What are the ecological impacts of winter water level drawdowns on muskellunge in Canada’s historic Rideau Canal? Exploring winter connectivity and habitat use to inform conservation strategies

Jordanna N. Bergman, PhD Candidate | Department of Biology, Carleton University

The Rideau Canal Waterway, located in eastern Ontario, is a 202-kilometres continuous route that forms a hydrological connection between the Ottawa River, at Canada’s capital city of Ottawa, and Lake Ontario, at the city of Kingston. Constructed 1826 to 1832, the system was originally created for Canadian commercial shipping and national defence; today, the Rideau Canal is primarily operated for recreation. The completed Rideau Canal includes a series of rivers, lakes, and constructed channels interconnected by 24 operating lockstations that form the navigable waterway, many with adjacent water-control dams. As a National Historic Site of Canada, a Canadian Heritage River, and a UNESCO World Heritage Site, the Rideau Canal is internationally significant and, as a result, is highly regulated by the federal agency Parks Canada. Parks Canada is legally mandated to prioritize public safety, meet navigation requirements, and protect federally listed at-risk species; although their focus is not wildlife conservation, continuous management of the system has indeed supported the organisms residing within. The Rideau Canal has been described as having one of the most diverse fish assemblages (107 documented fish species) in Canada, and additionally, it supports one of the few wild urban muskellunge fisheries in North America supported by natural reproduction. Similar to most freshwater ecosystems, muskellunge in the Rideau Canal are ecologically important as apex predators and are also recreationally important as iconic sportfish.

During the Rideau Canal’s navigation season, which runs each year mid-May to mid-October, a channel along the entire waterway is maintained (minimum depth 1.5-metres) for boaters to travel safely. Outside of the navigation season, however, water levels in many reaches of the system are lowered (i.e., drawdowns). Each winter, in an 8.2-kilometre stretch of the waterway from Black Rapids Lockstation (45.321438, -75.698007) to Long Island Lockstation (45.250954, -75.702111), water levels are lowered by approximately 3-metres (10-feet). We refer to this section as the “Eccolands Reach” because of the nearby local Eccolands park. Most of the Eccolands Reach ranges in depth from 4.5-7.5-metres with a max depth of 9.1-metres; lowering the water levels by 3-metres for winter therefore significantly reduces the amount of habitat available for aquatic animals to overwinter in. 

Protecting habitat – critical habitats in particular – plays a key role in effective conservation. Critical habitat is defined as “the habitat that is necessary for the survival or recovery of a (listed) wildlife species,” and specific to aquatic species, critical habitat includes “areas on which aquatic species depend directly or indirectly in order to carry out their life processes.” Thus, any area that supports a life history process necessary for the survival of a species would therefore be considered “critical.” Though not explicitly stated, habitats which supports overwintering of aquatic organisms in Canada are consequently critical. Winter in North America is already an ecologically challenging season for freshwater fishes, and annual winter drawdowns can exacerbate challenges fish are already experiencing like reduced habitat and refuge from areas with lethal dissolved oxygen levels. Our goal is to not wait until it’s too late, and instead take proactive measures to ensure critical habitat of muskellunge is protected. Of serious concern to the Eccolands Reach muskellunge population are the highly urbanized surrounding lands. Previous research has shown that persistent anthropogenic disturbances and environmental modifications, like shoreline alteration, runoff from developments, and decreased water quality, can be detrimental to freshwater ecosystems, particularly to habitat quality and quantity. By discovering what areas of the Rideau Canal are most important to muskellunge survival and population health, we can proactively take steps to protect (and potentially even enhance) those areas and work against population declines. Because of the significant winter water drawdowns, and project timing, we decided to evaluate overwintering habitats first.

We use acoustic telemetry to track muskellunge movements in the Eccolands Reach. Acoustic telemetry essentially has two parts to it: 1) acoustic tags and 2) acoustic receivers. The tags are surgically implanted into muskellunge and each tag emits a “ping” every 20-seconds with a unique ID and timestamp. Acoustic receivers are deployed and sit at the bottom of the river, waiting for a tagged fish to swim by. When a tagged fish swims by a receiver and its tag emits a ping, the receiver stores that information, providing a corresponding time and date for when that individual fish was near that specific receiver. Acoustic receivers are essentially “listening stations” whereby the receivers are listening for detections (“pings”) from tagged fish. In this way, as a long as the tagged fish is within the detection range of the receiver, we can determine where each fish was and when. With the generous help and expertise of Muskies Canada Inc. (MCI) Ottawa Chapter anglers, we captured and tagged 15 muskellunge in October 2020 for our overwintering study. Eleven acoustic receivers were deployed, relatively evenly spaced out, in the Eccolands Reach to monitor fish movements. We also deployed two receivers downstream of Black Rapids (into the Mooney’s Bay Reach) to see if fish left the reach by moving over the weir, but none of our tagged muskellunge were detected downstream. Interestingly, all our muskellunge were detected only upstream of the Eccolands boat launch, many of which in November showed upstream movements, potentially in search of the best available winter habitat. 

