U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2018–1009

Prepared in cooperation with the Pennsylvania Department of Transportation

Freshwater Mussel Salvage and Relocation 

at the Pond Eddy Bridge, Delaware River, 

New York and Pennsylvania

Prepared in cooperation with the Pennsylvania Department of Transportation

Freshwater Mussel Salvage and Relocation 

at the Pond Eddy Bridge, Delaware River, 

New York and Pennsylvania

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2018–1009
Cover. Photograph showing Delaware River at the Pond Eddy Bridge looking upstream on the Pennsylvania side of the river. 

Photograph by Jeffrey Cole, U.S. Geological Survey.
Freshwater Mussel Salvage and Relocation 

at the Pond Eddy Bridge, Delaware River, 

New York and Pennsylvania

By Heather S. Galbraith, Carrie J. Blakeslee, and Jeffrey C. Cole

Prepared in cooperation with the Pennsylvania Department of Transportation

Open-File Report 2018–1009

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

RYAN K. ZINKE, Secretary

U.S. Geological Survey

William H. Werkheiser, Deputy Director

 exercising the authority of the Director

U.S. Geological Survey, Reston, Virginia: 2018

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Suggested citation:

Galbraith, H.S., Blakeslee, C.J., and Cole, J.C., 2018, Freshwater mussel salvage and relocation at the Pond Eddy 

Bridge, Delaware River, New York and Pennsylvania: U.S. Geological Survey Open-File Report 2018–1009, 5 p., 

https://doi.org/10.3133/ofr20181009.

ISSN 2331-1258 (online)
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Methods of Salvage and Relocation ..........................................................................................................2

Results of Salvage and Relocation .............................................................................................................2

Limitations of the Study and Future Monitoring .......................................................................................2

References Cited............................................................................................................................................5

Figure

1. Photograph showing Pond Eddy Bridge site located at the mainstem Delaware 

River between New York and Pennsylvania ............................................................................3

Tables

1. Total number of salvaged mussels from the Delaware River at the Pond Eddy 

Bridge site, New York and Pennsylvania, June 9–10, 2016....................................................4

2. Weight and length of salvaged mussels from the Delaware River at the Pond 

Eddy Bridge site, New York and Pennsylvania, June 9–10, 2016..........................................4

3. Total number of mussels from the Delaware River at the Pond Eddy Bridge site, 

New York and Pennsylvania, found during Phase 1 of the Pond Eddy mussel 

surveys conducted in 2011..........................................................................................................5

Conversion Factors

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

Area

square meter (m2

) 10.76 square foot (ft2)

Flow rate

cubic meter per second (m3

/s) 35.31 cubic foot per second (ft3/s)

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

Freshwater Mussel Salvage and Relocation at the Pond 

Eddy Bridge, Delaware River, New York and Pennsylvania

By Heather S. Galbraith, Carrie J. Blakeslee, and Jeffrey C. Cole

Abstract

In a study conducted by the U.S. Geological Survey, in 

cooperation with the Pennsylvania Department of Transportation, freshwater mussels were salvaged and relocated from the 

anticipated zone of impact for the Pond Eddy Bridge construction project in New York and Pennsylvania. Five 25-meter (m) 

by 25-m cells along the Pennsylvania bank of the Delaware 

River were sampled in three generally straight-line passes by 

four surveyors wearing snorkel gear for a total of 180 survey 

minutes per cell. All mussels encountered were collected 

and identified to species. A subset of individuals was marked 

with shellfish tags, weighed, and measured prior to relocation 

upstream from the zone of impact. A total of 3,434 mussels, 

including 3,393 Elliptio complanata (eastern elliptio mussels), 

39 Anodonta implicata (alewife floaters), 1 Strophitus undulatus (creeper), and 1 Pyganodon cataracta (eastern floater), 

were salvaged and relocated. All non-eastern elliptio species 

were georeferenced using a high-resolution global positioning 

system unit; a subset of tagged eastern elliptio was placed in 

transects between georeferenced points. These mussels will be 

monitored to assess the effects of translocation on mortality 

and body condition at 1 month, 1 year, and 2 years.

