Simulation of the Impact of Dams and Fishing Weirs on Reproductive Potential of Silver-Phase American Eels in the Kennebec River Basin, Maine

Abstract

I modeled the cumulative impact of hydroelectric projects with and without commercial fishing weirs and water-control dams on the production, survival to the sea, and potential fecundity of migrating female silver-phase American eels Anguilla rostrata in the Kennebec River basin, Maine. This river basin has 22 hydroelectric projects, 73 water-control dams, and 15 commercial fishing weir sites. The modeled area included an 8,324 km 2 segment of the drainage area between Merrymeeting Bay and the upper limit of American eel distribution in the basin. One set of inputs (assumed or real values) concerned population structure (i.e., population density and sex ratio changes throughout the basin, female length-class distribution, and drainage area between dams). Another set concerned factors influencing survival and potential fecundity of migrating American eels (i.e., pathway sequences through projects, survival rate per project by length-class, and length-fecundity relationship). Under baseline conditions about 402,400 simulated silver female American eels would be produced annually; reductions in their numbers due to dams and weirs would reduce the realized fecundity (i.e., the number of eggs produced by all females that survived the migration). Without weirs or water-control dams, about 63% of the simulated silverphase American eels survived their freshwater spawning migration run to the sea when the survival rate at each hydroelectric dam was 90%; 40% survived at 80% survival per dam, and 18% survived at 60% survival per dam. Removing the lowermost hydroelectric dam on the Kennebec River increased survival by 6.0-7.6% for the basin. The efficient commercial weirs reduced survival to the sea to 69-76% of what it would have been without weirs, regardless of survival rates at hydroelectric dams. Water-control dams had little impact on production in this basin because most were located in the upper reaches of tributaries. Sensitivity analysis led to the conclusion that small changes in population density and female length distribution had greater effects on survival and realized fecundity than similar changes in turbine survival rate. The latter became more important as turbine survival rate decreased. Therefore, it might be more fruitful to determine population distribution in basins of interest than to determine mortality rate at each hydroelectric project.

Effects of metamorphosis timing and the larval growth rate on the latitudinal distribution of sympatric freshwater eels, Anguilla japonica and A. marmorata, in the western North Pacific

“…In the past three decades, dramatic declines in glass eel recruitment of temperate species like the American (Anguilla rostrata), European (Anguilla anguilla), Japanese (Anguil la japonica), and Australian (Anguilla australis) eels have raised concerns (Jellyman et al 2000;Hoyle and Jellyman 2002;Tatsukawa 2003;Dekker 2008;Richkus and Whalen 2000). The reasons for the declines are unclear but are probably due to reductions in spawning stocks Winter et al 2007;Clevestam et al 2011), overfishing Moriarty and Dekker 1997;Jellyman et al 2000;Hoyle and Jellyman 2002;Briand et al 2003;Chisnall et al 2003;Dekker 2003;Lin et al 2010), growth habitat and access reductions (Busch et al 1998;Haro et al 2000;McCleave 2001;McCleave and Jellyman 2004;Verreault et al 2004;Graynoth et al 2008), pollution (Amiard-Triquet et al 1988;Robinet and Feunteun 2002;Palstra et al 2006;van Ginneken et al 2009), swim bladder and gill parasites and viral infections (Haenen et al 2002;Szekely et al 2002;Kirk 2003;Sures and Knopf 2004;van Ginniken et al 2005;Han et al 2008Han et al , 2009aSasal et al 2008;Parker et al 2011), global climate change (Castonguay et al 1994;Kimura et al 2001;…”

Mortality of silver eel (Anguilla anguilla) migrating downstream through a small hydroelectric plant on the Drawa River in northern Poland

“…The character and severity of injuries sustained when eel passed through the turbines depended on many factors connected to the characteristics of both the turbines and eel, including size and behavior (Monten 1985, McCleave 2001, Leonardsson 2012. Some of the consequences of injury were immediate, while others appeared only after a period of time (Monten 1985, Richkus andDixon 2003).…”

“…Turbines cause injuries, and because of their shape eel are especially endangered (Larinier and Travade 2002). Eel mortality caused by turbines depends on many factors like the type of turbine, its size, rotation speed, and water flow (Èada 2001, McCleave 2001, Larinier and Travade 2002, Winter et al 2006, Vowles et al 2014. Turbines can cause 100% mortality (Monten 1985, Carr andWhoriskey 2008), but this number is usually lower (Monten 1985, Jansen et al 2007, Winter et al 2007, Larinier 2008, Calles et al 2010, Leonardsson 2012.…”

Conserving migratory species under human impacts and climate change

“…Reducing river flow might amplify the effect of existing barriers (Milton 2009) or create new barriers for migratory species Jaeger, Olden & Pelland 2014). Therefore, focusing on fishing pressure regulation without simultaneously maintaining river flow and connectivity could fail to maintain population persistence of Australian bass or other diadromous fish species (Parrish et al 1998;McCleave 2001). …”

“…Migratory life cycles are exemplified by diadromous fish, which migrate between fresh and saltwater habitats. These species are often both ecologically (Naiman et al 2002) and socioeconomically important , but they suffer from the interactive impacts of many threats (McCleave 2001). For instance, overfishing, pollution, habitat loss and climatic change in the oceans have contributed to the decline of diadromous fish such as Chinook salmon Oncorhynchus tshawytscha (Hilborn 2013) and European eel Anguilla anguilla (Kettle, Asbjørn Vøllestad & Wibig 2011).…”