Contacts
Mark Steingraeber, 608-783-8434
Rachel F. Levin, 612-713-5311
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.
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