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The consequences of dam passage for downstream-migrating American eel in the Penobscot River, Maine

Publication: Canadian Journal of Fisheries and Aquatic Sciences
12 August 2021


American eel (Anguilla rostrata) often pass hydropower dams during adult spawning migrations. We conducted a 4-year acoustic telemetry study that characterized passage risks through two dams (West Enfield and Milford) in the Penobscot River, Maine, USA. We released tagged fish (n = 355) at two sites, estimated survival and delay under variable river conditions, and compared performance among dammed and free-flowing river sections. Survival rates (standardized per river kilometre, rkm) were lower at West Enfield (Φrkm = 0.984 ± 0.006 SE) and Milford (Φrkm = 0.966 ± 0.007 SE) compared with undammed River sections (Φrkm = 0.998 ± 0.0003 SE). Cumulative mortality was 8.7% (4.4 km) and 14.2% (5.5 km) through dammed sections and 8.7% throughout the rest of the river (58.1 km). Fish that already passed an upstream dam incurred higher downstream mortality compared with individuals without passage experience. Additionally, fish endured long delays at dams, and >10% of fish were delayed >24 h. Low flows exacerbated the risk of mortality and delay. These results offer evidence for direct, latent, and sublethal consequences of dam passage for migrating eels.


Des anguilles d’Amérique (Anguilla rostrata) adultes passent souvent à travers de barrages hydroélectriques durant leurs migrations de frai. Nous avons mené une étude de télémétrie acoustique de quatre ans qui a permis de caractériser les risques associés au passage à travers deux barrages hydroélectriques (West Enfield et Milford) sur le fleuve Penobscot (Maine, États-Unis). Nous avons relâché des poissons étiquetés (n = 355) en deux sites, estimé la survie et le retard dans des conditions variables du fleuve et comparé les performances entre des tronçons du fleuve endigués et à écoulement libre. Les taux de survie (normalisés par kilometre de cours d’eau, rkm) étaient plus faibles à West Enfield (Φrkm = 0,984 ± 0,006 ÉT) et Milford (Φrkm = 0,966 ± 0,007 ÉT) que dans les tronçons non endigués du fleuve (Φrkm = 0,998 ± 0,0003 ÉT). La mortalité cumulative était de 8,7 % (4,4 km) et 14,2 % (5,5 km) dans les tronçons endigués et de 8,7 % dans tout le reste du fleuve (58,1 km). Les anguilles qui étaient déjà passées par un barrage en amont présentaient une mortalité plus forte en aval que les spécimens sans expérience de passage. En outre, les poissons subissaient de longs retards aux barrages, ce retard étant de >24 h pour >10 % des anguilles. De faibles débits exacerbaient le risque de mortalité et la durée des retards. Ces résultats témoignent de conséquences directes, latentes et sublétales du passage de barrages pour les anguilles en migration. [Traduit par la Rédaction]

