These juvenile winged mapleleaf mussels were collected from culture cages in the St. Croix River. - USFWS photo

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Service and other agency biologists successfully recovered 11 artificially propagated winged mapleleaf mussels from culture cages in the St. Croix River near Hudson, Wis., on Oct. 4.  This successful experiment marks the first time the mussels have been artificially propagated and is a major step toward helping to recover this endangered species.

The winged mapleleaf mussel has a complex life cycle that begins in early fall when a gravid (fertilized) female produces glochidia (larvae) and releases them into the river.  These glochidia float through the water until they perish or are inhaled into the gills of an acceptable host fish.   The glochidia attach to the host fish gills and stay there until the following spring when the mussels are large enough (3-5mm) to detach from the fish, settle to the river bottom and begin life on their own.

Because of the endangered status of the mussel and the complex nature of their reproductive cycle, developing a successful process for helping the mussel to reproduce is a significant part of their recovery plan.  Researchers overcame a major hurdle in the process in 2003 when they determined that blue and channel catfish were acceptable host fish for the mussel.

This latest attempt to artificially propagate the winged mapleleafs began in September 2004 when SCUBA divers and snorklers from the Minnesota DNR, Macalester College, the National Park Service and the U.S. Fish & Wildlife Service’s Twin Cities Field Office searched the St. Croix River and found two gravid female mussels. The mussels were taken to Macalester College where they were allowed to release their glochidia. These glochidia were then rushed to Genoa National Fish Hatchery where they were released into a tank of 100 channel catfish held to act as host fish.

 To mimic the natural cycle of the mussel, infested channel catfish were held at Genoa NFH in a recirculating tank with a chiller unit to replicate water temperatures recorded in the St. Croix River. In May 2005, as the waters of the St. Croix warmed, the channel catfish were acclimated to the warming waters then placed in cages set on the bottom of the St. Croix River. Divers removed the channel catfish in late June, leaving any successfully detached juvenile winged mapleleaf mussels in the river to continue growing in the cages.  On Oct. 4, divers checked the cages and found the 11 successfully propagated mussels in the sediment that remained in the bottom of the cages.

An attempt to duplicate this experiment began in September when divers found three new gravid winged mapleleaf mussels in the St. Croix.  Biologists infested 300 channel catfish with the glochidia from these mussels and will hold them at Genoa NFH over the winter until they are placed in cages in the river next spring.  Hopefully next fall, more successfully propagated mussels will be found. 

Information provided by Gary Wege and Nick Rowse, Twin Cities FO; and, Tony Brady, Genoa NFH