Fishing in an Uncertain Future

Global fisheries have been improving for several decades. Where do they go from here? In this post, we address the carbon threat and its effects on fish and the people who rely on them, but we end on a more positive note by looking at the remaining fishery potential.


Bad news first: Excess carbon dioxide (CO2) in our atmosphere from burning fossil fuels is changing the ocean in ways that are already affecting fisheries and the people that rely on them (and will continue to do so). Excess carbon is warming the ocean, changing primary productivity, and changing ocean chemistry.

Warm Water

Along with other greenhouse gasses, CO2 provides Earth with a kind of insulated blanket that protects us from cold space and allows life to flourish. Excess CO2 is rapidly making the “blanket” thicker, trapping more heat that would otherwise be radiated out to space. This extra heat is raising the temperature of the ocean. As habitat warms, it gets harder for fish to live in the area that it evolved to. Scientists believe that fish will migrate to water temperatures that better suit them, meaning a general shift away from the equator, toward the poles. Fish may also migrate to deeper, cooler water. This has many different consequences for fisheries.

  • Fish that were typically caught in one area will no longer be there. This will cost fishermen and women time and money looking for and adapting to fishes’ new locations.
  • Fish are not subject to geopolitical boundaries; some populations will end up in neighboring EEZs, essentially taking food and money away from one country and giving it to another. We are already seeing this happen in a number of fisheries; for example, Atlantic Cod are slowly moving north. US cod fisheries are struggling compared to their Northern neighbors.
  • Fish moving to new habitat will create conflicts and species interactions that did not exist before. The potential harm is similar to the introduction of an invasive species. Tropical rabbitfish have started moving toward the poles and have been wiping out kelp forests along the way. It is safe to say that other habitats and commercially important species are vulnerable.

Warm water also gives storms more energy and raises sea levels. Increased storm intensity makes fishing more dangerous and potentially more costly. Heavy storms making landfall are more likely to cause damage to boats and other infrastructure relied on by the fishing industry. Coastal infrastructure is especially at risk from rising sea levels. Thermal expansion pushes tides higher causing flooding, erosion, and more destructive storm surge.



As we discussed earlier in Seafood 101, fisheries are correlated to primary productivity, or the amount of plant matter (nutrients) in the ocean. Excess carbon in the water will actually boost photosynthesizing phytoplankton, which will nominally increase primary productivity and provide a bit more food for fish. However, animals that evolved in a low productivity environment will suffer as algae and other ocean plants become more dominant. This map shows productivity in the ocean as measured by chlorophyll concentrations in the water—you can see how generally unproductive the regions around the equator are, these areas are already most susceptible to warmer water and will be further disadvantaged by a boost to algae.


Ocean Acidification

Excess CO2 in the atmosphere dissolves in the ocean and chemically reacts with seawater to generate carbonic acid, making the ocean more acidic (i.e., lowers ocean pH). This is the same, simple reaction (CO2 + H2O) that produces carbonated water for your sodas and La Croix. A similar process can be felt when you hold your breath. When CO2 is held in the lungs, more of it dissolves in the bloodstream making your blood more acidic. More acidic blood is the signal to your brain to send (painful) contractions to your diaphragm prodding it to expel the CO2-riddled breath with fresh air. You breath much faster after holding your breath for a long time as the body works to rid itself of CO2 and normalize the pH of its blood.

Unfortunately, the ocean has no way to quickly ventilate the large amount of CO2 forcibly absorbed through anthropogenic carbon emissions. Since pre-industrial times, the ocean has gotten ~30% more acidic and will continue to acidify until CO2 flux between the atmosphere and ocean reaches equilibrium many decades from now. In other words, the concentration of CO2 in the atmosphere directly determines the ocean’s pH: more CO2 in the atmosphere means a more acidic ocean.

This is not good for organisms that rely on the ocean’s chemistry for life. Ocean acidification makes it more difficult for calcifying organisms (like coral and shellfish) to build calcium carbonate shells or skeletons. Shellfish fisheries and small-scale fisheries on coral reefs will continue to degrade. Impacts are already being felt: more than half of those in the U.S. West-Coast shellfish industry report already feeling negative impacts of ocean acidification on their businesses and personal lives.

Sherman's Lagoon by Jim Toomey

Ocean acidification seems to be affecting how marine species smell. This is troublesome for fish that rely on olfactory senses for finding food or mates. Salmon are particularly vulnerable as they use olfactory senses to track back to their native rivers to spawn. Larval development is also at risk due to ocean acidification. Researchers predict declines in Dungeness crab catch due to slowed larval development as a result of more acidic water.

Changes to overall seafood consumption due to ocean acidification are difficult to predict; some species may benefit through increases to primary productivity, though it is an uncertain, vulnerable future with a more acidic ocean. Curbing carbon emissions is the only way to reduce risk.