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Acou A., Laffaille P., Legault A., and Feunteun E. 2008. Migration pattern of silver eel (Anguilla anguilla, L.) in an obstructed river system. Ecol. Freshw. Fish, 17(3): 432–442.
Aldinger J.L. and Welsh S.A. 2017. Diel periodicity and chronology of upstream migration in yellow-phase American eels (Anguilla rostrata). Environ. Biol. Fishes, 100(7): 829–838.
ASMFC. 2017. 2017 American eel stock assessment update. Atlantic States Marine Fisheries Commission.
Baker N., Haro A., Watten B., Noreika J., and Bolland J.D. 2019. Comparison of attraction, entrance and passage of downstream migrant American eels (Anguilla rostrata) through airlift and siphon deep entrance bypass systems. Ecol. Eng. 126: 74–82.
Barbin G., Parker S., and McCleave J.D. 1998. Olfactory clues play a critical role in the estuarine migration of silver-phase American eels. Environ. Biol. Fishes, 53(3): 283–291.
Bates D., Mächler M., Bolker B., and Walker S. 2015. Fitting linear mixed-effects models using lme4. J. Stat. Softw. 67(1).
Béguer-Pon M., Castonguay M., Benchetrit J., Hatin D., Verreault G., Mailhot Y., et al. 2014. Large-scale migration patterns of silver American eels from the St. Lawrence River to the Gulf of St. Lawrence using acoustic telemetry. Can. J. Fish. Aquat. Sci. 71(10): 1579–1592.
Bell, H. 2007. 12-month finding on a petition to list the American eel as threatened or endangered. US Fish and Wildlife Service.
Besson M.L., Trancart T., Acou A., Charrier F., Mazel V., Legault A., and Feunteun E. 2016. Disrupted downstream migration behaviour of European silver eels (Anguilla anguilla, L.) in an obstructed river. Environ. Biol. Fishes, 99(10): 779–791.
Bolker, B. 2020. emdbook: ecological models and data in R. R package version 1.3.12. Available from
Brown L., Haro A., and Castro-Santos T. 2009. Three-dimensional movement of silver-phase American eels in the forebay of a small hydroelectric facility. Am. Fish. Soc. Symp. 58: 277–291.
Burnham, K.P., and Anderson, D.R. 2002. Model selection and multimodel inference: a practical information-theoretic approach. 2nd ed. Springer, New York.
Calles O., Olsson I.C., Comoglio C., Kemp P.S., Blunden L., Schmitz M., and Greenberg L.A. 2010. APPLIED ISSUES: Size-dependent mortality of migratory silver eels at a hydropower plant, and implications for escapement to the sea. Freshw. Biol. 55(10): 2167–2180.
Carr J.W. and Whoriskey F.G. 2008. Migration of silver American eels past a hydroelectric dam and through a coastal zone. Fish. Manage. Ecol. 15(5–6): 393–400.
Castonguay M., Hodson P.V., Couillard C.M., Eckersley M.J., Dutil J.-D., and Verreault G. 1994. Why is recruitment of the American eel, Anguilla rostrata, declining in the St. Lawrence River and Gulf? Can. J. Fish. Aquat. Sci. 51(2): 479–488.
Caudill C.C., Daigle W.R., Keefer M.L., Boggs C.T., Jepson M.A., Burke B.J., et al. 2007. Slow dam passage in adult Columbia River salmonids associated with unsuccessful migration: delayed negative effects of passage obstacles or condition-dependent mortality? Can. J. Fish. Aquat. Sci. 64(7): 979–995.
Durif C.M.F., Travade F., Rives J., Elie P., and Gosset C. 2008. Relationship between locomotor activity, environmental factors, and timing of the spawning migration in the European eel, Anguilla anguilla. Aquat. Living Resour. 21(2): 163–170.
Eyler S.M., Welsh S.A., Smith D.R., and Rockey M.M. 2016. Downstream passage and impact of turbine shutdowns on survival of silver American eels at five hydroelectric dams on the Shenandoah River. Trans. Am. Fish. Soc. 145(5): 964–976.
Ferguson J.W., Absolon R.F., Carlson T.J., and Sandford B.P. 2006. Evidence of delayed mortality on juvenile Pacific salmon passing through turbines at Columbia River dams. Trans. Am. Fish. Soc. 135(1): 139–150.
Halfyard E.A., Gibson A.J.F., Stokesbury M.J.W., Ruzzante D.E., and Whoriskey F.G. 2013. Correlates of estuarine survival of Atlantic salmon postsmolts from the Southern Upland, Nova Scotia, Canada. Can. J. Fish. Aquat. Sci. 70(3): 452–460.
Hall C.J., Jordaan A., and Frisk M.G. 2011. The historic influence of dams on diadromous fish habitat with a focus on river herring and hydrologic longitudinal connectivity. Landsc. Ecol. 26(1): 95–107.
Haro A., Richkus W., Whalen K., Hoar A., Busch W.D., Lary S., et al. 2000. Population decline of the American eel: Implications for research and management. Fisheries, 25(9): 7–16.
Havn T.B., Økland F., Teichert M.A.K., Heermann L., Borcherding J., Sæther S.A., et al. 2017. Movements of dead fish in rivers. Anim. Biotelem. 5(1): 7.
Hawkes J.P., Sheehan T.F., and Stich D.S. 2017. Assessment of early migration dynamics of river-specific hatchery Atlantic Salmon smolts. Trans. Am. Fish. Soc. 146(6): 1279–1290.
