By Amber Fedus, PhD Candidate at Trent University
After a long year of waiting to download our receivers, we recently ran some preliminary analyses which we shared with the community in our annual update meeting at Viamede Resort in August (2024). Some of you may have been present at our update meeting (thank you for those who made it!), in which case you may have seen these results. But we are sharing it here for those of you who missed it.
Many of the tags we’ve deployed into fish the last couple years have acceleration, pressure (depth), and temperature sensors in addition to telling us the fish’s location. From these sensor tags, we get a lot of finescale data that can tell us more about the fish’s behaviour. Acceleration sensors give the activity levels of fish, with higher acceleration values meaning the fish are swimming more, which can be indicative of foraging. Combining the activity data with the depth and temperature the fish are choosing can help reveal how the foraging strategies of fish differ, within and among species.
Figure 1 (above). Average activity levels of walleye (left) and smallmouth bass (right) over a 24-hour period from July – August 2024. This shows that walleye are more active from sunset – sunrise and smallmouth bass are more active during the day, suggesting these two species have opposite behaviour patterns in feeding.
Overall, our data suggest that fish are more active in the summer than in winter, which makes sense because cold temperatures really slow fish down. Walleye specifically are adapted for nocturnal foraging; their eyes help them see prey in low ligth. Our data shows this as their activity is much higher at night than in the day, with peaks at sunrise and sunset (Figure 1). Smallmouth bass, on the other hand, are active primarily during the day (Figure 1). We don’t see much activity from them at all as soon as the sun sets. This becomes important when considering how these two predators are able to co-exist, these as they have very similar diets and inhabit very similar areas of the lake according to their network plots (Figure 2). In fact, one question we had prior to analyzing the data was how the walleye and smallmouth bass can inhabit the same areas without one out-competing the another. The answer to this question may be that these two species have opposite feeding schedules, allowing them to occupy the same habitat but feed at different times.
Figure 2 (above). Network diagrams for walleye (left) and smallmouth bass (right) for July – August 2023. These plots show the connections and interactions between individuals and locations. The yellow circles show receivers that act as “hubs”, which are frequented more by the fish (larger circles = more fish detected there). The red lines show connections between the receivers in terms of movement, with darker/thicker lines indicating a stronger connection between those receivers.
Figure 3 (above). Activity levels of muskellunge over a 24-hour period from July – August 2024. This shows that musky are more active around sunrise and sunset.
Musky, on the other hand, show higher activity levels corresponding to the first couple hours of dawn and dusk (Figure 3). These peaks in activity suggest that these are times musky are actively hunting. The data we have only represent the 7 musky we tagged in 2022-2023. We tagged a ton of new muskies this year, so we will have way more data on their behaviour when we download the receivers next spring.
While the results presented above represent averages for each species, some interesting analyses lie ahead for us in looking at variation among individuals of the same species. An example of this is evident in Figure 4 (below). Individual walleye seem to have a wide range of depths (relative to the surface) they choose to occupy. This is something we will be diving into in future analyses to better understand among-individual differences in behaviour, including how persistent they are over time.
Figure 4. Differences in depth among individual walleye tagged with V13A and V13AP tags for July – August 2023.
We have some work being done on habitat modeling led by Jake Brownscombe (DFO). Currently, our data only show us the receiver the fish was detected, which means the fish could be anywhere in the radius of the receiver’s detection range. Habitat modeling will allow us to apply chemical, physical, and structural measurements we’re taking throughout the system to gain incredibly detailed insights into preferred habitats in the lake. We are also actively working on collecting samples for stable isotope analysis, which will allow us to determine each fish’s feeding habits and map out the food web in each lake.
Stay tuned for future updates. Get in touch if you have ideas for topics/questions we could address with the data.
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