An Exploratory Analysis of Biotic and Abiotic Factors Affecting Mortality and Recruitment of Monument River Alewife (Alosa pseudoharengus)

We developed 38 competing hypotheses about the causes of the decline of the Monument River alewife and used a forward-projecting statistical escapement-at-age model to test which factors may explain variability in our baseline model. Hypotheses included predation impacts by six species (striped bass, bluefish, spiny dogfish, gray seal, and double-crested cormorant), fishery impacts (the southern New England and coast-wide Atlantic herring fisheries), and zooplankton prey and environmental impacts (winter water temperatures and monthly cumulative rainfall).  Covariates were incorporated into the mortality and/or recruitment equations depending on the suspected causal link.  We used the hypothesis testing approach of Deriso et al. (2008) to determine covariate significance.

 Analyses indicated that striped bass abundance explained as a single factor significant variability when linked to mortality, whereas September rainfall, Gulf of Maine winter temperature in the first year at-sea, combined ages 0 and 1 bluefish abundance, and Gulf of Maine amphipod abundance in the first-year at-sea explained significant variability when linked to recruitment.  The best multifactor model included striped bass abundance linked to mortality, and the first principal component of the four recruitment covariates linked to recruitment.  These results indicate that likely more than one factor has caused the decline of Monument River alewife.