Image: A calm autumn day on East Grand Lake, on the New Brunswick–Maine border.
Photo credit: Neal Berry
East Grand Lake, situated on the Canada–U.S. border within the St. Croix River basin, is renowned for its large, self-sustaining population of togue (lake trout) and lake whitefish. The lake supports a high-quality recreational fishery, despite remaining relatively understudied, as its international nature complicates coordinated research and long-term monitoring.
To address these gaps, the St. Croix International Waterway Commission (SCIWC), in partnership with Acadia University (Nova Scotia) and the University of Windsor (Ontario), and with assistance from fisheries staff from the State of Maine and the Province of New Brunswick, launched the Tag & Track (T&T) project. This initiative uses acoustic telemetry to monitor year-round movement, depth use, thermal refuge, and habitat selection.
During the winter 2025 ice-fishing season, SCIWC and Acadia biologists worked closely with local anglers to capture and surgically implant acoustic transmitters into both species. After ice-out, a network of underwater receivers was deployed across East Grand Lake. These receivers detect signals emitted by tagged fish, allowing researchers to track their movements and environmental conditions, such as depth and temperature, over time.
Image: Researcher Matthew Warner with a captured togue (lake trout).
Photo credit: Marshall Elsemore
Preliminary data reveal clear behavioural differences between the two species during the first year of recording. Lake trout are highly mobile, particularly in colder months, changing depths frequently throughout the day. This pattern appears to reflect active foraging across the entire lake. During summer, as surface waters warm, lake trout tend to remain in deeper, colder areas, occasionally making short trips into shallower water, likely in search of a quick bite.
Researchers also identified likely spawning activity by combining local knowledge with active tracking of fish signals. As lake trout moved from deep summer habitats toward shallower areas in the fall, scientists followed stronger acoustic signals to pinpoint suspected spawning sites. Locating these areas allowed researchers to collect egg samples, which will be analyzed to better understand genetics and egg health—information that may have broader implications for lake trout conservation beyond East Grand Lake.
Image: Researcher Matthew Warner with a captured lake whitefish.
Photo credit: Marshall Elsemore
Lake whitefish, by contrast, appear to show more depth-specific behaviours. Tracking data show that whitefish tend to stay at more consistent depths for longer periods and follow more predictable routes. Nonetheless, when whitefish appear to move shallow, they do so during the evening or early morning. This suggests that these smaller fish are responding to predator pressure from diurnal hunters such as lake trout. These differences imply that lake trout and lake whitefish respond differently to the lake’s thermal structure and habitat options, despite sharing the same environment.
Together, these findings are helping researchers understand how East Grand Lake’s native cold-water species use the lake across seasons and how their behaviours differ during critical periods, such as spawning. As data collection continues, the T&T Project will support informed fisheries management, habitat protection, and water level decision-making. With receivers remaining in place for the next two years, lake trout and lake whitefish will continue to shed light on the inner workings of this unique international lake—one detection at a time.