Adult River Herring Age, Growth, and Spawning Variations Among Chesapeake Bay Rivers

Anadromous alewife Alosa pseudoharengus and blueback herring A. aestivalis have been documented to spawn in the Chesapeake Bay tributaries for centuries. Collectively termed river herring, these species have recently declined in abundance to levels that have initiated moratoriums on commercial and recreational harvesting bay-wide. Declines in population sizes, as well as declines in mean length, mean length-at-age, and percent composition of repeat spawners has been observed throughout the region. The purpose of this study is to compare the adult populations spawning in various Chesapeake Bay rivers to determine if sex ratios, mean length, mean age, mean length-at-age, growth parameters, and spawning frequencies differ between river systems. Five agencies provided data for alewife in nine rivers and for blueback herring in eight rivers. ANCOVA was used to determine differences based on length, sex, and/or river and two-way ANOVA was used for mean length-at-age. Analysis of Residual Sum of Squares was used to compare von Bertalanffy growth models for each population and a Likelihood Ratio comparison was used to determine which growth parameters was the driver in differences in growth models.  Preliminary results are indicative of differences among rivers and species, information likely to be useful for conservation and management.