Abstract |
Recruitments of striped bass (Morone saxatilis) in the Nanticoke River, Maryland, had failed for a 20-yr period, leading to postulations that the river was dysfunctional with respect to its ability to produce young striped bass. The authors investigated the early-life dynamics of striped bass egg and larvae in the Naticoke during the 1992 and 1993 spawning seasons to determine if episodic weather events and water quality affected survival, growth, and potential to recruit. Fortuitously, the two years were characterized by contrasting environmental conditions. A recruitment failure occurred during 1992, a relatively dry year, but a successful recruitment was generated in 1993, a relatively wet year. The successful year class produced in 1993 was the first strong recruitment in the Naticoke since 1972. Based upon ichthyoplankton surveys from April to June in 1992 and 1993, and otolithaging analyses, the authors determined the distributions and abundances, the age structure, and the growth and mortality rate, of the wild population of striped bass eggs and larvae in the Nanticoke River. The authors had hypothesized that episodic events associated with precipitation, acidification and releases of toxic metals would lead to poor survival of larval cohorts hatched during and immediately after such events. In addition, the authors tested the ability of the nursery environment to support larval striped bass survival and growth by strategically releasing hatchery-origin larvae during April and May in each year. In each year, in situ environmental data loggers provided hourly information on temporal and spatial variability in temperature, salinity, conductivity, and pH in the nursery environment. In addition, during each ichthyoplankton survey (14 surveys in 1992, 13 surveys in 1993), site-specific measurements of temperature, salinity, conductivity, oxygen concentration, pH, alkalinity, acid neutralizing capacity, and heavy metal concentrations were obtained at sampling
sites. Zooplankton samples, from plankton-net collections at two (1992) or three (1993) sites, were obtained during each survey.
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