First Evidence of Elliptio complanata (Bivalvia: Unionidae) from
the Patapsco River, Maryland
William Harbold, Jay V. Kilian, Gerald Mack, Jenny Zimmerman, and Matthew J. Ashton
Northeastern Naturalist, Volume 21, Issue 3 (2014): N35–N40
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2014 Northeastern Naturalist Notes Vol. 21, No. 3
W. Harbold, J.V. Kilian, G. Mack, J. Zimmerman, and M.J. Ashton
First Evidence of Elliptio complanata (Bivalvia: Unionidae) from
the Patapsco River, Maryland
William Harbold1,*, Jay V. Kilian1, Gerald Mack2, Jenny Zimmerman1, and
Matthew J. Ashton1
Abstract - In March 2012 and April–May 2013, we collected three dead specimens of Elliptio
complanata (Eastern Elliptio) in the tidal, freshwater portion of the Patapsco River, providing the
first evidence of this species from the river. Although these specimens do not definitively confirm
the presence of an extant population, they indicate that a remnant population may well persist in the
tidal, freshwater portion of the river. If it exists, this population could serve as a source for natural
recolonization into the non-tidal reaches of the river where the species is believed to have once occurred
but is now likely extirpated. Further mussel surveys are needed in the tidal, freshwater portion
of the river to confirm the presence of an Eastern Elliptio population, and to determine its size, age
structure, and distributional extent.
Discovery of specimens. On 16 March 2012, during surveys for anadromous fishes, we
observed a single valve of Elliptio complanata (Lightfoot) (Eastern Elliptio) from the Patapsco
River approximately 250 m upstream of the Interstate 295 bridge (39°13'44.27''N,
76°38'51.24''W; Fig. 1). The periostracum and nacre of this specimen were heavily eroded.
We could not make an accurate measurement because a portion of the valve was broken
off; however, we estimate the specimen to be approximately 110 mm long and 60 mm tall,
based on examination of other fully intact specimens of approximately the same size. During
additional surveys for anadromous species the following year, we observed two additional
Eastern Elliptio shells. We collected the first (75 mm length and 35 mm height) on 3
April 2013 from a sand/gravel bar approximately 150 m downstream of the Interstate 195
bridge (39°12'57.03''N 76°41'47.23''W) and a second (116 mm length and 63 mm height)
on 6 May 2013 from a sand bar approximately 150 m upstream of the Maryland 295 bridge
(39°13'45.63''N 77°20’45.38''W) (Fig.1). The first specimen was complete and relatively
fresh with both valves still attached by the hinge ligament. The second was even fresher
and contained decomposing soft tissue. We found all three specimens in a portion of the
Patapsco River that is considered tidal freshwater, downstream of the head-of-tide near
Elkridge, MD (Fig. 1), and upstream of brackish conditions near the river’s confluence with
Chesapeake Bay.
Significance of the discovery. Eastern Elliptio is a globally common freshwater mussel
distributed throughout Atlantic and Great Lakes drainages in a variety of aquatic habitats
(Matteson 1948, Williams et al. 1993). It is the most common freshwater mussel in Maryland
and, prior to our discovery, was known from all major Chesapeake Bay tributaries
in Maryland, with the exception of the Patapsco River (Fig. 2B). Our discovery of three
Eastern Elliptio specimens represents the first documented evidence of this species from
the Patapsco River. We obtained data from online databases or collection managers of the
following: Academy of Natural Sciences (ANSP), Philadelphia, PA; American Museum
of Natural History (AMNH), New York, NY; Canadian Museum of Nature (CMNML),
1Maryland Department of Natural Resources, Monitoring and Non-Tidal Assessment Division, 580
Taylor Avenue, C-2, Annapolis, MD 21401. 2 Montgomery County Department of Environmental
Protection, Watershed Management Division, 255 Rockville Pike, Suite 120, Rockville, MD 20850.
*Corresponding author - william.harbold@maryland.gov.
