NEW STUDY SUPPLIES GUIDELINES FOR ANGLERS
Editorial Introduction: Manitoba Regional Fisheries Manager Eric Mullen compiles some amazing research information conducted by the Fish Biology and Aquatic Conservation lab at the University of Winnipeg, led by Dr. Caleb Hasler, and Manitoba Fisheries. Several management relevant research programs have taken place to study Manitoba’s lake trout populations. This research was funded by the Fish and Wildlife Enhancement Fund with money generated from angling license sales. It is a must read!
Lake trout are a popular sportfish in Canada and every year thousands of anglers make trips into pristine cold-water lakes in the hopes of catching this iconic species. These fish can grow to lengths exceeding one metre and live past 60 years. They provide excellent table fare, are accessible to anglers both by ice fishing and in the open water and provide the experience of travelling into picturesque, backcountry lakes. Lake trout are an apex predator that require cold-water habitats, often found in Canadian Shield lakes with deep, clear water and an offshore food source (e.g., cisco).
Research has shown that lake trout can be particularly vulnerable to the effects of climate change, introduced species and excessive fishing pressure. Therefore, further research into this species is critical to ensure the sustainability of lake trout fishing.
This research by the U of W provides critical information to inform regulation. In this article, we will present the research of Brad Howell (M.Sc.), Giulio Navarroli (M.Sc) and Dr. Alexandra Schoen (Post-Doctorate fellow). These researchers have worked tirelessly over the past several years to contribute to the conservation of lake trout.
Seasonal Effects of Catch-and-Release on Lake Trout
Brad Howell graduated with a master’s degree in the summer of 2023 after completing his work studying the physiological and behavioral responses of lake trout to catch-and-release (C&R) angling. Howell conducted his research on Clearwater Lake in northwestern Manitoba, a popular lake trout fishery known for its trophy potential. Howell studied the impacts of C&R angling on lake trout for both ice fishing and open water fishing seasons. Howell caught lake trout using conventional angling methods and then took blood samples and conducted reflex tests at various recovery time points to collect stress level and behavioral impairment data.
While ice fishing, Howell found that the length of fight time was a predictor of disturbances in several stress indicators. This reinforced the practice of tailoring gear type deliberately for the size of fish you are targeting to limit exhaustion (e.g., don’t “play them out,” use the right gear and land them quickly!).
Additionally, Howell observed barotrauma in lake trout caught through the ice, which in several cases resulted in the death of fish post-release.
This result was interesting as lake trout are commonly known to belch excess gas to relieve the bloating caused by rapid changes in pressure. Howell’s observations remind us that this mechanism does not protect all lake trout from the harmful effects of barotrauma.
DELAYED MORTALITY
Out of the 74 lake trout caught in the summer at a depth of 70 to 80 feet, 23 per cent died post-release, and many of those fish showed signs of barotrauma. Behavioural impairment was more pronounced in deeper water, for larger fish and with extended fight times.
IMPORTANT RECOMMENDATIONS FOR FISH SURVIVAL!
Based on these results, anglers should consider avoiding C&R angling for lake trout on bottom in very deep water (e.g., 70 feet or deeper), and should consider having a deep-water release tool on the boat or on the ice.
When Howell conducted a similar study in the fall, he observed lower mortality and much less reflex impairment relative to the summer and winter studies. Howell’s findings reinforce the idea that in certain situations (e.g., high water temperatures, ice fishing, deep water, excessive fight times), lake trout are vulnerable to mortality and physical impairment from C&R angling. Therefore, anglers should plan their activities, select their gear and adapt their behaviours accordingly to ensure the best chance of survival.
The Life History and Biology of Lake Trout in Manitoba
Giulio Navarroli completed his master’s degree in the fall of 2023 studying lake trout stock metrics and life history characteristics across both the northern and southern regions of Manitoba. This information is crucial to our understanding of how lake trout fisheries across the province are performing in terms of growth and abundance.