Sherman's Lagoon by Jim Toomey

Triple Whammy to Coral Reefs & the Tropics

Coral reef ecosystems revolve around the intricate structures that coral provide for fish and other creatures on the reef. Without coral, the ecosystem suffers tremendously. Coral are highly vulnerable to carbon threats and are threatened by a wicked combination of warm water, higher productivity, and ocean acidification.

The ocean is warmest near the equator, meaning that everything living there now has evolved to live in the upper range of global water temperatures. Pushing coral beyond that maximum causes them to expel their zooxanthellae (symbiotic organisms that provide coral with food), a phenomenon known as bleaching. Once a coral bleaches, it has only a 50% chance to recover its zooxanthellae and survive. Historically, mass bleaching events occurred during El Niño years when exceptionally warm water persisted in the tropics for an entire season. Now, it is common for corals to bleach outside of El Niño years.

Coral reefs are also unproductive ecosystems, meaning algae and primary productivity plays a trivial role in the food chain; an influx of nutrients will increase the amount of macro algae on the reef. Macro algae grow quickly and smother coral. In many parts of the tropics, particularly the Caribbean, algae have already replaced coral. Coral also grow by slowly building on their calcium carbonate skeleton; ocean acidification slows this growth by up to a third.

All these issues spell trouble for coral reefs and the people that rely on them. In addition to the degradation of small-scale and artisanal fisheries that provide jobs and food, coral reef communities will lose tourism revenue, protection from storms, and a part of their home. Exacerbating the problem is the fact that most of the countries and communities on coral reefs are underdeveloped—often, coral reefs are the main economic resource providing food, jobs, and income to locals.

Sadly, the degradation of coral reefs and tropical fisheries due to excess carbon is one of the environmental justice issues of our time. The countries and communities reliant on reefs are least responsible for carbon emissions but will be affected the most. Read more about social and environmental justice issues related to fisheries here in Seafood 101.


Fishery Potential

The worsening effects of carbon will create winners and losers in global fisheries. Some species will suffer, some will be okay, and some might benefit from the various environmental effects of warm ocean temperatures, higher productivity, and ocean acidification. The distribution of fisheries will continue to change (and become less equitable) as fish migrate deeper and towards the poles, however the total amount of fish caught should remain about the same under oceanic transformation.

But what if there were large-scale management change? What would global fisheries look like if they were all at maximum sustainable yield? There would be more fish, more food, and more money supporting the millions of people working in the industry. This untapped seafood is called fishery potential. A fishery meeting its potential has maximized its benefits to people.

Currently, about 80 million tons of fish are harvested each year from the worlds oceans. Estimates vary for how much fish could eventually be sustainably harvested, but they range from about 95-120 million tons. A recent study estimated that if better management practices were implemented around the world, by 2030 over 90% of existing fisheries could be sustainable. By 2050, the amount of fish in the ocean would double, which would produce a global maximum sustainable yield of around 95 million tons.

However, this only accounts for existing fisheries. There are plenty of potential commercial fisheries around the world that do not exist yet, for varying reasons. Some potential fisheries do not have a market, meaning consumers don’t like eating them for reasons ranging from taste to perception. These potential fisheries are reliant on chefs, restaurants, and experimental home cooks to develop new recipes or marketing firms to change perceptions. Slimefish were once looked down upon as trash-fish, but are now a delicacy around the world rebranded as orange roughy. Other fisheries remain untouched due to capacity issues. Some fisheries are either too costly or too difficult to reach for the managing country. These fisheries will develop as technology develops and/or harvesting becomes cost-efficient.

Why don’t we just leave fish in the ocean?

We want to address the inevitable argument made by some preservationists that humans should underfish (or not fish at all) to leave extra fish in the ocean. This attitude towards natural resources shows kindheartedness for fish and other living creatures, but overlooks the benefits to humans and the planet. Fishing is one of the least impactful sources of food. Fishing to maximum sustainability benefits terrestrial animals and ecosystems that would otherwise be moved aside for traditional agriculture and reduces dietary CO2 emissions. A maximum sustainable harvest would also consider fishes’ ecological role to protect oceanic environments that depend on them.

Fisheries provide over 250 million people around the world with their primary source of income and hundreds of millions with their primary source of protein. Leaving fish in the ocean for the sake of the fish may seem compassionate, but overlooks the human costs and environmental impacts alleviated by fisheries. Ironically, eating seafood in place of most other proteins helps the ocean in the long run due to its lower carbon footprint. This isn’t to say that the only purpose of fish is food. Fish are worth protecting in some areas as they are important sources of enjoyment for many, from scuba divers to recreational fishermen and women—it is important that we continue to work towards sustainability in an uncertain future.

Also available in:


This post is part of Sustainable Seafood 101

Continue reading below:  

Seafood in a Global Context

Commercial Fishing

People & Fish