Study: Carp food plentiful

[USA] Todd Schrouder doesn’t stray far from the shoreline during his springtime fishing excursions.

The charter boat captain stays in shallow waters, where his charter fishing customers are more likely to hook a big fish in the cool Lake Michigan waters.

New research suggests that invasive bighead and silver carp, two of the four varieties commonly known as Asian carp, would share Schrouder’s shoreline space if they were to invade Lake Michigan.

The effects could be devastating.

“It may turn into a whole commercial fishery of a different sort, to supply cat food and all your fish dishes throughout the world,” Schrouder said.

Food is plentiful in Lake Michigan for bighead and silver carp, particularly along the shoreline and in bays, such as Grand Traverse Bay, a USGS report states. The invasive fish are filter-feeders whose primary dish includes phytoplankton.

Some suggested invasive zebra and quagga mussels’ cleaning effect on the lakes reduced plankton levels so drastically that there wouldn’t be enough to sustain a sizable invasive carp population, said USGS Research Fish Biologist Duane Chapman.

Chapman and other scientists found that conjecture to be true in most of the lake, but satellites showed a different story along Lake Michigan’s shoreline. Those areas have plenty of food for the carp, and those are the areas where the fish likely would spend their time if they invaded the lake.

“Lake Michigan is huge, but we’re talking about a band that is, roughly speaking, about a mile wide,” Chapman said. “It’s not a whole lot of the lake, but it is an important part of the lake. That’s where most of the people are, and that’s where a lot of the productivity we have left in the water is.”

Chapman and other USGS scientists used satellites to measure food availability for the bighead and silver carp in Lake Michigan. The fish eat green algae and blue-green algae, the plant also known as cyanobacteria that causes harmful algal blooms.

The carp could help curb blue-green algae and harmful algal blooms, but Chapman cautioned that the trade-offs of their presence likely would not be in favor of the Great Lakes.

It would take a lot of invasive carp to reduce harmful algal blooms, and that many carp likely would decimate Great Lakes perch and walleye populations, Chapman said.

The potential for problems caused by an Asian carp invasion are vast, but Chapman is confident in scientists’ abilities to keep the fish out of the Great Lakes. He said the electric barrier in Chicago is effective, and dams downstream of the barrier help keep young fish from reaching the barrier until they’re too big to break through.

Researchers are continually working on new methods to thwart the carp’s attempts to reach the Great Lakes.

“People are smarter than fish,” Chapman said. “I’m positive about this. I think if we keep the pressure up, by the time the odd chance (invasive carp reach Lake Michigan) will happen we will have worked up better defenses.”

Schrouder is less sure. He said increased political pressure and education are needed to really protect the Great Lakes from invasive carp. An invasion would hit his business, Hooked Sportfishing Charters, and the other businesses operating out of shoreline towns.

“It would hurt all of it, the fishery as a whole,” he said. “Not only the economic side of it, but the hotels, restaurants, the whole nine yards.”


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