Navarroli used a standardized netting protocol to collect lake trout in a variety of depths and habitat types. He recorded the length, weight, sex and maturity of the fish, as well collected otoliths (ear-bones) to age individual fish and ultimately determine growth patterns for these populations. In this study, Navarroli completed netting programs on two northwestern lakes (Clearwater and Second Cranberry lakes) and five southeastern lakes (Davidson, George, Mantario, High and West Hawk lakes).
Navarroli found that growth and abundance varied between lakes and between southern and northern populations. For example, Second Cranberry Lake trout had the greatest average length of 67 centimetres, while the rest of the lakes had an average length value around 52 centimetres. Navarroli only caught Master Angler-sized (at least 89 centimetres) lake trout at Clearwater and Second Cranberry lakes. Lake trout from Clearwater grew the fastest at a rate of 14.4 centimetres per year, while the Second Cranberry Lake population grew the slowest at a rate of 7.9 centimetres per year. High Lake had the fastest growth rate of southern lake trout fisheries at a rate of 10.2 centimetres per year. Interestingly, Navarroli found that lake trout in northern Manitoba existed at higher abundances relative to their southern counterparts, with Clearwater Lake having the highest density of lake trout observed in this study.
Age demographics varied across lakes as well. For example, Second Cranberry Lake had the oldest population with an average age of 18 years, while Clearwater Lake had the youngest with an average age of nine years. George Lake had the oldest population of the southern lakes at an average age of 13 years old. Further, Navarroli found that lake trout started to spawn at five to 10 years old, depending on the population.
On the topic of differences between lakes, Navarroli said, “one of the interesting parts of this research is that both Clearwater and Second Cranberry have Master Angler-sized lake trout. However, the way these two populations grow to these sizes is quite different. Based on this data, Clearwater lake trout reach trophy sizes at an earlier age than Second Cranberry trout. This highlights the diversity of strategies lake trout can employ to grow, survive and thrive”.
Effects of Angling Stress on Lake Trout Spawning Success
This fall, Dr. Alexandra Schoen began a research program to discover the effects of angling on spawning lake trout and how stress may impact the developing eggs and offspring. This research is critical as it is popular to target trophy lake trout during the spawn, and it is currently unknown whether stressing spawning adult fish will have an effect on the eggs and offspring they produce.
On the subject, Schoen said, “In other fish species, there is evidence that stressed females can transmit elevated levels of stress hormones into their eggs. Depending on the species, this could potentially lead to decreased egg quality and condition or could even have a neutral effect. On the other hand, this could also prepare the offspring for stressful conditions, which may be a good thing in the long-term. It is important to know what these impacts are for lake trout to guide future management strategies”.
STRESSES ON SPAWNING FISH
To learn more about this process, Schoen traveled to Clearwater Lake in the fall of 2023 to sample lake trout. These fish were angled on spawning reefs, and several treatment groups were established with blood and eggs collected from each fish. She aims to determine whether there is any difference in the quality, condition and stress indicators in eggs taken from stressed females as compared to unstressed females. Schoen also collected milt from several spawning males to fertilize the eggs and brought back the fertilized eggs to the University of Winnipeg.
Currently, the eggs are being raised in a lab and tested for mortality, stress hormones, energy content (e.g., how much energy was supplied by the mom) and genetic markers of stress. The results of Schoen’s project will teach us about the potential impacts of angling lake trout during the spawning season and will inform future management for the species.
Anglers Funding Conservation Research
The research conducted by these members of the Hasler Lab at the University of Winnipeg has provided an abundance of knowledge about lake trout in Manitoba. It is important to note that the Manitoba Fish and Wildlife Enhancement Fund (FWEF) provided funding for these projects. This fund uses proceeds from the sales of fishing licences in Manitoba to support a variety of fishery enhancement and research projects.
Anglers are invested conservationists, and we all share a passion to ensure the sustainability of the ecosystems and species we enjoy so that they will be healthy for generations to come. With the FWEF, anglers are supporting research programs that increase the success of our management programs, and in doing so, show that the angling community is committed to the conservation and sustainable management of our precious fisheries resources.