Davis, M. and S. Miller. 1996. A mussel survey of the Sunrise River, Minnesota 1996. Final report submitted to the Minnesota Department of Natural Resources. 11+ pp.
Mussel studies of the Sunrise River were initiated in response to reports by the MN Pollution Control Agency (PCA) of substrate composed entirely of mussels in one of their sampling sites. In addition, the presence of numerous rare mussel species in the nearby St. Croix River suggested the possibility of their presence in the Sunrise River. This study was initiated in September, 1996. A catchment area of approximately 100 square miles drains into the Sunrise River. The headwaters of the Sunrise River originate in and flow through the Carlos Avery Wildlife Management Area, and through two lakes whose outlets have been dammed. Three distinct segments of the Sunrise River were sampled, the North Branch, West Branch and the Main Stem which enters the St. Croix River near St. Croix RM 77. Fifteen sites were sampled in the Sunrise River system. Both quantitative and qualitative methods were used during this survey. Qualitative sampling was done at every site visited and consisted of visual searches while wading, feeling through the substrate, and searching the shoreline and gravel deposits for empty shells. More labor intensive, quantitative methods were employed at five carefully selected sites. To quantify a site's mussel community and species demographics, a one quarter meter square circular frame was randomly placed on the river bottom, all material was removed to a depth of fifteen centimeters, placed into a one quarter square inch mesh screen, and sieved to remove silt, sand and small gravel. Mussels from each of the five to eight samples collected at a site were placed in a mesh bag and stored in the stream until sampling was completed. A data entry was made for each mussel collected, included were the identifying frame number; species name; length, height and width in millimeters; and age (from annual growth arrest line counts). Twenty one species of mussels were collected from the Sunrise River during this survey, twenty alive. Four are listed in Minnesota as Threatened; Actinonaias ligamentina, Alasmidonta marginata, Elipsaria lineolata, and Pleurobema coccineum (sintoxia). Four others are listed as species of Special Concern; Eliptio dilatata, Lasmigona compressa, Lasmigona costata, and Ligumia recta. Average mussel density ranged from 8 per meter square to 188.8 per meter square. At the site of highest density, seventeen mussel species were found alive. Most abundant at this site were the state Threatened, Actinonaias ligamentina followed in abundance by Lasmigona costata, listed as a species of Special Concern. Other species found at this site and listed as Threatened were Alasmidonta marginata and Pleurobema coccineum, and of Special Concern Elliptio dilatata, Lasmigona costata and Ligumia recta. Length and age distribution analysis indicated continuous recruitment for the most abundant species, fourteen juveniles with byssal threads attached were collected during quantitative sampling, an indication of recruitment within the past year. Mussels were not found on the North Branch, raising questions about the suitability of this stream for aquatic life in general. Mussels were found in the West Branch, but were limited to xxx species. It is the intent of the Minnesota Department of Natural Resources to use the information collected during this survey to protect the mussel fauna of the Sunrise River and the integrity of its watershed in order to sustain the health of these significant mussel populations.