MILWAUKEE – Results from a year’s worth of assessment activities on southern Lake Michigan show yellow perch continuing to struggle -- and lend support to several theories explaining why so few fish have been produced in the last 14 years, state fish biologists say.
Underwater surveys conducted in June 2002 indicated that yellow perch are laying eggs in good numbers – at least compared to recent years. But surveys in late summer and early fall turned up low numbers of perch hatched from those eggs, continuing a 14-year-trend of paltry year-classes interrupted by "fair" year classes in 1995 and 1998.
"We actually saw a fairly big increase in the number of egg masses we saw compared to some of the earlier egg deposition surveys, and those eggs probably hatched as they always have," says Brad Eggold, Department of Natural Resources southern Lake Michigan fisheries supervisor.
"But that time between hatching and coming back to nearshore water and surviving that first winter – that seems to be doing them in. That’s the black hole."
The assessment results, Eggold and other fisheries biologists say, support continuing DNR’s ban on commercial fishing for yellow perch and a restrictive bag limit of five fish per day for sport anglers.
But also importantly, those results seem to support a theory and subsequent research to help explain that "black hole" in the yellow perch life cycle.
John Janssen, a senior scientist being funded by DNR and the University of Wisconsin-Milwaukee Water Institute to work on yellow perch, believes that wind and water currents on Lake Michigan may be blowing newly hatched yellow perch across southern Lake Michigan to where they may have a limited food supply.
So, Janssen and DNR crews in mid-summer 2002 towed a large, fine mesh net behind boats to track the fates of newly hatched yellow perch. About 10 days after hatching, the young perch had drifted and were most abundant about 10 miles offshore. A few days later, the young fish were found in good numbers as far as 25 miles offshore.
"We found that between 10 and 12 days after hatching in Wisconsin, we were getting good numbers of fish a third of the way to Michigan," Janssen says. The young fish find themselves far from home in an environment that may have little food, perhaps as a result of growing populations of the exotic zebra mussel.
On the east side of Lake Michigan, which tends to have a soft bottom, zebra mussels eat phytoplankton, Janssen says. Phytoplankton that settle to the bottom, particularly diatoms, are the primary food of the burrowing amphipod, the main organisms young perch feed on where there are soft bottoms. Zebra mussels also may filter the water, increasing the clarity so other fish may more easily see and prey upon the young perch.
"If you get fish blown to what is a food desert, you’ve got a problem," Janssen says. "Those fish have another problem in how do they find their way back home. It could be a substantial number of them don’t."
Typically, after yellow perch in Lake Michigan hatch they swim up to the surface and get caught in the currents. "After 40 or 50 days, if they’re lucky, they manage to come ashore in Wisconsin where there is rocky habitat," Janssen says. If the fish are unlucky, they get blown to the Michigan shore, where there may be a growing lack of food, presumably because of the zebra mussels.
Whatever the factors leading to the demise of young perch, the population assessments DNR and other cooperating agencies and universities did in 2002 seemed to point to the same trends visible since the mid-1990s. Young yellow perch aren’t surviving to enter the fishery; the 1998 year-class which is mainly contributing to sport fishing opportunities is declining fast.
Specifically, in 2002:
 | DNR crews using SCUBA gear to survey spawning sites in early June
found the highest number of egg masses – 573 egg masses or 11.53 per
1,000 square meters -- since such sampling began in 1997. That total
compares to a low of nine egg masses in 1997, and the second highest
total of 223 in 2001, and likely reflects the 1998 year-class in its
peak sexual maturity in 2002.
| Crews in June captured a total of 1,812 yellow perch during the
spawning season, including 167 females and 1,645 males in two lifts.
The number of fish and of female fish caught was down from 2001. Of
the 167 females, the majority of them had spawned already, 34 percent
were not yet ready to spawn, and 11 percent were ripe but hadn’t
spawned.
| Over summer 2002, DNR fisheries staff collected spines from 402
perch caught by anglers to determine the fishes’ age. Of that total,
94 percent were from the 1998 year-class.
| Crews in August and September conducted young-of-the-year (YOY)
sampling and found 1.3 yellow perch per 100 feet of seine haul, up
slightly from the last two or three years, but considerably lower than
in the 1980s. For the first time this year, DNR crews also used very
small mesh gill nets to do additional sampling, building an index to
assess the numbers of YOY yellow perch.
| DNR winter assessments in December 2002 and February 2003 using gill
nets with different size meshes hauled in only 81 fish, in some part a
reflection of windy conditions in December, January and February that
limited the amount of time the boat spent on the water. Again, the
1998 year-class showed up very well, with 88 percent of the fish from
that year class. There were few numbers of young perch.
| DNR analysis of creel surveys from 2002 showed that the Lake
Michigan perch harvest of 97, 747 declined from 2001’s sport harvest
of 133,660, but was still the second-highest since the five-fish bag
limit was implemented in 1996. It was driven by Milwaukee County,
which supplied two-thirds of the Lake Michigan total, and reflected
the 1998 year-class.
| In order to provide additional protection to the 1998 year-class,
especially mature females, the closed season was changed from all of
June to May 1 to June 15, effective 2002. | |
"What these assessments and the harvest data show is that the yellow perch population definitely is still struggling," Eggold says. "The harvest and creation of future year classes has been dependent on this 98 year class and they’re going to be age five this year. They’re still capable of spawning quite effectively.
The 2002 assessment results also are consistent with computer modeling done by Michigan State University that estimated that the yellow perch population has decreased 90 percent since the mid-1980s.
Eggold says that continuing the ban on commercial fishing and the low sport bag limit should provide the protection the fishery needs to recover, and he remains optimistic that the yellow perch population will bounce back – given the right conditions.
"Historically, they have rebounded from very low numbers in the past," he says. "But it’s going to take a set of environmental factors to come together to produce good year classes."
Results from 2002 yellow perch assessments on southern Lake Michigan are found on the Lake Michigan Fisheries Web page under yellow perch research.
FOR MORE INFORMATION CONTACT: Brad Eggold (414) 382-7921; John Janssen (414) 382-1733
