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

of A. heterodon. The apparent rarity of tessellated darter from a few sites where A.
heterodon was collected poses several management implications. Locally, the
populations may not be reproducing due to a lack of a suitable host or because host
abundance is too low to support consistent recruitment (Haag and Warren 1998).
Conversely, the absence of tessellated darter from a site does not entirely discount their
presence at nearby locations given their high site fidelity (McLain and Ross 2005).
Finally, other regionally suitable, yet to be documented hosts may exist. Glochidial
release rates of A. heterodon are highest during April and May (Michaelson and Neves
1995, McLain and Ross 2005); therefore, a comprehensive list of regional hosts would
require sampling when anadromous fishes ascend streams to spawn.
A diverse assemblage of host fishes exists for E. complanata in Maryland (Young
1911, Matteson 1955, Watters et al. 2005, Kneeland and Rhymer 2008); however, recent
studies indicate American eels are superior hosts for E. complanata (Lellis, unpublished
data). The diversity of host species likely allows them to inhabit a broad range of
habitats, though it is increasingly apparent that the absence of eels eventually results in
the absence of E. complanata or depressed populations (Devers 2009). It is unknown if a
density-dependent relationship exists between American eels and E. complanata that
would further explain patterns in their distribution (Haag and Warren 1998), but this is
likely given the high rate of glochidial transformation on eels and reproductive success of
E. complanata at varying densities (Downing et al. 1993, Lellis, unpublished data). Two
glochidial hosts (bluegill and largemouth bass) of E. fisheriana (O’Dee and Watters
2000) were extant throughout much of its range in Maryland, suggesting their absence
from streams may not entirely be related to the lack of a suitable host. These fishes are
not native to Maryland and often found in low abundance, indicating an unknown host
must have existed prior to their introduction. Three fishes native to Maryland that O’Dee
and Watters (2000) found not to transform glochidia were collected at sites with E.
fisheriana and may warrant further investigation. The common practice of stocking nonnative
centrachids into private and public waters has likely played a role in the ubiquitous
distribution of host generalists like P. cataracta and the presence of mussels in reservoirs
(Long 1983).
Investigating fish frequently collected with mussels or hosts of congeneric
mussels for glochidial infestations may answer whether mussel distribution in Maryland
is affected by host availability. For example, American eel was found at a majority of
sites where mussels were present; however, they have been confirmed as a glochidial host
for only a single mussel species in Maryland. Hosts of other Alasmidonta spp., including
fallfish, largemouth bass, and pumpkinseed, were sporadically collected at sites with A.
heterodon. Furthermore, nine species identified as hosts for P. grandis (Trdan and Hoeh
1982, Watters et al. 2005, Cummings and Watters 2009) were present at sites with P.
cataracta. The host fish of lanceolate Elliptios are poorly understood and the taxonomic
uncertainty of these species makes the process even more troublesome. Examining
congeneric fish for glochidia may be another possible strategy to identify glochidial
hosts. The congeneric to the widespread tessellated darter, Etheostoma nigrum (johnny
darter) has been documented as a host for E. fisheriana and the conger to P. cataracta,
yet johnny darter is not sympatric with either species in Maryland. Conversely, the
closely related tessellated darter was collected at most sites (≥80%) with these mussels.
Sculpin (Cottus spp.) serve as hosts for a suite of mussels, yet only for a few species in
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