Is a new-to-science form of rainbow trout at risk in the Canadian Skagit?
Seattle City Light is in the final stages of a re-licensing application for their three Skagit River dams in Washington State. The furthest upstream dam backs Ross Reservoir across the border into BC, where it is fed by the upper Skagit River. Most of the upper Skagit is protected within parks.
The terms of reference for the application and scientific studies arising from it stop at the Canadian border, excluding Canadian interests.
Some Skagit tribes within Washington State have been pushing for anadromous fish passage over all three dams, relying on traditional knowledge. There is no scientific evidence (so far) of previous salmon or steelhead trout presence or use above Ross Dam or in the BC Skagit.
There is no evidence of char or steelhead/rainbow gene flow from Ross Reservoir down through the lower Skagit.
A complication is that US federal legislation usually requires fish passage at all dams.
In preparation for Seattle City Light’s application, American scientists collected DNA samples from Ross Reservoir bull trout and rainbow trout south of the USA/Canada border. Analysis showed: (a) Ross Reservoir bull trout were closer genetically to Fraser River bull trout than to bull trout sampled downstream of the dams; and (b) Ross Reservoir rainbows were genetically distinct from rainbow/steelhead trout (Onchorhynchus mykiss irideus) downstream of the dams. Ross Reservoir rainbows appear to be intermediate genetically to the coastal rainbow trout subspecies (O. mykiss irideus) and the interior redband trout subspecies (O. mykiss gairdneri). They may be a new subspecies, or perhaps a unique hybrid between the two recognized sub-species, and perhaps evidence of a separate DU (designatable unit, the relevant term for Species at Risk Act). In any case, Ross Reservoir rainbows likely have been isolated for 1000s of years and have exceptional biodiversity values. They need protection and further research.
Ross Reservoir currently has one of the largest bull trout populations anywhere (estimated at 4000 adults), and perhaps the largest on the planet that is almost entirely protected within parks. That population is stable or increasing. In Washington State bull trout are considered endangered, and in BC they are blue-listed (special concern). Why would anyone risk this population?
Most Ross Reservoir trout spawn in the Canadian Skagit, so the Ross rainbows are likely genetically similar to Canadian Skagit rainbows, but this requires confirmation via DNA studies in the BC Skagit and adjacent watersheds.
Introducing anadromous fish to Ross Reservoir and the Canadian Skagit could have serious genetic, disease and other unintended consequences to native fish, plankton populations in Ross Reservoir, and the broader ecology of the Skagit Valley. We note that Canada bears most of the risk, and none of the benefits.
Proposed Actions
- BC and Canada should oppose fish passage until we understand what we have in Skagit/Ross Lake trout and what we are risking and represent that position to US authorities. BC and Canada should assert that fish may not be introduced to BC waters without their agreement, and that any fish that do cross into Canada then belong to Canada;
- BC should conduct trout DNA studies in the Skagit and adjacent watersheds forthwith (we understand such studies are now being planned);
- BC should seek evidence to determine if anadromous fish ascended the Skagit into Canada in the years prior to the first dam construction (the 1920s).