How do we know if the frogs we are catching at a re-introduction site are frogs we put there or a result of the establishment of a population?
This is a serious question that we have to address as we continue our captive breeding program for Oregon Spotted Frogs. Year after year we release juvenile frogs once they have undergone metamorphosis. And every year we release them into the same wetland in an attempt to establish a permanent self-perpetuating population. While this wetland historically had a population of Oregon Spotted Frogs, no breeding was confirmed in the area for a number of years before we began adding frogs to the site. This is helpful information to have because it gives us a pretty good idea that the frogs that we capture during our spring trapping are there as a result of our husbandry program.
But how do we know if those are the frogs that we released last year, or the year before? Or if they are frogs that hatched on site resulting from the breeding of frogs that we released previously?
The answer is that we tag all of the frogs that we release into the wetland. Depending on the size of the frogs we are releasing we can tag them with PIT (passive integrated transponder) tags or with VIE (visual implant elastomer). These are the same methods that we use in our capture mark recapture program, but we have specific VIE codes that change every year that correspond to husbandry frogs. The PIT tags have a unique identifying code for each individual frog and when we tag frogs and record information, we include their origin in our data. We have three places that frogs from our husbandry program come from including the Greater Vancouver Zoo, the Vancouver Aquarium, and the Toronto Zoo. Periodically, we also release unmarked tadpoles into the wetland adding a layer of complexity to this question. As of 2018 we have not found any Oregon Spotted Frog egg masses during our extensive surveys. Genetic testing of questionable egg masses have always come back as Red-legged frogs. With all of this information we can make a really good assumption as to whether or not a frog (depending on age, size, and the presence/absence of a tag) is a frog that we released or one that hatched on site.