Introduction

Native freshwater mussels (hereafter mussels) are a critically imperiled fauna threatened by a variety of disturbances 

to aquatic ecosystems (Strayer and others, 2004). Mussels 

perform important ecological functions; therefore, there has 

been increasing interest in their conservation and restoration 

(Spooner and Vaughn, 2006; Vaughn, 2010). The Pennsylvania 

Department of Transportation (PennDOT) began construction 

to replace the bridge crossing the Delaware River from Pond 

Eddy, New York (Sullivan County) to Pond Eddy, Pennsylvania (Pike County) in 2016. Pond Eddy is located within the 

Upper Delaware River Scenic and Recreational River and, as 

such, is regulated by the National Park Service (NPS) under 

the Wild and Scenic Rivers Act (16 U.S.C. 1271‒1287).

The Delaware River provides habitat for several populations of the Federally listed endangered Alasmidonta heterodon (dwarf wedgemussel) (Galbraith and others, 2016). In 

addition, populations of the New York State-listed Alasmidonta varicosa (brook floater) and critically imperiled (but 

unlisted) Anodonta implicata (alewife floater) have been found 

in the Delaware River. In summer 2011, a Phase 1 survey for 

dwarf wedgemussel was conducted in the designated zone of 

construction impact near the Pond Eddy Bridge, at which time 

no individuals of this species were found (Galbraith, 2012). 

The Elliptio complanata (eastern elliptio), Strophitus undulatus (creeper), and the alewife floater were the only species 

identified at this site. 

Construction activities in or near water bodies can have 

significant negative effects on mussels through hydrological 

alterations and increasing siltation (Neves and others, 1997; 

Watters, 2000). As a result, there may be incidental take of 

mussels as a direct result of construction efforts or indirectly 

by way of habitat alteration in the immediate vicinity of construction sites. Because of the potential impact to mussels and 

their importance to water quality in the Upper Delaware River, 

the NPS decided that all species within the causeway’s direct 

impact area would be salvaged and relocated. Specifically, 

mussels were only salvaged and relocated from the Pennsylvania bank of the river in locations with the highest densities 

of alewife floater. This area includes a stretch of river approximately 25 meters (m) wide along the Pennsylvania bank of the 

river, extending 75 m downstream and 50 m upstream from 

the existing Pond Eddy Bridge. The study was conducted by 

the U.S. Geological Survey (USGS), in cooperation with the 

Pennsylvania Department of Transportation; results of this 

salvage and relocation opportunity will be used to understand 

the short- and long-term effects of translocation on mussel 

survival and health. 

This report presents the methods and results of mussel salvage and relocation from an area that will be directly 

impacted during construction of the new Pond Eddy Bridge 

across the Delaware River. The number of individual mussel 

species salvaged and relocated is presented. Size and weight 

of some relocated mussels are also presented. 
2 Freshwater Mussel Salvage and Relocation at the Pond Eddy Bridge, Delaware River, New York and Pennsylvania

Methods of Salvage and Relocation

USGS surveyors worked on the Pond Eddy Bridge mussel salvage and relocation on June 9 and 10, 2016. Mussel 

salvage was conducted in five 25-m by 25-m cells along the 

Pennsylvania shoreline determined to be in the area of the proposed construction causeway (fig. 1). Cells were reconstructed 

from past surveys completed by Galbraith (2012) and marked 

with flagging tape on shore and anchored buoys in the water. 

Each cell was surveyed simultaneously by four individuals 

that snorkeled for 15-minute consecutive passes in generally 

straight-line transects, parallel to flow, along the length of each 

cell. All individual mussels encountered in each pass were 

collected. Surveyors also searched under moveable rocks to 

ensure that the maximum number of individuals was salvaged. 

Collected mussels were placed in mesh bags and held submersed near the shoreline until they could be processed for 

identification, measurement, and tagging (when necessary). 

