Abundance, Demography and Environmental Drivers of River Herring Spawning Runs in Chesapeake Bay Tributaries

River Herring harvests in Chesapeake Bay (Alewife Alosa pseudoharengus and Blueback Herring Alosa aestivalis) declined precipitously in recent decades. The purposes of this project were to establish baselines for abundance and demography of runs in key spawning streams (Choptank River, Nanticoke River, Lower Susquehanna River) and to investigate environmental drivers affecting the timing of runs. Fish counts were conducted at hourly intervals from March to May 2013-2015 using DIDSON multibeam sonar and species composition and demography were determined weekly from biological samples collected using electrofishing or net sampling.  Spawner age distribution was determined from otoliths and the percent of repeat spawners was determined from spawning marks on scales. In the Choptank River in 2014, preliminary estimates of upstream migrants were 422,736 Alewife and 629,500 Blueback Herring. These estimates compare favorably with run counts from 1972-1973 of 39,397-271,497 Alewife and 34,297-531,146 Blueback Herring. There were significant differences (p<0.05) in demographic parameters among species, sites and years. For example, repeat spawners made up as few as 50% of male Alewife and as many as 70% of female Blueback Herring.  Variability in the timing of the spawning run was dominated by variation in water temperature, flow and the diel cycle.