Retention of White Perch and Striped Bass Larvae: Biological- Physical Interactions in Chesapeake Bay Estuarine Turbidity Maximum

Physical and biological properties of the Chesapeake Bay estuarine turbidity maximum (ETM) region may influence retention and survival of anadromous white perch (Morone americana) and striped bass larvae (Morone saxatilis). To evaluate this hypothesis we collected data in five cruises, three during May 1998 and two during May 1999, in upper Chesapeake Bay. Time series of freshwater discharge, water temperature, wind, and water level explain differences in ETM location and properties between cruises and years. During high flows in 1998, a two-layer response to wind forcing shifted the ETM up-estuary, while a high discharge event resulted in a down-estuary shift in the salt front and ETM location. In 1999, extremely low discharge rates shifted the salt front 15 km up-estuary of its position in 1998. During 1999, the ETM was less intense and apparently topographically fixed. Gradients in depth-specific abundance of ichthyoplankton were compared with salinity and TSS concentrations along the channel axis of the upper Bay. During 1998, the high flow year, most striped bass eggs (75%) and most early-stage white perch larvae (80%) were located up-estuary of the salt front. In addition, most striped bass (91%) and white perch (67%) post-yolk-sac larvae were located within 10 km of maximum turbidity readings. Total abundance of white perch larvae was lower in 1999, a low freshwater flow year, than in 1998, a high flow year. In 1999, striped bass larvae were virtually absent. White perch (1977–1999) and striped bass (1968–1999) juvenile abundances were positively correlated with spring Susquehanna River discharge. The ETM region is an important nursery area for white perch and striped bass larvae and life-history strategies of these species appear to insure transport to and within the ETM. We hypothesize that episodic wind and discharge events may modulate larval survival within years. Between years, differences in freshwater flow may influence striped bass and white perch survival and recruitment by controlling retention of egg and early-stage larvae in the ETM region and by affecting the overlap of temperature/salinity zones preferred by later-stage larvae with elevated productivity in the ETM.