By Titus Seilheimer, Fisheries Specialist, University of Wisconsin Sea Grant Institute
The arrival of bloody red shrimp (Hemimysis anomala) in Lake Superior is a reminder that ballast water transport remains a major issue for the St. Lawrence Seaway and international shipping. Although only a single individual was captured in the Duluth-Superior harbor, the find highlights the connections between all the Great Lakes. This native of the Caspian Sea in Europe was first discovered in Lake Michigan, and since then has been found in all the lower Great Lakes.
Ballast water has been a major pathway of species introduction since the St. Lawrence Seaway opened in 1959. Ballast water treatment systems have the potential to reduce invasive species coming into the Great Lakes from international ports and from moving among Great Lakes ports. Ships entering the Great Lakes are required to first exchange their ballast water at sea to kill any potential Great Lakes invaders. This strategy seems to be working because only two new suspected ballast water introductions have been detected since 2006.
Lake Superior has fewer invasive species than the other Great Lakes and is largely dominated by native species. The arrival of bloody red shrimp in the Duluth-Superior area might not be all that surprising because of the high amount of ship traffic entering the harbor each year. The bloody red shrimp has been expanding its range in Lake Michigan where it is commonly found in harbors and rocky habitat. These harbors are often visited by freighters that are moving between Great Lakes ports.
Researchers have begun to investigate the impacts that the bloody red shrimp may be having on Great Lakes ecosystems. Studies from the University of Wisconsin-Milwaukee have found that species such as alewife and rainbow smelt have been feeding on bloody red shrimp, but impacts on other aquatic organisms through competition or predation are unknown. As a new prey species, bloody red shrimp might provide some predatory fish with a new food source, especially in Lake Michigan where quagga mussels have greatly altered the composition of the food web. Future changes to the Lake Superior food web from the bloody red shrimp are uncertain, so it will be important to carefully track their status going forward.
Editor’s Note: On April 18th the US Senate narrowly blocked legislation that would have weakened ballast water regulations aimed at halting the spread of aquatic invasives such as the bloody red shrimp. The failed legislation included a revision of the Vessel Incidental Discharge Act (VIDA) which would have exempted ballast water from Clean Water Act oversight by the Environmental Protection Agency (EPA) and stopped most states’ efforts to regulate ballast water. Minnesota Senators Amy Klobuchar and Tina Smith and Wisconsin Senator Tammy Baldwin voted against the legislation; Wisconsin Senator Ron Johnson voted for it.