Six generations of Hoopmans have fished the Great Lakes from Bayfield, Wisconsin, but Craig Hoopman isn’t sure there will be a seventh. Whitefish hauls are steady, he said this summer, and herring have rebounded; in fact, the fishery is in the best shape Hoopman’s ever seen. What’s dampening his optimism are two invasive fish from the Asian carp family threatening to take over the Great Lakes — species that could thoroughly disrupt the aquatic food web.
With so much anxiety surrounding Asian carp, separating the signal from the noise is challenging. University of Toronto conservation biologist Nick Mandrak agrees; that’s why he and 24 other Canadian and American fisheries scientists wrote a risk assessment in 2011 that detailed the likelihood and severity of silver and bighead carp’s impact on the Great Lakes basin. According to Mandrak, this “definitive document” found each lake would contain a sustainable population of Asian carp within 20 years of introduction; after 50 years, the moderate to high ecological impacts predicted by researchers would be a reality.
Resource managers lose sleep over silver and bighead’s insatiable appetites, which is what makes these two species (more than the aquatic vegetation-eating grass carp and mussel-eating black carp) of special concern to the Great Lakes. Silver, bighead, grass and black carp are four related carp species native to northern China and Russia’s Amur River region known collectively as “Asian carp.” It’s also silver carp that, when frightened, leap erratically from the water with velocity enough to break bones.
The impacts on the Great Lakes will be subtle, but have profound effects on native fishes. Silver and bighead carp feed low on the aquatic food web: their crimson gill rakers filter microscopic organisms and plants known as zoo- and phytoplankton as they swim. These two species consume 5-20 percent of their 30 pound average body weight each day, causing researchers to worry that silver and bighead carp could out-eat any other plankton-feeding fish in the Great Lakes.
If Asian carp hit the Great Lakes supply of zoo- and phytoplankton hard, fewer plankton-eating fish like alewives and smelt will survive to adulthood due to lack of food, ensuring top-predators like coho and chinook salmon and trout will suffer from similar food shortages.
Fierce competition for increasingly scarce plankton is already a problem. Invasive zebra and quagga mussels that arrived in the Great Lakes in the 1980s feast on the same phytoplankton eaten by silver carp and every other fish species in the basin for some (or all) of their lives. Alewife and smelt populations tanked once the invasive mussels took root in the Great Lakes, starving out deepwater game fish further up the food web.
“There’s probably going to be relatively few species that are not impacted by an Asian carp invasion,” says Mandrak.
These impact projections represent our best knowledge to date, but there’s no telling how bighead and silver carp might behave in the lake's deep waters. Marc Gaden, policy analyst with the Great Lakes Fishery Commission, says researchers have analyzed the impact of Asian carp on the Mississippi and Illinois rivers; but how they’ll perform in the Great Lakes is unknown.
Yet one thing is clear: “No Great Lake will be spared,” Gaden says. Asian carp will find habitat, food and spawning grounds everywhere they look. “It’s frightening.”
Gaden looks to sea lamprey for parallels to an Asian carp-filled Great Lakes future. The parasitic fish, which latches onto freshwater fish to drain them of their bodily fluids, entered the Great Lakes in the 1920s, quickly becoming the basin’s top predator. Lake trout populations were decimated by the 1940s, causing total commercial hauls from the Great Lakes to drop from millions of kilograms each year to a few thousand. At their postwar peak, sea lamprey killed 115 million Great Lakes fish annually.
The commercial fishing industry was hollowed out, as were shoreline communities dependent on commercial and recreational fisheries for survival. Charter fishing companies, marinas, motels, gas stations, boat and fishing retailers and restaurants all took a hit. Lamprey stunted fishing-related tourism throughout the basin, which only rebounded when the sea lamprey control program started in 1958 and annual losses were reduced to 10 million fish. Yet the dark days of the lamprey could return with Asian carp.
In the rush to quantify the importance of keeping these fish from the Great Lakes, Asian carp’s impact on the $7 billion Great Lakes fishery is often referenced. The figure comes from a 2011 study by American firm Southwick & Associates, which says that sportfishing in the Great Lakes sustains 50,000 jobs and contributes $3.79 billion to the region’s GDP.
Ontario’s commercial fishery is valued between $180 and $215 million each year in direct and indirect benefits, a figure that jumps to $13.8 billion when other socio-economic factors are considered. But the gradual deterioration of plankton communities brought on by zebra and quagga mussels has left the Great Lakes food web, and the fishery that relies on it, in perilous shape. Further declines in plankton brought on by Asian carp could “render commercial fishing operations unsustainable, abolishing the commercial fishing industry from Lake Erie ... and subsequently from the entire Great Lakes,” according to a 2014 analysis from Salim Hayder, policy analyst with Canada’s Department of Fisheries and Oceans.
We’re at a tipping point. Lake Erie, home to the largest walleye fishery in the world, accounts for 81 percent of all fish caught commercially in the Great Lakes: if Asian carp dramatically reduce Erie’s plankton population, it could take the entire Great Lakes fishery with it as well as seriously harming Ontario’s lucrative sport-fishing industry.
But it’s more than dollars and cents. Asian carp could “damage the public image of these lakes regionally, nationally and internationally,” Hayder wrote. “It would also harm the wellbeing of residents living close to such a unique natural resource.” While commercial fishing risks serious harm from Asian carp, recreational fishing, boating, wildlife viewing and the use of beaches and lakefronts could also be compromised. Who wants to spend a day on the water when it could result in a broken nose from a leaping silver carp?
The damage U of T biologist Mandrak and others foresee for the Great Lakes' fishery won’t happen overnight — that’s why assessments measure impacts on 20 and 50 year time frames. Changes in plankton volumes in the Great Lakes will be difficult to measure, and the effects of Asian carp may seem, at first, indecipherable or benign. But as happened in the Mississippi River, their population will slowly rise until, reaching a boiling point researchers still don’t fully comprehend, it will explode, revealing the full weight of their destructive influence on the aquatic ecosystem of North America’s inland seas.
For Craig Hoopman, all he can do is wait to see whether Asian carp undercut the fishery and his livelihood. But he’s doubtful his son can keep up the family tradition. “There is no way we’ll continue for another generation,” he says. “We really can’t.”
Andrew Reeves is a Toronto-based freelance environmental journalist who is working on a book about Asian carp.
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