This week, hundreds of tadpoles will be released into the Fraser River in hopes that a precious fraction of them will mature into a more stable population of Oregon spotted frogs.
The frogs once lived in the river, its streams and tributaries by the hundreds of thousands, but the species is now endangered in Canada, the likely victim of habitat loss and the invasive bullfrog, said Dennis Thoney, director of animal operations at the Vancouver Aquarium Marine Science Centre.
Because this frog spends most of its time in the water, it is particularly affected by changes in the floodplain.
"One of the reasons they're endangered – the main reason – is habitat change or modification involved with taking the floodplain out there in the Fraser River and changing how it flows – creating areas for agriculture, changing areas for cities, that kind of thing," Dr. Thoney said.
This is the northern edge of their range, said Christopher Stinson, curatorial assistant of the Beaty Biodiversity Museum in Vancouver.
"And it just happens to fall in the most heavily populated area of British Columbia lower mainland," he said adding that amphibians are a good indicator of ecosystem health. "They have permeable skin, so they're the first to absorb toxins. If there's a healthy amphibian population, [it] is usually indicative of a healthy ecology all around, a healthy environment."
As well, frogs are an important part of the food web, controlling insect populations and serving as food for larger carnivores, such as birds and fish, Dr. Thoney said.
To combat the rapidly declining population, the aquarium began breeding the species in captivity as part of B.C.'S Oregon Spotted Frog Recovery Team.
Between 2010 and 2014, more than 16,000 tadpoles and juvenile frogs produced in human care were released into suitable habitats to increase small existing populations in the wild.
Their efforts are paying off.
For the first time since the program began, the recovery team has discovered juvenile frogs in the wild, indicating the tadpoles released in recent years are growing and healthy. The juveniles were found near Chilliwack, where they are released.
"We've found metamorphs, or froglets, in the area where we introduced the tadpoles last year, so that shows that actually some of them are surviving to that size," Dr. Thoney said.
"Also, where we released some metamorphs – because we had some surplus froglets that we released – they actually produced eggs, so it looks like we're being somewhat successful in regards to this program."
Mr. Stinson said it is a positive sign that the introduction site is producing juvenile frogs and eggs.
"It is great news for the recovery of the species," he said.
Even though just half a dozen froglets were spotted, Dr. Thoney said: "If you saw half a dozen, there's a lot more out there."
He said that when they mate, the Oregon spotted frog's call sounds a bit like knocking on wood.