It’s a cold, overcast day at the end of March and Petrifying Springs Park is brown and leafless – still waiting on its spring greenery. Which means it’s a great day to find some fish here where Pike Creek flows into the Pike River.
Specifically, John Rodstrom, a graduate student at the University of Wisconsin-Madison’s Center for Limnology, is searching for migratory fishes – species that move inland from Lake Michigan each spring to spawn. Native northern pike migrate each spring, as do the steelhead that the Wisconsin DNR stocks into Wisconsin waterways. But Rodstrom is primarily on the hunt for suckers, a bottom-feeding fish that moves by the millions from the Great Lakes into inland tributaries each year. In terms of sheer biomass, the sucker migration rivals that of the iconic salmon making their way from oceans to fresh, inland waters.
This massive migration will also help Rodstrom and other scientists at the Center for Limnology better understand the impact the occurs when streams meet roads.
There are 43 migratory species of fish in the Great Lakes (both native and non-native) and 661 tributaries for them to use. There are also well over 100,000 road crossings. Many of these are bridges, where the river or creek runs unconstrained below. Many, however, are not. And it’s these culverts or other obstacles that can become an impassable barrier for a fish trying to get upstream.
“When fish hit a wall, they’re not going to be able to get any farther upstream and that really limits the amount of habitat that’s available for them to spawn in,” says CFL post doctoral researcher, Allison Moody. “This is a really big issue in the Great Lakes.”
Moody, along with her colleagues in the CFL’s McIntyre Lab, have literally put this issue on the map. The result is an impressive visualization of the entire Great Lakes basin complete with tributaries and road crossings. This giant GIS mapping project is the reason Rodstrom is out wading hip-deep in cold water just a few miles inland from Lake Michigan. He is helping “ground truth” the earlier computer models used to develop the map.
Upon reaching a new site, he takes out a small computer and pulls up the map. He is then able to add information that wasn’t captured by the mapping process – what the river underneath the crossing looks like. Is it likely to keep fish from heading further upstream, or is it passable?
“What we’re doing,” says Rodstrom, “is surveying during the fish migration to see how many of these barriers they’re able to pass by. We want to know which barriers are truly barriers to fish migration.”
The information he’s able to provide will help researchers better understand how fish populations are impacted when their paths upstream are blocked. It will also help guide stream conservation efforts as it can identify regions of the watershed where dam or road culvert removal will yield the best results by targeting prime spawning habitat or focusing on making the longest possible stretches of stream passable.
In addition to updating the map, Rodstrom is counting fish. Specifically, he’s looking at how many white and longnose suckers he finds in each pool or riffle. It’s not an attempt to take a complete census of sucker populations, so much as it is an attempt to see just how far upstream the fish will go and what sorts of barriers prove impassable.
Rodstrom straps on a device that looks vaguely like a backpack taken from the set of the Ghostbusters movie and begins waving a yellow wand back and forth in front of him as he wades upstream. Moody and field tech, Alex Koeberle, flank Rodstrom, wading a yard or so downstream, holding nets on the end of long poles. The wand produces a mild electrical field which stuns fish. They briefly float to the surface and are quickly netted, identified, counted, and sent back into the stream.
Aside from the occasional flash of silver from a steelhead building a redd (or nest) the stream looks deserted. But, in the span of only a couple of hours, Rodstrom’s work yields several dozen fish, mostly white suckers.
Rodstrom stops to pull one sucker out of a net and get a better look at it. Considered a “rough” or “trash” fish by many Wisconsin anglers, the sucker migration is an important source of nutrients for stream ecosystems each spring. And, says Rodstrom, “they’re also an important indicator of water quality. Suckers don’t always get the love they deserve, but I think they’re pretty cool.”
He lowers the fish back into the stream and it slips back into its annual migration. From larger rushing rivers, to tiny winding streams, fish are on the run again in Wisconsin.
(Follow John’s field work on Twitter: @migratoryfishes #fishontherun)