Complementing fish movement data with water chemistry

By Miracle Denga, Undergraduate Honours Thesis Research Student, Department of Biology, Trent U Limnologists have always been interested in studying the vertical patterns of lake variables like temperature and dissolved oxygen. Thanks to recent improvements in the sensors used for water monitoring, we can now look at the vertical patterns of many variables in water at incredibly high resolution. A vertical profiler (we use the RBRmaestro³ Multi-Channel Logger, as seen in the pictures below) is a sensing tool that measures different lake variables as you lower the instrument into the lake, including dissolved oxygen, temperature, chlorophyll a, pressure, and several others. These advanced vertical profilers can take eight measurements of each of the above variables per second, creating an extremely detailed image of how lake conditions vary with depth. The data that a profile generates are incredibly useful – they can tell us the different phases the lake is in; for example, whether it's stratified or well mixed. The profiler data can also show us the amount of oxygen available to creatures at the bottom of the lake and provide an estimate of how much phytoplankton is in the water column. The information gained with a profile can give us baselines of what a lake should look like and help understand the factors that cause lakes to change (for better or worse). Ultimately, these sorts of data can be useful for developing best practices for lake management which are undeniably of benefit to stakeholders and to the creatures living in the lake. Below you can see some of the data we collected on Stoney Lake this May.

About me: I am an undergraduate student at Trent University doing my honour’s thesis in Dr. Marguerite Xenopoulos’ Aquatic Ecology Lab. I am investigating the factors affecting differences in the rates of deep-water oxygen depletion in the Kawartha Lakes, which involves taking monthly vertical profiles from a selection of Kawartha Lakes over the summer. This work started in May and Stoney Lake is one of the lakes we are focusing on. Stoney was profiled intensely once last summer with the intent of creating a 3D distribution of the lake variables listed above (done by Drs. Raby, Frost, and Pearce, see link). This year, I will continue sampling Stoney throughout the summer and fall. The data will be paired with data on fish tracking to see what drives fish movements and get a better sense of the dynamics of water quality in the system.

(Above) Deploying the RBR profiler in Stoney Lake on May 12.

Spring update 2023

Hi folks,

Happy spring. I hope you’re enjoying the weather and making plans to spend some time on the water soon (either on Stoney Lake or elsewhere).

I have lots of updates but I’m going to just focus on a few things for this first post of the season and save the rest for later.

This winter, we received more generous support from the Szego and Ingleton families for the project, primarily to fund the purchase of acoustic transmitters to put into fish. Their generosity means the project will continue to grow this year as we had hoped.

We also received a donation from the Kawartha Lakes Chapter of Muskies Canada, and a small research grant from Muskies Canada. Those funds have been used to purchase transmitters to put into muskies, which was always our hope with this project. Muskies Canada has a strong history of supporting research. Fun fact: muskie anglers rarely harvest any of their fish (the release rates are ~100%), and the fish that are released have very high survival if best practices for angling are used (source).

In the end, because of the donations above, and because of further support from our DFO partner (Dr. Jake Brownscombe) and other grants I hold at Trent, we have 173 transmitters in hand for 2023. The plan is to allocate those tags for: walleye (60), smallmouth bass (44), muskellunge (20), yellow perch (24), and black crappie (25). We’ve already tagged 19 walleye this year (41 to go). Muskies (‘the fish of 10,000 casts’) will be a particular challenge, but we’re hoping our friends in the Kawartha Lakes Chapter of Muskies Canada will help a bit on that front.

To that end, we’ll be on the lake over the next couple weeks trying to capture and tag as many fish as possible before the water gets too warm (we tend to avoid doing surgeries on fish at about 21°C or higher). If you or anyone you know is going to be on the water fishing and would like to help catch fish for the project (especially on weekdays), get in touch with me. grahamraby@trentu.ca

Graham

The features of the lake that you can't see.

By Dr. Nolan Pearce, post-doctoral researcher in the Trent Aquatic Research Program (Xenopolous/Frost Lab)

The cove, the rock, the hole, the point; all popular names for fishing spots I have heard over the years. But what about the features of the lake you can't see?

This past summer, we spent a day mapping the water quality of Stoney Lake to better understand the 3D distribution of water quality variables across the lake. Unlike landscapes that can be imaged from above, mapping underwater features is inherently difficult. To map features like water quality that differ across the lake as well as with depth, we needed to rely on a geostatistical method called spatial interpolation. Spatial interpolation uses mathematical relationships and discrete measurements of the variable you would like to map to estimate its value at locations where we haven't actually sampled the water.

(Above) Dissolved oxygen (mg/L) from the surface (0 m) to the bottom of the lake. The animation shows that there are hypoxic zones near the bottom in the deepest parts of Lower Stoney, and in the depths of Clear Lake, but that the deep basin of Upper Stoney (~100 feet) maintains good oxygen saturation right to the bottom. The more real measurements you make the better, but there is a trade-off between sampling effort and interpolation accuracy. To map water quality, we went to 22 locations across Stoney Lake and used a vertical profiler to take measurements of chlorophyll-a (algae), dissolved oxygen, temperature, and many other variables every 5 cm from the surface of the water to the bottom of the lake. Back in the office, these data were compiled and imported into a geographic information system (GIS) to produce a three-dimensional map of water quality in Stoney Lake using spatial interpolation. As you can see by in the animations of chlorophyll-a and dissolved oxygen, there is a lot of variation in water quality across the system. We have more work to do in mapping the three-dimensional distribution of these variables out more frequently throughout the year. When complete, these maps will be used to help us understand the potential impacts of changing water quality on fish movement and behaviour.

(Above) An animation showing the chlorophyll-a concentration in Stoney Lake, from the surface to the lake bottom. Chlorophyll-a serves as a rough index of the amount of algae in the water.