TEMPERATURE EFFECTS ON THE TIMING OF STRIPED BASS EGG-PRODUCTION, LARVAL VIABILITY, AND RECRUITMENT POTENTIAL IN THE PATUXENT RIVER (CHESAPEAKE BAY)

The relationships between egg production (spawning behavior), larval g rowth and survival, and environmental conditions that larvae encounter were investigated in the Patuxent River tributary of Chesapeake Bay i n 1991. Striped bass (Morone saxatilis) eggs and larvae occurred predo minantly above the salt front where conductivity was less than or equa l to 800 mu mhos cm(-1). There were three prominent peaks in egg produ ction, each coinciding with increasing temperatures. Estimated growth rates of 6-d, otolith-aged cohorts, which ranged from 0.15 mm d(-1) to 0.22 mm d(-1) (mean = 0.17 mm d(-1)), were not demonstrated to differ significantly from each other. Observed zooplankton densities and tem perature did not significantly affect growth rates. Stage-specific cum ulative mortalities of combined cohorts were calculated for eggs (Z(st age) = 0.20 = 18.1%), yolk-sac larvae (Z(stage) = 5.80 = 99.7%), and f irst-feeding larvae (Z(stage) = 2.95 = 94.8%). The very high mortality of yolk-sac larvae suggests that dynamics during this stage may have had a major impact on subsequent recruitment. Cohort-specific mortalit y rates of larvae were variable, ranging from Z = 0.045 d(-1) to 0.719 d(-1), and were strongly temperature-dependent. Cohorts that experien ced average temperatures <15 degrees C or >20 degrees C during the fir st 25 d after hatching had significantly higher mortality rates than t hose which experienced intermediate temperatures. Estimated hatch-date frequencies of larvae greater than or equal to 8 mm SL indicated good , very good, and very low potential recruitments for cohorts spawned d uring early-season (April 2-11), mid-season (April 12-24) and late-sea son (April 25-May 5), respectively. Because seasonal temperature trend s and fluctuations are unpredictable, striped bass females cannot sele ct a spawning time that guarantees their offspring will be exposed to optimum temperatures. Consequently, selection may have occurred for sp awning over a broad range of temperatures and dates, a behavior insuri ng that some larval cohorts will encounter favorable temperatures.