Lake Trout Sensitive to Oxygen Levels in Loughborough Lake

Lake Trout is a rare species in Ontario and that means Lake Trout lakes are rare as well. Only about one percent of Ontario’s lakes contain Lake Trout, and this represents 20-25% of all Lake Trout lakes in the world (1). Loughborough Lake is lucky to have a healthy, naturally producing population in its West Basin. It is also stocked every year with cultured fingerlings through efforts of the Ministry of Natural Resources and Forestry, assisted side-by -side with members of our Lake Association. 

As a species, Lake Trout are very sensitive to environmental change. Changes in climate, temperature of the lake and the levels of nutrients, such as phosphorus run-off from agricultural and lawn fertilizers, dishwashers and septic fields surrounding the lake, may affect this species. This is because high levels of nutrients lead to algae growths that use up the available oxygen in the water. Lake Trout need about 6-7 mg of oxygen per litre of water to remain healthy and reproduce. Unhealthy habitat with algae blooms can be found just south of us in Dog Lake. While Dog Lake is too shallow to have Lake Trout, we need to avoid this kind of contamination in our lake to maintain healthy levels of fish stock. Shoreline development and agricultural practices are important determining factors in this delicate equation. 

To find out the historical levels of oxygen in Loughborough Lake for comparison with present-day levels, a recent undergraduate thesis by Hillary Quinn-Austin examined the oxygenation of Loughborough Lake over the past 200 years (2). From a core taken by researchers from the lake bottom at 38 metres, the deepest point of the West Basin, Quinn-Austin counted deposits of Lake Fly larvae exoskeletons in the lake’s sediments. These are the parts of the larvae that are shed when they emerge as flies. From those exoskeletons, Quinn-Austin then isolated samples of the Lake Fly larvae heads and mandibles, identifying specific species in the process. Counting the number of larvae heads per volume of sediment of a particular species provides an indication of the level of oxygenation of the lake at the time the larvae metamorphosed into a Lake Fly. The study also determined the amount of chlorophyll in the lake sediments through spectroscopy as an indication of algae production. 

Findings suggest Lake Flies of the genus Micropsectra (Midges) dominate the count. The high counts for this species indicate that oxygen levels have been relatively stable and high over the past 200 years, at between 6-7 mg of oxygen per litre of water. Because oxygen levels are negatively affected by nutrients from run-off and erosion, the presence of a healthy forest surrounding the lake is important. During periods of clear-cutting, especially in the mid-1800s, lake oxygen levels appeared to decline for a few decades. However, oxygen levels bounced back in the 1900s, enough to support a healthy population of Lake Trout. Between 1987 and 2009, there is evidence of a reduction in oxygen levels in the West Basin, a worrying finding that may, in time, put the population of Lake Trout at risk again. 

One of the causes of the decline of Lake Trout is the continued environmental pressures provided by development surrounding the lake. Impact from human activities such as leaching septic beds, increased fertilizer run-off, removal of trees, and clearing shorelines all negatively affect the delicate balance of oxygen in the water. 

To maintain our population of Lake Trout, Loughborough Lake’s West Basin has been identified as a “Highly Sensitive Trout Lake” and is considered to be “at capacity” for development due to concerns that additional nutrient loads may adversely affect water quality (3). It is only through awareness of the critical role humans play in affecting water quality, evidence-based development practices, and careful monitoring of scientific data that we can ensure Loughborough Lake remains a healthy habitat for Lake Trout and other environmentally sensitive species. 

References

1. Government of Ontario, Lake Trout Management for inland lakes, 2015. 

2. Hillary Quinn-Austin. A chironomid-inferred paleolimnological reconstruction of past hypolimnetic oxygen concentrations in Loughborough Lake, Ontario: Implications for the local Lake Trout habitat. Queen’s University, April 2017. 

3. South Frontenac Township’s Official Plan, Highly Sensitive Trout Lakes, Section 5.2.8a, March 2003.