Problem Fish: Gizzard shad is a natural part of Pennsylvania waterways, but too many can destroy a thriving sport fishery
June 3, 2012 4:00 AM
Bass love to eat gizzard shad, but too many of the forage fish can destroy a lake.
By John Hayes Pittsburgh Post-Gazette
Depending on who you talk with, the gizzard shad is a savior or a menace.
Ask a bass, and the gizzard shad is a fast-food forage fish -- abundant, fleshy, easy to catch and softer on the palate than spiny panfish.
Ask bluegills, sunfish and crappies, and gizzard shad are voracious, fast-growing invaders that consume so much of the available food that panfish populations are left stunted and less healthy.
Ask some anglers, and the gizzard shad is a silver-bullet solution to filling a lake with big, muscular bass. Talk with anglers on Lake Wilhelm and other regional impoundments, however, and you'll hear a different story -- millions upon millions of gizzard shad provide the bass with so much to eat they barely notice their lures.
Then ask Rick Lorson, southwest area fisheries manager for the Pennsylvania Fish and Boat Commission.
"All of those accounts are just about right," he said. "The accidental or intentional introduction of gizzard shad into a lake would help the bass, but it hurts everything else. Including, ultimately, the bass fishermen. When we have gizzard shad in our lakes, largemouth bass populations are dense with big fish to the demise of panfish in the lake ... and the well-fed bass become harder for fishermen to catch."
Dorosoma cepedianum, a member of the herring family, is native to much of North America with a range stretching from the Great Lakes to the Gulf of Mexico and from the East Coast to the Dakotas. Instead of building a nest, a spawning female followed by several males weaves through near-shore vegetation depositing adhesive eggs that stick to plants, where the eggs are fertilized. It's a successful spawning method that reduces predation, resulting in greater hatches.
Gizzard shad fry feed on zooplankton. At about 1 inch they develop a fuller bodied front end, or gizzard, and graze on small invertebrates and plankton, growing in Pennsylvania to as large as 15 inches. Despite its potential size, the gizzard shad is a boring target for anglers, unappetizing on the plate and is not classified a sporting fish.
In rivers, streams and natural lakes, gizzard shad, panfish and other forage fish are brought into balance by factors including predation and cold winters.
"In the Three Rivers system they are an important staple," said Lorson. "There is enough room for them and the emerald shiners and other forage fish. They vary between a year of dominance of the gizzard shad to a year of emerald shiners to a mix of both, depending on conditions."
But most of Pennsylvania's lakes are man-made impoundments with confined populations of fishes.
"The problem in impoundments is there's more consistent spawning among the shad," said Lorson. "They're in direct competition for food that normally is taken by crappies and bluegills and perch, and an imbalance occurs in predation from the bass. The shad overwhelm those populations. Pretty soon you have more gizzard shad than the lake can handle -- they're taking up a disproportionate share of the biomass -- resulting in an unhealthy lake."
Increased winter mortality at higher elevations helps to control gizzard shad in mountain lakes such as 252-acre Lake Someret (Somerset County), but human intervention is also necessary.
"When [gizzard shad] came into the lake, we had to change our management," said Lorson. "We started stocking predators heavily -- walleyes, channel catfish, tiger muskies and muskies -- in an attempt to basically try to keep ahead of them."
Controlling gizzard shad is an expensive proposition for the cash-strapped agency. But the alternative is the destruction of a lake due to the uncontrolled growth of one species.
Sometimes dam rehabilitation or dredging operations can give wildlife managers a chance to start over. Before Beaver County's Raccoon Lake was refurbished in the mid-'90s it was overrun with gizzard shad. Lorson said an overpopulation of gizzard shad in North Park Lake (Allegheny County), before its recent rehabilitation, kept panfish populations down and made it harder to catch bass.
Canonsburg Lake in Washington County is currently choked with gizzard shad. And in Mercer County, anglers on 1,740-acre Lake Wilhelm are frustrated with the small size of crappies and tedious bass fishing, due in part to an explosion in the population of gizzard shad.
In a 2004 fish population survey at Wilhelm, PFBC researchers found only four gizzard shad. In 2010 they netted 1,945, or 48 percent of the total fish captured. Night electro-fishing surveys revealed a significant drop in largemouth numbers from 2004 to 2010, while the abundance of bass 12 inches and larger and 15 inches and larger remained about the same -- common indicators of too many gizzard shad.
"They kind of exploded and expanded their population, which often happens when you get a species in a new environment," said Al Woomer, PFBC fisheries manager for the Allegheny watershed. "They take advantage of everything and have very few things to control them."
In an attempt to control the Lake Wilhelm shad, Fish and Boat routinely stocks muskellunge fingerlings, more than 1 million walleye fry and as many as 34,000 walleye fingerlings. It's not a cost-effective solution and ultimately, Woomer said, it may not work.
"It's tough. You've got to just hope that over time the predators and different things will have a negative effect [on the shad]," he said.
Sometimes the problem corrects itself. Gizzard shad overpopulation at Crawford County's Conneaut Lake is slowly abating, said Woomer.
How did the gizzard shad get into the impoundments?
Not from the state, and in most cases not through natural means. Anglers put them there.
Sometimes it's incidental. Gizzard shad are not sold for bait, but shad seined or trapped for bait can get off a hook and survive, or are dumped from bait buckets at the end of a fishing trip.
Some amateur fisheries managers, however, believing shad will build bigger bass, intentionally stock the problem fish in lakes that can't handle a new, fast-growing forage species.
"They don't have the biomass information we have ... they don't know what they're doing," said Lorson. "No doubt it's a double-edged sword. I'd just say, don't do it. We have much more experience than they do, and we see the results."