Hedger R.D., Dodson J.J., Hatin D., Caron F., and Fournier D. 2010. River and estuary movements of yellow-stage American eels Anguilla rostrata, using a hydrophone array. J. Fish Biol. 76(6): 1294–1311.
Heisey P.G., Mathur D., Phipps J.L., Avalos J.C., Hoffman C.E., Adams S.W., and De‐Oliveira E. 2019. Passage survival of European and American eels at Francis and propeller turbines. J. Fish. Biol. 95(5): 1172–1183.
Hitt N.P., Eyler S., and Wofford J.E.B. 2012. Dam removal increases American eel abundance in distant headwater streams. Trans. Am. Fish. Soc. 141(5): 1171–1179.
Holbrook C.M., Kinnison M.T., and Zydlewski J. 2011. Survival of migrating Atlantic salmon smolts through the Penobscot River, Maine: a prerestoration assessment. Trans. Am. Fish. Soc. 140(5): 1255–1268.
Jessop B.M. 2010. Geographic effects on American eel (Anguilla rostrata) life history characteristics and strategies. Can. J. Fish. Aquat. Sci. 67(2): 326–346.
Jessop B.M., Cairns D.K., Thibault I., and Tzeng W.N. 2008. Life history of American eel Anguilla rostrata: new insights from otolith microchemistry. Aquat. Biol. 1: 205–216.
Kiraly I.A., Coghlan S.M., Zydlewski J., and Hayes D. 2015. An assessment of fish assemblage structure in a large river: an assessment of fish assemblage structure in a large river. River Res. Appl. 31(3): 301–312.
Laake, J.L. 2013. RMark: an R interface for analysis of capture–recapture data with MARK. Alaska Fish. Sci. Cent., NOAA, Natl. Mar. Fish. Serv., 7600 Sand Point Way NE, Seattle, WA 98115, USA. Available from
Limburg K.E. and Waldman J.R. 2009. Dramatic Declines in North Atlantic diadromous fishes. BioScience, 59(11): 955–965.
Limburg, D.K., Oliveira, D.K., Wiedenmann, D.J., and O’Boyle, D.B. 2012. American eel benchmark stock assessment. American States Marine Fisheries Commission.
Lundqvist H., Rivinoja P., Leonardsson K., and McKinnell S. 2008. Upstream passage problems for wild Atlantic salmon (Salmo salar L.) in a regulated river and its effect on the population. Hydrobiologia, 602(1): 111–127.
Maine DEP. 2014. March. Hydropower relicensing. Maine Department of Environmental Protection.
Mathur D., Heisey P.G., Skalski J.R., and Kenney D.R. 2000. Salmonid smolt survival relative to turbine efficiency and entrainment depth in hydroelectric power generation. J. Am. Water Resour. Assoc. 36(4): 737–747.
Michel C.J., Ammann A.J., Lindley S.T., Sandstrom P.T., Chapman E.D., Thomas M.J., et al. 2015. Chinook salmon outmigration survival in wet and dry years in California’s Sacramento River. Can. J. Fish. Aquat. Sci. 72(11): 1749–1759.
Muir W.D., Smith S.G., Williams J.G., and Sandford B.P. 2001. Survival of juvenile salmonids passing through bypass systems, turbines, and spillways with and without flow deflectors at Snake River dams. N. Am. J. Fish. Manage. 21: 135–146.
Norrgård J.R., Greenberg L.A., Piccolo J.J., Schmitz M., and Bergman E. 2013. Multiplicative loss of landlocked Atlantic salmon Salmo salar smolts during downstream migration through multiple dams. River Res. Appl. 29(10): 1306–1317.
Nyqvist D., Calles O., Bergman E., Hagelin A., and Greenberg L.A. 2016. Post-spawning survival and downstream passage of landlocked Atlantic salmon (Salmo salar) in a regulated river: is there potential for repeat spawning?: Post-spawning survival and migration of landlocked Atlantic salmon. River Res. Applic. 32(5): 1008–1017.
Oliveira K. 1999. Life history characteristics and strategies of the American eel, Anguilla rostrata. Can. J. Fish. Aquat. Sci. 56(5): 795–802.
Pankhurst N.W. and Lythgoe J.N. 1982. Structure and colour of the integument of the European eel Anguilla anguilla (L.). J. Fish Biol. 21(3): 279–296.
Parker S.J. and McCleave J.D. 1997. Selective tidal stream transport by American eels during homing movements and estuarine migration. J. Mar. Biol. Assoc. 77(3): 871–889.
Piper A.T., Wright R.M., Walker A.M., and Kemp P.S. 2013. Escapement, route choice, barrier passage and entrainment of seaward migrating European eel, Anguilla anguilla, within a highly regulated lowland river. Ecol. Eng. 57: 88–96.
Pollock K.H., Nichols J.D., Brownie C., and Hines J.E. 1990. Statistical inference for capture–recapture experiments. Wildl. Monogr. 107: 3–97.
Powell L.A. 2007. Approximating variance of demographic parameters using the Delta Method: a reference for avian biologists. Condor, 109(4): 949–954.
R Core Team. 2013. R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. Available from
Saylor R., Fortner A., and Bevelhimer M. 2019. Quantifying mortality and injury susceptibility for two morphologically disparate fishes exposed to simulated turbine blade strike. Hydrobiologia, 842(1): 55–75.
