drawdowns are also used to establish terrestrial vegetation along shorelines, which, when flooded in the spring, serve to increase a lake’s fertility. Vegetation also helps reduce shoreline erosion.

“Flooded vegetation acts a nursery for the young-of-the-year fish and the rotting vegetation increases the fertility of a reservoir by adding nutrients,” says Odenkirk. “It’s the beginning of the food chain.”

Overall, however, lakes that have a stable water level throughout the year tend to have better bass populations thanks largely to higher recruitment rates for newly hatched bass and other gamefish, according to St. John.

“We rarely drop the water level on Agency-owned lakes and our sampling efforts show better bass populations overall,” he noted. “There tends to be a better size and age structure in stable reservoirs.”

As Farmer argues, these lakes may “belong” to the Corps or Engineers or the TVA, but they are owned by the taxpayers and recreational angling is a major source of revenue for the small towns around these reservoirs.

“I’ve always felt that these government agencies don’t pay enough attention to anglers,” he says.