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Thousands of wetland acres and hundreds of stream miles along Green Bay's western shore lie dry and invisible most of the year. These ditches, intermittent streams and grassy areas form ephemeral wetlands and waterways that are only soaked in springtime when they are full of spring rainfall and snowmelt. For a short time the shallow, flooded landscape creates watery pathways that connect with each other and eventually with Green Bay. During this short high-water period, northern pike migrate miles up these small streams and wetlands to lay eggs.
Northern pike are sometimes called "water wolves" due to their aggressive behavior, torpedo-like bodies, long snouts and rows of razor sharp teeth that keep them near the top of the aquatic food chain. Northerns provide fine eating, great sport and they control large numbers of unwanted prey species, including several exotic species that are now found in Green Bay. They are an important component of the Green Bay ecosystem and have been evolving with the system for the past 10-12,000 years. Ironically, northerns don't get much respect and are the Rodney Dangerfields of the piscine world.
In 1988, DNR fisheries personnel started noting a gradual decline in the commercial catch of northern pike and an apparent decline in the number of adult pike in Green Bay. That population drop combined with continued loss of wetland acres caused great concern and warranted studies to examine northern pike spawning behavior. Our intent was to protect the spawning habitat northerns were using and to find areas where spawning habitat could be restored.
Most northern pike that reside in Green Bay travel inland to spawn. Most spawning takes place on the west shore of the bay that slopes gradually inland for 40-50 miles. The Niagara Escarpment, a layer of really hard rock forms the steep, precipitous east shoreline whose rocky coast has few wetlands. We suspect pike have followed this behavior since glacial times more than 10,000 years ago almost perfectly matching their spawning and rearing runs to the springtime formation of these shallow waters in late March and early April.
Radio tracking studies demonstrated that northern pike sometimes travel great distances on these inland spawning runs. They initially move from the bay in larger streams then progressively into smaller and smaller waterways. Regardless of how far they travel, they almost always end up spawning in shallow waters 10 inches deep or less in ephemeral streams or wetlands. We've caught young of the year in traps as far as 45 miles inland and our radio-tracking studies have followed spawning adults 15 miles inland. We know some of the Green Bay pike travel at least that far and we suspect these fish travel to the very headwaters of the west shore watersheds.
In the spring of 1998, our crews implanted radio transmitters in 22 northerns caught in the mouth of the Pensaukee River. We followed the fishes' movements every day and documented them. Road culverts that were too high for the fish to jump into posed the biggest obstacle to migrating fish. In some areas sediment and algae caused by runoff from agricultural operations coated spawning beds and made it difficult for the eggs to attach to the vegetation.
The formative weeks in shallow waters
As they travel, adult pike form spawning groups that usually consist of one or two relatively small males and a larger female who is full of eggs. Suitable vegetation provides all the stimuli they need to prompt the simultaneous discharge of eggs and milt. The vegetation may be true wetland plants or even submerged terrestrial vegetation, but it must be clean and have plenty of places for the adhesive eggs to attach. The vegetation also must be sturdy and dense enough to keep the fertilized eggs off the bottom in well-oxygenated water for two weeks until the fry hatch. Sedges and other true wetland species were used historically, but submerged grasses including the persistent exotic reed canary grass will do.
Newly hatched pike are only about a quarter-inch long. They swim very actively for a day or so then, remarkably, these tiny fish secrete a mucous-like substance from specialized epithelial cells on their foreheads. This material forms a globule, and the fry bump into clean stalks and re-attach to vegetation by means of a mucilaginous "sucker." The fry then back off a quarter-inch or so to form a thread-like strand between the vegetation and their heads. They remain attached to vegetation for four to five days while absorbing their yolk sacs. Thereafter the small fry break off the attachment and begin to feed voraciously on zooplankton they find in the warm shallow water where they were born. Shortly afterward they begin to feed on insects and fish.
When they reach about 20 millimeters (3/4 inch) in length, the young northern pike are physiologically prompted to emigrate back to the body of water that their parents came from - in this case, Green Bay. The fry drift very slowly downstream with the current. It can take weeks or even months for the young to reach Green Bay.
