Use of Didson Imaging Sonar for Run Counts of River Herring (Alosa pseudoharengus and Alosa aestivalis) in Coastal Plain Tributaries of Chesapeake Bay

River herring populations of the U.S. Atlantic coast (alewife Alosa pseudoharengus and blueback herring Alosa aestivalis) have declined precipitously in the last decade. New conservation initiatives seek to reduce mortality and improve spawning runs within the next decade. A significant challenge to these efforts in Chesapeake Bay is a lack of scientifically-rigorous spawning run counts. This has been due to the flat topography and turbid water of coastal plain tributaries of the Bay, among other reasons. The purpose of this project was to use DIDSON imaging sonar to conduct spawning run counts for river herring. DIDSON units recorded fish passage continuously in Marshyhope Creek (Nanticoke River) and Mattawoman Creek (Potomac River) from March to mid-May, 2013. Electrofishing and ichthyoplankton sampling were conducted at weekly intervals to determine species composition, monitor spawning activity, and to serve as potential low-cost proxy methods for estimating run size. Although the study is ongoing, it is anticipated that the results will provide species-specific spawning run counts that can be used as a metric to evaluate progress toward conservation goals.