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

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)

Chris Free.

Chris Free is a Postdoctoral Scholar at the University of California, Santa Barbara, and was a Ph.D. student at Rutgers University when this research was conducted. The work was funded by the U.S. National Oceanic and Atmospheric Administration (NOAA) through a NOAA-Sea Grant Population Dynamics Fellowship. This op-ed was originally published on The Conversation

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%.

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.


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.


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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Warming is affecting virtually all regions of the ocean. (Chris Free, CC BY-ND)


Bryan Meek August 24, 2019 at 9:04 am

Reading the headline, I was expecting some real data on water temperatures and ranges.

Instead we get….In our study we combined maps of historical ocean temperatures with estimates of historical fish abundance and exploitation…..

Because everyone knows that real science is based on “estimates” of what someone thinks happened 80 years ago. Really?

According to real science the volume of the earth’s ocean is 1.37 billion cubic kilometers. It’s surface area 361 million square kilometers. https://hypertextbook.com/facts/2001/SyedQadri.shtml

Real science teaches us that the definition of a Calorie is the amount of heat energy it takes to increase the temperature of 1 gram of water by 1 degree Celsius.

Real science teaches us that the definition of a milliliter is 1 cubic centimeter in volume. Also that one CC of water weighs 1 gram which can vary with temperature and atmospheric pressure, but is generally accepted value at sea level and 4 degrees C.

Holding those constant and converting 1 square kilometer into the equivalent 10,000,000,000 square centimeters, we can calculate that the ocean’s first centimeter in depth makes up a volume of 3.61 X 10^18 cubic centimeters, which by extension would take 3.61 X 10 ^ 18 calories of energy to raise one degree Celsius. 1 Calorie is the equivalent of 4.2 joules, which is the standard unit of measure for energy. This shows we need 1.5 X 10 ^ 19 joules.

According to the International Energy Assoc, this amount of energy is roughly 10 times what humans currently produce in a single day. https://www.iea.org/weo2017/

Without going into further discussions of thermodynamics and rates of diffusion, anyone with an undergraduate knowledge of physics can quickly demonstrate that we simply do not possess the technology to warm the ocean’s waters, not to mention that photons from the sun produce 10,000 times the energy described above.

Any you don’t even really need the physics background. Anyone who owns a pool knows how impossible and expensive it is to continually heat. And I’m only talking about the first centimeter of the ocean. It’s actually a lot deeper than that.

And while we are on the topic of inevitable short term catastrophic ocean warming and sea levels rising, I found it interesting that President Obama would buy a $15 million beach front home on Martha’s Vineyard. What does he know that we don’t?

George August 24, 2019 at 9:36 am

Are you refering to the raise of ocean surface temps? Here is a link to a NASA time graph from 1982 to 2017. You can see that not much has changed at the suface in the mid Atlantic in that time frame. It took 30 seconds to look this up.

Bryan Meek August 24, 2019 at 2:58 pm

Appreciate your efficiency, George. Good work. 90% of the oceanic environment has never been explored, but we’re shedding PhDs at a record pace.

RayJ August 24, 2019 at 5:39 pm

@Brian. Good strong argument……….But I’ll go out on a limb here and admit I don’t have a degree in physics so the value of joules is just a number to me. Your analysis is the amount of energy that humans produce.

But global warming theory advocates claim that warming is occurring due to the sun’s energy being trapped by greenhouse gases. So the sun would be producing that energy. Further adding fuel the discussion is the statement that the sun produces 10,000 times the joules described which plays into the climate science position.

Steve August 24, 2019 at 8:35 pm

We have at least one google doctor as a commentator. The IEA website is about a host of information that is unrelated to the amount of energy necessary to heat ocean water. Having just spent two weeks in an area centered on fishing in Canada I can guarantee you that fishermen overwhelmingly believe that climate change is happening and effecting ocean temperatures. But of course fishermen and oceanic scientists don’t hold a candle to suburban accountants who can google

george August 25, 2019 at 8:04 am

With the ice age of the 1970’s that was predicted and reported by Walter Chonkite and Johnny Carson’s toilet paper shortage scare being related these so called “scientists” seem to never look at actual facts. It is now simple enouch to find facts. If NASA does not count as a fact based source and fisherman..oh sorry…fisherpeople do count as a fact based source then I must be wrong. But Mr. Carson clearly knew a toilet paper shortage was coming.

Here is another fact based video from Tony Heller. The 3 days that ended the world. If you have 8 minutes to spare take a look.

Bryan Meek August 25, 2019 at 10:11 am

@Steve. Math and physics are pesky things. I’ve been fishing off New Foundland and that is most certainly an overfished area. They’ve stopped dragging nets there and the wildlife is coming back…..I guess we have global warming to thank for that.

Steve August 25, 2019 at 8:03 pm

Bryan they stopped dragging nets there because the government stepped in and regulated the overfishing. Another great example of the value of government conservation in action. Thanks

Bryan Meek August 26, 2019 at 10:40 am

The Cod are back and yes, thanks to some regulation. So how do we propose to get China to stop supplying 2/3s of its energy with coal and growing if it’s all greenhouse gas related? Water traps 4x the heat that air does and that hasn’t changed much with increase or decrease in CO2 levels as minuscule as it is at 400 parts per million. And, at the end of the day, why isn’t the shore line up to Fitch street right now, like the experts said it would be?

Ed August 26, 2019 at 3:17 pm

So I looked at the abstract of the study. I see this line: “Hindcasts indicate that the maximum sustainable yield of the evaluated populations decreased by 4.1% from 1930 to 2010, with five ecoregions experiencing losses of 15 to 35%.” Should we trust 1930’s fish population estimate technology? I can’t read the report so maybe someone can explain this.

Is there a report out there that says we lost all X kind of fish last year due to rising sea temperatures? I see a lot of sentences with the word “may” or “might” in regard to this study.

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