Exploring the Aquatic World of “Jurassic Pond”
By Margaret Letkeman, Northern BC Summer Field Assistant
Margaret Letkeman was Northern BCβs very first summer field assistant, helping project coordinator Cindy Verbeek get better organized for more consistent field work and helping with some studies that have been on the back burner for a long time. Here is her report on one of the many projects Margaret worked on:
Silverthorne Lake is a unique place. Nestled in the forest of North Central British Columbia it is part of a series of drainages from the alpine country of Morice Mountain. This little lake has earned its nickname, βJurassic Pond,β for the incredible diversity of aquatic invertebrates and the creatures that rely on them for feed. It is mostly unaffected by the industry that our community relies on and has been made accessible by local cross-country ski and mountain bike clubs.
We aim to understand the timing of emergence, species composition and conservation concerns in the area. Since Silverthorne has been identified as a local biodiversity hot spot due to its varying ecosystems (lake, forest, bog), it has become one of our focal points for biodiversity research in the watershed as representative of a lake ecosystem.
Heeding the spring song of the wood frogs in June near the hatchery, Cindy and I headed to the lake in hopes of hearing the same there. We were disappointed to hear none and to discover that we were too late: The HATCH had already happened! Empty strings and egg clusters were safely tucked among the reeds and sedges at the southeast shoreline of the lake, and clumps of pinhead sized tadpoles were swimming close by. A sweet reminder that βemptyβ is not the end, but only the beginning!
Weeks passed and the little pinheads gradually grew into almost dime sized tadpoles with black heads, no bodies, and just a tail for propulsion. Spring turned into summer and we started to note that there were clearly two species in the masses. The larger ones were substantially larger, with grey bodies and broader tails. A little digging and we determined that the smaller black ones were Western Toad and βassumedβ that the larger greys were wood frogs.
The favorite hang out was in a corner of the lake where a small outflow stream had been dammed years before. Here the water was warm and undisturbed.Β In mid-August both species developed legs, first the back legs, then non-functioning little βarmsβ and finally full four legged swimmers.
The strangest thing occurred with the little toads, however. As the bodies of the little tadpoles developed, their heads shrunk and their overall size decreased by about half! The frogs similarly changed shape, but their bodies elongated and they did not shrink nearly as much.
As the change happened, Cindy and I began to question our assumption that the frogs were indeed wood frogs. We had assumed this based on hearing wood frogs near the hatchery but when we were finally able to capture one, we turned it over, and the slight red colouring on its inner thighs confirmed our questioning. We had instead been watching an βarmyβ of Columbia Spotted Frogs developing from tadpoles into juvenile adults!
One late August weekend the cool wet summer weather finally stopped and for three days, it was sunny and warm. We thought the season was over. The last time we had visited the shallow water, the mud was warm and the tadpoles were almost fully developed. After a few warm days, they were gone!
During this time, the strange looking larva of the three-toed salamander showed up in smaller numbers. When their legs and gills became evident their numbers soon decreased as they continued their development and exited the pond for the forest floor.
A couple of weeks later however, four legged, short-tailed toads accumulated in the same place. Tiny versions of their adult selves, complete with adult markings made the shoreline crawl underfoot.
Unfortunately our season ended abruptly when someone breached the dam. They were not strong enough to swim against the flow of the water, and just like that they were gone again. It is our hope that they were fully developed enough that this was simply the first step in the migration back to the forest.
Although the data set is far from complete and maybe the scientific information a little rough for the preliminary study, we are certain this is only the first step of years of research to come! We have two other spots – the Upper Bulkley as a river ecosystem and the Duck Pond as a wetland/pond ecosystem that we are hoping to focus our monitoring efforts on over the next 5-10 years. One thing I have learned this summer, for every question I think I have found an answer, there are a thousand more! The amphibians in this little lake are not going anywhere soon, and neither are we!
The estimated timeline is complete and as the winter sets in, and the lake freezes once again, we will look through the pictures and plan for the next adventure!
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