By Ian Wendrow
Lake Huron whitefish are suffering from ecosystem changes caused by invasive quagga and zebra mussels, according to a new study.
“It’s the same decline in whitefish as has been found previously in the other Great Lakes where the mussels become established,” Jenilee Gobin, a co-author of the report from
Trent University in Ontario, explained in an email.
Other emerging research shows the source of food for the whitefish in these locations
has changed because of the mussels.
Gobin and her team proved that Lake Huron is going through what researchers have been seeing in the other Great Lakes for years: invasive species like the zebra and quagga mussels working in tandem with other key events to contribute to a decline in profitable fish species, including whitefish.
“Our study represents the first that we are aware of to build a life history simulation model that explicitly addresses how the ecosystem changes have impacted harvest of a Great Lakes population of lake whitefish,” Gobin said.
These ecosystem changes have been ongoing for several decades. The study found that whitefish growth and recruitment in Lake Huron may have been reduced by up to 50 percent since the 1990s.
The study doesn’t say that the mussels are the only culprits. The invasive spiny water flea holds a portion of the blame for Lake Huron’s recent environmental mutations, according to the study.
But much of it ties back to the mussels, starting with the near-complete disappearance of alewives in 2003, said David Fielder, a fisheries biologist at the Michigan Department of Natural Resource’s Alpena Fisheries Research Center.
Alewives are small fish that are an important food source for larger fish such as Chinook salmon or lake whitefish within Lake Huron.
Those fish suffered when the mussels ate up the diporeia, a tiny macroinvertebrate that was an important source of food for the alewives that these larger fish ate.
Diporeia populations diminished significantly with the arrival of the mussels. Both the mussels and the diporeia are filter feeders, which most fishery researchers argue led to a competition for food between the two.
The mussels won that competition.
Another mussel-related food chain alteration may have harmed recruitment, or the number of new whitefish added to the population each year, Fielder said.
“Some other recent research has illustrated that part of the food web changes has included less nearshore productivity, at least in the form of zooplankton,” he said.
Zooplankton are microscopic organisms that are food for newly hatched fish. However, zooplankton have to eat as well. Their food is phytoplankton, microscopic organisms that feed through photosynthesis like plants.
“We used to see nice blooms of zooplankton in the spring just as fish were hatching, but they have disappeared in recent years, Fielder said. Researchers theorize that the phytoplankton that zooplankton eat have been filtered out by the abundant mussels.
“So without ample spring zooplankton, newly hatched whitefish quickly starve and never produce much of a year class,” he said.
The Ontario study acknowledges Fielder’s assessment in their research, while also pointing a finger at the predacious spiny water flea as another reason for zooplankton decline, thus further limiting food supply for larval fish.
In spite of these observed changes, not all fish sellers and anglers see the situation the same way.
“Whitefish produce lots of eggs and their survival rate is high,” said Mike Donlan, a fourth-generation fishmonger and general manager at Donlan’s Fish and Seafood in Flint, Michigan.
Donlan doesn’t exclusively stock from Lake Huron, his supply comes from all over the Great Lakes. Like most other species of fish, supply changes year to year, Donlan said. This year has been a trying year when it came to whitefish.
“There hasn’t been as much availability as prior years. For instance this year it was a real, real hot summer,” he said.
In hotter temperatures, whitefish and other species will migratei nto deeper water where it’s cooler, which puts them out of range of most commercial fishing boats.
“Sometimes the fish are not where the fishermen want them to be,” Donlan said.
Looking long term, however, Donlan says he’s unconcerned by the findings in the study
“We haven’t heard of anything mentioned that there’s an alert that we’re gonna run out of white fish in the Great Lakes.”
Jerry and David Serafin, the owners of Pinconning, Michigan’s, Serafin Fishery, daid they are incredulous about a whitefish decline in Lake Huron.
“They’re in better shape than they were a few years ago,” Jerry Serafin said.
DNR fishery researchers took some of Serafin’s whitefish to assess the health of the population last fall. According to what they told Serafin, his whitefish had significantly higher fat content than 10, 15 years ago.
David Serafin says he is more concerned about the planting of lake trout and the ever- growing walleye population.
“My concern with the whitefish is that the DNR want to plant herring in Lake Huron to feed the walleyes,” David Serafin said.
“Well walleyes eat whitefish, they eat anything. They’re cannibals, they eat each other, and these things are so overpopulated that we catch a lot of whitefish but there’s gonna come a time when the population goes down,” he said.
While the causes of and proposed solutions to these fishery population changes remain varied, Gobin said he’s certain on one point:
“What is clear is that we need to continue to study and monitor these valuable populations to ensure that there is good quality data on which to base management decisions and that we are harvesting within the safe biological limits that are appropriate for the present set of environmental conditions.”