To a certain point, a slower trip is better because the young pike can spend a long time in this shallow nursery. It provides the same comforts as any good nursery – it's warm (as compared to Green Bay), there's plenty of food, and plenty of protection from predators. Submerged grasses, sedges, other vegetation, and leafy detritus form great cover with many places to hide. The warm, shallow water produces large numbers of zooplankton and insects and the young pike grow very rapidly. By the time they reach Green Bay in the middle of June, the ephemeral streams and wetlands have dried up. Before the end of their first summer, well-fed northern pike may be 10 inches long, a size that makes them competitive with the larger fish in Green Bay proper – if they survive.
Green Bay proper is a hostile place for young northern pike. In smaller inland lakes, young pike usually find cover in the shallow littoral habitat along the shoreline. In Green Bay, there isn't much of this weedy habitat. The shorelines are windswept and very turbulent. It's difficult to hide from predators, and the huge mass of water is slow to warm. So pike learned over millennia that survival meant staying in the shallow wet areas of the bay's western shore until they were big enough to fend for themselves in the open waters.
A need to protect seasonal wetlands
Ephemeral wetlands receive little legal protection. Since these shorelands and uplands only remain saturated with water for a few months, they often do not develop the soil characteristics necessary to be classified as wetland according to current state and federal standards. Likewise, many of the streams young northerns use as migration routes are not considered navigable by current standards. As a result, they are not afforded the same protection as navigable streams. That makes these lands more prone to development and alteration during drier months.
Wisconsin has lost about half of the 10 million acres of wetlands it had before statehood as residents and governments filled in or drained them for agriculture, development and highways. Green Bay has lost about 70 percent of its wetlands. Beyond their value as northern pike nursery, these lands mitigate flooding, help maintain surface and groundwater quality, recycle nutrients and provide habitat for a variety of plants and animals.
There are some hopeful signs. We're defining and ranking the spawning grounds and migration routes that need to be saved. Already, a few projects are underway to save some of these vital spawning grounds. For example, bulldozers contoured portions of a 40-acre field about a mile from Green Bay so that during spring snowmelt the field resembles a five-acre pond with the hummocks that form fertile spawning grounds.
Across the road from that site, pike are already benefiting from a spawning ground restoration project DNR fisheries technicians designed and the Department of Transportation created. In Brown County, the Department of Natural Resources, the Brown County Parks Department, the U.S. Environmental Protection Agency, Wildlife Forever and the US Fish and Wildlife Service combined efforts to create an eight-acre spawning marsh site on the Barkhausen Waterfowl Preserve. In nearby Outagamie County and a portion of Brown County, the combined efforts of the Outagamie County Land Conservation Department, Brown County Planning Commission, USDA-NRCS and the Oneida Tribe created more than 12 miles (over 80 acres) of streamside buffer to provide northern spawning habitat. This protected area gives young pike a place to hang out while they grow.
Other supporters of "the people's fish" are also making a difference for the Green Bay population. PikeMasters is one such sportfishing group that has helped me out on several occasions. For instance in the dry spring of 2003, I feared adult pike would not be able to make it upstream to their spawning marsh at Barkhausen Waterfowl Preserve. I set fyke nets in the Suamico River and asked the PikeMasters for help. At their cost and on a weekend we lifted nets, removed the ripe northern pike and transported the fish to the spawning marsh. Fortunately, we got lots of precipitation later in spring and more than 50,000 very robust young pike migrated from the marsh back to Green Bay later that year. Given support, we'll continue restoring spawning habitat parcel by parcel to help sustain these magnificent fish.
Though we've lost many acres of wetlands from the Green Bay ecosystem, we're fortunate that, to a degree, northern pike have been able to adapt to habitat created by man. Such habitat restoration, however, is very expensive and its success isn't guaranteed. Our first goal remains protecting the ephemeral wetlands nature provides each spring and other areas to ensure that healthy, diverse aquatic ecosystems on Green Bay's west shore include peaceful backwater nurseries for the water wolf.
Richard Rost is a DNR fisheries habitat and management technician based in Peshtigo. Lisa Gaumnitz is public affairs manager for DNR's water programs.