If the number of individuals collected during the second pass 

exceeded 10 percent of the number of individuals collected 

during the first pass, a third 15-minute pass was completed for 

that cell. No more than three passes were done in each cell. 

Following salvage, all mussels were identified to species. Rare species (alewife floater, creeper, and Pyganodon 

cataracta [eastern floater]) were weighed, measured, and 

tagged by affixing a small shellfish tag to the shell using 

superglue. All individual eastern elliptio mussels collected 

from cell 2 were weighed and measured because this cell 

contained the most individuals and the greatest variation in 

individual mussel body size. A haphazardly selected subset of 

the cell 2 eastern elliptio mussels was also tagged for future 

monitoring efforts.

A suite of potential relocation sites supporting both 

alewife floaters and eastern elliptios was identified prior to 

salvage with the closest potential relocation site located just 

upstream from the Pond Eddy Bridge, on the Pennsylvania 

bank of the river, upstream from the confluence of Mill Brook 

which enters on the New York bank of the river. An on-site 

snorkel assessment of this site conducted in June 2016, prior 

to salvage, revealed that it supported an ample number of 

both the alewife floater and eastern elliptio mussel. Salvaged 

mussels were hand placed in the substrate at the relocation site in an approximately 3,100-square-meter stretch of 

river (fig. 1), equivalent in area to that from which they were 

collected. A high-resolution global positioning system unit 

(Trimble GeoXH) was used to georeference each individual 

rare mussel relocated upstream, and tagged eastern elliptio 

mussels collected from cell 2 were placed in transects between 

georeferenced rare species for future monitoring. The remaining eastern elliptio mussels, collected from all cells, were hand 

placed haphazardly throughout the entire relocation area.

Results of Salvage and Relocation

The number of individual mussels salvaged from consecutive passes generally decreased (table 1), but the number 

of mussels salvaged in the second pass was never less than or 

equal to 10 percent of the first pass; therefore, a third pass was 

completed for each cell resulting in a total of 180 minutes of 

survey time per cell. A total of 3,434 mussels were salvaged 

and relocated from the five cells (table 2), including 39 alewife 

floater (size range: 36‒90 millimeters (mm)), 3,393 eastern 

elliptio (size range: 9‒88 mm), 1 eastern floater (60 mm), and 

1 creeper (59 mm). 

Limitations of the Study and Future 

Monitoring

The number of mussels salvaged from the five cells was 

substantially greater than the number of individuals located 

during Phase 1 surveys completed by Galbraith (2012) 

(table 3). Specifically, there were almost 8 times the number 

of eastern elliptio and 4 times the number of alewife floaters collected in the 2016 salvage compared to those located 

in the 2011 Phase 1 survey. River flows during the Phase 1 

survey were substantially (32–39%) higher than during the 

salvage, which may have affected the surveyor’s success 

in finding mussels. In particular, river discharge measured 

at USGS streamgage 01434000 (fig. 1) ranged from 128.8 

to 156.7 cubic meters per second (m3/s) and from 86.6 to 

95.1 m3/s during the Phase 1 survey and salvage, respectively. 

Even though both ranges of discharge are considered “suitable” for mussel surveys, the difference may be partially 

responsible for the differences in surveyor success. Another 

more likely explanation for differences in surveyor success 

and mussel detection between the 2 survey years is variations 

in sampling methodology. 

A substantial portion of the salvaged mussels were found 

buried in clumps under large rocks beneath the substrate that 

was not surveyed during the 2011 Phase 1 surface assessment 

(Galbraith, 2012). The Phase I survey was completed with 

minimal disturbance to the existing substrate, as is standard 

for such surveys, focusing primarily on surface mussels, with 

the condition that if listed species were found, follow up quadrat surveys with excavation would be completed. Since most 

of the salvaged mussels were found buried in large clumps 

beneath the substrate, performing some level of “excavation” during the Phase I sampling may have produced a better 

estimate of actual mussel density at the site. This in turn would 

have resulted in a more precise estimate of the time necessary 

to salvage all mussels from the impacted site to depletion, 

and a greater number of mussels being relocated than these 
Limitations of the Study and Future Monitoring 3

Figure 1. Pond Eddy Bridge site located at the mainstem Delaware River between New York and Pennsylvania.

