By KIMBERLY HIRAI
Capital News Service
“The last few years we’ve basically set limited gear,” Jensen said. “We haven’t set as many nets as we’re licensed for, just kept our foot in the door.”
Jensen’s company, Marine Management Ltd., shares a half-million pound whitefish quota with neighbor Petersen’s Fisheries, but Jensen said the companies rarely meet it. They own the only two Michigan commercial fishing licenses for whitefish in the southern part of the lake.
Jensen has turned to other business opportunities due to the unpredictability of catching fish.
The whitefish, the Great Lakes fishing industry’s most valuable resource, has gone through ups and downs of its own.
The largest decline in whitefish populations started in the 1940s, according to the Great Lakes Fishery Commission. The declines were mainly due to overfishing and sea lamprey, which prey on whitefish.
The ebbs and flows of the commercial catch mirror that trend.
Commission data shows that in the 1950s, average catches decreased by more than 17 percent each year, from an average of more than 10 million pounds to about 6 million.
But when populations began to recover in the 1970s through the late 1990s, the average annual catch increased by more than 5 percent. The commission attributed that recovery to sea lamprey control, better commercial fishing industry management, introduction of salmon to control competition by smaller, plankton-eating fish and other factors.
Today, populations vary within lakes and among lakes.
The data shows that the commercial catch is beginning another decline. But one whitefish population has recolonized a historical spawning ground in the northern part of Lake Michigan said Scott Hansen, a fisheries biologist for the Wisconsin Department of Natural Resources at Sturgeon Bay.
Hansen said the population found in the Menominee River could be from a stock in Lake Michigan that migrated up to the water source, which borders both Michigan and Wisconsin.
Mark Ebener said revitalized populations have shown up in the Fox and Cedar Rivers where they’ve been absent for the better part of a century.
“This recovery has been speeding up over the last decade or so in those tributaries,” said Ebener, an inter-tribal biologist with the Chippewa Ottawa Resources Authority.
But the focus now seems to be on quality, not quantity.
Commercial operators threw whitefish of marketable length back into the Great Lakes in the 1990s because they hadn’t reached the appropriate weight, according to a Great Lakes Fishery Commission technical report.
Scientists like Ebener are conducting studies to try and explain slower growth rates, smaller sizes and possible declines in reproduction.
One idea correlates the decline of diporeia — a small shrimp-like organism and the whitefish’s nutritious main food source — with the arrival of invasive zebra and quagga mussels.
But populations of diporeia persist in areas where there are mussels, Ebener said.
“I think if we’ve learned anything, it’s that the changes in diporeia aren’t changing the whitefish populations,” he said.
He said whitefish are highly adaptable, eating whatever is abundant. “It’s tough to describe whitefish diet because it changes so drastically depending on parts of lake.”
For example, scientists have found populations in Lake Ontario shift diet from diporeia to quagga mussel, tiny clams and zooplankton.
In Lake Michigan where diporeia are no longer found in near-shore areas, whitefish eat zebra mussels, gastropods like snails and midges, which are small insects.
Ebener said he thinks size, growth, age at maturity and reproductive success may have something to do with density dependence, in which fish decrease their size, slow growth or respond in other ways when a population becomes too large for a habitat’s food and resources.
A third contributing factor needing further investigation is the role of infectious diseases in the Great Lakes stocks of whitefish. Also, scientists have cited environmental change due to global warming as another possible factor.
While researchers continue their work Jensen, of Muskegon, said he’ll continue to “tread water” until they find answers.
He’s made up for the uncertainty and expense of continued fishing through other businesses, such as boat building, mechanical and electronic work on research vessels and the marina.
“Time will tell,” he said.
© 2010, Capital News Service, Michigan State University School of Journalism. Not to be reproduced without permission.