Each spring when the ice begins to break up, northern pike get the yen to migrate. They leave the waters of Green Bay, where they spend most of their adult lives, and swim up Duck Creek, the Little Suamico River and other tributary streams to spawn.
This ancient pilgrimage in search of shallow wetlands where female pike release their eggs and males fertilize them is not new. But the challenges they face along the way are. Wetlands have been drained and converted to other uses. Streams are now bisected by thousands of road crossings.
“Northern pike are a major focus of The Nature Conservancy’s conservation work in the Green Bay watershed,” said Nicole Van Helden, who directs the Conservancy’s work in the watershed. “If we can protect and improve their habitat, many other species of fish, crayfish and mussels will benefit.”
The northern pike is a top predator in Green Bay, feeding on other fish and helping to keep their populations in balance. It is also a big contributor to the bay’s multi-million-dollar sport fishing industry. But pike populations in the bay have been declining, and loss of spawning habitat is believed to be a major factor. The Conservancy has launched a project to identify and remove barriers to fish migration that will give northern pike and other aquatic species a fighting chance.
Barriers to Fish Passage
Roads and streams intersect in thousands of places across the 10.6-million-acre Green Bay watershed. At these crossings, culverts and bridges have been installed to channel water under the road.
While bridges can constrict water flow, culverts are the biggest problem. The wrong type of culvert or improperly installed and maintained culverts disrupt fish migration by blocking access to miles of feeding and spawning habitat. They are also barriers for mussels, whose larvae disperse by hitching a ride on fish gills.
“Poorly constructed and placed culverts can cause many different kinds of problems for fish and other aquatic organisms,” said Mark Fedora, a USDA Forest Service hydrologist. “If the drop at the outlet of a culvert is too great, fish can’t jump up into it. If the water velocity is too fast, fish may tire before they make it through the culvert and get washed back out. Too little water in the culvert, and fish can’t swim through.”
Identifying Problem Culverts
With support from the EPA’s Great Lakes Restoration Initiative, last year the Conservancy and the Wisconsin Department of Natural Resources (DNR) began identifying places where road-stream crossings could pose barriers to fish passage in the Duck-Pensaukee watershed, a sub-watershed of Green Bay on the west shore. This year, the project is being expanded throughout the Green Bay coastal zone.
“We started by inventorying the entire Duck-Pensaukee river system, which meant visiting more than 1,400 locations where maps indicated there were potential road-stream crossings,” said Matt Diebel, aquatic ecologist with the Wisconsin DNR.
“We mapped 1,100 actual road-stream crossings, and then Nature Conservancy staff, University of Wisconsin-Madison graduate students and volunteers spent hundreds of hours gathering data on the size and condition of the culverts, the velocity and depth of water in them and other factors such as whether or not there was an outlet drop,” Diebel added.
All the information was put into a database and analyzed using a program that Diebel developed to show which barriers to fish passage in a watershed should be repaired or replaced to open the most stream habitat for northern pike. His program also factored in the cost to replace each culvert, allowing him to calculate how much benefit was derived for each dollar invested.
“This tool will help the Conservancy and our partners make smart, cost-effective decisions about where to invest in fish barrier removal in the watershed,” said Van Helden. “We’ll also share it with towns and other municipalities and encourage them to consider fish passage along with stream size, flow rates and other factors when they prioritize where to invest in culvert repair and replacement.”
Workshops Promote Fish-friendly Culverts
In addition to the fish barrier assessment, the Conservancy has been working with multiple partners in Wisconsin and Michigan to host workshops for road engineers and resource managers on designing and constructing fish-friendly culverts. The 2.5-day workshops include in-class instruction and field activities that illustrate problem culverts and possible solutions.
“Road engineers have a lot to think about when designing safe, effective road-stream crossings,” Diebel, who is a workshop instructor, commented. “We hope these workshops will provide them with practical design approaches that will allow fish passage and be more resilient to high stream flows and floating debris, which should reduce the long-term cost of maintenance and replacement.”
“Our focus on improving fish passage for northern pike in the Green Bay watershed is part of a broader Nature Conservancy effort in the Great Lakes basin,” Van Helden commented. “What we learn here can be utilized elsewhere to restore the connectivity among tributary streams and open waters, as well as surface and groundwater, which is essential to a healthy Great Lakes system.”