Manuscript Editor:Robert Hershler
Notes of the Northeastern Naturalist, Issue 21/3, 2014
2014 Northeastern Naturalist Notes Vol. 21, No. 3
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W. Harbold, J.V. Kilian, G. Mack, J. Zimmerman, and M.J. Ashton
Ottawa, ON, Canada; Carnegie Museum of Natural History (CM), Pittsburgh, PA; Delaware
Museum of Natural History (DMNH), Wilmington, DE; Florida Museum of Natural History
(FLMNH), Gainesville, FL; Illinois Natural History Survey (INHS), Champaign, IL;
Museum of Comparative Zoology (MCZ), Boston, MA; North Carolina Museum of Natural
Science (NCSM), Raleigh, NC; Ohio State University Museum (OSUM), Columbus, OH;
University of Michigan Museum of Zoology (UMMZ), Ann Arbor, MI; United States Natural
History Museum (NMNH), Washington, DC; and Virginia Museum of Natural History
Figure 1. Locations within the Patapsco River watershed where Eastern Elliptio specimens were collected
(closed circles) in reference to local landmarks.
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2014 Northeastern Naturalist Notes Vol. 21, No. 3
W. Harbold, J.V. Kilian, G. Mack, J. Zimmerman, and M.J. Ashton
(VMNH), Martinsville, VA. We found no current or historical records of Eastern Elliptio
from the Patapsco River, even though Maryland has been widely surveyed by malacologists
since the mid-19th century (Bogan and Proch 1997).
Figure 2. A) Sites in the Patapsco River watershed that have been surveyed for mussels since 1990
where no Eastern Elliptio were detected (open squares). B) Distribution of historic (pre-1990) and
contemporary (1990–2012) records of Eastern Elliptio (crosshatched area) in Maryland watersheds
draining to the Chesapeake Bay (MDNR Maryland Biological Stream Survey and J. McCann, MDNR
Natural Heritage Program, unpubl. data).
2014 Northeastern Naturalist Notes Vol. 21, No. 3
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W. Harbold, J.V. Kilian, G. Mack, J. Zimmerman, and M.J. Ashton
The Patapsco River is a large 5th-order tributary (Strahler 1957) located on the western
shore of Chesapeake Bay near Baltimore City (Fig. 2A). Its 953-km2 watershed drains
predominately agricultural and urban land in Baltimore, Carroll, Howard, and Anne Arundel
counties and Baltimore City. Approximately 66 river kilometers (rkm) of the Patapsco
River mainstem are non-tidal; the remaining 12 rkm are tidally influenced. Prior to our
discovery, four species of freshwater mussels were known from the Patapsco River watershed.
Anodonta implicata (Say) (Alewife Floater), Pyganodon cataracta (Say) (Eastern
Floater), and Utterbackia imbecillis (Say) (Paper Pondshell) are known from reservoirs in
the headwaters of the Patapsco River basin (J. McCann, Maryland Department of Natural
Resources,Annapolis, MD, unpubl. data). Although these species are native to Maryland,
they have not been recorded in the basin outside of the reservoirs. Their presence in these
lentic habitats is likely the result of the stocking of game and bait fishes infected with their
parasitic glochidia (e.g., Long 1983). The fourth species, Alasmidonta undulata (Say)
(Triangle Floater), is currently known from approximately 11.2 rkm of the lotic, non-tidal
portion of the Patapsco River (Harbold 2010).
The fresh condition of the two dead specimens we found in 2013 suggests that a
population of Eastern Elliptio persists in the tidal, freshwater Patapsco River. However,
the scarcity of specimens from the area suggests that, if extant, this species is present in
very low abundance. Although an Eastern Elliptio population in the non-tidal, freshwater
portion of the Patapsco River has yet to be confirmed, the presence of robust populations in
non-tidal portions of nearby rivers (Fig. 2B), historic records, and archaeological specimens
(Johnson 1991) suggest that the species was likely historically present within the non-tidal
Patapsco River as well.
