Where have all the toads at the Atlin Warm Springs gone?
This is a question that people are starting to ask in earnest.
There used to be hundreds and hundreds of tiny toadlets in early spring. Now there are none. Not a single toad or even a tadpole has been seen in the past two years.
One man with a keen interest in observing toad populations is Brian Slough.
He has been watching the Western toads at the Atlin Warm Springs since he first visited in 1988.
Brian Slough is a wildlife biologist with 30 years’ experience. He worked for the Yukon government for 15 years as a wildlife management biologist.
He is currently a self-employed researcher and consultant. His main research interests are amphibians, bats and other small mammals.
The rapid population decline at the warm springs is characteristic of the incursion of disease says Slough.
Despite this, he maintains that the cause of the decline and apparent extirpation of the population in 2005 or early 2006 is unknown.
“There are a lot of other factors leading to declining amphibians around the world,” says Slough.
Habitat loss, habitat fragmentation and degradation, introduced predators and competitors, chemical pollution, viruses, climate change and UV-B radiation all play a part.
“Amphibians are sentinels for environmental degradation,” he claims.
Aspects of their biology make them sensitive to environmental change.
Their lifecycle from egg to larvae takes place in water, and their adult stage takes place on land.
As adults they take up air and water through their skin (as well as lungs).
Their eggs are encased only in gelatin, which is permeable to water and light (UV-B).
Thus, they are particularly vulnerable to any changes or contamination to water, land, air or sunlight, says Slough.
Despite these possibilities, Slough thinks a fungal disease is causing the decline.
“Batrachochytrium dendrobatidis is the most likely suspect in the Atlin Lake situation,” he alleges. This is an ancient saprophytic fungus that causes the disease chytridiomycosis in amphibians.
The Western toad, Bufo boreas, also known as the Boreal toad, is highly susceptible to Bd in some cases says Slough.
With funding from the BC ministry of Environment, Slough searched many known breeding sites in and around Atlin Lake this summer. He found nine adult toads. Seven tested positive for the chytrid fungus, or Bd. Nine samples taken from the Tutshi Lake/Log Cabin area came out negative.
Mark Connor, habitat steward for the Taku River Tlingit First Nation, co-ordinated sampling on the Nakina River south of Atlin in the Taku drainage. One of two toads sampled tested positive.
Slough sampled one lone female toad at Warm Springs Homestead across from the public warm springs. She tested negative.
“The rate of infection and the wide distribution of infected locations is a concern,” says Slough, noting that the infected specimens came from both sides of Atlin Lake, from Teresa Island, and from the Nakina River south of Atlin in the Taku drainage.
The disease was also detected in 29 of 95 Western toads tested in Southeast Alaska, collected in 2005-2006 near Haines and Skagway.
Slough says that other studies have found the chytrid fungus present in Western Toad populations on Vancouver Island and in the lower mainland of BC.
The toads have been documented as being present at the warms springs since at least 1924. The last time tadpoles or toads were observed was spring 2005.
Slough found no indication of breeding on Atlin Lake at all this summer, even at known breeding sites.
The only location breeding was confirmed was at Tutshi Lake.
Tutshi Lake west to the Haines Triangle marks the north-western extremity of the Western toads’ range in the interior of the continent.
The north-eastern extremity is in the Liard River Basin with breeding documented at Coal River Springs.
Even if Bd is the cause, populations may start to increase naturally, but that depends on the survival of at least some individuals and the ability to expand to former breeding sites says Slough.
“The springs may actually be prime for re-colonization by healthy individuals, if these exist,” says Slough, explaining that the fungus cannot persist more than a few months without an amphibian host.
Thus, since all the toads are gone and the only one left tested negative, the springs have a good chance to be re-occupied once the disease has run its course.
“It would really only take one male and one female to re-establish a population,” he says, “Since they have such large clutches (of eggs).”
Toads are capable of moving more than 500 metres per day, says Slough. Movements of up to seven kilometres in one day have been observed.
“Toads from distant sources on Atlin Lake will eventually find their way to the springs and to other habitats which may have been affected by population declines and extirpations caused by the fungus,” he claims.
This ability to disperse long distances will make the natural re-colonization of habitats more probable, says Slough.
The golden toad of Costa Rica is cited by Slough as one of the more famous examples of species extinction that may have been caused by Bd.
This species had no natural or captive breeding stock to re-establish the population.
The Western toad fortunately is still widespread in western North America.
“Not much is know about the extent of damage that we can expect to local Western toad populations, and how long it may take to recover,” says Slough.
In 2002, the Committee on the Status of Endangered Wildlife in Canada listed Bufo boreas as a species of Special Concern under the Species at Risk Act due to population declines, population extirpations, range reduction, and because the species is vulnerable to habitat loss and disease.
This means that they could easily become a Threatened or an Endangered Species if a combination of biological characteristics and identified threats present themselves.
“I would call this an imminent threat,” declares Slough.
A conference was convened last month in Arizona on amphibian declines and chytridiomycosis. Two hundred participants from nine countries put their heads together to come up with ways to identify actions to limit the spread and impact of Bd.
Purnima Govindarajulu, a small mammal and herpetofauna specialist at the BC government Wildlife Science Section, attended the conference.
She reports that although Bd surveillance is still very patchy, Bd has been found in all continents with amphibians.
The Aquatic Animal Commission of the World Organization of Animal Health is considering a proposal to make chytridiomycosis an internationally notifiable disease she says. Such required reporting would then allow member countries to better understand the distribution of Bd.
Slough says that biologists within the BC government would like to spend more on Western toad surveys and chytrid surveys, but there are many competing pressures from other emerging wildlife diseases.
“I think the interest will increase as more population declines are documented,’ says Slough. “The Yukon government has shown no interest in amphibian diseases or population monitoring to date.”
Parks Canada funded toad surveys in the Chilkoot Trail National Historic Site a few years ago, but declined to fund chytrid surveys that he proposed since the species still has a wide distribution.
Slough believes that an imminent threat might result in the species being up-listed to Threatened or Endangered.
“Then they might fund surveys,” he says
For now Slough continues much of his amphibian research on his own dime and dedication. If you have any observations to report please contact him at “mailto:firstname.lastname@example.org”
Stephen Badhwar is a writer who lives at Warm Springs Homestead in Atlin, BC.