Effects of Salinity on Striped Bass Eggs and Larvae from the Savannah River, Georgia

Abstract Operation of a tide gate installed in the Savannah River by the U.S. Army Corps of Engineers to reduce dredging activities increased salinities upstream in important spawning habitat for striped bass Morone saxatilis . To assess the effects of salinity on survival and growth of striped bass at early life stages, newly fertilized eggs and 48‐h‐posthatch larvae were exposed to serial dilutions of seawater, with salinities ranging from 0 to 33‰ (g/L) in increments of 3‰; in addition, older larvae (5‐d posthatch) were exposed to salinities of 0, 6, 12, 18, and 24‰. Eggs were exposed until 24 h posthatch, 48‐h‐posthatch larvae were exposed for 10 d, and 5‐d‐posthatch larvae were exposed for 6 d. Eggs died within 24 h in salinities greater than 18‰. Both survival and total length of larvae hatched from eggs exposed to salinities of 15‰ or higher were reduced. Percent mortality and mean total lengths of newly hatched larvae followed the same pattern for each of three sets of salinity regimes (i.e., changes in salinities over time) that striped bass eggs might encounter during passage downstream in the Savannah River. Hardening eggs in freshwater did not increase survival or length of hatched larvae over that shown by eggs hardened in saline water. The 5‐d‐posthatch larvae were less sensitive to salinity than the 48‐h‐posthatch larvae. Survival of larvae was negatively correlated with both salinity and exposure time. For 48‐h‐posthatch larvae, the 10‐d LC50 (the salinity lethal to 50% of the test fish within 10 d) was 10‰. Probabilities of survival for larval striped bass exposed to different salinities for different amounts of time can be estimated from curves generated from models of survival analysis. Salinities judged to be critical to Savannah River striped bass eggs and larvae are those greater than 9‰.