The Mysterious Case of 3 Grizzlies and Salamander Sushi
By Stephanie Crowshoe
On a hot July morning in 2002, landowners northeast of the Crowsnest Pass were shocked to look out their window and see three grizzly bears roaming the shores of a small lake on their property. The bears appeared to be intently feeding on something just above the water line. What was so appetizing that it would draw these large animals out of their shady retreats?
When the coast was clear, the landowners ventured out to survey the area and were surprised to see hundreds of tiger salamander carcasses littering the shores of the lake. The marks of disease, a blood red belly and white, sloughing skin, were evident on each dead and dying salamander. While this die-off created a protein-filled, grizzly bear picnic, it was a nasty surprise for the landowners.
This disease outbreak would later be confirmed as the first known case of Ambystoma tigrinum virus (ATV) in Alberta, and would happen repeatedly, but unpredictably, in this same lake in the following years. ATV belongs to a larger group of viruses called Ranaviruses, and is currently known to only infect tiger salamanders. While salamanders do not always show physical signs of infection, the virus can persist within a population for years between outbreaks. When massive die-off events do occur, up to 90% of a salamander population can be wiped out. Due to the short duration of these die-offs (one to two weeks), they are rarely witnessed or reported.
In the decade since the first tiger salamander die-off, ATV has been detected in at least three more ponds across southern Alberta. While already widespread across the western United States, recent data show that this virus is steadily making its way north. Unfortunately, the mechanisms by which ATV is spread among ponds in southern Alberta, and even between individuals in a single pond, remain poorly understood.
Tiger salamanders, as a species that is seldom seen due to their secretive and nocturnal nature, can sometimes be overlooked when considering animal population declines. This is especially evident at the site northeast of the Crowsnest Pass. In years before the first die-off, the landowners had only noticed the occasional salamander wandering through their garden, and never imagined that a large population of larval salamanders was present just a few hundred meters away. Sadly, by the time this large population of tiger salamanders was discovered, almost all had died from ATV. In the years following the first die-off, the population has begun a slow recovery. However, it may never fully recover since smaller outbreaks still occur every few years.
Currently researchers from the University of Lethbridge are assessing other sites for the presence of tiger salamanders and ATV. In 2012 and 2013 a wide variety of waterbodies across southern Alberta will be visited to evaluate the demography of salamander populations and their rates of infection with ATV. Using a combination of live-trapping methods and molecular fingerprinting techniques, researchers can detect the virus, even in healthy looking individuals.
What can you do?
If you have seen tiger salamanders that you suspect may have been infected with ATV, let us know! Become an Amphibian Monitoring Program volunteer. Once you have signed up to become a member you can enter your observation into a form. When filling out the form for a dead or diseased salamander, please mention in the comments section that you suspect an ATV infection. This information will be extremely helpful in locating unknown outbreak sites.