Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
When the leaves begin to change it’s time to look for winged mapleleaf
Midwest Region, September 10, 2012
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The full display of the winged mapleleaf indicates to divers that this mussel is ready to go release larvae for propagation
The full display of the winged mapleleaf indicates to divers that this mussel is ready to go release larvae for propagation - Photo Credit: Bernard Sietman

September brings the beginning signs of fall. Along with cooler temperatures and a wonderful palate of red and orange in the trees comes the spawning season for the federally endangered winged mapleleaf. Most mussels that are propagated at Genoa National Fish Hatchery in Wisconsin spawn in the fall and hold their larvae over-winter until they are released in the spring. However, the winged mapleleaf only holds its larvae for a few weeks and then releases them during the month of September. Several years of research indicate that the mussels will begin their displays as the water temperature drops from 70F down to 60F.

Several factors make propagating the winged mapleleaf problematic. The first is that in the Upper Mississippi River drainage, winged mapleleaf can only be found in a short reach of the St. Croix River. Second, the mussels only display about 48 hours before releasing their larvae. This means that biologists must be prepared to dive every other day during the winged mapleleaf brooding period. Finally, individual host fish for the winged mapleleaf (channel catfish) have to be longer than 8 inches to serve as a suitable host for the winged mapleleaf larvae. This means that hatchery raised host catfish require two growing seasons to reach a sufficient size. All of these factors make propagation of the winged mapleleaf a challenge.

This September all of the factors in the field lined up well and we were able to collect 10 gravid female winged mapleleaf, double the number observed in previous years. These mussels were carefully transported to Genoa NFH where they expelled their larvae and hatchery biologists placed them on over 300 channel catfish. The catfish will be held over the winter and placed out in mussel culture cages next spring. If all goes well the juveniles may be the size of a grain of rice at this time next year and marble size at this point two years from now. At that point the recovery team will determine the best locations for the animals to be released, a place that will foster good growth and survival as well as moving us closer to achieving the goals set forth in the recovery plan for the species.

Contact Info: Nathan Eckert, 608-689-2605 ex 115, Nathan_Eckert@fws.gov
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