Growth, mortality, and recruitment of larval Morone spp. in relation to food availability and temperature in the Hudson River

We measured age and growth of larval striped bass (Morone saxatilis) and white perch (M. ameri- cana) and tested whether growth and survival were enhanced in relation to a seasonal pulse ("bloom") of high zoo- plankton abundance. Growth rates were lowest before the zooplankton bloom and highest afterwards for both fish species. An index of recruitment po- tential (instantaneous growth rate, G, divided by instantaneous mortality rate, Z) did not relate clearly to either water temperature or to zooplankton abundance in the case of striped bass but did relate to both factors for white perch. Retrospective analysis of hatch dates in recruited juvenile striped bass from the same year class indicated that later, faster growing cohorts were un- der-represented when compared to the larval cohort distribution, and that co- horts that co-occurred with high densi- ties of the cladoceran zooplankton Bosmina freyi were over-represented. Comparison of these results with simi- lar analyses from other systems sug- gests that biotic controls on year-class strength may predominate in estuarine systems where physical factors are rela- tively damped (Hudson) but may play relatively minor roles in those systems with high physical variability. venile hatch dates should reflect the differential survival (assuming ad- equate sampling). These measures can also be used with repeated sam- plings of the population to track the growth and mortality of specific age classes (e.g. weekly cohorts) over time. Relationships between these cohort-based rates can be analyzed with respect to variables such as food availability, predation, and the physicochemical environment. We previously documented that larval striped bass (Morone saxa- tilis) and white perch (M. ameri- cana), which co-occurred with in- creases in crustacean zooplankton in the tidal Hudson River, showed a potential energetic advantage compared with larvae that preceded the zooplankton increase (Limburg et al., 1997). A major increase ("bloom") in zooplankton in early summer is a key feature of the Hudson estuary. Larvae occurring before the bloom are exposed to sparse zooplankton densities and low temperature, both of which are associated with mortality risks (Rogers and Westin, 1981; Chesney,

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