Freshwater mussel records collected by the Maryland Department of ...

In 2009, E. complanata remained the most frequently encountered mussel;
collected at 44 sites (Table 1). Since 1995, they have been collected 251 times from 209
sites, a distribution spanning 46, 8-digit watersheds in Maryland (Figure 7); most of these
observations were made in the Chester River basin. Five confirmed host fishes were
common to very frequent at sites with E. complanata (Table 3). Anguilla rostrata was
found at nearly every site where E. complanata was also present. Other documented, but
uncommon host fishes were represented primarily by non-native and migratory species.
Congenerics of confirmed host fish and hosts of congeneric mussels were rarely
collected. The distribution and means of nearly every environmental variable examined
was different between sites of E. complanata presence (N = 97) and absence (N = 187)
(Figure 8). Means of 12 water chemistry variables were higher at sites with E.
complanata than sites without. The conditions documented in those variables were also
much lower at sites where E. complanata was absent. Conversely, much of the observed
dissolved oxygen and chloride concentrations at sites with E. complanata fell within a
narrow range compared to the concentrations at sites without. Scores of habitat metrics
at sites they were present usually ranged from marginal to optimal and were higher than
habitat scores at sites where they were absent. Furthermore, biological index scores were
rarely