Fisheries

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Warming water temperatures could increase the depth of the thermocline altering the amount of appropriate thermal habitat for fish.
Increase in warm water habitat. This could mean that Largemouth Bass may become established in more lakes on Manitoulin and that lakes that already contain Bass species will be able to support more of these fish.
  • If lakes become more suitable for Bass species, their numbers could increase which has the potential to lead to an increase in competition leading to stunted growth. (More Bass but smaller Bass)
  • In lakes where Walleye and Bass are both present the number of Walleyes decreases significantly compared to lakes with just Walleye. If Bass populations increase in size it could lead to a decrease in the numbers of Walleye.
Decrease in cold water habitat. This could mean that cold water fish like trout, salmon and Whitefish will either have increased inter and intraspecies competition or they will need to move out of their optimum thermal range in order to forage and hunt.
  • An increase in competition due to decreasing habitat size could lead to the extirpation of the less successful species and eventual stunted growth of the surviving species.
  • If cold water fish are forced to search for food outside of their optimum thermal range, it could negatively affect their metabolism and rate of growth leading to smaller cold-water fish.
Warming water temperatures and decreased ice cover could lead to earlier and longer lake stratification or layering which would prevent the mixing of the oxygen rich upper-warm layer and the nutrient rich bottom-cold layer.
Longer periods of stratification without mixing could lead to the development of a hypoxic or even anoxic zone at the bottom of lakes.
  • Without adequate oxygen supply this could lead to the death of cold-water fish species in deeper lakes or it could force cold water fish into suboptimal thermal guilds leading to stunted growth.
Warming water temperatures as well as an increase in spring and fall precipitation could lead to an increase in nutrient runoff and primary productivity within lakes.
An increase in productivity could lead to an increase in algal growth some of which contain toxins harmful to fish.
  • Smaller bait-fish are more susceptible to toxins in the water, and an increase in HAB’s could lead to the loss of prey species within lakes (especially small shallow lakes) which could lead to decreased population size or stunted growth of larger sport fish.
  • An increase in toxic algal blooms could even lead to the deaths of larger sport fish given the size and extent of HAB’s.
  • An increase in nutrient loading, primary productivity and algal growth will lead to an increase in decomposing organic material. This reduces the amount of dissolved oxygen within a lake and can lead to fish-kill or die-off. Smaller, shallow lakes are especially susceptible to this throughout the winter when the organic matter decomposes beneath the ice.
Fish are cold-blooded and their metabolism relies on surrounding water temperatures. Under warmer conditions fish move more and spend more energy which requires more food.
If prey availability increases, an increase in metabolic rate due to warmer water would lead to faster and larger growth of fishes. If prey availability remains the same or decreases fish growth will be stunted.
  • Because fish can move throughout the water and can thermoregulate by finding the optimal thermal guild certain species will be more effected. In deeper lakes there is more depth for cold water fish to find the optimal thermal guild and therefore these fish will not experience as great of a temperature change as cool water fish in shallower lakes. For example, Yellow Perch a cool-water fish is expected to experience greater decreases in growth compared to Whitefish a cold-water fish under constant or reduced prey availability.
Fish rely on temperature cues for spawning, warming temperatures could alter typical spawning regimes.
  • Changes in spawning time could lead to reduced success of eggs and juveniles due to predation of other fish species that may become more active under warmer temperatures.
  • Fish species such Cisco and Whitefish lay their eggs in nearshore environments in the early winter. Warmer temperatures leading to reduced ice cover could increase the amount of wave action in nearshore environments leading to reduced success of these species.