Ocean warming has fisheries on the move, helping some but hurting more



An Atlantic cod on ice. Cod fisheries in the North Sea and Irish Sea are declining due to overfishing and climate change.
Robert F. Bukaty/AP

Chris Free, University of California, Santa Barbara

Climate change has been steadily warming the ocean, which absorbs most of the heat trapped by greenhouse gases in the atmosphere, for 100 years. This warming is altering marine ecosystems and having a direct impact on fish populations. About half of the world’s population relies on fish as a vital source of protein, and the fishing industry employs more the 56 million people worldwide.

My recent study with colleagues from Rutgers University and the U.S. National Oceanic and Atmospheric Administration found that ocean warming has already impacted global fish populations. We found that some populations benefited from warming, but more of them suffered.

Overall, ocean warming reduced catch potential – the greatest amount of fish that can be caught year after year – by a net 4% over the past 80 years. In some regions, the effects of warming have been much larger. The North Sea, which has large commercial fisheries, and the seas of East Asia, which support some of the fastest-growing human populations, experienced losses of 15% to 35%.

The reddish and brown circles represent fish populations whose maximum sustainable yields have dropped as the ocean has warmed. The darkest tones represent extremes of 35 percent. Blueish colors represent fish yields that increased in warmer waters.
Chris Free, CC BY-ND

Although ocean warming has already challenged the ability of ocean fisheries to provide food and income, swift reductions in greenhouse gas emissions and reforms to fisheries management could lessen many of the negative impacts of continued warming.

How and why does ocean warming affect fish?

My collaborators and I like to say that fish are like Goldilocks: They don’t want their water too hot or too cold, but just right.

Put another way, most fish species have evolved narrow temperature tolerances. Supporting the cellular machinery necessary to tolerate wider temperatures demands a lot of energy. This evolutionary strategy saves energy when temperatures are “just right,” but it becomes a problem when fish find themselves in warming water. As their bodies begin to fail, they must divert energy from searching for food or avoiding predators to maintaining basic bodily functions and searching for cooler waters.

Thus, as the oceans warm, fish move to track their preferred temperatures. Most fish are moving poleward or into deeper waters. For some species, warming expands their ranges. In other cases it contracts their ranges by reducing the amount of ocean they can thermally tolerate. These shifts change where fish go, their abundance and their catch potential.

Warming can also modify the availability of key prey species. For example, if warming causes zooplankton – small invertebrates at the bottom of the ocean food web – to bloom early, they may not be available when juvenile fish need them most. Alternatively, warming can sometimes enhance the strength of zooplankton blooms, thereby increasing the productivity of juvenile fish.

Understanding how the complex impacts of warming on fish populations balance out is crucial for projecting how climate change could affect the ocean’s potential to provide food and income for people.

Warming is affecting virtually all regions of the ocean.

Impacts of historical warming on marine fisheries

Sustainable fisheries are like healthy bank accounts. If people live off the interest and don’t overly deplete the principal, both people and the bank thrive. If a fish population is overfished, the population’s “principal” shrinks too much to generate high long-term yields.

Similarly, stresses on fish populations from environmental change can reduce population growth rates, much as an interest rate reduction reduces the growth rate of savings in a bank account.

In our study we combined maps of historical ocean temperatures with estimates of historical fish abundance and exploitation. This allowed us to assess how warming has affected those interest rates and returns from the global fisheries bank account.

Losers outweigh winners

We found that warming has damaged some fisheries and benefited others. The losers outweighed the winners, resulting in a net 4% decline in sustainable catch potential over the last 80 years. This represents a cumulative loss of 1.4 million metric tons previously available for food and income.

Some regions have been hit especially hard. The North Sea, with large commercial fisheries for species like Atlantic cod, haddock and herring, has experienced a 35% loss in sustainable catch potential since 1930. The waters of East Asia, neighbored by some of the fastest-growing human populations in the world, saw losses of 8% to 35% across three seas.

Other species and regions benefited from warming. Black sea bass, a popular species among recreational anglers on the U.S. East Coast, expanded its range and catch potential as waters previously too cool for it warmed. In the Baltic Sea, juvenile herring and sprat – another small herring-like fish – have more food available to them in warm years than in cool years, and have also benefited from warming. However, these climate winners can tolerate only so much warming, and may see declines as temperatures continue to rise.

Shucking scallops in Maine, where fishery management has kept scallop numbers sustainable.
Robert F. Bukaty/AP

Management boosts fishes’ resilience

Our work suggests three encouraging pieces of news for fish populations.

First, well-managed fisheries, such as Atlantic scallops on the U.S. East Coast, were among the most resilient to warming. Others with a history of overfishing, such as Atlantic cod in the Irish and North seas, were among the most vulnerable. These findings suggest that preventing overfishing and rebuilding overfished populations will enhance resilience and maximize long-term food and income potential.

Second, new research suggests that swift climate-adaptive management reforms can make it possible for fish to feed humans and generate income into the future. This will require scientific agencies to work with the fishing industry on new methods for assessing fish populations’ health, set catch limits that account for the effects of climate change and establish new international institutions to ensure that management remains strong as fish migrate poleward from one nation’s waters into another’s. These agencies would be similar to multinational organizations that manage tuna, swordfish and marlin today.