In recent years, there have been extensive mussel surveys (Harbold 2010) and numerous
stream assessments (Harbold et al. 2013) throughout the non-tidal portion of the Patapsco
River. Many of the sites sampled as part of these efforts have been annually surveyed since
2009. To date, these surveys have yielded no evidence of Eastern Elliptio (Fig. 2A). The
methods used in these mussel surveys (e.g., Strayer and Smith 2003) routinely detected
live Triangle Floater even at low abundance, and we frequently encountered valves of this
species at biological monitoring sites where we sampled. Presumably, these methods would
detect Eastern Elliptio if it were still present in the non-tidal portion of the Patapsco River.
Although Eastern Elliptio remains the most common mussel in Maryland, its distribution
has been reduced in numerous Chesapeake Bay tributaries, and many populations
show little evidence of recruitment (e.g., Strayer and Fetterman 1999). This phenomenon
appears to be related to disruption of mussel reproduction caused by the upstream exclusion
of Anguilla rostrata (Lesueur) (American Eel) by river dams in the region; American Eels
are the primary host fish of Eastern Elliptio in the Mid-Atlantic (Lellis et al. 2013, Wiley
et al. 2004). The Patapsco River also has a long history of agricultural and industrial pollution
(MDE 2005, 2009a, 2009b) and has been called one of the most dammed rivers in
the US (Travers 1990). It is likely that the apparent extirpation of Eastern Elliptio from the
non-tidal portion of the river resulted from the combined effects of degraded water quality,
altered habitat, and disrupted mussel reproduction that has occurred over the past two
hundred years.
Conclusions/recommendations. The tidal portion of the Patapsco River—located downstream
of historical dams and, thus, in an area historically accessible to American Eel—may
have been the only refuge where Eastern Elliptio could persist while populations in the
non-tidal reaches declined and were extirpated. Due to low conservation priority, poor water
quality, and difficult access, the tidal, freshwater portion of the river has received little
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2014 Northeastern Naturalist Notes Vol. 21, No. 3
W. Harbold, J.V. Kilian, G. Mack, J. Zimmerman, and M.J. Ashton
attention in comparison to recent survey efforts focused in non-tidal reaches. Further mussel
surveys are needed in the tidal, freshwater portion of the river to confirm the presence of an
extant Eastern Elliptio population and determine the size, age structure, and distributional
extent of the population if one can be detected. Our recent discovery is encouraging and
suggests that a portion of the river may harbor a population that could serve as a potential
source for the recolonization of Eastern Elliptio into upstream, non-tidal reaches. American
Eel passage in the Patapsco River has seemingly improved with the addition of fish
ladders, the removal or destruction of most historic dams (Travers 1990), and the recent
removal of Union and Simkins Dams (Harbold et al. 2013). Plans are underway to remove
Bloede Dam (the most downstream dam remaining in the river) and to build an eel ladder
on Daniels Dam (J.Thompson, MD Department of Natural Resources Fisheries Service,
Annapolis, MD, 2013 pers. comm.), the only other remaining instream blockage (Fig. 2 A).
Additionally, water quality has improved in the Patapsco River since the implementation of
the Clean Water Act of 1972 (Friedman 2009) and is now within the range Eastern Elliptio
appears to tolerate (Ashton 2010, Harbold et al. 2013). An extant tidal, freshwater Eastern
Elliptio population may facilitate the natural recolonization of this species into non-tidal
reaches as American Eel passage is restored throughout the basin, although recolonization
potential will ultimately be influenced by multiple factors, such as host dispersal and
mussel-population size (Downing et al. 1993, Schwalb et al. 201 1).
Acknowledgments. We would like to thank Arthur Bogan of the North Carolina Museum
of Natural Sciences for verifying the identification of the Eastern Elliptio specimens. These
specimens are currently stored at the Maryland Department of Natural Resources, Annapolis,
MD. We would also like to thank Scott Stranko and Ron Klauda for their editorial advice
and guidance in improving this manuscript.
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