Investigation of bird and fish mortalities at Fort Chipewyan, Alberta
In mid-July, 2013 Alberta Canadian Wildlife Health Cooperative (CWHC) received a phone call from Parks Canada Wood Buffalo National Park office situated in Fort Chipewyan, reporting a large number of dead birds and fish at various locations in the Peace-Birch-Athabasca Delta. Fish were first reported dead around Lake Claire at the end of June but by mid July, both dead fish and birds were reported from locations downstream to the east at Lakes Mamawi and Galoot and adjacent creeks. As the first ever Alberta CCWHC intern, I was lucky enough to be available to respond to the event alongside wildlife pathologist Dr. Padraig Duignan. We arrived on July 24 and headed out on an airboat to survey the area on July 25. At first glance the area heading into Galoot Lake was clear and calm, it appeared to be pristine bird habitat. Then I asked myself: Where are all the birds?
Once we arrived at Franklin gull colony sites on the south shore of Galoot lake we started to get our answer. We counted at least 269 dead gulls within a short period of time. All of the gulls were year’s young and ranged in age from day old chicks to fully feathered juveniles and the carcasses appeared to be in various stages of decomposition. Clinically, the young Franklin’s gulls that were still alive appeared weak, depressed, reluctant or unable to fly, had trouble getting away as we approached slowly by boat and “limped” or fluttered over the water surface and floating vegetation. Remarkably, there were no adults to be seen in the area. However, we observed many other species of birds, such as American coots, lesser yellowlegs, knot, grebes, various ducks, kingfishers, Canada geese and hundreds of wood frogs all of which appeared normal. We saw numerous fish and aquatic invertebrates and no evidence of recent fish mortality.
We noted that the water level was high and had receded recently leaving debris in the branches of trees and shrubs almost a meter above the present level. The water was clear and did not have marked discolouration or odour. A film was present only in areas of standing water associated with decaying vegetation. Speaking with locals, we learned that this summer there was unusually high water levels that peaked approximately two weeks prior, coinciding with the onset of mortalities.
We collected the freshest carcases we could locate as well as a range of environmental samples. In addition, we captured some sick and dying birds for clinical examination and blood sampling. After necropsy of nine birds, the most consistent findings were metabolic bone disease (rickets-like), severe muscle atrophy, lack of internal fat reserves, heavy parasite burdens and anemia.
We tested the water for hydrocarbons and blue-green algae, both came back negative. The birds were tested for botulism and for high aluminum levels that could explain the apparent neurological problems and bone disease respectively but both were negative. On histopathology there was no evidence for an infectious disease such as West Nile Virus, avian cholera or other such pathogens.
We did necropsies and histopathology on a small sample of fish that had been collected and frozen prior to our field investigation. Unlike the birds, the fish included a number of species such as white fish and jack fish, and also unlike the birds, the fish were large mature specimens with good body fat reserves that appeared to have died suddenly. Although most of the specimens were very poorly preserved, the most consistent finding here was that their gills were packed with fine river silt.
Our final conclusion from our field observations and laboratory findings was that this was a naturally occurring event associated with the very unusual environmental conditions. Heavy June rainfall in the catchment of the Peace and Birch Rivers had resulted in record runoff and flooding from west to east across the delta. The heavily silted water with its decrease oxygen carrying capacity appears to have caused the death of the larger fish by asphyxiation as the floods passed through and mortalities ended after the floods abated. As for the gulls, it appears that the floods hit at the peak of the nesting season and as the colonies flooded, the adults seem to have abandoned the area leaving the nestlings to their fate.
Written by: Dr Monica Kovacs DVM, CCWHC intern
Photos courtesy of Dr. Padraig Duignan