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Invasive ‘bloody red shrimp’ reach Lake Superior
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- An invasive shrimp native to the Black Sea has now infested all five Great Lakes.
- Researchers confirmed a breeding population of bloody red shrimp in Lake Superior’s Duluth-Superior Harbor.
- The small crustaceans likely arrived in the Great Lakes via ballast water from ocean-going vessels.
An invasive shrimp is swimming in Lake Superior. This is the last Great Lake to be invaded — all five Great Lakes now are infested by the crustaceans..
Researchers for the first time have confirmed a breeding population of an invasive Black Sea-native shrimp in Lake Superior.
The number and extent of the shrimp’s spread in Lake Superior is not clear. However, there is a breeding population in the Duluth.
The findings by researchers at the University of Minnesota-Duluth, Lake Superior Research Institute at the University of Wisconsin Superior, and the Hobart and William Smith Colleges in New York, published in the Journal of Great Lakes Research in April, found that the shrimp are now reproducing and surviving year-round in the Duluth-Superior Harbor, the farthest west the European species has been confirmed.
“Samples we collected in 2025 from two locations in the Duluth-Superior Harbor, a major inland shipping port in the Great Lakes, contained juveniles, adult males, and (pregnant or with young) adult females, indicating a self-sustaining population. Additionally, we document earlier evidence from 2018 samples we collected in the harbor that contained two juvenile specimens,” the article in the Journal said.
In an interview on the CBC’s “Superior Morning” show with Mary-Jane Cormier on June 10, lead researcher Donn Branstrator, of the University of Minnesota, said studies in the Duluth-Superior Harbor this spring after ice was off the lake found adult males and females.
“It’s pretty clear evidence of overwintering,” Branstrator told Cormier. “It would be very unlikely for the population to extinguish (at this point).”
Branstrator told Cormier ongoing bi-weekly research in the harbor, and along the Lake Superior shoreline will exam those questions.
According to the research, the non-native shrimp, about a quarter to half inch long, were first detected in the lower Great Lakes in 2006 in lakes Michigan and Ontario. By 2008, they were found in lakes Huron and Erie as well.
“It has also spread to Oneida and Seneca Lakes in New York … as well as the St. Lawrence River and various canals in northern New York State,” the research said.
Branstrator said the Black and Caspian sea region natives, also have spread throughout Europe into areas they were not native. He said they likely hitchhiked with ballast or bilge water, but the exact mechanism will never be known.
What we know about bloody red shrimp.
What is a bloody red shrimp?
Bloody red shrimp are small crustaceans native to the Black Sea and Caspian Sea region of Europe. They are adapted for fresh and brackish water.
This freshwater shrimp can be ivory-yellow in color or translucent, but exhibits pigmented red pigment cells in the carapax and tail, according to the USGS.
The quarter to half inch long shrimp feed on both phytoplankton and zooplankton at various stages of life.
While relatively small, they are among the larger creatures in the Great Lakes feeding on those food sources.
“They are very large bodied, at the upper end of what we consider zooplankton,” Branstrator said.
Branstrator said the shrimp live in near-shore environments and like to hide in crevices during the day, making use of dock pilings, breakwaters and other human-made structures.
They come out at night and “swarm” together in groups of up to 135 per square foot, the University of Wisconsin Sea Grant said.
Bloody red shrimp have a lifespan of about nine months, grow to adults in just 45 days, and an produce up to four generations per year. Females have been documented to carry up to 66 eggs in a clutch. Broods carried by females in the Muskegon population ranged from two to seven.
Where have the shrimp been found?
The shrimp have spread throughout Europe and now have been found in all five Great Lakes, as well as some locations away from the lakes.
The recent study found a breeding population in the Duluth, Minnesota, harbor, the first in Lake Superior.
According to the research, the non-native shrimp, about a quarter to half inch long, were first detected in the lower Great Lakes in 2006 in lakes Michigan (near Muskegon) and Ontario. By 2008, they were found in lakes Huron and Erie as well.
A single specimen was found in Duluth in 2017, and two were found in 2018. It wasn’t until 2025 that the researchers found a sustaining population when they captured 81 individuals.
How did the shrimp arrive in the Great Lakes?
The shrimp likely hitched a ride in the ballast water of ocean-going vessels, although Branstrator noted during an interview on CBC’s “Superior Morning” that we will never know for certain.
He added that the shrimp have multiple opportunities to hitch rides with vessels during the shipping season.
What impact will the shrimp have on Lake Superior and the Great Lakes?
Branstrator said that question hasn’t been answered. They feed on the same sources as other water-dwelling creatures, but they are large enough that small fish may find them to be a new food source.
Are any shrimp native to the Great Lakes?
The opossom shrimp is a Great Lakes native and looks similar to the bloody red shrimp.