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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Fisheries biologists estimate perch populations based on every phase of their life, from young of year, to yearling and adult. © Matt Mangan
Fisheries biologists estimate perch populations based on every phase of their life, from young of year, to yearling and adult. © Matt Mangan

April 2006

Early signs of recovery?

Are yellow perch inching back from a 15-year decline?

DNR communications staff

Frequent sampling during their first years in Lake Michigan
Even longer-term sampling on Green Bay
Early indications of a comeback?

Fisheries biologists are cautiously optimistic that yellow perch in Green Bay and southern Lake Michigan are showing early signs of recovery from a sustained 15-year population decline.

Several survey techniques biologists employ to track perch throughout their development from eggs through adult size indicate yellow perch may be at the beginning of a slow comeback. More sampling and surveys will determine if these prized fish are recovering lakewide or if the populations are primarily making a comeback in smaller areas. Teams of biologists, operations crews and university researchers continue to study perch, follow their progress and take steps to enhance their populations.

The vast size of the Lake Michigan system, variable weather and varied underwater conditions add to the challenge of predicting how these fish are responding to change. "So many factors are involved – food availability, exotic competitors, fishing pressure, predators, and weather, that we don't like to make predictions," said Bill Horns, DNR Great Lakes fisheries coordinator.

A systematic approach to assessing fish populations on the Great Lakes is only about 35 years old. Before 1970 fish populations on the lake were estimated by reviewing records from commercial catches and, naturally, those harvests fluctuated with the demand for fish, different fishing regulations in each state and new technology for finding and netting perch. "An absence of consistent long-term data about fish populations makes it more difficult to determine if the fluctuations we see now are cyclical, an anomaly, or can be attributed to a condition we can measure," Horns said.

Perch typically live about seven years and reach sexual maturity at two to three years in Green Bay, three to four years in Lake Michigan. Commercial catches (which have been closed for 10 years) and an annual creel survey from sport anglers provide information about the adult perch population, but the fish are much more vulnerable to predation and the elements as fry, larvae and fingerlings than as adults. To assess population trends, biologists routinely sample perch at several stages in their development.

Frequent sampling during their first years in Lake Michigan

During the spawning season, typically early to mid-June, divers traveling on the research vessel Perca examine the lake bottom at traditional spawning grounds where fertilized masses of perch eggs might accumulate. Divers count the number of the accordion-like egg masses found on the rock and rubble on the lakebed. When the population is strong, divers might see as many as 50 egg masses per 300-meter transect, in poor years, less than one. Last year they recorded 11.7 egg masses per 1,000 square meters.

Similarly, adult perch are netted and sampled each spawning season to get a sense of their overall health. Biologists set a goal of examining 3,000 adult perch each year. Fish are measured and weighed. Gametes and eggs may be collected for scientific studies. A few fish are tagged and released for lakewide studies. Others are kept and tissues are analyzed for signs of contaminants.

Larval perch less than a half-inch long are sampled in fine-mesh nets at the surface to measure survival and dispersal rates after hatching.

Young of the year perch are again netted in late summer/early fall using beach seines, bottom trawlers and gill nets in at least 22 different sampling stations in the nearshore area of Lake Michigan from Kenosha north to Sheboygan.

In winter, graded mesh gill nets are set offshore near the Green Can Reef in Milwaukee to estimate the survival rates of young perch adrift in the open waters of Lake Michigan. Since the survey uses gill nets from one to three inches, we get an excellent picture of the overall yellow perch population.

Even longer-term sampling on Green Bay

Perch population studies have even a longer history in Green Bay, where spring spawning samples have been collected annually at Little Tail Point for 27 years. Seining stations at 15 sites spread over 130 miles of the Green Bay shore have served as sites to sample young developing perch during June and July for each of the past 23 years. Perch have been sampled every year in late summer at 60 trawling stations on the bay since 1978, and at 18 deeper water trawling stations since 1988.

Trawling Lake Michigan aboard the Perca. © Matt Mangan
Trawling Lake Michigan
aboard the Perca.

© Matt Mangan

Biologists keep close tabs on commercial netting and the sport harvest of perch from the bay. The commercial harvest has been regulated under a quota system since the 1983-84 season. Quotas as high as 475,000 pounds a year dwindled to the current low of 20,000 pounds as perch populations plummeted. Sport creels followed similar patterns, ranging from a peak harvest of three million pounds in 1990-91 to reduced bag limits and a low of 52,429 perch in 2004.

Early indications of a comeback?

Results from all these sampling programs show perch populations that grew steadily in both Green Bay and Lake Michigan through the 1980s strongly declined in the '90s, with only one strong year class of perch in 1998 that grew into a strong class of adult perch in 2003.

Last summer's sampling results were more encouraging. Summer trawling surveys for yellow perch in Green Bay indicated 2005 produced another good year class, following decent year classes in 2002 and 2004 and the excellent year class in 2003. As expected, increased production over the past few years has started to improve fishing, and should yield good fishing in 2006 as well.

"Still, we recommend caution before increasing commercial and sport harvests too quickly," said Horns. "We are looking for unambiguous evidence that the young fish have survived and are capable of supporting larger harvests."

In December 2005, following fisheries recommendations, the Natural Resources Board approved a modest easing of restrictions on the perch harvest on Green Bay. Daily bag limits on Green Bay will increase from 10 to 15 yellow perch and the annual commercial harvest limit will climb from 20,000 to 60,000 pounds.

More sustained research will determine if bag limits can be eased lakewide. "The 2005 year-class looks good in Lake Michigan too," said Brad Eggold, DNR fish supervisor for southern Lake Michigan. "They certainly seem to have the size to survive well over the winter and we're optimistic about their continued survival and contribution to the Lake Michigan fishery in the future."