Fish and Wildlife

Fish and Wildlife

  • Coldwater fish populations will likely decline in population as warmwater fish populations become more abundant.
  • Lake stratification and an increased frequency of hypoxic conditions will reduce overall biomass productivity in lakes and waterways.
  • Many animal species will need to migrate north to adapt to rising temperatures.

  • Increased evaporation rates will decrease the total wetland area in the region, creating additional stresses on species.

Climate change is amplifying existing pressures on a wide range of vulnerable species in the Great Lakes region. Loss of habitat to changes in land use, competition from invasive species, impacts from pollution, and the ability to migrate may all be exacerbated by rapid changes in climate.

Temperature Groupings of Common Great Lakes FishPreferred Temperature Ranges of Common Great Lakes Fish

Sensitivity to Temperature

Native species have adapted over long periods of time to the temperature regimes in the region, so abrupt changes to this regime make a large impact. Cold-blooded species such as insects, reptiles, and fish are particularly vulnerable because their metabolic rate is closely tied to their body temperature, which is dependent on the temperature of the environment. Although warm-blooded species such as birds and mammals maintain a constant body temperature, they experience heat stress as temperatures increase. Species that currently exist close to their physiological tolerance limits, such as the moose in the Great Lakes region, are particularly susceptible and have shown declines in survival rates that correlate with recent warming trends.1 2 Many species have shown flexible responses to climate forcing as conditions have varied among years. Species that currently exhibit a capacity to be flexible may exhibit declines in the future as their ability to be flexible is pushed beyond a critical threshold.

GLISA networked boundary chain modelProgression of Lake Stratification

Changes in Lake Processes

Changes in lake temperature, caused by direct or indirect processes such as ice cover changes or wind, have the potential to significantly alter the function of large lakes in the Great Lakes region. One of the most significant effects of climate change on lake processes are changes in the in the natural timing or duration of stratification. Stratified lakes provide a diverse range of living conditions for aquatic organisms, allowing species with a variety of temperature, light, and habitat requirements to persist in the different layers of the lake. The timing of stratification, as well as the fall "turnover" process that replenishes oxygen to deeper waters, can be critical in influencing the viability of lake species, especially cold-water fish.3

Smaller and shallower lakes warm more rapidly and are less likely to show stratification. The warm water is able to hold less oxygen, creating oxygen-poor “dead zones” and leading to increased respiration rates for aquatic species. As warming continues, the number of dead zones are expected to increase, while other bodies of water transition from stratifying in the summer to not stratifying at all. This would lead to the decline and loss of species dependent on the cold water and lake processes that they have long adapted to.


Changes in Species Range and Relative Abundancies

Shifts in the ranges of species can result from several different mechanisms. Movements in species can be direct responses to temperature, such as fish seeking out colder water, or can be the result of natural selection acting on more random movements by populations on individuals, as those that become established in areas with more suitable climates are more likely to survive and reproduce.

For species to "track" changes in temperature by shifting ranges, they need to be mobile at some stage in their life and have a suitable path without insurmountable barriers. Landscapes in the Great Lakes (and larger Midwest) are typically flat, so shifting to a higher latitude to experience cooler temperatures is not an option. For example, to reach land areas that are 1 degree Celsius cooler, a species in mountainous terrain would have to shift approximately 549 ft, while in flat terrain this would require a shift of roughly 90 miles north. The Great Lakes also create a large barrier to land based movement through the region.4 Recent studies predict that in the second half of the century (2050-2100) with a rapid-growth emissions scenario (A1B) will require species in the Midwest to move over 0.62 mi/yr, when compared to the average global "velocity" of 0.26 mi/yr.5

Species that can move quickly (i.e. birds, large mammals) are more likely to be able to keep up with climate change than species that move more slowly (i.e. amphibians, most invertebrates). Though even mobile species that depend on food sources or habitat components which move more slowly will be more vulnerable if those species decline.

Changes in Seasonal Cycles (Phenology)

In many species seasonal changes in temperature serve as cues that trigger development and changes in species (e.g. transition from egg to larvae in insects). Warming trends can impact the timing of these events through shifting seasonal cycles, examples of such shifts are shifting timing of snow melt, spring flooding, ice-out on lakes/streams, or lake stratification. An example of this pertinent to the Great Lakes is the effect of earlier ice-out on streams is having on the spawning patterns of walleye. As ice-out has occurred earlier on spawning streams, spawning of walleye has also been occurring earlier.6In most cases, the implications of changing phenology are unclear, but as longer term datasets are built in the Great Lakes and surrounding areas, it is likely that patterns will continue to emerge.

Changes in Genetics, Growth, and Development (Morphology)

Changes in body shape or size, behaviors, and underlying gene frequencies have been linked to warming temperatures. Examples of this include reduced genetic diversity in populations at the "leading edge" of range expansions.7 8 Evidence supporting these types of changes is strongest in invertebrate populations while evidence of similar genetic changes in vertebrates is rare.9


External Resources

Changing Climate, Changing Wildlife: A Vulnerability Assessment of 400 Species of Greatest Conservation Need and Game Species in Michigan The Michigan Department of Natural Resources and Michigan Natural Features Inventory conducted a comprehensive review of vulnerable wildlife in the state of Michigan.