Critters that sport fish feed on are dwindling
Written by Rochester Democrat & Chronicle   
Tuesday, 20 June 2006 13:05

Lake Ontario is known for its monster lake trout — muscular, gray-green fish that keep anglers awake at night with anticipation. The slimy sculpin — a 3-inch-long, mottled brown fish with mucus-coated skin that more than lives up to the fish's name — gets considerably less attention.

"Why should we care about the little critters? Without them, there are no big critters," said Sean Hanna, director of the state Department of Environmental Conservation's regional office in Avon, Livingston County.

Without thousands of tiny prey fish like the sculpin, the underwater stars of Lake Ontario couldn't survive. And the numbers of those little critters are plummeting, scientists say, putting at risk the trout and salmon that draw fishermen to Lake Ontario.

Federal and state biologists are trying to find out why. Every summer they spend several weeks tracking prey fish — rainbow smelt, alewife and sculpin — to build a picture of the drastic changes in what lives beneath the waves.

"So much is changing so fast. Every year it's a new lake out there," said Bob O'Gorman, a biologist with the U.S. Geological Survey in Oswego.

What is known:

Native lake trout at the top of the food chain would have disappeared if they weren't being stocked for sport fishing.

Invasive species like the round goby are breeding at tremendous rates.

Native prey fish like the slimy sculpin are declining.

The tiny native organisms that provide the base of the food chain are disappearing.
Scientists have only "fragmentary evidence" of how the system of all the native species functioned, said O'Gorman. The first major study was done in 1972, when the system was already degraded. Biologists have watched species disappear, but they've lacked the data to explain the losses.

Now, data from the research cruises are beginning to fill in the blanks.

Since May 31, the biologists have taken more than 100 samples, traveling east from Olcott, Niagara County, to Mexico Bay in Oswego County.

"We cover pretty much the whole U.S. shoreline," said USGS biologist Maureen Walsh. "But we do realize that we're sampling a small area of the lake. It's meant more to capture trends than the population status at a given point in time."

Tracking invasive species

Last week, the R/V Kaho — a federal research boat named after the Chippewa word for "searcher" — cruised the waters off Rochester. Many of the prey species that the biologists pursued — as well as the economically important predators that eat them — had no presence in the lake centuries ago, O'Gorman said.

The lake's food chain is in constant transition. Well-meaning biologists introduced foreign species like Coho salmon. Harmful invasive species like zebra mussels hitched a ride in ships' ballast water. Just understanding the ecological system requires constant vigilance.

"We're acting as sentinels," O'Gorman said.

When the lake changes, biologists on board the Kaho and its DEC counterpart, the R/V Seth Green, see it first.

The joint state-federal research effort, ongoing since 1978, found the first round gobies in Lake Ontario eight years ago and has tracked the invasive fish's expansion east to Oswego and into the deepest reaches of the lake.

The research has found quagga mussels — a close relative of the shore-dwelling zebra mussel — 400 feet below the surface, far deeper than anyone realized they could survive.

The four-person crew of the Kaho lives on the boat for two weeks, dragging a 60-foot trawl net along the lake bottom at different depths to understand why populations of prey fish are declining. Although the reasons remain mysterious, the impact is clear.

Already, state fisheries managers have been forced to reduce the number of hatchery-raised sport fish they release into the lake.

"There's no sense in stocking fish if they're going to starve to death," Hanna said.

Predator-prey relationships require a perfect balance, said Jason Franz, whose sport fishing business, Trout-N-About, takes anglers out on the lake.

"If the alewives crash, we're not going to have healthy salmon and trout to fish," he said.

Statewide, sport fishing is a $3.1 billion annual business, according to a recent industry study. More than 200 charter boats operate along the south shore of Lake Ontario, making a substantial contribution to the local economy, said Sam Zucco, captain of Dream Catcher charters and president of the Genesee Charter Association.

Prey fish different

The lake's ecosystem has changed so much over the past century that no one hopes to restore the lake to its natural state.

Chinook salmon and brown trout were introduced for fishermen. Native Atlantic salmon have entirely disappeared.

Neither smelt nor alewives are native to Lake Ontario, arriving via the canal system in the 1920s. But as native prey fish such as the sculpin have declined, they've become critical to the food chain. "Basically the prey community of Lake Ontario is totally different," Walsh said.

Meanwhile, populations of the invasive round goby, which eats the eggs of larger fish and is rarely preyed upon, are growing exponentially, Walsh said.

Data from the research cruises also have shown the devastating effect of zebra mussels.

The mussels remove plankton from the water — a critical food source for the invertebrates that prey fish eat. And plankton levels are already down because we've cleaned up the nutrient pollution from shore that charged the water with phosphorus and nitrogen and fed the plankton.

A tiny shrimp-like creature called diporeia has almost completely disappeared from the lake bottom since zebra mussels invaded. Prey fish such as slimy sculpin relied on it for food.

"It's frightening. A large part of our ecosystem just disappeared on us. Just ... poof," O'Gorman said.

New invasive species are found every few years, to unpredictable consequences. Fisheries' managers need to predict populations to set sustainable fishing limits in the short term, and ecologists need to understand the myriad cause-and-effect relationships if they're to have any hope of restoring a functional ecosystem to the lake in the future, O'Gorman said.

"Unless you understand how it works, you're dead," he said.

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