Climate Change Impacts to Fish and Fisheries
From the rumbling of rocks through roaring rivers to the silent stillness of a brook that’s run dry, the state’s waters and their aquatic inhabitants are experiencing the extremes that come with our changing climate. Take the plunge with us to learn just how these evolving conditions affect Vermont’s fish and aquatic ecosystems, the people who enjoy them, and the work being done to manage it all.
Climate change is causing an increase in the frequency and intensity of extreme weather events like droughts and floods, each of which present a unique set of stressors on aquatic life. Aquatic communities have evolved to survive periodic drought and flood events, but what are the impacts of the extreme events we see more and more often?
Droughts are stressful to fish populations, especially species like brook trout that require cold, well-oxygenated water, optimally between 50° and 60°. During drought years, water temperatures rise quickly and low water levels reduce the availability of deep, cool habitat that provides refuge from the heat. Looking for relief, fish will crowd into remaining pools, often at a density that is not sustainable.
A cool, free-flowing, connected river will allow trout to move to cooler waters when temperatures get too warm. Maintaining woody vegetation on streambanks to shade the water, removing dams and replacing impassable culverts helps improve climate change resiliency for trout and other species as summers get longer and hotter.
During flood events, like in July 2023, fish in rivers and streams will seek shelter from fast flowing water near downed trees, undercut streambanks and behind boulders. These natural features slow water velocity and create nooks and crannies that protect fish. However, it is harder for young, small fish to swim against high currents even with these features, and many will be forced downstream or may not survive the flood at all. Although we often find lower numbers of fish immediately following a flood, those numbers do rebound, especially in areas where we have complex river and stream habitats with fallen trees, boulders, gravel bars, and a variety of places for fish to shelter, spawn, and feed. Rivers that have robust riparian habitats and access to floodplains are more resilient during flood events, as this slows water and allows it to spread out, resulting in less long-term impact to fish populations.
In fact, smaller floods can improve aquatic habitats. Ground water mixing into the stream cools the temperature, nutrients are released and trees and gravel moving around in the stream create new areas for shelter and spawning. What we might consider to be a “messy” stream actually has new, complex fish habitat, and in streams and rivers where trees, boulders and gravel bars are not removed are often those where fish populations are able to recover quickly.
What about our beloved lakes and ponds -- the waters where we caught our first yellow perch as a child? Climate change is causing lakes and ponds to ice over later in the season and ice out earlier in the spring, and winter thaws and rain decrease ice cover mid-winter. Shorter periods of ice cover means that water warms faster in the spring, lengthening the open water period when aquatic plants can grow. Many species of aquatic plants provide habitat and food sources for fish and are an important part of a lake ecosystem. Unfortunately, invasive plants and harmful algae blooms also benefit from these longer growing seasons, and they can outcompete the native plants that fish and their prey depend on. Minimizing the spread of invasive plants and the amount of nutrients we put in our waters will help native plants and fish communities stay resilient as the climate changes.
Fish Culture Stations — Stepping Up To The Challenge
Our nationally recognized fish culture stations raise and stock over 750,000 fish each year in carefully controlled settings, and these facilities contend with big challenges due to climate change. Fish culture systems require consistency in their environment to maximize fish growth and meet high standards for fish health.
As in the wild, high water temperatures and low flows during droughts can reduce the volume and quality of water entering our fish culture stations. Heavy rain events can introduce sediment, pollutants and invasive species into the water supply. These impacts on water quality can negatively impact fish development, reproduction, health, and survival rates.
To protect against these threats, fish culture stations use a variety of cutting-edge technologies to ensure clean water for raising fish. This includes treating and recirculating the water on-site to greatly reduce the total amount of water and energy used in operations.
With so many fish being raised in close quarters, we also diligently monitor water quality and fish health to ensure we are stocking healthy fish. Fish pathologists test for a variety of pathogens at each facility on an annual basis and provide rapid response for any potential disease outbreak. Their swift response allows for a precise diagnosis and recommendation to culture staff for medication and treatment.
Climate Resilient Habitats
Like the fish, plants, wildlife and their habitats that we work to conserve, Vermont Fish and Wildlife must also adapt to meet climate challenges. We have been studying trends in fish and their habitats for decades, to better understand how species respond to environmental changes and weather extremes, and we have been developing conservation initiatives to meet these challenges head-on.
Conservation and restoration of high-quality fish habitat is at the forefront of our work. We work closely with the public and conservation partners to restore riparian areas with tree plantings, conserving quality habitat through land acquisition, enhancing instream habitat by strategically adding woody material, reconnecting rivers by removing dams, and protecting instream and riparian habitat through technical review of a wide variety of permits, including Act 250.
Several large flood events in the past 15 years have highlighted how our built infrastructure impacts aquatic habitat and how it is vulnerable to climate change. We have been working for decades to improve aquatic organism passage and flood resilience at culverts and bridges. We have assessed 15,000 culverts and bridges across the state and found that 94% of them were undersized and either fully or partially blocking aquatic organism passage! In response, we have been working with partners statewide to install stream crossings that allow aquatic organisms to move through. By doing so, we improve the surrounding wildlife community in many areas across Vermont.
These improvements not only allow fish and other species to pass, but also allow water, gravel and woody material to move through the river system, which significantly decreases the likelihood of infrastructure failure during large flood events. In the July 2023 floods, culverts and bridges that had been replaced to new standards fared much better than those that had not, indicating that as we continue to work toward more resilient crossings for fish, we are also building more resilient human communities.
Vermont is well positioned to deal with the impacts of climate change thanks to dedicated science, conservation and restoration efforts. Maintaining the status quo is not an option. We continue to learn and look for science-backed solutions to conserve fish communities and aquatic systems that enhance our quality of life and provide enjoyment for generations.
What Anglers Can Do
When water temperature climbs above 70°F, coldwater fish such as our native brook trout are stressed. Anglers practicing catch-and-release should remember to land a fish quickly, keep it in the water, and release it quickly to reduce stress and improve the fish’s chance of survival.
Many of Vermont’s warmwater sportfish aren’t bothered by higher water temps. Fishing for warmwater species such as bass, pike, bowfin, or panfish is a great option for anglers looking to get out on hot summer days. This is a great way to help coldwater species survive a warming climate while still enjoying the sport you love.
When possible, steward your property for Vermont’s fisheries. Keep lakeshores and riverbanks forested, and plant trees to restore floodplains. As we always say: fish grow on trees!
Consider buying a Vermont Habitat Stamp. The best part? Your donation is matched with federal funds, tripling your impact for projects, including improving aquatic organism passage, riparian restoration, dam removal, and more! Learn more at https://vtfishandwildlife.com/vthabitatstamp.
Most importantly, you already contribute to fisheries conservation when you purchase a fishing license! The cost of your license directly funds the science-based fisheries management and habitat work we are doing state-wide. Thank you to every angler who fishes Vermont in 2025.
