The effects of elevated salinity on river herring embryo and larval survival.

River herring (Alewives; Alosa pseudoharengus and Blueback Herring; Alosa aestivalis) populations have undergone dramatic declines in recent years. Although the exact causes for these population declines are unclear, evidence suggests that factors such as habitat loss and dam construction may prevent upstream migration to spawning grounds, resulting in river herring spawning below the head of tide. As below the head of tide spawning may prematurely expose river herring embryos and larvae to saline environments, a series of experiments were conducted to determine the effect of elevated salinity on embryonic and larval survival. Embryos of both species were acutely exposed to salinities of 2, 5, 10, 15, 20, 25, and 30 g/L as well as to simulated tidal salinity fluctuations, and survival was assessed. Larvae (1-8 days post hatch; DPH) were acutely transferred to 2.5-30 g/L water, and survival was assessed after 24 h. Larvae (0-12 DPH) were also gradually acclimated to salinities ranging from 2.5-30 g/L, and survival assessed 24 h post exposure. Embryonic alewife survival was high (>97%) at salinities ≤10 g/L while blueback herring embryos displayed a wide salinity tolerance throughout the range. Embryos of both species exhibited high survival in tidal salinity exposures. Survival of acutely-transferred alewife and blueback herring larvae decreased with increasing salinity (>20 g/L). Both species were tolerant of high salinity conditions by 15 DPH. These experiments demonstrate that survival of river herring embryos and larvae may be possible in tidally-influenced areas, depending on the developmental stage and rate of salinity exposure. [ABSTRACT FROM AUTHOR]