NEW YORK

PENNSYLVANIA

DIRECTION OF FLOW

R1

R2

R3

R4

C1

C2

C3

C4

C5

R1

R2

R3

R4

C1

C2

C3

C4

C5

Pond Eddy Bridge

NY STATE ROUTE 97

RAILROAD

ROSA SWITCH ROAD

FLAGSTONE ROAD

0

0

0.1

0.1

0.05

0.05

MILE

KILOMETER

Delaware River

NEW YORK

PENNSYLVANIA

MARYLAND

DELAWARE

78° 76°30' 75° 73°30'

43°30'

42°

40°30'

39°

NEW

JERSEY

PIKE COUNTY

SULLIVAN COUNTY

ATLANTIC OCEAN

LAKE ERIE

Base from U.S. Geological Survey digital data

Map image is the intellectual property of Esri and is used 

herein under license. Copyright © 2014 Esri and its 

licensors. All rights reserved.

EXPLANATION

25-meter (m) by 25-m cell from 

which freshwater mussels 

were salvaged

25-m by 31-m cell to which 

salvaged mussels were 

relocated

Georeferenced placement of

non-eastern Elliptio complanata

mussel species

C2

R3
4 Freshwater Mussel Salvage and Relocation at the Pond Eddy Bridge, Delaware River, New York and Pennsylvania

Table 1. Total number of salvaged mussels from the Delaware River at the Pond Eddy Bridge site, New York and Pennsylvania, 

June 9–10, 2016. Mussels were collected from a total of five 25-meter (m) by 25-m cells in three successive passes.

[#, number; %, percent]

Cell Pass # Alewife floater # Eastern elliptio # Eastern floater # Creeper Total # mussels % of first pass

1 1 6 245 0 0 251 100.0

2 3 197 0 0 200 79.7

3 6 177 0 0 183 72.9

2 1 4 241 0 0 245 100.0

2 1 203 0 0 204 83.3

3 2 197 0 0 199 81.2

3 1 1 218 0 1 220 100.0

2 3 201 0 0 204 92.7

3 2 169 0 0 171 77.7

4 1 1 255 0 0 256 100.0

2 1 286 1 0 288 112.5

3 1 232 0 0 233 91.0

5 1 2 234 0 0 236 100.0

2 4 276 0 0 280 118.6

3 2 262 0 0 264 111.9

TOTAL 39 3,393 1 1 3,434

Table 2. Weight and length of salvaged mussels from the Delaware River at the Pond Eddy Bridge site, New York and Pennsylvania, 

June 9–10, 2016.

[g, gram; mm, millimeter; n, total number of individuals; Avg, average; SD, standard deviation; SE, standard error; Min, minimum; Max, maximum; N/A, not 

applicable]

Species n

Weight (g) Length (mm)

Avg SD SE Min Max Avg SD SE Min Max

Alewife floater 39 22.91 10.39 1.66 3.20 56.75 76.7 79.6 12.7 36 90

Eastern elliptio1 761 15.80 12.08 0.44 0.05 63.60 53.2 14.4 0.5 9 88

Eastern floater 1 17.28 N/A N/A N/A N/A 60.0 N/A N/A N/A N/A

Creeper 1 24.35 N/A N/A N/A N/A 59.0 N/A N/A N/A N/A

1

Data represent a subset of total salvaged individuals.
References Cited 5

Table 3. Total number of mussels from the Delaware River at 

the Pond Eddy Bridge site, New York and Pennsylvania, found 

during Phase 1 of the Pond Eddy mussel surveys conducted in 

2011. Surveys were completed in the same five 25-meter (m) by 

25-m cells where salvage efforts were conducted in the present 

study.

