The reason the issue of escaped salmon deserves our attention is that there are legitimate environmental concerns that result from a farmed fish escaping. In British Columbia, both Atlantic and Pacific salmon are being raised in farms and each of these two species poses unique risks once they do escape. For Atlantic, there's hybridization, which is basically Atlantic and salmon crossbreeding -- Atlantic and Pacific salmon crossbreeding. The other is predation and competition. This involves the Atlantic feeding on wild Pacific salmon, as well as other food supplies, and then the taking of space and the wild habitat in general.
Another major concern is spawning site disruption by Atlantic salmon. The stems from the fact that Atlantic salmon spawn later than Pacific salmon so there's a risk that they enter the same streams that the Pacifics have already spawned in and then they disrupt the eggs that the Pacific salmon have already placed. And also, Atlantic salmon mature faster than Pacific salmon, and so they have a competitive, or they give to the Pacific salmon a competitive disadvantage due to their smaller size. Another concern is colonisation of Atlantics in BC, which would have severe impacts on the wild stocks -- mainly because they would be using the same streams that wild Pacific stocks presently use to spawn. And finally, there is the issue of the spreading of diseases from the farmed salmon to the wild Pacific salmon.
Despite all of the obstacles juvenile fish encounter, recent NMFS survival studies show that, with current mitigation measures, spring/summer chinook in-river passage survival is as follows:Project Survival:
The average survival through a dam and reservoir on the lower Snake River for juvenile salmon is in the mid-90th percentile (for example, spring/summer chinook passage through Little Goose Dam is 96 percent).
Cumulative survival for juvenile salmon through all four dams and reservoirs is over 80 percent.
Cumulative survival for juvenile salmon through all eight dams on the Columbia/Snake River System ranges from 45 to 60 percent.
Cumulative survival for adult salmon through all four lower Snake River dams and reservoirs ranges from 88 to 94 percent. Per-project survival rate is 97 to 98 percent.
What is understood less is the indirect or delayed mortality of juvenile fish that may occur after they have passed Bonneville Dam. That mortality may have been caused by passing in-river through the hydrosystem, the series of eight dams and reservoirs from Lower Granite Dam to Bonneville Dam or from transportation of fish.
Lower Monument Dam
Little Goose Dam
Lower Granite Dam
Another complex, often emotional issue, in which there is very little science to guide us:
Cost/Benefit Analysis is difficult and often driven by hidden agendas Save Fish vs. Lose of Jobs ?
Costs of dam breaching are difficult to estimate but are in the range of $1 billion and up.
Will it work?
Current Socio-Economic Benefits of these 4 Dams:
Mid 1990's viewpoint (but still relevant)
The Science is Murky (and difficult).
Four Alternatives Identified:
Some possible undesireable consequences from Dam Breaching:
In the short term, when the dams are breached, the rapid lowering of the reservoirs could strand some fish in shallow pools that will eventually stagnate. In addition, high turbidity and sediment in the water could cause trauma and injury, and low water levels could expose more fish to predators.
In the long term, the resident fish population will be altered, as some species will not thrive in the faster flowing river. Declines are expected in crappies, peamouth, pumpkinseed, bluegill, yellow perch, bullheads, and largemouth bass. Other species, including the chiselmouth, redside shiner, speckled dace, suckers, sculpin, white sturgeon, northern pikeminnow, bull trout, and smallmouth bass might benefit from natural river conditions.
Dam breaching could result in significant movement of sediments. Estimates are that 50 to 75 million cubic yards of existing sediments may be eroded and moved downstream. The majority of fine-grain silts would move quickly in the first few years following breaching. The coarser sands would move slowly downstream over 5 to 10 years. These existing and future sediments could move freely downstream toward McNary Dam and may cause some temporary adverse effects on food supplies for fish and bottom-feeding aquatic organisms. In addition, silt and sand now accumulated behind the dams could cause damage to pumps, valves, and other water system components.
Resuspension of sediments following dam breaching could result in exposing chemical contaminants that have been contained in reservoir sedimentation. Three chemicals are of concern total DDT, dioxin TEQ, and manganese. Only total DDT has any potential for affecting the biological system. In addition, there is concern about heavy metals from Idaho mining industry and the nuclear waste from the Arco Reactor