RED DEER ADVOCATE (Alberta) 24 September 05 Disappearance of frogs studied (Brenda Kossowan)
Stronger evidence is needed before people leap to conclusions about the sudden disappearance of northern leopard frogs, says an Edmonton biologist.
Kris Kendell is part of a team monitoring the progress of a group of leopard frogs released in the Raven River near Caroline from 2001 to 2004.
New theories have suggested that an African fungus may have been responsible for virtually wiping out Alberta's leopard frog populations during the 1970s. However, Kendell said there is still no evidence to determine whether it was the fungus itself or whether some change in the environment weakened the animals' resistance to disease.
"When amphibians are in stressful situations - in other words, the quality of their environment is decreased - they may become weakened and disease can set in. As far as this one, it's just one of several diseases that can affect amphibians." Kendell said the release site near Caroline has been the most successful in Alberta in terms of the high survival rate among the frogs released from The Raven trout brooding station.
Necropsies performed on dead frogs discovered in the release area showed that some had been infected with the African fungus, batrachochytrium dendrobatidis, which causes abnormalities in skin structure. The necropsies did not determine whether or not the fungus was the cause, or "a nail in the coffin," said Kendell.
While there have been large numbers of survivors from the released frogs, there is no evidence to suggest that any of them have successfully reared a new generation, he said.
It's not that they aren't there, so much as they have not yet been found.
"When we release frogs, they do have the ability to disperse several kilometres over a year. Leopard frogs have evolved to deal with flood events. It is possible that there is a population that has established itself and we just haven't found it yet."
Last summer's heavy rains provided ideal conditions to disperse leopard frogs over a much wider area than they would travel in a drier year, he said.
Frog populations will tend to concentrate or disperse, depending on how much water is available. That makes them easier to find in a dry year, when they congregate in large groups around whatever water is available.
"Amphibians are not always the easiest animals to study. It can be a challenge. It all depends on your local knowledge of the area. That's why monitoring amphibians is so important."
Leopard frogs are considered a marker species, valued because the health of their populations helps gauge the health of the environment they are in, said Kendell.
A leopard frog recovery team has been established and has recently drafted a recovery plan, he said.