The Dynamics of Bay Anchovy in the Hudson River Estuary: Process-Oriented Studies and Long-Term Changes

摘要

We review three areas of recent research on Hudson River bay anchovy Anchoa mitchilli. One focus has been the along-estuary movement of early life stages. A cohort analysis of samples collected in a spatiotemporally extensive monitoring program confirmed that early-stage anchovy migrate up-estuary at an estimated rate of 0.6 km/d. Complementary fine-scale field sampling found that early-stage anchovy can show preferences for depth and can conduct periodic vertical migration. To determine whether these behaviors were sufficient to produce up-estuary migration, larval flux and velocity were estimated. These estimates were consistent with local retention rather than concerted migration. High priority should be given to examining individual migration histories through analysis of otolith microchemistry. A second focus of research on Hudson anchovy has been on local population structure, permitting comparison to anchovy in other locations. Anchovy that spawn in the Hudson River are larger than those spawning in the Chesapeake Bay region and are mostly 2 years old, whereas yearlings predominate in other estuaries. Batch fecundity was lower and egg mortality higher in the Hudson River than in Chesapeake Bay. A key issue arising from these recent findingsis the degree to which the Hudson anchovy pool is connected with other large anchovy pools, such as Narragansett Bay and Chesapeake Bay. A third focus of research on Hudson anchovy has been interannual variability in early-stage abundance. A more than 20-year time series of juvenile bay anchovy abundance shows that juvenile abundance has varied over one order of magnitude. There has been no significant change in abundance over the entire time series, but abundance has declined 10-fold since a peak in the late 1980s. Anchovy abundance was negatively associated with the abundance of early-stage striped bass Morone saxatilis and positively associated with the abundance of early-stage Atlantic tomcod Microgadus tomcod. We suggest that these associations reflect direct interactions among the species and urge further work on the ecological role of striped bass in the estuary.