NMFS Identifies Sources of Downstream Fish Kill

In a 2021 opinion the National Marine Fisheries Service came to several important conclusions about the existing system of downstream fish passage at the Brunswick dam.

“Although the fishway was designed and constructed to be a volitional fishway that could be operated 24-hours a day; it is currently operated as a trapping facility due to the State of Maine’s concerns regarding the potential spread of invasive species, particularly white catfish. This reduced operation affects the effectiveness of the fishway as fish can only pass when it is being staffed.” page – 9

“Downstream passage is provided at the Brunswick Project via a surface sluice and associated 18-inch pipe that discharges fish into the project tailrace. The existing sluice gate and pipe were installed in 1983.” page – 9

“The Brunswick Project affects out migrating diadromous fish by injuring and killing juveniles and adults directly though turbine entrainment and indirectly by creating pond-like water conditions in the impoundments that support fish and bird predation, as addressed above. The Project’s impoundments also alter water quality, stream channel migratory routes, and the timing and behavior of out migrating fish.”  page – 76

“The results of the studies indicated that the majority of the tagged smolts passed the project via the spillway or the project turbines. The downstream bypass effectiveness rate was found to range between 0%-10% over the three years…” page – 76

“Some proportion of the salmon smolts that pass the Brunswick Project survive but are subjected to internal or external injury, scale loss, or loss of equilibrium. These injuries can lead to mortality that occurs after the smolts leave the study area, or else may reduce overall fitness which may reduce an individuals’ ability to evade predators or locate prey.” page – 76

“Dams can significantly delay smolt outmigration, especially in low water years, because the individual fish must search and find an available passage route. Delays can lead to mortality of Atlantic salmon by creating conditions that increase the risk of predation (Blackwell & Juanes, 1998), and can also reduce overall physiological health or physiological preparedness for seawater entry and oceanic migration (Budy et al., 2002). …The Brunswick Project causes migratory delay of Atlantic salmon smolts in the Androscoggin River.” page – 76-77

A small percent of fish are able to pass into river above the dam and reproduce. Of those, the dam kills roughly 20% of the fish returning to sea. “To summarize, there are several sources of mortality associated with downstream passage through the Brunswick Project, including passage mortality through the dam, and hydrosystem delayed mortality. Given the mortality rates estimated above (i.e., average of 12.1% mortality through the project (including impoundment mortality within 200 meters of the dams), and an additional 6% delayed mortality) we anticipate that if 100 smolts migrated through the action area, only 82 would survive (direct survival x delayed survival = 81.9%). This does not include background levels of mortality in the action area that would occur regardless of the presence of the dam.” page – 79

“…the Brunswick Project will continue to affect out migrating salmon by: 1) injuring and killing smolts and kelts passing downstream through the project facilities; 2) delaying outmigration; and, 3) increasing stress levels, which, in the case of salmon smolts, can lead to a subsequent decrease in saltwater tolerance.” page – 96