Luzerne County lake deals with invasion of the alewives
HARVEYS LAKE (AP) – In early and mid-April, if you stood near Harveys Lake in Luzerne County and closed your eyes, you might have thought you were at the seashore.
The characteristic cries of gulls resounded as the scavengers arrived in droves to feed on hundreds of dead fish floating on the lake.
Where did all the dead fish come from?
That’s a fish story without a happy ending.
One day in 1979, the ones that got away were from an angler’s bait bucket: Alewives, a small member of the herring family normally found in salt water.
Thirty-five years later, that little fish is causing big problems at Harveys Lake.
When alewives were introduced, there was a healthy population of lake trout, Atlantic salmon and rainbow smelt in the lake, said Robert Wnuk, a biologist in the state Fish and Boat Commission’s Sweet Valley office.
The alewives out-competed the smelt for food. When the smelt were gone, it impacted the lake trout and salmon that fed on them.
Harveys Lake isn’t the only local body of water with alewife issues.
Wnuk said the Fish and Boat Commission has trouble with people introducing them into the Elmhurst Reservoir in Lackawanna County, and the population is starting to take off there.
Anglers will empty alewives into the lake when they are done fishing; some do it deliberately, thinking it will improve the fishery, he said.
But that’s not the case.
“In general, they’re detrimental,” Wnuk said.
Alewives and gulls
The alewife, which averages around 6 inches in length, primarily is a saltwater fish but can adapt to fresh water. It’s commonly used for bait, and is edible by humans, usually smoked like herring.
Although technically a saltwater species, alewives can survive and thrive in fresh water.
But alewives are physiologically better suited to salt water, so they are sensitive to environmental disturbances in fresh water. The combination of dramatic water temperature changes and their weakened physical conditions after an unusually cold winter with scarce food caused them to die off in large numbers this spring.
Wnuk said alewife die-offs probably happen to some degree each spring, but this year’s was a big one, likely due to the prolonged ice cover on Harveys Lake and the snow on top of the ice.
John Levitsky, a private-sector field biologist who lives in the borough, likes to keep an eye on the aquatic birds that visit the lake. Mallards and Canada geese are common year-round residents at the lake, but there also are sightings of bald eagles, American coots, bufflehead ducks, cormorants and loons.
“Harveys Lake is quite the stopover for waterbirds,” Levitsky said.
A few gulls usually are among the migratory waterfowl that visit Harveys Lake for spring break and stop in again in the fall.
But this year, the gulls came in unprecedented numbers. Levitsky counted more than 70 on April 22.
The gulls hung out at Harveys Lake longer than they usually do, too, Levitsky said.
‘Junk food’ for game fish
The angler who, whether accidentally or deliberately, introduced alewives to Harveys Lake never was caught, Wnuk said.
And since that fateful fishing trip in 1979, the alewife population has exploded.
Wnuk said the effects from invasive species start at the bottom of the food chain, with zooplankton.
Alewives eat the tiny organisms that other species, such as rainbow smelt, might need to grow. Alewives also lower the population of other game fish, such as crappies and bluegills, by eating their young, Wnuk said.
Alewives sometimes are purposely stocked as a forage fish, for bigger fish to eat. However, Wnuk said the only time the Fish and Boat Commission introduces them is when a body of water is a poor fishery and there is no other option.
One of the consequences of inserting non-native species into the food chain is that contaminants can be unintentionally introduced as well, said Brian Mangan, professor of environmental science and biology at King’s College.
In addition, the introduced organisms might not be suitable for the native organisms: “It turns out some of the species, it’s almost as if they’re ‘junk food’ for natives of the area,” he said.
As a case in point, on April 16, the U.S. Geological Survey released a report based on research indicating fish in the salmon family in the Great Lakes are suffering from a Vitamin B1 (thiamine) deficiency from eating alewives. The alewives contain an enzyme that destroys thiamine in the fish that consume them.
As a result of the vitamin deficiency, trout and salmon are spawning offspring that die young – a major obstacle in restoring their natural populations.
Another invasive species problem is the explosion in the rusty crayfish population in the Susquehanna River. The crustaceans were introduced around 1976 – possibly by an angler.
From the Sunbury area down, the Fish and Boat Commission put significant restrictions on fishing for smallmouth bass in the Susquehanna River because of population decline, Mangan said. He is convinced that might be related to the rusty crayfish: they could be invading the nests and gobbling up the smallmouth bass eggs before they reach maturity. He plans to do some tests on that theory this summer.
Wnuk said the best way to prevent the spread of invasive species is to be careful with your bait buckets. It’s also important to clean and disinfect your gear before moving from one body of water to another, he said.
Once an invasive species takes hold, it’s almost impossible to get it out.
The best the Fish and Boat Commission can do to control the alewives is to stock a high density of predators, such as brown trout and walleyes, Wnuk said.