[#, number]

Cell # Alewife 

floater

# Eastern 

elliptio

# Eastern 

floater # Creeper Total # mussels

1 2 94 0 0 96

2 1 109 0 0 110

3 0 44 0 0 44

4 3 76 0 1 80

5 3 86 0 0 89

TOTAL 9 409 0 1 419

efforts achieved. Future evaluation of sampling methodologies 

required at bridge construction sites is warranted. The results 

from these surveys indicate that combined surface and subsurface techniques are necessary to accurately estimate mussel 

abundance. 

Owing to the unexpected number of mussels requiring 

salvage, surveyors were unable to collect all mussels from 

each cell to depletion within the allocated time and budget. 

Although the number of eastern elliptio generally decreased 

with successive passes, it never declined to less than 70 percent of the first pass, indicating that a large number of mussels likely remain in these cells and within the area directly 

impacted by bridge construction. There was no clear trend in 

the number of alewife floaters salvaged: similar numbers of 

individuals were collected during all three passes. Significant 

additional salvage time and effort would be required to reduce 

the mussel populations in each cell to less than 10 percent 

of the first pass. Representatives from PennDOT, NPS, and 

USGS had several consultations after the initial salvage to 

determine whether additional survey passes were warranted to 

salvage mussels to depletion. The NPS concluded that additional survey passes were not necessary. 

Relocated individuals will be monitored as part of a longterm USGS study to assess the effects of translocation on the 

mortality and body condition of relocated mussels 1 month, 

1 year, and 2 years after relocation. Monitoring mussel populations remaining in the zone of impact is beyond the scope 

of this study; however, there is some indication that mussels 

remaining in this area may be important for recolonization following completion of bridge construction (Villella, 2005). 

References Cited

Galbraith, H.S., 2012, Phase 1 freshwater mussel survey and 

comparison to historical surveys at the Pond Eddy Bridge, 

Delaware River, New York and Pennsylvania: U.S. Geological Survey Open-File Report 2012‒1224, 17 p.

Galbraith, H.S., Lellis, W.A., Cole, J.C., Blakeslee, C.J., and 

White, B.S.J., 2016, Population demographics for the federally endangered dwarf wedgemussel: Journal of Fish and 

Wildlife Management, v. 7, p. 377–387. 

Neves, R.J., Bogan, A.E., Williams, J.D., Ahlstedt, S.A., and 

Hartfield, P.W., 1997, Status of aquatic mollusks in the 

southeastern United States: A downward spiral of diversity, in Benz, G.W., and Collins, D.E., eds., Aquatic fauna 

in peril: The southeastern perspective: Decataur Georgia, 

Southeast Aquatic Research Institute, Lenz Design and 

Communications.

Spooner, D.E., and Vaughn, C.C., 2006, Context-dependent 

effects of freshwater mussels on stream benthic communities: Freshwater Biology, v. 51, p. 1016‒1024.

Strayer, D.L., Downing, J.A., Haag, W.R., King, T.L., Layzer, 

J.B., Newton, T.J., and Nichols, S.J., 2004, Changing perspectives on pearly mussels, North America’s most imperiled animals: BioScience, v. 54, p. 429‒439.

Vaughn, C.C., 2010, Biodiversity losses and ecosystem function in freshwaters: emerging conclusions and research 

directions: BioScience, v. 60, p. 25‒35.

Villella, R.F., 2005, Survey of freshwater mussels within the 

direct and indirect areas of impact at the Kennerdell Bridge, 

S.R. 3008, Section B00: Second post-construction monitoring final report, Final Report to Pennsylvania Department of 

Transportation 29.

Watters, G.T., 2000, Freshwater mussels and water quality: a 

review of the effects of hydrological and instream habitat 

alterations: Proceedings of the First Freshwater Mollusk 

Conservation Society Symposium, v. 1999, p. 261‒274.

For more information about this report, contact:

Center Director

USGS Leetown Science Center

11649 Leetown Road

Kearneysville, WV 25430

Publishing support provided by the 

West Trenton and Pembroke Publishing Service Centers
Galbraith and others—Freshwater Mussel Salvage and Relocation at the Pond Eddy Bridge, Delaware River, New York and Pennsylvania—OFR 2018–1009

ISSN 2331-1258 (online)

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