Hydroacoustic mapping of habitat for threatened and endangered native mussels in the Upper Mississippi River

Science Center Objects

Understanding the distribution of threatened and endangered freshwater mussels is needed to conserve and restore populations. Sampling for native freshwater mussels typically involves taking quadrat samples in soft substrates and counting the number of mussels in a defined area. However, this methodology is unsuitable for detecting populations of the Spectaclecase mussel (Margaritifera monodonta, federally listed as endangered) and the Salamander mussel (Simpsonaias ambigua, under review for listing). These species occupy similar and unique habitats in rivers and typically reside associated with rock structures (e.g., flat rocks, wing dams). Given that traditional sampling methods rarely detect these species, resource managers from the U.S. Fish and Wildlife Service and state natural resource agencies are struggling to define what constitutes habitat for these two species and this information gap is limiting recovery efforts. 

 

Bathymetric dataset of the St. Croix River at Prescott, Wisconsin

Bathymetric dataset of the St. Croix River at Prescott, Wisconsin

(Credit: Hanson, Jenny L.. Public domain.)

A 3D bathymetric dataset used to analyze benthic habitats.

 

A 3D bathymetric dataset used to analyze benthic habitats.

(Credit: Hanson, Jenny L.. Public domain.)

 Hydroacoustics (underwater sonar) is a remote sensing technology currently used for mapping habitat features in aquatic systems for sedentary biota such as freshwater mussels. Hydroacoustic technology has the potential to identify and quantify habitat features for mussels associated with rock structures (such as M. monodonta and S. ambigua)) to inform management decisions. This research will evaluate the use of hydroacoustic technologies as tools to better characterize habitats in which these mussels reside.

 

depth-averaged river velocities

Depth-Averaged Velocities of the St. Croix River by Folsom Island at normal water level. The river velocities were measured using an acoustic Doppler current profiler, and visualized using the Velocity Mapping Toolbox (Engel, F.L. and Jackson, P.R. 2017. The Velocity Mapping Toolbox: User guide for version 4.09. U.S. Geological Survey).

(Public domain.)

 The objective of this research is to quantify the water depth, flow, rock structure, and rock configuration associated with habitat occupied by S. ambigua and M. monodonta.  Specifically, multibeam echo sounder and mega-imaging sidescan sonar data will be used to explore rock type and rock structure, and an Acoustic Doppler Current Profiler will be used to estimate depth and flow. An underwater camera will also be used to validate rock characterization. Combining datasets derived from each of these hydroacoustic tools should help define the distribution of these species in the Upper Mississippi River. This information will directly address management needs to identify and characterize existing occupied habitats, identify potential reintroduction areas, and implement restoration programs.

 

Images of rock substrate captured using an underwater video camera in the St. Croix River.

Images of rock substrate captured using an underwater video camera in the St. Croix River.

(Credit: Hanson, Jenny L.. Public domain.)