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Fighting Fish


This summer, Lake Michigan perch anglers can expect to see modified harvest regulations, lots of five-to seven-inch and 10- to 15-inch fish, and if all goes well, a big hatch of baby fish, according to experts from the Department of Natural Resources.

Lake Michigan perch study provides a glimmer of hope for the future.

The Department recently announced that it is eliminating the "slot limit" that required anglers to release any fish shorter than eight or longer than 10 inches. Also, the closed season has been moved to July from June. Unchanged are the 15-fish daily catch limit and the prohibition of commercial fishing. The June closure had been in effect since 1995, while the slot limit, daily catch limit and commercial fishing ban have been in effect since 1997.

The changes are a direct result of the Yellow Perch Lakewide Research Initiative begun in 1996 to find what caused the population of these popular fish to crash in the early 1990s. Study participants include the Illinois, Indiana, Michigan and Wisconsin departments of natural resources, the Illinois Natural History Survey, the National Oceanic and Atmospheric Administration, the U.S. Fish and Wildlife Service, the universities of Illinois, Maryland, Michigan and Wisconsin, and Central Michigan, Loyola, Michigan State and North Carolina State universities.

Typical of the fish caught by NHS researchers during perch spawning season is this adult male measuring almost a foot long. (NHS Photo)


February 2001


NHS researchers

NHS researchers prepare a fine-meshed neuston net for larval perch sampling. The one-by-two-meter nets generally are used for nighttime sampling. (NHS Photo)

"We've pulled in people from just about everywhere," laughed Dan Makauskas, perch project manager for the Illinois DNR's Lake Michigan Program. "We had a Purdue connection too, but he moved on."

Makauskas said the perch initiative wasn't so much a new study as it was an attempt to coordinate all the studies taking place lakewide.

"All the (fisheries) managers saw the same thing," Makauskas said. "We were collecting adult fish, and for the years up to the 1990s were collecting young-of-year, three-month-old fish. Starting in 1991, we stopped collecting young-of-year fish. Maybe we were missing them in our collection devices, but they never showed up as adults later on. That's what led us to this study. Something's happening in those first few months. That's what most of the research initiative isó the early life history starting from eggs and working all the way up to the three-month-old stage."

Dr. John Dettmers, director of the Lake Michigan Biological Station for the Natural History Survey, said larval research begun by his agency in 1987 provided a good starting point for the study, as did DNR's perch assessment begun in 1976.

Natural History Survey researchers use a bottom trawl to capture 2-to 3.5-inch young-of-year perch during their fall survey. (NHS Photo)

"Because of the long data set we have from the fish assessment and on early life stages from the NHS data, Illinois probably has the best long-time series of all life stages of the yellow perch of anyone on the lake," Dettmers said. "So our assessment is really useful on a lakewide perspective."

The DNR assessments take place in June in waters up to 60 feet deep near Lake Bluff and off Foster Avenue in Chicago, while the NHS surveys are conducted numerous times between May 1 and Oct. 15 at depths ranging from 15-30 feet at locations one mile north and one mile south of Waukegan Harbor.

A recent study by Beak Consultants Inc., launched in response to commercial fishermen's complaints that DNR assessments were inaccurate, found just the opposite to be true. In its two-year study, Beak sampled five areas, four times per year, in depths up to 97 feet, and concluded that the majority of yellow perch were found in less than 60 feet of water. There was no consistent trend in the number of fish caught at various times of the year, though the study did conclude that nearly equal numbers of males and females were caught in September, and more male fish were caught in June.

"Some of the complaints people had about our adult assessment were that it was conducted in the same places at the same time of year and the fish had moved as conditions changed and we didn't move with them," Makauskas said. "If anything, the Beak study showed we were getting an accurate assessment, and there's no burning need to change it."

With the veracity of the assessments no longer in question, the lakewide research initiative will attempt to discover why, with the exceptions of 1995 and 1998, the recruitment of new yellow perch in the 1990s was so abysmal.

The initiative has two main components: sampling of larval fish from conception to three months of age, and trying to determine why the larvae are not surviving past three months.

Dettmers said that at age three, female perch begin laying egg masses once a year. The number of eggs in a mass varies from 60,000



larval yellow perch
A 15-day-old larval yellow perch measuring 12 mm as seen through a microscope. (NHS Photo)

to as many as 150,000, with fish ages 4-6 (peak fertility years) laying more eggs than younger fish.

"Some of our work entails diving to count the egg masses and bringing samples into the lab to check for viability," Dettmers said. "These eggs are very viable and hatch at 90 to 95 percent. We can raise the larvae quite well in the lab on zooplankton and things like that. It appears to us that it's not an issue associated with poor fertilization. It seems the problems occur after the larvae hatch."

When a perch egg hatches, the larva feeds on the yolk sac for about a week, Makauskas said. After that, it feeds on zooplankton for 30 to 40 days and then on benthos (amphipods, scuds and insect larvae) until it gets big enough to eat crayfish and other fish.

Dettmers said a number of reasons have been hypothesized for the drop-off in larvae numbers that began in the mid-1990s. These include a reduction in zooplankton due to the presence of zebra mussels; predation by alewives on either larval perch or zooplankton; and adverse water currents that may be moving larval fish away from food supplies.

