Ministry of Natural Resources and Forestry

Abstract Objective Test whether dietary differences among hatchery strains of Lake Trout Salvelinus namaycush were associated with variation in egg thiamine concentrations and assess the potential for using strain-specific traits to mitigate thiamine deficiency complex (TDC) in Lake Ontario restoration efforts. Methods Stomach content analysis and stable isotope mixing models were used to compare diets among four hatchery strains of Lake Trout, representing lean and humper morphotypes. Egg thiamine concentrations were measured to test whether dietary differences correlated with susceptibility to TDC. Results Significant differences in diet and egg thiamine concentrations were observed among Lake Trout strains. A humper-like morphotype strain exhibited elevated thiamine levels, which were associated with reduced consumption of prey known to degrade thiamine levels when consumed, Alewife Alosa pseudoharengus and Rainbow Smelt Osmerus mordax, and increased reliance on Round Goby Neogobius melanostomus or sculpin species (Slimy Sculpin Cottus cognatus and Deepwater Sculpin Myoxocephalus thompsonii). These findings support the link between the consumption of Alewife and Rainbow Smelt and thiamine deficiency. Conclusions Our findings support a link between strain-specific dietary preferences and susceptibility to TDC in Lake Trout. Preferential stocking of strains less prone to TDC, such as the strain derived from a humper morph from Lake Superior, could enhance restoration success in Lake Ontario. This strategy may be especially effective given the continued dominance of Alewife in the lake's prey base and the current management priorities supporting fisheries for Pacific salmon Oncorhynchus spp.

Muskrat (Ondatra zibethicus) populations have been declining in North America for decades. The precise cause of these widespread declines has not yet been identified. Over a similar timeframe, wetlands across large regions of North America have been experiencing an invasion of hybrid cattail Typha x glauca. This invasion is associated with many negative consequences for wetlands, including a reduction in biodiversity, open water habitat, and interspersion of water and vegetation. Muskrats are strongly tied to wetlands, especially where there is a high degree of interspersion of water and emergent vegetation. Therefore, a widespread reduction in interspersion caused by T. x glauca invasions may be contributing to widespread muskrat population declines. We sought to better understand the impact of marsh interspersion on fine-scale muskrat habitat use in light of widespread invasions of T. x glauca. We measured intensity of habitat use by muskrats in a large, Typha-dominated marsh in south-central Ontario using camera traps, stratifying camera placement along a gradient of interspersion. We found no correlation between interspersion and intensity of use. The ubiquity of T. x glauca and low overall interspersion at our study site may have prevented a robust test of our hypothesis. Further research is needed to determine precisely how interspersion affects muskrat habitat use at a fine scale, and how potential changes in habitat quality and use may be contributing to widespread muskrat population declines.

Thermal habitat selection is a key consideration when assessing the capacity of ectotherms to tolerate warming conditions during summer. We used high dimension acoustic arrays in three lakes to determine diel thermal habitat selection by free-ranging adult brook trout (Salvelinus fontinalis (Mitchill, 1814)), with surgically implanted acoustic tags (fork length range, 26.2–54.5 cm). Brook trout occupied a range of temperatures during lake stratification when warm surface waters and cold hypolimnetic waters were present. The overall mean occupied temperature was close to literature estimates of a single preferred temperature (15°C), but few individuals spent most of their time at this temperature. The preferred temperature range was 13–17°C in each lake while < 10°C and > 20°C were avoided. Individual variation was extensive and closely associated with body size. Despite wide diel variation in patterns of thermal habitat selection, thermal time (degree-hours; °C-hrs) was consistent and inversely related to body size over a month. Large adult brook trout accumulated fewer degree-hours than smaller brook trout. The intercept of this relationship was close to their sublethal threshold as defined by physiological stress. We hypothesize that adult brook trout actively manage metabolic rate as a function of body size over periods greater than the diel cycle.

Research and development for a real-time wildfire decision support system was undertaken to support appropriate response decision-making in Ontario, Canada. We describe the context, history, requirements, research and development process, and components of FireGUARD (Fire Growth under Uncertainty for Appropriate Response Decision Support) and show examples of its prototype products. The work was a collaborative effort between researchers, specialists, and fire management experts. FireGUARD prototype outputs include a weather forecast and high-resolution maps of burn probability out to 14 days, fuel type, impact, and risk. Additional uses of include triaging multiple new fires, prioritizing scarce suppression resources, and large fire management. FireGUARD was very useful and remains in demand; its success led to further decision-support initiatives.

Mass reproductive events, where large numbers of organisms aggregate for synchronous reproduction, are often captivating and ecologically significant, boosting offspring survival and reducing time spent searching for mates. However, mass reproduction can also instigate cryptic but consequential responses across entire food webs. Reproductive materials are abundant and accessible resources that can attract mobile consumers from up to thousands of kilometers away. Yet, their consumption, especially in aquatic systems, is difficult to detect and rarely characterized. Here, we combine molecular techniques with acoustic telemetry, literature review, and extensive natural history observations to investigate the food web consequences of synchronized reproduction in freshwater fishes. First, we demonstrate that a common but underappreciated fish species, white sucker, creates a resource pulse used ubiquitously by consumers, from local invertebrates and fishes to mobile predatory fishes, birds, and terrestrial mammals. Spawning white sucker create trophic hotspots that attract consumers across trophic levels and ecosystems to feed on eggs, spawning adults, and aggregated egg predators. Then we show that egg provisioning and predation is widespread among north-temperate freshwater fish species, highlighting that resource pulses instigated by mass reproduction may play a critical but underappreciated role in freshwater and terrestrial ecosystems.

Abstract In rodents, different selective pressures influence behavioural, physiological and life-history strategies between sexes. Anisogamy and the reproductive cost hypothesis suggests that differences in gamete size and trade-offs in reproduction are driving mechanisms of sex-specific reproductive strategy. However, relationships between behaviour and energetic investment in income-breeding rodents are not fully explored. We investigated behavioural and physiological traits in two rodent species from Algonquin Provincial Park, Canada using two standardized behavioural assays and faecal glucocorticoid metabolites (FGMs) as a proxy for movement and energetic stress. We hypothesized that sex differences in reproductive investment throughout a single breeding season would influence behavioural and physiological traits. We predicted that males would be more explorative and less docile than females due to increased risks associated with mate acquisition. We also predicted that FGMs would be greater in females compared to males due to the increased investment in the development and care of young. In contrast to our hypothesis, we observed some differences in behaviour between sexes in the opposite direction. Male deer mice ( Peromyscus maniculatus ) were more docile (mean difference = 0.312, 95% CI = [−0.24; 0.87], ), and male red-backed voles ( Clethrionomys gapperi ) were less explorative (mean difference =-73.8 s, 95% CI = [−127.5; −19.029], ) than female counterparts. There was also a high degree of within-individual variation in FGMs in both species. Between-individual variation was only observed in red-backed voles (26.7%), however neither species had a significant relationship between sex and FGMs. Our findings reveal some relationships between behaviour and physiology in income-breeding rodents.

Stable isotope analysis is a widely used to quantify the flow of energy, nutrients, and biomass through aquatic food webs, where values of carbon (13C) and nitrogen (15N) have been used to estimate littoral carbon use (LCU) and trophic position (TP)