Assessing the relationship between critical acidic conditions in Maryland coastal plain streams and predicted mortality of early life stages of migratory fish

Abstract

This study was designed to assess the relationship between critical acidic conditions (pH, monomeric aluminum) in Maryland coastal plain streams and predicted mortality of early life stages of migratory fish such at yellow perch, white perch, blueback herring and alewife (focal species). Physicochemical parameters were evaluated in three acid-sensitive coastal plain streams in Maryland (Mattawoman Creek, Bacon Ridge Branch and Faulkner Branch) during rain events. Monitoring of focal species was conducted to determine whether potentially toxic acidification conditions from episodic acidic rain events occurred simultaneously with the presence of susceptible early life stages of the four migratory species. Critical acidic conditions for larval alewife were reported in Mattawoman Creek concurrently when these life stages were present in the creek. Critical acidic conditions were also reported for blueback herring and alewife in Bacon Ridge Branch; however, populations of these two species were not reported during our monitoring efforts. Populations of yellow perch and white perch were also very low or absent. The few yellow perch collected in Bacon Ridge Branch were likely a result of a stocking effort. Alewife, blueback herring and white perch ichthyoplankton were collected at Faulkner Branch; adults of all four focal species, except blueback herring, were also collected. Critical acidic conditions for blueback herring and alewife were reported for only two out of eight possible intervals in this stream. Episodic acidification events in Maryland coastal plain streams are stressful to alewife and blueback herring and are inhibiting recovery of these depleted stocks.