Posted by Mark A. Conboy and Sarah M. Larocque
The eastern musk turtle (Sternotherus odoratus), otherwise known as the stinkpot, is a provincially and nationally threatened species. Despite being quite rare throughout most of Ontario, research (summarized in a previous post) suggests that in Lake Opinicon stinkpots may be almost as numerous as the more familiar painted turtle (Chrysemys picta). Occasionally a stinkpot is seen in one of the large lakes adjoining Lake Opinicon, but until recently there were no known occurrences of this species in the QUBS Back Lakes. On August 20, 2011 while sampling fish, we found a hitherto undocumented population of stinkpots in Round Lake. We captured five males and four females among three unbaited fyke nets set in the littoral zone of the lake.
Stinkpots normally inhabit water that is less than 2 m deep, so the presence of stinkpots in Round Lake is somewhat surprising because shallow water habitat is relatively limited. Round Lake is the deepest lake at QUBS (mean depth = 12.6 m; maximum depth = 30.1 m). The shallow littoral zone is confined to two narrow bands in the Lake’s north and south ends. According to recently completed bathymetry measurements, only 6.7 % of Round Lake’s total surface area contains water that is 2 m or shallower. When considering depth alone, it seems that Round Lake is not ideal for stinkpots. However, the limited littoral zone that does exist seems like perfect habitat for a number of reasons: (1) Potential prey species abound; Round Lake hosts the most diverse fish community of any QUBS Back Lake yet surveyed (with 13 species). It should be noted that aquatic invertebrates, rather than fish, tend to comprise most of the stinkpot’s diet. Even if fish represent a small fraction of the stinkpot’s diet, the fish diversity is indicative of a generally healthy and productive ecosystem that includes lots of invertebrates. (2) The shallow bays are heavily vegetated and contain plenty of submerged woody debris for shelter and foraging opportunities. (3) The wetland at the south end of the lake contains potential nesting sites, such as muskrat (Ondatra zibethicus) lodges.
This coming summer we plan to look for stinkpots in Garter Lake which connects to Round Lake by a broad marshy channel. We expect to find them there. In addition to the obvious conservation importance of the Round Lake stinkpot population, there is the potential for future research opportunities. For example researchers will be able to compare the diet and heavy metal concentration in stinkpots and their prey between sites invaded by zebra mussels (such as Lake Opinicon) and non-invaded sites (such as Round Lake). Researchers can then determine whether or not zebra mussels are an important pathway for the transfer of mercury in stinkpots. Of course, high loads of heavy metals such as mercury can have all kinds of negative impacts on turtles so studies such as the one described above can be important in developing essential knowledge when planning a conservation strategy for this threatened species.