Climate Change | American Fisheries Society

Resources for Fisheries Professionals Talking about Climate Change

Storm over a river in Seedskadee National Wildlife Refuge

Seedskadee National Wildlife Refuge, Wyoming, credit: Tom Koerner/USFWS.

AFS President Scott Bonar has challenged AFS members to step outside of your comfort zone and talk to at least 10 friends, family members, and acquaintances this year who disagree with climate change or related conservation issues. Here are some resources to help you get started.

World Aquatic Societies Statement on Climate Change

The American Fisheries Society (AFS) joined forces with 110 aquatic scientific societies representing more than 80,000 scientists across the world to sound a climate change alarm. The societies call for drastically curtailed global greenhouse gas emissions to avoid the worst impacts of man-made climate change to fish and aquatic ecosystems. Unless urgent action is taken to reduce emissions, scientists predict catastrophic impacts to commercial, recreational, and subsistence fisheries and human health and global economies.

Read statement

Web Pages

PowerPoint Graphics

Short Bibliography

By Scott Bonar, AFS President

I compiled an overview of effects and information related to climate change effects on fish/aquatic systems and associated references for use during my AFS Presidency and for my university research/education duties. The below is not comprehensive but focuses on impacts already seen – less emphasis is on modeling of future scenarios. Most of this is taken from the IPCC 5th Assessment Report, the 2018 U.S. Fourth Assessment Report, and the AFS Fisheries Issue on Climate Change.

Understanding how climate change works and the role humans have in contributing to it:

Sun shines on the earth, and the earth heats up. Heat from the earth is then reradiated back into space. Atmospheric molecules, called greenhouse gasses, trap this heat before it leaves and radiate some of it back to earth¹.
Greenhouse gasses include water vapor (H₂O), carbon dioxide (CO₂), ozone (O₃), methane (CH₄), and nitrous oxide (N₂O)¹.
Increase in atmospheric CO₂ concentration is the most important factor in increasing the heat-trapping capacity of the atmosphere.²
Since the industrial revolution, humans have dug, drilled, and burned massive amounts of oil, coal and other fuels previously stored underground, releasing enormous quantities of CO₂ and other greenhouse gasses to the atmosphere. CO2 levels (400 ppm) in the atmosphere are now higher than any time in at least the last one million years.³
Globally, over the past few decades, about 78% of CO₂ emissions were from burning fossil fuels, 20% from deforestation and other agricultural practices, and 2% from cement production.³
Current temperatures are higher than those seen in the Northern Hemisphere, and likely globally, for at least 1,700 years.^4,5
These global temperature increases are highly correlated to increased human-caused greenhouse gas emissions. Natural factors such as sun irradiance, volcanoes etc, have been studied extensively and contribute little to the temperature rise.^1,2
Temperature of the atmosphere closest to earth (troposphere) has warmed while the outer layer of the atmosphere (stratosphere) has cooled. If change in irradiance directly from the sun was responsible for temperature increases, the stratosphere should be warming fastest.¹
Reason for immediate climate action is intensified because we cannot go back to previous conditions if we reduce emissions. Carbon that we have already emitted is stored in the oceans and atmosphere for hundreds of years for continued release.³
Reasons for immediate U.S. action are critical. U.S. is the 2nd largest greenhouse gas emitter in the world⁶, has the highest per-capita emission of greenhouse gasses⁶ and exerts significant world leadership.

Climate change has already had large effects on aquatic systems and associated fisheries. Effects include:

General:

A meta-analysis of 27 studies concerning a total of 976 species found that 47% of local extinctions reported across the globe during the 20th century could be attributed to climate change.⁷ This is significantly higher for animals and for freshwater habitats.
Recent survey of 136 freshwater, marine, and terrestrial studies suggests species interactions are often the immediate cause of local extinctions due to climate change.⁸
Global ecological and monetary costs associated with invasive species are substantial (more than $1.4 trillion annually). New species interactions are being created with climate change, combinations never before seen.⁸
Invasive species have more opportunities to invade because the defense of natural communities are reduced in a stressed environment, and conditions can become more favorable for nonnative species in an altered environment.⁸
Many ecosystem changes can be avoided only by substantially reducing carbon dioxide and other greenhouse gas emissions.⁸

Freshwater: Freshwater ecosystems are considered among the most threatened on the planet.⁹ Here are some of the effects that climate change has already brought and will bring.

