Keeping a Close Eye on Amphibians
As I stare into the tea-coloured water of a small, shallow pond somewhere south of Wabasso Lake in Jasper National Park, I can’t see the salamander eggs Park Ecologist Brenda Shepherd is pointing to. “Look along the submerged log,” she says. “They’re on the plant near the last branch.”
My eyes are starting to water, and even equipped with the polarized glasses designed to reduce glare, I’m having trouble distinguishing slimy strands of algae from actual plants. Then, suddenly I see them. Carefully wrapped around the plant’s tip is a mass of clear, jelly-like eggs. In the centre of each egg is a dark nucleus; a neatly coiled larva that will emerge this summer, and transform into a young adult sometime this August.
If there are fish in the water, however, the future of these fragile eggs becomes much less certain. Says Shepherd, “if fish are present, there is an 80-per-cent chance the long-toed salamanders at this site won’t survive.”
This is one of the things Shepherd and aquatics biologist Ward Hughson are learning from their amphibian monitoring program, in effect since 2007.
“From our work sampling over the past two seasons, we’ve picked up a couple of trends that are quite helpful in understanding how to maintain healthy populations of these species. They are trends that other researchers have observed elsewhere in the province and North America.”
Jasper National Park is home to five species of amphibians: the wood frog, Columbia spotted frog, boreal chorus frog, the western toad and the long-toed salamander. Investigating the status and trends of these amphibian populations is one way Jasper National Park measures and reports on the health of its aquatic ecosystems.
“We need a good understanding of how our amphibian populations are doing so that we can detect broad-scale species declines,” says Shepherd. She points to places like the Sierra Nevada of California, where the combination of fish stocking in fishless ponds and diseases like chytrid fungus have decimated some amphibian populations like the yellow-legged mountain frog.
However, information about the relationship between fish and amphibians was an unanticipated bonus. “We designed our monitoring program to detect and respond to changes in amphibian population distribution. The relationship to fish was something this program wasn’t designed to find. Our program uncovers not only the condition of the population but the process (predation by fish) that is driving whether these species survive. ”
Shepherd and Hughson also found that the presence of fish at a site impacts wood frogs. “Wood frogs are not affected to the same degree, but fish increased the risk of [local] extinction by about 40 per cent,” says Shepherd.
While long-toed salamanders and wood frogs are sensitive to the presence of fish in their breeding ponds, it turns out that western toads are not. “This surprised me,” says Shepherd, “so I did some digging.”
She discovered that western toad adults and larvae secrete a mild poison. The poison is produced by enlarged paratoid (poison) glands on the shoulders, and deters fish that would otherwise gobble up their eggs and young.
This resilience to predation is not the only advantage western toads have over the rest of their amphibian cohort. They are the only ones that are likely to increase their range in areas that have a high density of wetlands. This may be because they have much larger home ranges than the others and can easily move from wetland to wetland. Western toads range up to four hectares, about the same area as nine football fields. In comparison, long-toed salamanders only range up to 0.03 hectares, which is less than one football field.
Western toads are listed as a species of special concern in Canada, as their populations are declining from habitat loss and disease. Says Shepherd, “this makes healthy populations in the national park even more important.”
For all the differences in survivability, the numbers of wood frogs, salamanders and toads have remained similar over the study period. Says Shepherd, “in the last two years, there’s been no change in [the habitat the amphibians occupy].”
This is good news. She cautions, however, that given what is happening in other areas, it will be important to keep monitoring. Global disease trends are constantly changing, and in other parts of the province, the introduction of fish where they haven’t been previously is a major threat for species like the long-toed salamander.
In addition, Shepherd says, “some species may not be sensitive to fish predation, but may be sensitive to disease carried by fish.” For that reason, Shepherd and Hughson will sample the same areas once every three years to keep an eye on local populations. Says Shepherd, “these programs help us know what’s really happening, instead of guessing or basing our [aquatic] management on trends that are occurring in other places.”