Gizzard shad leading to skinny, small crappies at Lake Wilhelm

A Fish & Boat Commission biologist says shad are wreaking havoc on Lake Wilhelm’s panfish by outcompeting them for forage, while providing larger predators with alternative meals. (Photo courtesy Pa. Fish & Boat Commission)

Butler, Pa. — Anglers can blame gizzard shad for an overabundance of skinny crappies and bluegills on Lake Wilhelm in Mercer County.

Shad are wreaking havoc on Wilhelm’s panfish by outcompeting them for forage, while providing larger predators, such as walleyes, muskies and largemouth bass, with alternative meals, according to Tim Wilson, a biologist with the Pennsylvania Fish & Boat Commission.

“Before the gizzard shad were put in there, Wilhelm was a wonderful, well-balanced fishery for so many species,” he said. “It was full of big bass and 8- and 10-inch bluegills.”

The commission plans to evaluate relative abundance of young-of-year largemouths this month, with an eye toward future stockings, but Wilson admits that trying to restore a healthy predator-prey balance is a tough challenge.

“Once you get into a stunted fishery situation, it’s very hard to get out of it,” he said. “All we can do is keep stocking walleyes, muskies and bass, and hope the lake eventually adapts to a new normal, where shad are part of the fishery and not a total negative. But it’s taking a very long time.”

Gizzard shad – a type of herring – were most likely introduced to Wilhelm by an angler, said Wilson, who notes that the species multiplies rapidly.

Shad were first collected at Wilhelm in 2004 during a spring survey that trap-netted four adults, or 0.01 per hour. In 2010, 1,937 gizzard shad were collected at a rate of 3.5 per hour.

This year, 6,851 shad, or 8.06 per hour, were collected. “You can see from those numbers that we haven’t reached the tipping point yet where predators are controlling the gizzard shad,” Wilson said.

Interactions among fish are complex and dynamic, but all species remain in competition for a limited amount of food, Wilson said. “Crappies can utilize shad until the shad grow too large for anything but the biggest predators in the lake.”

Even at 6 inches, though, shad will continue to eat the zooplankton that young crappies depend on. “So the crappies and bluegills get deprived, and the bigger fish aren’t eating them,” he said. “We’re seeing more bluegills than ever before, and they’re stunted like the crappies. There’s an overabundance of both species.”

As panfish reproduce, they exacerbate overcrowding, he said.

The Fish & Boat Commission has been stocking Wilhelm with walleyes, muskies and bass for years, and while they are no longer keeping panfish in check, there isn’t a quick fix going forward, Wilson said.

Reducing creel limits on walleyes as a means of keeping more predators in the lake probably wouldn’t make much difference, and there’s a limit to the number of walleyes, muskies and bass state hatcheries can raise, Wilson said.

It might help if anglers were to keep the stunted panfish they catch, but most folks probably don’t want them, he said. “You’d have to clean quite a few to make a meal.”

Nature could, at some point, correct the problem, as it did at Pymatuning Reservoir, where the 30-year average for shad is now about one per hour. “We saw a massive spike in shad – 10.1 per hour – in 2017, which produced poor fishing for anglers,” Wilson said.

“Then we had a large die-off this past March and our catch of shad fell back to 2.2 per hour. The fishing this spring was very good.”

A die-off also occurred at Wilhelm this spring, but it was small and failed to kill off enough shad to ease the imbalance in the fishery, Wilson said.

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