Environmental Correlates of River Herring Spawning Run Timing in the Chesapeake Bay Watershed

River herring (Alewife Alosa pseudoharengus and Blueback Herring Alosa aestivalis) have received increasing attention in recent years due to dramatic population declines and their importance as forage and fishery species. Relatively little information about river herring spawning runs exists for Chesapeake Bay tributaries, which likely make up a substantial portion of the mid-Atlantic stock for each species. Relationships between spawning run timing and environmental variables are an important, but poorly understood, aspect of spawning runs in the region. We have conducted hourly river herring spawning run counts in three tributaries of Chesapeake Bay since 2013 (Choptank River, Deer Creek, Marshyhope Creek) using Dual-Frequency Imaging Sonar (DIDSON). In the present study, we evaluated relationships between the timing of pulses of both upstream and downstream adult migrants and environmental variables (temperature, flow, light:dark and lunar cycles). Preliminary analyses indicated that upstream migration was primarily correlated with increasing temperature during the afternoon and evening, and that downstream migration was correlated with low and decreasing flow. There was no apparent relationship between run timing and the lunar cycle. These results provide important information for the design of run monitoring strategies and the operation of fish passage structures.