Booming year for frog eggs

Posted onApril 27, 2021|News and Events, Oregon Spotted Frog, Species at Risk
The Oregon spotted frog is Canada’s most endangered frog, with fewer than 300 breeding individuals in the wild. The recovery plan for Oregon spotted frog calls for conservation breeding, headstarting and release to re-establish viable populations in at least six sites. Wildlife Preservation Canada began coordinating these efforts in 2010, adding a conservation breeding program to the headstarting work taking place at the Greater Vancouver Zoo. This expanded on the breeding efforts underway at the Vancouver Aquarium. The 2021 breeding season is off to to a booming start!

The breeding season for Oregon spotted frogs (OSF) has proven to be exciting, busy and abundant. We tried a few different husbandry changes in WPC’s breeding program this year. Some changes were planned and some were based on our real-time observations as we watched the egg-laying season of wild frogs.

It all starts with communication.

Shouldn’t it always? We communicated closely with the team surveying frogs in the wild. By mimicing the behaviour of wild frogs, we hoped to increase the chances of healthy and successful breeding in our conservation tubs. We also hoped to avoid past years’s issues when our overzealous males moved into amplexus position (where the male tightly grasps the female) very early. This early amplexus was resulting in what is effectively frog bedsores on the females, which can lead to infection and death.

To avoid this we planned to keep the males and females in separate tubs over winter, so they wouldn’t have access to each other until the time was right. The field crews reported that they often see a lot of movement by males right before the appearance of eggs. That got us to thinking. Maybe the males are moving more during breeding season and aren’t “hibernating” around the females, further confirming our decision to keep the males and females separate.

Amplexus position, where the male tightly grasps the female during mating.

Frog, meet frog.

Once the field team reported the frogs were moving in the wild, we prepped our tanks for introductions. One of the main things we do to put frogs in the mood to breed is drop the water in the tanks really low – so low that there isn’t more than one inch of standing water above the submerged vegetation and debris at the bottom of the tank. In the wild, frogs lay their eggs in shallow water, when water levels naturally drop right around breeding time. We also make sure there are plenty of emergent plants and less open water, further mimicing wild laying sites.

And then we wait.

In a few days we started to see egg masses, lots of them. One thing we noticed right away is how closely the egg laying pattern was matching the wild. In previous years the females in the captive program laid their eggs gradually, over the course of a few weeks. One or two egg masses a night, and scattered around the tank and not clustered together. This is on contrast to wild egg masses which tend to be laid in a relatively tight time frame and are laid clustered together in a large group.

Our females were behaving more like wild females.

Oregon spotted frog egg masses

We also noticed out of the first 14 egg masses…all were laid in one tub, the tub the females were overwintered in. Interesting. With that many masses being laid we would expect to have at least some in the other tubs, which had held males over winter. To satisfy our curiosity we transferred some pairs, who were already in breeding position back into the tub that held females overwinter.

BOOM!

Within 20 hours of being transferred from the male overwinter tub to the female, all the females had laid their eggs, again in a tight group and right were the females had laid previously. Must be a nice spot!

So we tried again. We removed the laid egg masses to their hatching tubs (to avoid them being trampled by the adults), we moved the frogs that had laid into a holding tank and moved in more pairs. These pairs didn’t even wait a day, they laid within 5 hours of being transferred into the female overwinter tank.

That got us thinking…is there actually “something in the water”?

Well, we don’t know, but we suspect so! Since we have one shot per year to observe anything related to frog breeding we have to wait till 2022 to develop and test any further hypothesis, but as of now we have great success! Not only did we get 41 of our 43 females to breed, 19 of those females were only 2 years old, which is young for an Oregon spotted frog.

As a result of getting so many females to lay we also had no female death due to egg binding. Egg binding has been a problem in previous years, where females just seemed to not be able to release their eggs. This causes infection and ultimately death.

Now to see how many eggs develop and hatch – stay tuned!

Andrea Gielens

Lead Biologist – Fraser Valley Wetlands Recovery Program

Andrea manages WPC’s captive breeding and release programs for the Oregon spotted frog and the coastal western painted turtle. Andrea has studied at-risk reptiles and amphibians in Canada and abroad, including a term at the Durrell Wildlife Conservation Trust in Jersey. Andrea also manages the Taylor’s checkerspot butterfly recovery program in BC.

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