Lake Superior has a new resident: The bloody red shrimp

Greg Stanley, The Minnesota Star Tribune on Jun 26, 2026

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DULUTH, Minn. — Donn Branstrator and his team pulled up the traps just offshore of the Duluth-Superior Harbor. There, in the nets, were dozens of tiny wriggling red-spotted shrimp, both male and female, some pregnant, some juvenile.

It was the first evidence that Hemimysis anomala, commonly known as bloody red shrimp, which is native to the Caspian Sea, had established a self-sustaining population in Lake Superior, according to a study published recently in ScienceDirect.

The invasive shrimp, which were found last summer, had survived at least one winter in the frigid Superior waters, and are likely here to stay, said Branstrator, a biologist for the University of Minnesota Duluth.

“So they’re here now,” he said. “But the jury is still out on how abundant they’re going to become and how widespread throughout Lake Superior they’re going to be.”

The fear with any invasive species is that it will disrupt and change the food web and ecology in a lake. Zebra mussels from the same Caspian Sea have upended aquatic life in the Great Lakes and forever changed their water clarity. Sea lamprey have hammered native fish populations for generations. But scientists say there is hope that the impact of the new Eurasian invaders will be limited.

The shrimp have been known to cause algae blooms and other problems in some of the western European reservoirs they invaded before reaching the U.S. They’ve been in the Great Lakes since 2006, first in Lake Michigan and Lake Huron, and then quickly spreading to Lakes Ontario and Erie. Scientists still aren’t sure what harm, if any, the shrimp have caused to those four lakes.

They certainly compete with small native shrimp, Branstrator said.

“They feed on algae and on the other zooplankton out there, which are very important food sources for native species and small fish,” he said. “But at the same time, they also become a potentially very desirable food for native fish, themselves.”

The shrimp are mostly translucent, with bright blood-red spots that give them their name. They can grow to be the size of a thumbnail, which makes them bigger than native shrimp.

Predator fish are typically drawn to the biggest prey they can find, Branstrator said.

The shrimp swim, but they don’t swim very fast. They’re typically shy and hard to spot. They try to stay in the shallows, and hide in any rocks, crevices or man-made structures they can find. For the most part, they avoid the sun and swim at night or in the shadows. But, at times, the shrimp swarm together by the thousands, much like starlings do in the sky, into swirling red masses of life.

They don’t live long, typically surviving only 9 months. But females can have up to four broods in a single summer, with up to 70 young in each brood, according to the Minnesota Department of Natural Resources.

A few bloody red shrimp were found in Superior in 2018. But those individuals were all adults, and there was no evidence that they had been able to survive a winter and establish a colony.

Branstrator believes the shrimp were likely introduced to Superior by a shipping freighter traveling from one of the other Great Lakes.

The shrimp have not been found in any inland lakes in Minnesota. The Minnesota Department of Natural Resources warns that recreational boats or bait buckets could introduce them to smaller and warmer waters, where their impact may be more significant.

Researchers with the University of Minnesota Duluth said they will continue to monitor the Duluth and Superior, Wisconsin, shorelines to learn how far and fast the shrimp are spreading.

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