Schmidt R.E., O’Reilly C.M., and Miller D. 2009. Observations of American eels using an upland passage facility and effects of passage on the population structure. N. Am. J. Fish. Manage. 29(3): 715–720.
Shepard, S.L. 2015. American Eel biological species report. US Fish and Wildlife Service, Hadley, Massachusetts.
Skalski J.R., Townsend R., Lady J., Giorgi A.E., Stevenson J.R., and McDonald R.D. 2002. Estimating route-specific passage and survival probabilities at a hydroelectric project from smolt radiotelemetry studies. Can. J. Fish. Aquat. Sci. 59(8): 1385–1393.
Skalski J.R., Buchanan R.A., Townsend R.L., Steig T.W., and Hemstrom S. 2009. A multiple-release model to estimate route-specific and dam passage survival at a hydroelectric project. N. Am. J. Fish. Manage. 29(3): 670–679.
Smith D.R., Fackler P.L., Eyler S.M., Villegas Ortiz L., and Welsh S.A. 2017. Optimization of decision rules for hydroelectric operation to reduce both eel mortality and unnecessary turbine shutdown: A search for a win-win solution. River Res. Appl. 33(8): 1279–1285.
Smith S.G., Muir W.D., Williams J.G., and Skalski J.R. 2002. Factors associated with travel time and survival of migrant yearling chinook salmon and steelhead in the Lower Snake River. N. Am. J. Fish. Manage. 22(2): 385–405.
Stich D.S., Bailey M.M., and Zydlewski J.D. 2014. Survival of Atlantic salmon Salmo salar smolts through a hydropower complex: smolt survival through a hydropower complex. J. Fish. Biol. 85(4): 1074–1096.
Stich D.S., Zydlewski G.B., Kocik J.F., and Zydlewski J.D. 2015. Linking behavior, physiology, and survival of Atlantic salmon smolts during estuary migration. Mar. Coast. Fish. 7(1): 68–86.
Tesch F.W. 2004. The eel. J. Fish Biol. 65(3): 893–893.
Trancart T., Carpentier A., Acou A., Danet V., Elliott S., and Feunteun É. 2020. Behaviour of endangered European eels in proximity to a dam during downstream migration: Novel insights using high accuracy 3D acoustic telemetry. Ecol. Freshw. Fish, 29(2): 266–279.
van Ginneken V. 2005. Eel migration to the Sargasso: remarkably high swimming efficiency and low energy costs. J. Exp. Biol. 208(7): 1329–1335.
Verhelst P., Bruneel S., Reubens J., Coeck J., Goethals P., Oldoni D., et al. 2018. Selective tidal stream transport in silver European eel (Anguilla anguilla L.) — Migration behaviour in a dynamic estuary. Estuar. Coast. Shelf Sci. 213: 260–268.
Verreault G., Mingelbier M., and Dumont P. 2012. Spawning migration of American eel Anguilla rostrata from pristine (1843–1872) to contemporary (1963–1990) periods in the St Lawrence Estuary. Can. J. Fish Biol. 81(2): 387–407.
Watson J.M., Coghlan S.M., Zydlewski J., Hayes D.B., and Kiraly I.A. 2018. Dam removal and fish passage improvement influence fish assemblages in the Penobscot River, Maine. Trans. Am. Fish. Soc. 147(3): 525–540.
Welsh S.A. and Liller H.L. 2013. Environmental correlates of upstream migration of yellow-phase American eels in the Potomac River drainage. Trans. Am. Fish. Soc. 142(2): 483–491.
Wertheimer R.H. and Evans A.F. 2005. Downstream passage of steelhead kelts through hydroelectric dams on the Lower Snake and Columbia rivers. Trans. Am. Fish. Soc. 134(4): 853–865.
Winter H.V., Jansen H.M., and Bruijs M.C.M. 2006. Assessing the impact of hydropower and fisheries on downstream migrating silver eel, Anguilla anguilla, by telemetry in the River Meuse. Ecol. Freshw. Fish, 15(2): 221–228.
Zydlewski J., Stich D., and Sigourney D. 2017. Hard choices in assessing survival past dams — a comparison of single- and paired-release strategies. Can. J. Fish. Aquat. Sci. 74(2): 178–190.

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cover image Canadian Journal of Fisheries and Aquatic Sciences
Canadian Journal of Fisheries and Aquatic Sciences
Volume 78Number 8August 2021
Pages: 1181 - 1192


Received: 22 October 2020
Accepted: 15 February 2021
Version of record online: 12 August 2021


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Matthew A. Mensinger [email protected]
Department of Wildlife, Fisheries, and Conservation Biology, University of Maine, 5755 Nutting Hall, Orono, ME 04469, USA.
Erik J. Blomberg
Department of Wildlife, Fisheries, and Conservation Biology, University of Maine, 5755 Nutting Hall, Orono, ME 04469, USA.
Joseph D. Zydlewski*
US Geological Survey, Maine Cooperative Fish and Wildlife Research Unit and Department of Wildlife, Fisheries, and Conservation Biology, University of Maine, 5755 Nutting Hall, Orono, ME 04469, USA.


Joseph D. Zydlewski served as an Associate Editor at the time of manuscript review and acceptance; peer review and editorial decisions regarding this manuscript were handled by Bror Jonsson.
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