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Hunting Invasive Crayfish in Michigan Rivers and Streams

man netting crawfish samples in a river

In 2014, when Kelley Smith began his master’s degree program at MSU, crayfish were not on his professional radar. That changed when the Michigan Department of Natural Resources put out a call for proposals from researchers to execute a statewide survey of Michigan’s rivers and streams in search of evidence of the red swamp crayfish.

The southern Ohio native had just completed two and a half years as a contractor for the U.S. Geological Survey’s fisheries division when Michael Jones — Peter A. Larkin professor of quantitative fisheries in the MSU Department of Fisheries and Wildlife and MSU AgBioResearch assistant director of natural resources programs — approached him about a crayfish research project.

Once Smith began his work, he was joined by Brian Roth, MSU AgBioResearch ecologist and invasive species expert.

Netting Results, One Crayfish at a Time

“All it takes is a five-gallon bucket, a pair of waders and a net on a long pole,” Roth explained how the team collected data on crayfish. “Kelley and his field technicians waded the streams, overturning rocks on the bottom and scooping with the nets to see what they could find.”

This method, called dip netting, was adopted because it could be implemented across the diversity of Michigan river and stream systems, allowing for consistent results. Many streams in the state, for example, feature coarse substrates like boulders or stone cobbles that would render other techniques unusable. While data collection may have been simple, selecting the streams for sampling was not. Using the MDNR stream database, the agency’s collection of information on every river and stream in the state, the team randomly selected streams, and segments of those streams, in every region of Michigan.

This gave a statistically valid estimation of crayfish populations throughout the state without having to tackle the task of surveying each and every stream. In the first year, the project only had funding to survey the Lower Peninsula, but the MDNR was so satisfied that they extended it for a second year in order to cover the Upper Peninsula as well. Gauging wild populations of crayfish was only one aspect of their work, however. In order to fully assess the risk of invasion Michigan faced, the team had to look for other ways crayfish could arrive.

One of the team’s hypotheses regarding the origin of the first red swamp crayfish carcasses found by anglers was they had been purchased for live bait and escaped. As this is similar to how the crayfish had first become established in other regions, they decided it was worth investigating. At the time, it was legal under Michigan law and MDNR policy to import live red swamp crayfish for personal consumption, and there was concern they were also being brought in for other purposes, not only for bait, but as pets or classroom science projects.

Smith and his team identified and visited numerous bait shops, pet stores and seafood markets to assess the potential for red swamp crayfish to enter the state. They also surveyed 157 public school science teachers regarding use and disposal of live crayfish.

No Red Swamp Crayfish – Yet
After two years and surveying hundreds of stream sections in the Upper and Lower Peninsulas, Smith’s team did not find any live red swamp crayfish in the wild, nor did they find that stores or classrooms presented a particularly serious invasion gateway.

“In general, we didn’t find that there was one pathway that was by far the most likely through which an invasion could occur,” Jones said. “Instead, we found that we have to pay attention to all of them.”

In response, MDNR has placed new restrictions on importing any non-native live crayfish, including red swamp crayfish, in order to limit potential invasion.

“Red swamp crayfish are still a concern, because the Ohio population is still located very close to Michigan, but we were relieved to find out they weren’t already here,” Roth said. “Your best opportunity to control any invasive species is very early, before they get firmly established, and we know now that we have that chance to take preventive action.”

The team did uncover a more comprehensive picture of the crayfish population in Michigan than had been available since the first statewide survey 80 years ago. Having such a complete data set will allow MDNR officials to make sound, science-based, natural resources management decisions that will impact anyone who relies on Michigan’s ecosystems, from recreational anglers to commercial fishermen to anyone buying local seafood at the store.

… But Rusty Crawfish Are Here

The lack of red swamp crayfish was certainly welcome, but not all of the insights derived from the project were so optimistic. Smith discovered that another invasive species, the rusty crayfish, has spread significantly in the last 40 years.

“They’ve gone from being in just a few counties to spreading across the entire Lower Peninsula and into the Upper Peninsula,” Jones said. “From our findings, we can say that rusty crayfish are present in about 60 percent of our watersheds. Of equal importance is what that means for our native species.”

While not all of the data has been processed, Smith said he learned from similar research conducted in Wisconsin that rusty crayfish frequently outcompete native species, such as northern crayfish and northern clearwater crayfish, pushing them into less desirable habitats where they are exposed to greater fish predation. By cutting vegetation with their pincers, they have also threatened important fish populations like bluegill and bass, whose young rely on vegetation for shelter.

In addition to finding the extent of rusty crayfish expansion, the team was able to describe the most desirable habitat conditions. In streams with beds of rock or stone cobble, for example, rusty crayfish spread rapidly and displace nearly all native species. In streams with more malleable beds of mud or sand, however, native species have proven resilient despite their new neighbors.

– excerpted from James Dau, Futures, Fall/Winter 2016

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