For the Department of Natural Resources the first step in managing the fish populations in any body of water is to understand what's there.

The large lakes -- in Michigan there are 92 inland lakes of 1,000 acres or more -- pose a particular challenge for fisheries managers since it takes more work to assess the status of fish populations in these waters than local DNR crews can accomplish.

So in 2001, the DNR Fisheries Division started its Large Lakes Program with an eye toward pooling state personnel and equipment to survey the larger bodies of water.

"A single fisheries crew tending a dozen nets on a lake the size of Houghton Lake (20,075 acres) is not enough effort to make a detailed biological assessment of the fishery," said Patrick Hanchin, fisheries biologist at the DNR's Charlevoix Fisheries Research Station. "Four crews tending a dozen nets each for two weeks, however, can produce tremendous results."

Surveys begin immediately after ice-out and consist of intensive netting and electro-fishing operations. The weather can be severe in early spring, but DNR crews have to set their nets before the pike and walleye begin spawning.

"During the summer, we often hear comments from the public such as 'I wish I had your job,'" Hanchin said. "That doesn't happen during the ice-out surveys."

Fisheries personnel count and measure fish and collect spines or fin rays to determine fish ages. Workers often place metal jaw tags on legal-size walleyes, northern pike, smallmouth bass and muskellunge, hoping anglers will turn them in to the DNR when they catch the fish.

"Tag returns allow us to estimate the percentages of legal-size fish that are harvested in a given year," Hanchin said. "Occasionally, we also learn some interesting things about fish movement from the tag returns."

Hanchin said walleyes tagged in the Muskegon River, for example, have been caught by anglers in more than a dozen different tributaries to Lake Michigan and as far away as the Menominee River on the Michigan-Wisconsin border, a distance of more than 200 miles.

In fact, a walleye caught in a 2007 DNR survey of Portage Lake (Houghton County) traveled at least 400 miles from the Nipigon River, where it had been tagged by the Ontario Ministry of Natural Resources in 2002.

Year-long creel surveys, conducted as part of the program, help quantify angler harvest and effort on each body of water.

"Although our netting surveys tell us quite a lot, the creel survey completes the picture for each water body," Hanchin said. "A 2001 survey, for instance, revealed there was more effort by anglers on Houghton Lake (Roscommon County) in a single year than there was on the Michigan waters of Lake Erie or the Michigan waters of Lake Superior. That piece of information, gained in the first year of the program, told us quite a bit about the significance of the fisheries on these large inland lakes."

Information from the Large Lakes Program benefits managers in several ways. Recently, information from monthly angler harvest surveys helped the DNR decide to extend walleye, northern pike and muskellunge seasons in the Upper Peninsula.

"Tag return data was instrumental in providing a scientific rationale for extending those seasons," Hanchin said.

Fish population estimates have changed fish stocking practices on some lakes, too.

"We found that on South Lake Leelanau, walleye abundance was high, growth was slowing and natural reproduction was improving," he said. "In order to efficiently use our limited production of spring fingerling walleyes, it just didn't make sense to stock South Lake Leelanau anymore."

The large-lake survey effort also is yielding additional information on the life history of some species. This year, the DNR surveyed Elk and Skegemog lakes in cooperation with the University of Michigan. Surgically implanted transmitters in eight muskellunge will allow active tracking of fish movements.

"We are using the survey on Skegemog Lake to learn more about muskellunge behavior in the Torch Lake chain of lakes," Hanchin said. "We are most interested in learning about spawning locations and timing, along with over-wintering habitats."

Although the Large Lakes Program depends on cooperation from numerous district teams, that effort is not unusual, he said.

"The cooperation demonstrated by everyone on the Large Lakes Program is great, but it's nothing new. Our employees team up on numerous statewide projects every year, from salmon and steelhead egg-takes to fish stocking to even fighting forest fires."

To learn more about the Large Lakes Program, visit the DNR Web site at www.michigan.gov/dnrfishing.