Finally, nations will have to aggressively curb greenhouse gas emissions. Even the best fishery management reforms will be unable to compensate for the 4 degree Celsius ocean temperature increase that scientists project will occur by the end of this century if greenhouse gas emissions are not reduced.

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Chris Free, Postdoctoral Scholar, University of California, Santa Barbara

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Biodiversity and our brains: how ecology and mental health go together in our cities


Zoe Myers, University of Western Australia

Mental health in our cities is an increasingly urgent issue. Rates of disorders such as anxiety and depression are high. Urban design and planning can promote mental health by refocusing on spaces we use in our everyday lives in light of what research tells us about the benefits of exposure to nature and biodiversity.

Mental health issues have many causes. However, the changing and unpredictable elements of our physical and sensory environments have a profound impact on risk, experiences and recovery.




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Green for wellbeing – science tells us how to design urban spaces that heal us


Physical activity is still the mainstay of urban planning efforts to enable healthy behaviours. Mental well-being is then a hoped-for byproduct of opportunities for exercise and social interaction.

Neuroscientific research and tools now allow us to examine more deeply some of the ways in which individuals experience spaces and natural elements. This knowledge can greatly add to, and shift, the priorities and direction of urban design and planning.

What do we mean by ‘nature’?

A large body of research has compellingly shown that “nature” in its many forms and contexts can have direct benefits on mental health. Unfortunately, the extent and diversity of natural habitats in our cities are decreasing rapidly.

Too often “nature” – by way of green space and “POS” (Public Open Space) – is still seen as something separate from other parts of our urban neighbourhoods. Regeneration efforts often focus on large green corridors. But even small patches of genuinely biodiverse nature can re-invite and sustain multitudes of plant and animal species, as urban ecologists have shown.




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The small patch of bush over your back fence might be key to a species’ survival


An urban orchard in Perth.
Zoe Myers

It has also been widely demonstrated that nature does not effect us in uniform or universal ways. Sometimes it can be confronting or dangerous. That is particularly true if nature is isolated or uninviting, or has unwritten rules around who should be there or what activities are appropriate.

These factors complicate the desire for a “nature pill” to treat urban ills.

We need to be far more specific about what “nature” we are talking about in design and planning to assist with mental health.




Read more:
Increasing tree cover may be like a ‘superfood’ for community mental health


Why does biodiversity matter?

The exponential accessibility and affordability of lab and mobile technologies, such as fMRI and EEG measuring brain activity, have vastly widened the scope of studies of mental health and nature. Researchers are able, for example, to analyse responses to images of urban streetscapes versus forests. They can also track people’s perceptions “on the move”.

Research shows us biodiverse nature has particular positive benefit for mental well-being. Multi-sensory elements such as bird or frog sounds or wildflower smells have well-documented beneficial effects on mental restoration, calm and creativity.

Other senses – such as our sense of ourselves in space, our balance and equilibrium and temperature – can also contribute to us feeling restored by nature.

Acknowledging the crucial role all these senses play shifts the focus of urban design and planning from visual aesthetics and functional activity to how we experience natural spaces. This is particularly important in ensuring we create places for people of all abilities, mobilities and neurodiversities.

Neuroscientific research also shows an “enriched” environment – one with multiple diverse elements of interest – can prompt movement and engagement. This helps keep our brains cognitively healthy, and us happier.




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Reducing stress at work is a walk in the park


Beyond brain imaging of experiences in nature, there is growing and compelling evidence that contact with diverse microbiomes in the soil and air has a profound effect on depression and anxiety. Increasing our interaction with natural elements through touch – literally getting dirt under our nails – is both psychologically therapeutic and neurologically nourishing.

We also have increasing evidence that air, noise and soil pollution increase risk of mental health disorders in cities.

What does this mean for urban neighbourhoods?

These converging illustrations suggest biodiverse urban nature is a priority for promoting mental health. Our job as designers and planners is therefore to multiply opportunities to interact with these areas in tangible ways.

A residential street in Perth.
Zoe Myers

The concept of “biophilia” isn’t new. But a focus on incidental and authentic biodiversity helps us apply this very broad, at times unwieldy and non-contextual, concept to the local environment. This grounds efforts in real-time, achievable interventions.

Using novel technologies and interdisciplinary research expands our understanding of the ways our environments affect our mental well-being. This knowledge challenges the standardised planning of nature spaces and monocultured plantings in our cities. Neuroscience can therefore support urban designers and planners in allowing for more flexibility and authenticity of nature in urban areas.

Neuroscientific evidence of our sensory encounters with biodiverse nature points us towards the ultimate win-win (-win) for ecology, mental health and cities.


Dr Zoe Myers is the author of Wildness and Wellbeing: Nature, Neuroscience, and Urban Designn (Palgrave Macmillan, 2020).The Conversation

Zoe Myers, Lecturer, Australian Urban Design Research Centre, University of Western Australia

This article is republished from The Conversation under a Creative Commons license. Read the original article.