It is an all-too-familiar story and those who know the Saginaw Bay fishery can recall it vividly. Around the middle of the 20th century, Saginaw Bay's fish community was found to be severely degraded and the walleye population collapsed in the mid-1940s. Why?

"It was due to pollution, habitat destruction and over fishing," said Dave Fielder, fisheries research biologist aboard the DNR research vessel Chinook. "Things began improving in the 1970s with the passage of the Clean Water Act and that's also when the DNR began a walleye fingerling stocking program in the early 1980s to take advantage of the improving conditions."

Over the past 35 years, fishery management efforts have focused on the recovery of walleye which serves as the keystone predator of the bay and provides one of its primary fisheries.

Fundamental to this management and recovery effort has been evaluation of the status of the entire fish community of the bay and gauging the effect of management activities like stocking. The DNR began those studies in 1971 with an annual trawling survey to sample fishes. The effort was expanded in 1989 to also include a gillnet-based survey. These two surveys continue and today provide the basis for most of the understanding of the status and trends in the fish community as well as a gauge of progress toward recovery.

Perhaps the word "trawling" is most familiar with oceanic coastlines. But, trawling has a more universal application, including here in the Great lakes.

Trawling is done by towing a large baglike net along the bottom of the lake for 10 minutes at a time. This method is very good at capturing juvenile fishes and small forage fishes. Trawling in recent years has been performed by the Channel Cat, a research vessel out of the Lake St. Clair Fisheries Research Station. The gillnetting portion of the study also is used to sample some juveniles but mostly adults of important species such as walleye and yellow perch. Gillnetting is performed by the Chinook out of the Alpena Fisheries Research Station. The two parts of the overall fish community survey happen each year in September and provide two very different looks at the bay's fish community.

The gillnet collections use a variety of mesh sizes to obtain a cross section of all sizes and ages of fish. Mesh sizes range from a small one-and-a-half-inch stretch mesh up to five-inch stretch mesh. Each panel is 100 feet long for a total net set of 1,100 feet. These nets are set on the bottom overnight and marked with surface buoys. The Chinook returns in the morning to lift the nets and remove the fish. The entire process is elaborate; first recovering the buoy and anchor on one end of the long net. The buoys and anchors are removed and the net is fed into a hydraulic lifter that actually does the pulling. The net spills onto a table and the fish are tangled in the net. The crew of the Chinook then has to remove each fish by hand. The crew is very skilled and experienced at this process and normally makes a fast job of it. Still many of the fish are difficult to remove and the entire effort is a delicate process especially when the wind and weather pulls the boat against the net.

It is especially challenging for the boat captain who has to continue to maneuver the boat to try and maintain position so as not to drag the net.

"Once the fish are on board, the 'work up' begins," Fielder said. Each fish is identified, counted and measured for total length. 'Target' species, where more information is required, also will be weighed and examined to determine sex, maturity, stomach contents and more. Scales or spines are collected to allow the age of the fish to be determined later. Those samples are examined under magnification to count the annuli, the fish's equivalent to a tree's growth rings. Each annulus represents one year of age. The age data is very important to assessing the status and health of any given fish population. It takes about 16 net sets spanning eight different sites to fully characterize the status of the fish population in Saginaw Bay. The entire survey takes about eight days but can last longer if bad weather slows down operations. In the months after the survey, laboratory analysis continues and finally the data is entered into a computer database and analyzed. Analyses include comparison to measurements in past years to see how the populations are trending.

The survey requires that most of these fish are sacrificed but like giving a blood sample at the doctor's office, biologists learn an enormous amount about the health of the fish populations. Often the same specimens are provided to others for more study. Many universities request some of these fish to be retained for further study. They also often make use of the same data sets for investigation of still more questions. After all the data is collected, any fish remaining of any consumption value are donated to food pantries.

"Saginaw Bay's fish community continues to reflect considerable change," Fielder said. "There has been an unfortunate and steady progression of exotic species invasions over the last 20 years, including white perch, zebra mussels and round gobie, which have altered the fish community in various ways."

The trawl and gillnet surveys have proven critical to enabling biologists to understand the effects of these nonnative species. Most recently, alewives have declined greatly in Lake Huron and since about 2003 have not been using the bay for spawning. The absence of adult alewives has allowed for greatly improved walleye and yellow perch reproduction. This has been an unexpected boon for the walleye fishery, helping to make great strides in recovery of that species. Unfortunately, the yellow perch juveniles have not survived as well as the walleye juveniles and the overall perch population has not greatly benefited from this new situation.

"If there is one thing we've learned on Saginaw Bay," Fielder said "is that the only thing constant is change."

By that he means the fish community and overall ecosystem of Saginaw Bay is dynamic and is evolving.

"Every year we learn something new," he said.

For more information on the status of the Saginaw Bay fishery and all fish research conducted by the DNR and its cooperating agencies, visit the DNR Web site at www.michigan.gov/dnr.