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.

More fishy friends join the project: fall 2022 update

I have a fall update to share.

Things are going well with the fish tracking work. In October, we spent more time on Stoney Lake trying to catch fish to tag. We were mostly catching fish by angling. When I say “we”, what I really mean is Dr. Jake Brownscombe and his crew from DFO. A few of my lab members and me were out to help on some days, but Jake and his crew continue to lead the field work and data management.

There’s a well-developed science of catch-and-release angling. Catch-and-release is stressful for fish, but when it’s done well, with minimal air exposure, most fish recover well. Water temperature plays a big part; if the water is cold, catch-and-release is usually benign, although what is defined as ‘cold’ is species-specific, and there are loads of other factors that can cause problems. Anyway, you may recall from an earlier post that we were out tagging fish (catching them and implanting transmitters) in early June (only 18 in total), but then stopped for the summer. We are avoiding warm water temperatures (20°C) when doing this work to maximize fish health and survival after they’re released. Fall weather (as warm as it’s been) has brought lower water temperatures, which is why we’ve been out again lately. We’re now done with catching and tagging fish for the season (I think). Here’s where we sit in terms of total numbers of fish we have swimming around in the lake with transmitters:

Walleye: 24

Smallmouth bass: 22

Yellow perch: 13

Muskellunge: 2

We’re still looking for donations to help bring these numbers up a lot, but we still have a few tags in hand and will now start preparing for a big spring tagging season. The muskellunge are big enough to handle larger tags: the transmitters we’ve put in them will last for 10 years! We’re excited about learning more about the lives of these fish, and the individual ‘personality’ of each animal.

While we were on the water in October, we caught up with Ed and Jackie from USLA, and Josh Feltham from Fleming College. Ed and Jackie have been helping develop a bioenvironmental monitoring plan for the lake, in partnership with the lake community including local First Nations. We spent some time checking out the long-term monitoring sites and continued our conversion about how we might add to what is up and running. It’s important that lake communities take environmental monitoring into their own hands, and we’re excited to (hopefully) help with developing that program. The information we’ll generate from the fish tracking work over the next several years will just be one part of how we can contribute to helping monitor ecosystem health.

(Above) En route to check out a long-term benthic biomonitoring site on Upper Stoney Lake.

Another fun update from today: one of the small walleye we tagged in late spring was captured and harvested this past weekend. Thanks to Trent U graduate Laura for getting in touch with me; I just picked up the tag (picture below), which I’ve now shut off so it can be re-used in a new fish next year. In the spring we’ll likely work on putting up notices around boat launches and post more info online to spread the word about what to do if you catch a tagged fish (i.e., how to get in touch).

(Above) The fish transmitter that was just recovered from one of our tagged walleye.

We’ll likely be out again once or twice between now and when the lake freezes. We need to check on our shallow water receiving stations once the water level drops, to make sure they’re not too shallow. Then we move into planning mode for a big 2023, with new students joining the project and (hopefully) a new research vessel we’ve ordered from Paris Marine.

Cheers,

Graham

Exploring the use of underwater video for fish monitoring in the Kawarthas

By Jacob Bowman, undergraduate research technician in the Raby Lab

As many local anglers know, Stoney Lake is home to a diverse assemblage of fish species. One important habitat for fish is the nearshore zone where light can easily penetrate, and plants grow in abundance to provide cover. As ecologists, we are interested in how fish relate to conditions in the nearshore habitat. One plant, the invasive starry stonewort (Nitellopsis obtusa) is of particular interest because it is spreading rapidly in Stoney Lake and the Kawarthas, and there is concern that it may negatively impact native organisms. We are investigating this concern by using Remote Underwater Video Systems (RUVS), while more broadly exploring whether RUVS might be useful for long-term monitoring of nearshore fish communities in the Kawartha Lakes. We are starting the project by focusing on Stoney Lake and the Otonabee River (around Trent U). My work on this project in 2022 was made possible by a donation from Ralph and Carol Ingleton.

What are RUVS?

RUVS are underwater camera stations that are deployed to film aquatic animals in their natural habitat. We are using videos from RUVS to count the number of fish species at a site and to estimate the number of individual fish there. Our RUVS setup consists of a GoPro camera attached to a cement base with a rope and small buoy. There is also a sighter arm that gives us a sense of how far we can see (the size of the visual field). RUVS are commonly used in studies of marine animals and are starting to be used more frequently in freshwater. RUVS have a few advantages when compared to the usual fisheries monitoring techniques like netting. They can be used by inexperienced researchers like students, volunteers, and community members, because very little training is required. Other types of fish monitoring that involve capturing fish may cause fish to be stressed or injured. RUVS on the other hand have little or no direct impact on fish, and don’t require a scientific collection permit.

RUVS in Stoney Lake

This summer we have been deploying RUVS at sample sites across the nearshore waters of Upper Stoney Lake. At each sample site we measure water temperature and clarity. We then deploy a RUVS and record a one-hour video. A big job for the winter will be reviewing the videos to count the fish and identify the plant species at each site. In the videos we have reviewed so-far, we have identified 11 fish species. The most common fish species in our videos so far have been pumpkinseed and bluegill sunfish. Some other fishes we have observed include golden shiner, brown bullhead, black crappie, and juvenile walleye. In addition to fish and plants, we were surprised that we also filmed a pair of otters checking out our camera at one site (scroll down for the video). RUVS could be potentially used to monitor the presence and abundance of many underwater animals like otters, invertebrates, or turtles.

Our hope with this project is that RUVS can be as a long-term option for the Stoney Lake community to monitor the nearshore fish assemblage, supplementing the fisheries monitoring work that is done by the Ontario MNRF every five years (using gillnets). Long term monitoring is essential for detecting environmental change. For example, as new invasive species enter Stoney Lake, a long term RUVS study could be used to quantify their impacts on the ecosystem and better understand why they're spreading.

Video (above): RUV footage from Upper Stoney Lake, with a pair of otters scaring away all the fish in sight.

Video (above) shows a curious smallmouth bass (Upper Stoney Lake) checking out or RUV setup.