Warm weather brought warm waters this summer, making some rivers and lakes in Alberta lethal, and creating higher potential for fish kills. At least one newspaper reported fish kill at McLaren Dam in Alberta was blamed on hot weather. While lethal water temperatures have certainly occurred in Alberta in past years, climate change is likely to increase the occurrence of these incidents.

August 2009 Advisory

This summer's warm water temperatures hit a critical point prompting the Alberta government to issue an advisory on August 3, 2009. The advisory asked anglers to take voluntary precautions to avoid streams with higher temperatures, fish during the early mornings or late evening, and refrain from angling in locations with warmer temperatures. The advisory referred to streams located in the foothills between Rocky Mountain House and the Montana border where water temperatures exceeded 26.5 C putting fish populations under considerable stress. Optimum temperatures for many trout species are in the range of 15 C while lethal temperatures exceed 24.5 C.

The voluntary ban in Alberta could be shifted to regulated closures of certain areas if high stream temperatures persist over an extended period of time. The voluntary ban asks anglers to carry a thermometer when fishing helping them to explore other area likely to be cooler. On August 17, 2009, Sustainable Resource Development lifted the voluntary advisory.

Fish kills not new to Alberta

Fish kills result from a combination of factors including low stream flows, warm weather, and increased water temperatures. As water becomes warmer, it is able to hold less oxygen and results in a fish die-off. According to Sustainable Resource Development, a water body can become a "death trap" after prolonged warm temperatures when oxygen levels become too low to support fish life. Algae blooms (rapid growth of microscopic plants) in some water bodies contribute further as algae decays further lowering oxygen levels

Fish kills are not new in Alberta. In 1998, the Alberta government reported incidents of dead fish in shallow parts of rivers, reservoirs and lakes at least 16 locations across the province including Sturgeon Lake, Cutbank Lake, Slave Lake, Gregoire Lake, Trout Pont, Bennett's Pone, and several reservoirs. During the summer of 2000 - considered one of Alberta's more significant droughts - anglers and Trout Unlimited staff reported fish kills in Pekisko Creek, Sheep River, Jumpingpound Creek, in the Bow River below Bassano Dam, as well as in the Oldman River sub-basin. Low flow conditions partially caused by water diversions were considered to have contributed to fish kills on the Highwood River eight times between 1977 and 2000 according to a Trout Unlimited background paper.

Fish kills more likely with increasing climate change

Scientists are also considering the long-term impacts of climate change and resulting warming temperatures of water on fish populations. A Natural Resources Canada study completed in 2007 suggests that climate change is likely to "have significant impacts on fish populations and sustainable harvests." As conditions change over the long-term in freshwater streams and rivers including temperatures, so will the fish populations. For example, snow crab populations in marine ecosystems will decrease as reproduction is expected to decrease with the onset of climate change. Arctic marine ecosystems will be particularly hard hit from changes to sea-ice cover affecting marine productivity, fish distributions, and accessibility to fishing itself.

But climate change will also impact fish diversity and populations on the Canadian prairies. Some prairie aquatic ecosystems are at risk for extirpation (localized extinction) because certain species are sensitive to small changes in temperature and oxygen. Fish communities are considered to be an indicator of the impacts of climate change. Bull trout in particular are considered extremely sensitive to warm water temperatures and considered "canaries in a coal mine" as an indication of disruptive habitat change. One study in the Cariboo-Chilcotin watershed in BC, evaluating the potential impacts of climate change on bull trout populations, indicated that more significant warming would likely result in the complete disappearance of cold water habitats in most of the watershed by the 2080s. Even under the best case scenario, bull trout habitat (cold water) across North America is expected to become markedly reduced.

In addition to broad societal action on climate change, local action is possible. One such action is maintaining strong natural shoreline vegetation. The shade provided by trees over water helps reduce heat increases while playing a vital role in riparian ecology. Efforts to minimize water diversions are also important to mitigate the long-term impacts of lower stream flows.

Sources

Government of Alberta. 2009. Anglers asked to help protect fish in foothills streams, news release, July 28. (accessed August 25, 2009)

Government of Alberta. 2009. Angler advisory lifted as foothills' stream temperatures drop, news release, August 17. (accessed August 25, 2009)

Government of Alberta. 2007. Hot fish need help from anglers, news release, August 3. (accessed August 25, 2009)

Government of Alberta, 1998. Alberta Fish Threatened By Summer Kill, news release, August 27. (accessed August 25, 2009)

James et al. 2001. Predicting the Impact of Climate Change on Fragmented Prairie Biodiversity: A Pilot Landscape. Final Report to the Climate Change Action Fund. August 2001.

Lemmen, D.S., Warren, F.J., Lacroix, J., and Bush, E., editors (2008): From Impacts to Adaptation: Canada in a Changing Climate 2007 Ottawa, ON: Government of Canada.

Nick Lewis and Richard Cuthbertson, Hot Alberta weather spurs call to avoid fishing in warm waters Calgary Herald, July 29, 2009. (accessed August 25, 2009).

Pat Kolafa, Weather, algae likely cause fish deaths in McLaren Dam Drumheller Mail, August 2009. (accessed August 25, 2009).

Stacey O'Brien, Warm water tough on fish Red Deer Advocate, August 5, 2009. (accessed August 25, 2009).

Think Salmon. May 15, 2009. A future outlook on the effects of climate change on bull trout habitats in the Cariboo-Chilcotin

Trout Unlimited Canada, Alberta Council. 2001. Anglers Asked to Take Extra Care to Minimize Stress to Fish During Drought: Fish Kill Hotline Established, news release, July 20. (accessed August 25, 2009).