Several interesting patterns emerged from movement analysis. First, fish moved more so than I anticipated – I expected muskellunge to be detected on the same 1-2 acoustic receivers for the duration of winter, but interestingly most fish were detected consistently across several stations, moving often through habitats across a 1-mile distance. Second, most fish overwintered near tributaries where there were deep areas (4.5-6-metres/15-20-feet). Third, it appears the portion of the river beneath the Vimy Bridge is so shallow that during winter it acts as a potential barrier to winter connectivity; essentially, once ice freezes over in December, if fish were upstream or downstream of the Vimy Bridge then that’s where they were confined to until ice-off in April. To date, it is unclear to what extent winterkill events occur in the Eccolands Reach, or if events are region/site specific. If muskellunge winterkill events are occurring in certain areas upstream or downstream of the Vimy Bridge, providing a connection between those areas could offer a chance for fish to escape. It therefore could be important to increase depths beneath the bridge to allow fish to move freely. Finally, we found that several of the larger, presumably sexually mature, individuals showed increased movements in April. Evaluating spawning movements was not an original objective of our overwintering study, however it may be one of the most important findings. We believe that the increased activities we noted in April are most likely linked with muskellunge pre-spawning movements in search of spawning sites. Parks Canada does not (start to) raise water levels in the Eccolands Reach for the navigation season until early May, so if muskellunge are searching for spawning areas in April when water levels are still low, their reproductive efforts may end up unsuccessful because habitat is still so limited at that time. Fish movements are highly regulated and directed by water temperatures – if it’s a warm spring (muskellunge usually spawn when water temperatures are 9-15°C), spawning has been documented in northern-latitude lakes as early as mid-April. We have not incorporated this data yet as special temperature loggers have just been recently recovered, but we will be carefully inspecting temperature data to see when muskellunge spawning might have commenced this past spring.

We are currently in the process of finalizing data analysis and have been fortunate to collaborate with hydraulic engineers, Parks Canada scientists, researchers, and MCI anglers to ensure we have a thorough understanding of muskellunge spatial ecology. Our goal is to factor in environmental characteristics of the river, like depth and bottom composition (e.g., sand, pebbles, boulders), to determine which areas are most suitable to muskellunge. We will also be evaluating if fish size has any effect on habitat preferences, as it may be that larger fish choose different areas compared to smaller fish. Though we have investigated overwintering of muskellunge in the Rideau Canal, this is only one annual aspect of their spatial ecology; because the winter drawdowns are so considerable in this reach, we felt it was best to quickly evaluate those movements and release that information rapidly. We are, however, tracking muskellunge movements year-round in the Eccolands Reach, and will be doing so until 2023. In the spring of 2021 MCI anglers again donated their time and expertise, and with their efforts to supplement ours, we tagged an additional seven muskellunge (we currently have 23 acoustically tagged muskellunge in the Eccolands Reach). Our aim is to assess other critical habitats used, like spawning habitats, and additionally we know very little about lock connectivity. We also note that protecting habitat and connectivity is only one part of conserving muskellunge; there are several other issues that threaten the local population like water quality and invasive species. We are working with several universities, the Rideau Valley Conservation Authority, and Parks Canada to evaluate the various threats to species within the Rideau Canal. Investigating muskellunge movements is only component of my PhD research – we are also tracking the movements of several other native and invasive fish species and will be compounding that information with our muskellunge movement data to better understand overall fish connectivity in the Rideau Canal. If you’d like to find out more information about our work, you can check out Dr. Steven Cooke’s Fish Ecology and Conservation Physiology website at http://www.fecpl.ca/ or my personal website at https://jordannabergman.wixsite.com/jordannabergman.

We use acoustic telemetry to track fish in the Rideau Canal. Size-specific acoustic tags (top left) are surgically implanted into our study species so that we can monitor their movements year-round. In the Eccolands Reach of the Rideau Canal, we are focusing our efforts towards monitoring the movements of muskellunge. In other parts of the waterway, however, we are also tracking northern pike, largemouth bass, common carp, and round goby. Acoustic receivers (bottom left) are stationed beneath the waters’ surface and are essentially “listening stations” – when a tagged fish swims by one of our receivers, and that tag emits a “ping” with a unique ID and timestamp, the receiver detects and stores that information so we can later determine where each tagged muskellunge was swimming and when. 

Angler and collaborator Luc LaRochelle releases a tagged muskellunge in the Rideau Canal. Note the white tag near the dorsal fin – this way, if an angler catches one of our tagged muskellunge, they can contact us to report where and when they caught their fish (there’s a unique ID # and contact info on the tag). Anglers who report tagged fish are entered in a $200 prize draw, and they also provide critical information about fish movements and health. 
Angler and collaborator Luc LaRochelle releases a tagged muskellunge in the Rideau Canal. Note the white tag near the dorsal fin – this way, if an angler catches one of our tagged muskellunge, they can contact us to report where and when they caught their fish (there’s a unique ID # and contact info on the tag). Anglers who report tagged fish are entered in a $200 prize draw, and they also provide critical information about fish movements and health.
Jordanna Bergman surgically implanting an acoustic tag into a muskellunge. After inserting the tag and suturing the incision, she takes length measurements and externally tags the fish. The entire process takes 3-4-minutes, and fish are quickly released thereafter.