Climate change is altering abundance, predator-prey dynamics, growth and recruitment of North American freshwater fishes, especially coldwater species like trout.¹⁰
Suitable habitat of for trout is expected to decline by 47% under an ecologically friendly emission scenario.¹¹
The geographical ranges of many freshwater plant and animal species have moved over the last several decades – approximately 17 km per decade poleward and 11 m up in altitude per decade.⁹ (This is for aquatic organisms that can move).
By the end of the century (2090), cold water recreational fishing days are predicted to decline leading to losses in recreational fishing value ranging from $1.7-3.1 billion per year, depending on emissions scenario.⁸
Salmon populations are being affected by low snowpack, decreasing summer stream flow, higher storm intensity and flooding, physiological and behavioral sensitivity, and increasing mortality due to warmer stream and ocean temps.⁸
Climate change is already affecting food webs and species interactions. For example, brown bears in Alaska have switched from salmon to feeding on earlier-ripening berries, causing shifts in salmon mortality and nutrient seeding of Alaskan streams. ^8,12
Higher temperature and heavy precipitation, runoff from nutrient rich habitats are associated with harmful algae blooms in Lake Erie.⁸
Lamprey thermal habitat increasing in the Great Lakes.⁸
In the Southwest, droughts, intense downpours, increased evaporation, reduced snowpack combined with growing population is increasing water demands both for fish and people.^13,14
Forest area burned by wildfires from 1984-2015 is estimated to be twice what it would have been in the absence of climate change.¹⁵ Increased wildfire has huge effects on aquatic systems through floods, and reductions in water quality.¹⁴
Drought exacerbates declines in groundwater when other water sources are taxed and people turn to increased groundwater pumping. This is impacting spring and groundwater dependent ecosystems.¹⁴
Increased glacier melting under climate change affects hydrological regimes downstream (stream temperature, runoff timing), in turn affecting aquatic ecosystems.¹⁴
Habitat loss and fragmentation reduces both abundance and diversity of freshwater species. Vulnerability of bull trout due to low genetic diversity is highest where maximum temperature and winter flood risk is highest.¹⁶
Reestablishing connections or assisted migration in fragmented systems important in face of climate change (e.g. salmon and trout accessibility to colder waters).⁸
Freshwater sportfishing has 30.1 million anglers contributing $29.9 billion per year on trips and equipment.¹⁷

