Little Fish Proves a Big Mystery at Phalen Lake

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by Chuck Debevec

The Riverview Times
October 2001 (Volume 8 Issue 10)
Rainbow Darter

The rainbow darter is normally found in fast-moving streams but somehow has found its ways to Lake Phalen and established a viable population that is puzzling to experts.

St. Paul's Lake Phalen is harboring a piscatorial anomaly.

It's been five years since the first Rainbow Darter was found in Phalen but the mystery of how the streams species of fish came to dwell and even thrive in the East Metro lake and no others remains unsolved.

The Rainbow Darter, a cousin of the more rare, Snail Darter, was discovered in 1996 by state Department of Natural Resources employee Melissa Drake, according to Konrad Schmidt, a DNR nongame fish biologist who has been trying to figure out whether the bait-sized fish is native to Phalen or a more recent transplant. The Rainbow Darters are not on the endangered species list but live in only six to eight streams in Minnesota and no other lakes.

"At first we did not believe that an almost 100 percent stream species would have been found in the lake. Darters like rapid, clear streams and there are not any populations anywhere in Ramsey County," Schmidt said. "So this is a real puzzling thing."

Rainbow Darter populations can be found in the St. Croix River downstream of Taylors Falls, in a few southeastern Minnesota rivers such as the Zumbro and Root, up into the headwaters of the Minnesota River, the Yellow Medicine and Redwood rivers. Interestingly, they can be found in the Ottertail River- the only population found in a stream flowing north into Hudson Bay. All the others are in streams that drain into the Gulf of Mexico.

The initial speculation was that the Rainbow Darters, which grow to about 2 1/2 inches, were "a bait pail introduction"-some angler simply dumped his darter minnows into the lake at the end of a day of fishing. Usually, it's anglers who are responsible for non-native species where they don't belong, Schmidt says. "The bait pail hypothesis is strong because that is what they (anglers) do-it?s illegal but they throw their bait in the lake."

But Schmidt says there are holes in the bait bucket theory because using Rainbow Darters for fishing is very rare. "I've never seen a rainbow darter in a bait bucket or a bait store. They don't work as bait. They die on you. That's why I have a problem with that (theory). But I don't have a better answer."

If the darters weren't being used as bait, then someone could have netted some in a stream in outstate Minnesota and deliberately put them in Phalen for some unknown reason. Regardless, the fish then would have had to adapt from a stream to lake conditions quickly enough to create a self-sustaining population.

So, is it possible the darters are native to Phalen, having perhaps migrated up from the Mississippi River back when the lake was connected to the nearby big river?

"It's a possibility but we have no records, to support that," Schmidt said. "Who knows? You could say now the Mississippi River is the cleanest it's been in a century. We've really cleaned it up. The mussel populations are resurging. What was it like before we started the flour mills and dumping raw sewage into the river? It could have been Rainbow Darters were right here in downtown St. Paul. We don t know. They definitely could have migrated up when there was a connection with Lake Phalen. But I'm not ready to take that leap.

"It's always kind of fun to hypothesize how something might have gotten there in the first place. But we have no evidence, no proof, to say that is what happened."

The bait pail theory "is the only really plausible idea," he says. "But again, if the DNA says they are very different from other Minnesota populations-that they really stand out--then your original suggestion that they did migrate up over a century ago and actually adapted through evolution to a lake environment is possible. Until we get that DNA evidence, we really can't say anything."

"You really have opened up a can of worms here," said Schmidt, who says there have been citations referring to darter population in reservoirs. "But they never seem to flourish well in reservoirs. There is not a single citation of populations living in a lake."

Still, the bait pail theory was generally accepted until Ray Katula of the Native Fish Conservancy began collecting samples and spawning them. "He said right from the beginning...these things are just peculiar," Schmidt said. "These things are acting more like a true lake species. They seem to avoid current. He said he thought the color patterns were different from those he had collected from other Rainbow Darter sites."

Schmidt said this raised his curiosity level and he contacted Dr. Lawrence Page, a noted freshwater fish expert from Illinois, who was also puzzled by the wide variation of color and scales of these unusual lake darters.

"It raised a big question mark. What are these things? We don't know. How did they get there? We don't know. They are different from other populations." Schmidt said.

Specimens also have been sent over to the Bell Museum at the University of Minnesota for study. But research funding is limited and progress has been slow. Schmidt has been volunteering his time to the effort to learn more about the darters but he says he would like to see someone come forward to do more comprehensive research on them, perhaps a graduate or doctoral student.

"I'm waiting here quite anxiously (to find out whether) the DNA will tell us anything," Schmidt said.

"I don't know how much longer it'll take to find out if we have something different here or not. It's raised a large question mark but there are no hard answers."

Schmidt says it's "really tough to say" how many darters are living in Phalen but notes some observers have spotted good numbers of them in the spring after ice out when they move into the shallows to spawn. "They seem to be well established. They still seem to like rocky areas. I have seen them schooling in sand but near rocks. They still have that in common with their stream cousins.

Schmidt worries that the darter population could be adversely affected by other actions, such as last year when the DNR transplanted 20,000 channel catfish fingerlings in Phalen. Catfish are predators and he was concerned they might decimate the darter population before it was determined whether they are native to the lake or not. But so far that hasn't happened.

Regardless of how the Rainbow Darters came to reside in Lake Phalen, their presence is good news for the urban lake. "Darters, in general, are indicators of really good water quality," Schmidt said.