Circumstantial evidence points to zebra mussels as the most likely culprit, he said, noting that the last year of really strong yellow perch recruitment was 1988. A year later, zebra mussels were first discovered in the lake. The mussels, alien invaders from eastern Europe that arrived here in the ballast of cargo ships, feed by filtering phytoplankton or algae from the water. Zooplankton also feed on phytoplankton.

Dettmers said the NHS has been counting the amount of zooplankton in the water since 1987. In 1988, the zooplankton density was about 55 per liter. Since 1996, zooplankton densities have ranged from 5 to 30 per liter, with the 30 coming in 1998, the last year of decent perch recruitment.

"It appears as though critical minimum density of zooplankton for good recruitment of yellow perch is somewhere between 50 and 100 per liter of water," Dettmers said. "They're not real efficient feeders at that point, and that gives them enough targets so they don't have to work too hard. We see a strong correlation between the amount of zooplankton present when larvae are first out there and the number of young-of-year fish we get back in our trawls and seines in the fall."

Makauskas said that while zebra mussels compete with zooplankton for phytoplankton, another alien invader, the alewife, competes with perch for zooplankton. Alewives first appeared in the lake in 1949, ushered in by construction of the Welland Canal bypass of Niagara Falls.

In addition to eating zooplankton, alewives eat larval perch. Therefore, increases in the alewife population could mean decreases in the perch population.

A third hypothesis is that larvae spawned near shore may be moved too far off shore by winds or currents to find benthos when they reach that stage of life.

"Once they hatch, yellow perch come up in the water column to feed on zooplankton," Dettmers said. "When they're an inch or so long, they want to settle down and feed on benthos in relatively near-shore areas. If currents are transporting larvae far off shore where there may be higher zooplankton densities, in the short term, it may be beneficial. But if they're trying to settle out in 200 or 300 feet of water, they won't find benthos.

"We have no idea what happens to those fish," Dettmers continued. "Do they just kind of go away? Do they somehow find a way to get back before they drop down? Or, can they make their way back up from the depths? Those are unanswered questions."

A NHS diver looks for yellow perch egg masses at a survey site near Waukegan Harbor. (NHS Photo)

NHS diver

February 2001


Yellow perch Larvae

Week-old yellow perch larvae are less than a half-inch long. The bottom larva still has a portion of its yolk sac attached. (Photo by Steve Robillard)

To help provide answers, Dettmers said larval sampling was begun in 2000 in 150 to 200 feet of water north of Waukegan. He added that the sampling will continue this year and next and that other states may also begin sampling at those depths.

The perch study has produced some good news: the number of eggs being laid appears to be increasing. "We went from two or three egg masses per transect in 1996 to seven or eight per transect last year," Dettmers said. "We're on what apparently is a rising curve and are hopeful that it will continue this year as more fish from the 1998 year class become mature."

The 1998 class was apparently spawned in 1995, Makauskas said. "In 1998, 85 percent of the females we had in our assessment were from the '95 class. It's possible 2001 will be a good year. It seems like we should have more eggs this year. If they stay as viable as they have been, we should have more larvae out there. All we need to do is get them some grub."

DNR Biologist Rich Hess (left) and Technician Dave Gene seine for young-of-year perch near Waukegan. (Photo by Dan Makauskas)
Rich Hess

To enhance the chances for a good spawn, DNR has made slight alterations in the perch harvest regulations. A major one is moving the closed season to July from June.

Makauskas said June was originally chosen because 25 to 28 percent of the year's total perch harvest is taken during that month and because it was the only month all four Lake Michigan states could agree on. To further reduce the catch and increase the chances for good spawns, the 8- to 10-inch slot limit was added in Illinois because most of the fish in that range were males.

"There was a big slug of fish growing real slowly, mostly males spawned in the late '80s," Makauskas said. "That slot had so many males and so few females that your odds of catching a female were pretty small. As that population of fish has grown, and we've gotten a few younger fish in there, it's gotten to the point where the percentage of females and males in that range is more equal. Your odds of catching a female might be one in four now."

Because the slot was eliminated, a different way had to be devised to keep perch harvests low, Makauskas said. The Department proposed keeping the June closure, but reducing the daily catch to 10 fish; or keeping the 15-fish limit and closing the season in July when 44 percent of the fish are traditionally taken. At a November meeting, constituents proposed a third option-closing the season from April 15 to June 15 and keeping the 15-fish limit-but the Department vetoed it because only 21 percent of the yearly catch is taken in that span.

Makauskas and Dettmers said the other three states have no plans to alter their current regulations. Wisconsin has a five-fish limit and June closure; Michigan a 35-fish limit with no closed season; and Indiana a 15-fish limit with no closed season.

Michigan and Indiana have more liberal regulations than Illinois because they don't have as much fishing pressure, Makauskas said. "In the late 1980s, when perch fishing was really going, Indiana was taking out 100,000 to 120,000 fish in their shore fishery. We were taking out a million and a half. They just don't have the access or the effort."

As the lakewide perch initiative proceeds, plans are to build a population model that takes in all ages of fish. Dettmers said that would be three to five years away, while Makauskas estimated it wouldn't be finished until 2010.

"To put an age structure model together, you need a long-term database from sport fisheries, the assessments and whatnot," Makauskas said. "It needs to be taken in a coordinated, consistent way around the entire lake. Right now we don't have that."



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