Marine

Fisheries and aquaculture important to global food security are already facing risks from ocean warming and acidification.¹⁸
The marine recreational and commercial fisheries sector of the United States alone contributes $200 billion in economic activity each year and supports 1.6 million jobs.¹⁹
Projected increases in ocean temperature are expected to lead to declines in maximum catch potential in all U.S. regions (Gulf of Mexico, West Coast, East Coast) except Alaska, which will increase.²⁰
Total fish catches in Alaska waters projected to increase, but species specific fisheries will decline such as Bering Sea pollock.⁸
Cumulative consumer losses of $230 million across all U.S. shellfish fisheries are anticipated by 2099 under higher emission scenario.²⁰
Climate change combined with other practices (pollution, overfishing, unsustainable coastal development) will drive many small-scale fisheries out of existence as a food source.¹⁸
Potential global catch for marine fisheries will likely decrease by over 3,000,000 metric tons for each degree of warming.¹⁸
Climate change is creating aquatic communities ecologically different from those currently occupying areas. This affects regional economies, fisheries harvest, cultural heritage and shoreline protection.²⁰
Carbon emissions affect the oceans through warming, acidification and deoxygenation.²⁰
Warming affects sea levels, ocean circulations, stratification, productivity and entire ecosystems.²⁰ These factors interact with each other and other stressors in the environment.
A warming ocean and freshwaters cause fish and other aquatic organisms to shift their ranges to those more suitable for their temperature tolerances.²¹
Marine organisms are shifting their biogeographical ranges to higher relatively cooler latitudes at rates that range from 0-40 km/yr.¹⁸ This has implications for local commercial/sport/aquaculture fisheries and the economies that depend on them.
Higher global temperatures are likely to result in decreases in marine biodiversity at the equator and increases at higher latitudes.²⁰
Temperature changes affecting ocean current and wind patterns have affected phytoplankton and zooplankton communities, impacting ocean food webs.²⁰
Timing for species processes have shifted dramatically – for example timing of phytoplankton blooms in both marine and freshwater systems are shifting, with affects across the entire aquatic ecosystem.⁸
Texas Gulf Coast temps increase grey snapper expanding northward, while summer flounder, a popular catch becoming less abundant impacting recreational and commercial catches.⁸
Shifts in production and phenology of economically important fish and shellfish including marine groundfish, inland fishes, migratory fish such as salmon, northern shrimp and lobster.⁸
Blue crab, fiddler crab moving farther north, changing ecosystems.⁸
Range changes of herbivorous fishes have changed kelp forests to kelp-free sites.⁸
Potential changes in Ocean productivity because of greater stratification due to warming.⁸
The most valuable fisheries in the United States, American lobster, is expected to decline under a high emission scenario.²⁰
Loss of sea ice in the arctic affecting algae blooms and where and when they occur. Impacts fisheries and top-level predators.²⁰
Krill depend on sea ice, sea ice habitat for krill declining.¹⁸
Summer sea ice declined 130,000 km2 per year (this is about the area of Louisiana) from 1997-2014. This was four times as fast of the decline during 1979-1996.¹⁸
Climate change presents risk for seagrass and mangrove communities through temperature increases and sea level rise.¹⁸
Major heat waves have already occurred along the Northeast (2012) and West Coasts (2014-2016). Changes seen include appearance of warmwater species, increased mortality of marine mammals, harmful algae blooms. These factors economically stressed some of the nations most valuable fisheries.²⁰
Heat wave in 2012 responsible for earlier and larger lobster catch overwhelming processors and market demand. Price collapsed and reduced income for lobster fishermen.⁸
Large toxic algal blooms affecting Dungeness crab fisheries, contributing to deaths of sea lions and humpback whales in North Pacific 2014-2016 heat wave.²⁰
Climate change could have a positive effect on those activities that benefit from warmer weather (beachgoing, etc.)
Excess carbon entering the ocean causes the ocean water to turn more acidic (ocean acidification).²⁰
The majority of marine ecosystems in the United States now experience acidified conditions that are entirely different than those before the industrial revolution.²⁰
The ocean has absorbed about 30% of the anthropogenic CO2, resulting in ocean acidification and changes to carbonate chemistry that are unprecedented for at least the last 65 million years.¹⁸
Models estimate that under higher emission scenarios, by 2050, 86% of marine ecosystems will experience temperatures and pH that have never been experienced by modern species.²⁰
Coral reefs and sea ice ecosystems currently among those most drastically being affected by climate change.²⁰
Organisms with calcium carbonate shells at high risk with ocean acidification.¹⁸
Multiple lines of evidence indicate that the majority (70-90%) of tropical coral reefs that exist now will disappear, even if global warming is constrained to 1.5C.¹⁸
In the last three years alone, large coral-reef systems such as the Great Barrier Reef have lost as much as 50% of their shallow-water corals.¹⁸
Some coral reefs already flattening without recovery.¹⁸
Warming led to mass bleaching and/or outbreaks of coral diseases off Puerto Rico, U.S. Virgin Islands, Florida, Hawai’i, and U.S. Affiliated Pacific islands. Coral reefs experience moderate to severe bleaching during 2015-2016 bleaching events.²⁰
Loss of recreational benefits alone from coral reef ecosystems in the United States alone is expected to reach $140 billion by 2100.²⁰
Nearly all existing species will be excluded from tropical reef communities by 2115 under higher emission scenarios.²⁰
A more acidic ocean prevents shellfish from forming shells. Bivalves, pteropods, shell dissolution already occurring.¹⁸
Pacific and Atlantic Coast shellfish growers are now monitoring pH and CO2 and adjusting waters to reduce acidity.²⁰
Coastal wetlands providing storm protection and habitat for fishes and other aquatic organisms are being lost. Between 2004-2009 it was estimated that wetland environments were being lost on average at a rate of 80,160 acres per year.²²
Coastal wetland loss rate in Louisiana huge due in part to high rates of sea level rise. Rate of wetland loss – one football field every 34-100 minutes.⁸
“In the absence of significant reduction in carbon emissions, transformative impacts on ocean ecosystems cannot be avoided.”²⁰

References

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