Fish and Wildlife


  • Coldwater fish populations will likely decline 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 during periods of low water levels, creating additional stresses on species.

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 this ability is pushed beyond a critical threshold. 

Nonnative or invasive species such as alewife and zebra mussels have caused major disruptions in native fish populations in the Great Lakes. 3 4 Warming temperatures may lead to increased invasive species success and increase the impact of invasive species that are already present. For example, sea lamprey, parasitic fish native to the Atlantic Ocean, are now found in the Great Lakes. Climate change will make control efforts more difficult as the lamprey thrive in warming temperatures. In the Lake Superior watershed, lamprey have been observed to reach larger body weights before spawning during years with longer growing seasons. 5

The preferred temperature groupings of several species of fish in the Great Lakes region.

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 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. 6 As warming trends continue, it becomes possible that a full “turnover” may not occur each year. 7 For example, lake surface temperatures failed to drop below the 39°F threshold for destratification during the 2012 and 2017 winters in parts of southern Lake Michigan and Lake Ontario. 8 

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 will lead to the decline and loss of species dependent on the cold water and lake processes that they have long adapted to. Decreases in the populations of phytoplankton and zooplankton that form the basis of aquatic food webs may potentially lead to cascading effects on the health and abundance of species across all levels of Great Lakes food webs. 9 10 11

Visual of the stratification processes for lakes.

Changes in Species Range and Relative Abundances

Shifts in the geographical 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. 12 13 

Species that can move quickly (e.g., birds and large mammals) are more likely to be able to keep up with climate change than species that move more slowly (e.g., amphibians and most invertebrates). However, 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 (i.e., transition from egg to larvae in insects). Warming trends can impact the timing of these events through shifting seasonal cycles. Examples of such shifts include shifting timing of snow melt, spring flooding, ice-out on lakes/streams, or lake stratification. An example in the Great Lakes is the effect that earlier ice-out on streams is having on the spawning patterns of walleye. As ice-out (i.e., the disappearance of ice from the surface of a lake as a result of thawing) has occurred earlier on spawning streams, so has the spawning of walleye. 14 In most cases, the implications of changing phenology are unclear, but as longer term data is collected 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” (i.e., reductions in diversity due to spatial arrangement) of range expansions. 15 16 Evidence supporting these types of observed changes is strongest in invertebrate populations while evidence of similar genetic changes in vertebrates is rare. 17

Human Impacts

For fish and wildlife populations in the Great Lakes, human influence plays just as great a role as the changing climate. For example, habitat loss and degradation are caused by land conversion, pollution, coastal wetland damage, and disruptions by buildings and human structures. 18 19 

Increased nutrient inputs coupled with warmer water temperatures also contribute to algal blooms, including cyanobacterial algae harmful to humans, animals, and many native species. Agricultural runoff can also carry large volumes of sediment and nutrients into the Great Lakes, which may reduce oxygen levels and water quality. 20 21 


The recognition and implementation of climate change adaptation methods are on the rise in the Great Lakes region. Restoration of natural systems, increased use of green infrastructure, and targeted conservation efforts, especially of wetland systems, can all help protect fish and wildlife populations in the region.

One example is the monarch butterfly: following observed high rates of decline, the species is now the focus of a network of outreach and multi-partner conservation efforts working to help raise awareness of pollinator declines and show how pollinators impact habitat availability. 22 

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 the Michigan Natural Features Inventory conducted a comprehensive review of vulnerable wildlife in the state of Michigan.


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