A species of catfish appears to be the “missing link” in the life of a rare freshwater mussel.
Scientists with the U.S. Fish and Wildlife Service recently confirmed that the blue catfish is a critical “host species” for the winged mapleleaf—setting the stage for recovery of this highly endangered mussel species.
Mark Steingraeber of the Fish and Wildlife Service’s La Crosse, Wis., Fishery Resources Office and Dr. Mark Hove of the University of Minnesota and Macalaster College collaborated on the research that resulted in this finding.
All species of native mussels--or river clams, as they are commonly called--need a fish host to complete their life cycle. Each mussel species requires a specific fish species or several species of fish to attach to and parasitize as a juvenile in order to develop into adults. The mussel larva or “glochidia” remain attached to the gills of their fish host for several weeks or months, depending on the species, before dropping off onto the river bottom.
For many freshwater mussels, biologists know which fish host species is needed. However, in the case of the winged mapleleaf, biologists did not know which species of fish the mussel needed for hosting—and ultimately survival—until now.
“ Until recently we had suspicions, but not confirmation of the fish host for the winged mapleleaf,” Steingraeber said. “We now have documentation that blue catfish and channel catfish serve as fish hosts. However, blue catfish appear to be a much better host.”
The only known reproducing populations of winged mapleleaf on the planet are in a small stretch of the St. Croix River, which separates Minnesota and Wisconsin, and the Ouachita River in Arkansas. They were already teetering on the brink of extinction when non-native zebra mussels were introduced into the St. Croix River. Zebra mussels have devastated freshwater mussel populations in areas of the Mississippi River by colonizing native mussel shells and suffocating them. Biologists are concerned that this same fate could befall mussels in the St. Croix River.
Once common in the Mississippi River drainage, the migratory blue catfish has only rarely been spotted in the stretch of river above Lock and Dam 19 at Keokuk, Iowa. Biologists suspect winged mapleleaf mussels have probably been able to maintain a minimal population in the St. Croix River by using the channel catfish as a secondary host.
“ Now that we know the fish host, we will be able to employ the conservation restoration technique of artificial propagation to help recover the winged mapleleaf and hopefully save it from extinction,” Steingraeber said.
Biologists will harvest gravid female winged mapleleafs from the St. Croix River next fall, transport them to the Service’s Genoa National Fish Hatchery in Genoa, Wis., where they will remove the glochidia and infect blue catfish and channel catfish with the developing mussels. The infected catfish will be held in cages in the river until the juvenile mussels drop off their gills.
“ We have been successful in using this technique on the endangered Higgins’ eye mussel and it holds promise for the recovery of winged mapleleaf,” said David Heath, chair of the interagency winged mapleleaf recovery team and fish manager for the Wisconsin Department of Natural Resources. “Finding the fish host is the first step in the journey of restoring this endangered species.”
For Dr. Mark Hove, finding the “missing link” in the winged mapleleaf’s life history has been a goal for several years. He credits the success of unraveling the mystery to the great cooperative efforts of agencies and institutions. The U.S. Geological Survey’s Upper Midwest Environmental Sciences Center provided laboratory facilities and technical expertise and the University of Minnesota also provided laboratory space.
Minnesota and Wisconsin Departments of Natural Resources also assisted with diving for the collection of mussels and provided invaluable technical expertise.
Funding for this project was through the U.S. Fish and Wildlife Service, the St. Paul District of the U.S. Army Corps of Engineers and Macalaster College.
The U.S. Fish and Wildlife Service is the principal federal agency responsible for conserving, protecting and enhancing fish, wildlife and plants and their habitats for the continuing benefit of the American people. The Service manages the 95-million-acre National Wildlife Refuge System which encompasses more than 542 national wildlife refuges, thousands of small wetlands and other special management areas. It also operates 66 national fish hatcheries, 64 fishery resource offices and 78 ecological services field stations. The agency enforces federal wildlife laws, administers the Endangered Species Act, manages migratory bird populations, restores nationally significant fisheries, conserves and restores wildlife habitat such as wetlands, and helps foreign governments with their conservation efforts. It also oversees the Federal Aid program that distributes hundreds of millions of dollars in excise taxes on fishing and hunting equipment to state fish and wildlife agencies.
