Cold, windy December day yields important data for Lake Michigan fisheries management

ABOARD THE RESEARCH VESSEL COREGONUS – At a time of year when most Lake Michigan anglers are content to count their blessings, Wisconsin Department of Natural Resources fisheries staff are out counting fish.

The 60 foot Research Vessel Coregonus plays a critical role in DNR fisheries research including winter yellow perch assessments in early December. The boat is used heavily throughout the year for a variety of scientific data collection and offshore stocking projects.
The 60 foot Research Vessel Coregonus plays a critical role in DNR fisheries research including winter yellow perch assessments in early December. The boat is used heavily throughout the year for a variety of scientific data collection and offshore stocking projects.
Photo Credit: DNR

With a cold northwesterly wind blowing across 5 miles of open water on this December day, it’s not an easy job. Lifting two gangs of graded mesh gill net stretching some 1,600 feet, the four fisheries team members aboard the DNR Research Vessel Coregonus are collecting data that will help inform management decisions on yellow perch and round whitefish.

The team is led by Dave Schindelholz, a DNR fisheries technician with more than 15 years of experience who is serving as biologist-in-charge. Working in an enclosed lab and processing space behind the boat’s pilot house, Schindelholz alternates between freeing fish from the incoming net and recording data from the entire team so that surviving fish can be quickly released.

Joining him are Brandon Bastar, the research vessel’s captain; Tim Kroeff, a fisheries technician based with Bastar in Sturgeon Bay; and Tom Burzynski, a fisheries technician with Schindelholz out of Milwaukee. As the men wait for the hydraulic winch to reel in the next round of fish, they talk casually about how cold air moving over warm water creates bigger waves – seemingly oblivious to the effects of the unpredictable swells as the 60 foot boat pitches forward, backward and side to side.

“The Coregonus is a critical part of our research effort and really allows to us work safely and efficiently in all kinds of weather,” Schindelholz says. Commissioned in 2011, the vessel’s name derives from the genus of nine species of fish native to Lake Michigan including the commercially important lake whitefish, lake herring and bloater chub.

With safety equipment including a 10-person life raft, emergency positioning beacon, cold water survival suits and watertight compartments to keep the boat afloat if the hull is punctured, the Coregonus represents a major advance over the 74-year-old RV Barney Devine that was retired after the 2010 season. A key feature of the Coregonus is the large winch system used for hauling in weighted gill nets that are hung in established locations and strung together in gangs of up to 2,000 feet.

View a video of the crew of the Coregonus at work on the DNR Facebook page.
View a video of the crew of the Coregonus at work on the DNR Facebook page.

The boat also supports the use of trawl nets and diving survey work. The size and scope of its capabilities keep the Coregonus busy almost continuously from early April through December as fisheries staff conduct assessments of whitefish, lake trout, burbot, forage fish such as alewife, bloater chubs and yellow perch as well as Green Bay offshore stocking activities. From its home port in Sturgeon Bay, the Coregonus travels from northern Lake Michigan and Green Bay south to Algoma, Port Washington and Milwaukee.

The yellow perch work that takes place in early December is conducted over known spawning habitat in 65 to 80 feet of water. To maximize the benefits of the time on the water, Schindelholz and the crew are also collecting data on round whitefish populations and alewife numbers as well as information about the yellow perch.

“Our focus at this time of year is on the yellow perch because we do have ongoing concerns about the survival rates given the changing Lake Michigan ecosystem,” Schindelholz says. The spread of filter feeding aquatic invasive species such as quagga and zebra mussels reduce the volume of phytoplankton and ultimately zooplankton available to young perch, which also face competition for habitat from invasive round gobies. The December perch surveys follow spawning assessments conducted in early June with both gill nets and dive team members.

The invasive mussels and gobies make their presence known as the gill net rolls up from the depths, streaming in through a sliding window and onto the stainless steel table inside the processing area of the Coregonus. Hung the previous day, the net yields a remarkable diversity of aquatic species — including invasive mussels that are caught in the plastic mesh and clatter around on the table as the fisheries team members pull them off. Round gobies meet a fitting end as they are tossed back outside the window to a flock of waiting seagulls.

The net also pulls in both stocked and naturally reproduced lake trout. While open water swimming species such as chinook and coho salmon generally avoid the gill nets, alewives, brown trout, burbot and round whitefish fill out the catch of the day. The round whitefish are kept for further data collection back on shore while the other fish are quickly released.

A few young perch have found their way into the net, important evidence that the biologically significant and highly sought-after species continues to reproduce on the historic spawning grounds. It will take additional data collection and analysis in the weeks ahead to determine how overall numbers fit into the broader trends observed in recent years.

Back on shore, inside UW-Milwaukee’s School of Freshwater Sciences, Schindelholz and Burzynski set to work on the whitefish, measuring, weighing and dissecting them with surgical skill to check on the overall health of the fish and remove the delicate otoliths or ear bones needed to ascertain age. With precision that can only be achieved through years of practice, they take turns with knife and pen, processing and preparing samples for 28 fish in about 30 minutes.

Brad Eggold, DNR Great Lakes fisheries supervisor, said the success of DNR’s Lake Michigan management efforts depends on the abilities of the team members as well as the research infrastructure required to support their work in the harshest of conditions.

“We’re fortunate to have the dedicated people that we do, as well as access to the tools we need to perform our full range of work,” Eggold says. “This type of applied research is critical to understanding the population dynamics of key species and the impacts of lake-wide changes in the Lake Michigan food web. The work is fundamental to our fisheries management efforts.”

To learn more, visit and seach “Research Vessel Coregonus.” For more information about Lake Michigan management efforts and news of upcoming opportunities for stakeholder engagement, visit “Fishing Lake Michigan.”