Background and Rationale
In the coming decades, climate change and angling pressure will be two of the greatest threats to freshwater fish species in North America (Van Zuiden et al. 2016; Dudgeon 2019). One species particularly vulnerable to these threats are walleye (Sander vitreus; Van Zuiden et al. 2016). Walleye are a native freshwater predatory species that are widely distributed across North America (Fig 1; Van Zuiden et al. 2016; Bozek et al. 2011). Walleye are estimated to inhabit 32% of all available freshwater in North America (Bozek et al. 2011). In Canada, walleye are found from Québec to northeastern British Columbia (Hartman 2009; Pothoven et al. 2016). Walleye are an ecologically important species and extirpation can result in cascading effects on aquatic community structure (DFO 2016; Van Zuiden et al. 2016). Walleye are also an important commercial and recreational fishing species (Alberta Environment and Parks 2020). In 2019, an estimated $260,000 was generated from walleye special harvest licences and draw applications in Alberta alone (not including recreational fishing licences or equipment purchases; Alberta Environment and Parks 2020).
Temperature can determine the reproductive potential, maturation, fitness, and survival of fishes (Alofs et al. 2014). Therefore, changes in temperature can alter habitat suitability and reproductive potential (Alofs et al. 2014). Walleye are described as a coolwater species, and have a thermal optimum of around 22°C for growth and activity (Bozek et al. 2011). However, during spawning and reproductive development, walleye require and seek areas with lower water temperatures (Bozek et al. 2011). Increasing water temperatures, as a result of climate change, are anticipated to reduce walleye fitness in warmer lakes at southern latitudes (Hansen et al. 2017).
In addition to climate change, angling pressure (harvest) represents a threat to walleye abundance (Sullivan, 2002; Bozek et al. 2011). Walleye mature slowly and have relatively low productivity (Bozek et al. 2011; Sullivan 2002), therefore require low angling pressure to maintain sustainable populations. However, in the coming decades angling pressure is expected to increase due to the increasing number of fishing access points and the proximity and size of human settlements (Sullivan 2002; Alberta Environment and Parks 2019). Consequently, high angling pressure can reduce walleye recruitment and abundance (Sullivan 2002). Bozek et al (2011) found that walleye tend to grow largest in deep lakes, indicating that less angling pressure occurs at greater depths. Therefore, deep lakes may provide some refuge against angling pressure.
Figure 1. Map of the study area in Canada and lakes sampled in our study (n = 100)
Research Objectives
In this study, we will determine how climate change affects the fitness of walleye in Canada and (2) how angling pressure affects the abundance of walleye in Canada. Therefore we hypothesize that (1) higher temperatures resulting from climate change affect walleye fitness and (2) angling pressure affects walleye abundance. Results from our study will also help guide management of walleye populations in the future.
Expected Results
- Temperature can determine the reproductive potential, maturation, fitness, and survival of fishes (Alofs et al. 2014). Therefore, changes in temperature can alter habitat suitability and reproductive potential for fish (Alofs et al. 2014). As walleye require colder water temperatures for spawning and development, walleye fitness is expected to decrease at lower latitudes due to warmer water temperatures (Van Zuiden et al. 2016).
- Walleye mature slowly and have relatively low productivity (Bozek et al. 2011; Sullivan 2002), therefore require low angling pressure to maintain sustainable populations. Consequently, high angling pressure is expected to have adverse impacts on walleye abundance (Sullivan 2002).
- Bozek et al (2011) found that walleye tend to grow largest in deep lakes, indicating that less angling pressure occurs at greater depths. Therefore, deep lakes may provide some refugia for walleye under high angling pressure.