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.

‘Climigration’: when communities must move because of climate change



Flood damage in Bundaberg, Queensland, in 2013. Most communities are at some risk from extreme events, but repeated disasters raise the question of relocation.
srv007/Flickr, CC BY-NC

Tony Matthews, Griffith University

This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.


Climate change increasingly threatens communities all over the world. News of fires, floods and coastal erosion devastating lives and livelihoods seems almost constant. The latest fires in Queensland and New South Wales mark the start of the earliest bushfire season the states have ever seen.

What happens when climate change causes extreme events to become chronic, potentially rendering some communities unviable? This question is fuelling a new strand of global research focused on “climigration”. Climigration is the planned relocation of entire communities to new locations further from harm. And it has already begun.

The Isle de Jean Charles community is the first to receive US government funding to relocate because of climate change.



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It takes a lot to convince a community to move. But extreme events disrupt communities socially, economically and physically. Buildings and infrastructure are damaged, as are community cohesion and morale. Lives may be lost; many others are changed forever.

When extreme events disrupt communities, responses usually occur in one of two ways. We can try to repair damage and continue as before, which is known as resilience. Or we try to repair and fortify against future damage in a process of adaptation. Climigration is an extreme form of climate change adaptation,

This article draws on our recently published research, which investigated how land-use and strategic planning frameworks can prepare for climigration.

From imagination to reality

Climigration is no longer a concern for the future; it is a challenge today. The notion of strategically relocating entire communities has quickly moved from imagination to reality.

For instance, in 2016 the US Department of Housing and Urban Development provided US$1 billion to help communities adapt to climate change in 13 states. The grants included the first direct allocation of federal funding to move an entire community.

Isle de Jean Charles in Louisiana is the first US community to undergo federally sanctioned climigration. The move has been forced by the loss of coastal land to rising seas and storm surges. Last December, the state bought land at residents’ preferred site to develop their new community.

Property damaged by extreme weather and later abandoned on Isle De Jean Charles.
Maitri/Flickr, CC BY-NC-SA

Climigration options were previously considered in Alaska. Climate-induced coastal erosion has threatened the viability of the village of Newtok for many years. Its residents voted in 2003 to relocate to higher ground but the relocation looks unlikely to be completed before 2023.

In Australia, more than 100 households in Grantham, Queensland, were relocated to higher ground with government assistance after devastating floods caused by an exceptionally strong La Niña in 2011.




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Moving Grantham? Relocating flood-prone towns is nothing new


Critical factors in climigration

Climigration is, of course, not a phenomenon restricted to the US and Australia. It is a growing concern for many countries.

Our research sought to establish a framework for effective climigration planning. We systematically reviewed international case studies of community relocations undertaken because of environmental hazards. As part of this we developed a hierarchy of influencing factors in planning for climigration.

We found that the degree to which a community agrees on the need to relocate is a crucial influence. Consensus generates social capital, which supports action and improves the prospects of successful outcomes.

Perception of the timing and severity of risks is another critical factor. Immediate, obvious risks are more likely to motivate action. Motivation can be low if risks are seen as a problem for the distant future, even if impacts may eventually be devastating.




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Why move back? Floods and the difficulty of relocation


Political, economic and logistical support from government moderately influences the success of community relocation. Relocation may still occur without government support, but this is not preferable and the chances of success are lower.

Strong local leadership can improve the capacity of communities to face the reality of relocation and then to resettle. Strategic leadership from outside agencies is a complement to local leadership, not a substitute.

How to plan successfully for climigration

Strategic and land-use planning systems will be central public agencies in many climigration cases.

Planners already have relevant skills and training. These include community consultation, mediation and stakeholder engagement. Planners can coordinate land acquisition and development applications. They can provide temporary housing, infrastructure and transportation.

Planning for climigration also requires other professional input, including disaster management, social psychology and engineering.

Strategic planning for climigration should begin as early as possible. Vulnerable communities can be identified using risk mapping.




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Alternative sites can then be shortlisted and potential logistical demands identified.

Securing land for relocation may place planners in the middle of competing forces. They need to be careful and deliberative to balance the expectations of residents, government, and the market.

Consultation is vital to secure community consensus in the event of climigration. It is a key tool for planners to explain risks and engage residents in crucial decisions.

Specific policy frameworks for climigration are preferable but not essential. When used, they can improve coordination and reduce the risk of negative outcomes.

A confronting concept

While climigration is not yet a common planning issue, it is likely to become an increasingly urgent agenda. Climigration events like those in Louisiana, Alaska and Queensland are just the first wave.

There are limits to the feasibility of climigration. It might only be viable for small towns and villages. Undoubtedly there will be cases where climigration is rejected as too much of challenge.

Triage-based planning could be helpful in deciding which communities to relocate.




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Accepting the notion of climigration may be the biggest challenge for planners. The idea that the only viable future for a community is to be relocated elsewhere is unusual and confronting. Managing climigration through planning practice may prove more straightforward than adjusting to the idea in the first place.The Conversation

Tony Matthews, Senior Lecturer in Urban and Environmental Planning, Griffith University

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