Shrinking Nemo – global warming to make fish smaller

From the University of British Columbia , a fish story inspired by a model:

Fish getting smaller as the oceans warm: UBC research

Changes in ocean and climate systems could lead to smaller fish, according to a new study led by fisheries scientists at the University of British Columbia.

The study, published today in the journal Nature Climate Change, provides the first-ever global projection of the potential reduction in the maximum size of fish in a warmer and less-oxygenated ocean.

The researchers used computer modeling to study more than 600 species of fish from oceans around the world and found that the maximum body weight they can reach could decline by 14-20 per cent between years 2000 and 2050, with the tropics being one of the most impacted regions.

“We were surprised to see such a large decrease in fish size,” says the study’s lead author William Cheung, an assistant professor at the UBC Fisheries Centre. “Marine fish are generally known to respond to climate change through changing distribution and seasonality. But the unexpectedly big effect that climate change could have on body size suggests that we may be missing a big piece of the puzzle of understanding climate change effects in the ocean.”

This is the first global-scale application of the idea that fish growth is limited by oxygen supply, which was pioneered more than 30 years ago by Daniel Pauly, principal investigator with UBC’s Sea Around Us Project and the study’s co-author.

“It’s a constant challenge for fish to get enough oxygen from water to grow, and the situation gets worse as fish get bigger,” explains Pauly. “A warmer and less-oxygenated ocean, as predicted under climate change, would make it more difficult for bigger fish to get enough oxygen, which means they will stop growing sooner.”

This study highlights the need to curb greenhouse gas emissions and develop strategies to monitor and adapt to changes that we are already seeing, or we risk disruption of fisheries, food security and the way ocean ecosystems work.


Note the press release headline: Fish getting smaller as the oceans warm: UBC research – they tout that as if it were measured, it isn’t.

Of course actual field experiments with real data trump models every day of the week and twice on Sunday. For example here’s a graph from the paper The effect of temperature and fish size on growth, feed intake, food conversion efficiency and stomach evacuation rate of Atlantic salmon post-smolts by Handeland et al published in the journal Aquaculture in June 2008:

Fig. 1. Mean weight in Atlantic salmon smolts (±SE, n=23) transferred to seawater at 6 (□), 10 (Δ), 14 (⋄) and 18 (○) °C. The first point (week 0) refers to the freshwater group (control). Different letters indicates significant differences (Student–Newman–Keuls, pb0.05) between temperature groups at same time of sampling, n.s., non significant.

The authors conclude:

In conclusion, the present study shows ontogenetic variation in optimum temperature for growth in juvenile Atlantic salmon smolts, with increased temperature optimum for growth and decreased temperature for feed conversion efficiency as the fish grow bigger.

Temperature tolerance increases with size, but Atlantic salmon smolts are eurythermal (Able to tolerate a wide range of temperatures.) in the size range investigated. 

Full paper here (PDF)

Now as Willis would point out, clearly this is tank studies, and not the open ocean, and you can’t duplicate the complexity of the ocean in a tank. But the fish don’t seem to have a temperature issue, in fact they seem to thrive at warmer temperatures. The claim is that as oceans warm, less oxygen will be available, and that will stunt the growth of fish. This claim in the modeling paper comes from the elemental saturation curve for dissolved oxygen (DO) in water, which is much like that of CO2. From a lecture on water chemistry at

I found this part of the lecture interesting, and was something I didn’t know:

Nota bene:  100% saturation does not mean that no more O2 can be held in solution.  I have measured DO >200%.  Does this mean that bubbles should be forming?  No, not necessarily. Saturation here means that 10.92 mg/l can be held at equilibrium; if 200% is produced by intense photosynthetic activity, the extra amount will be lost (diffused) at the air/water interface.

  • a nomogram can be used to determine degree of saturation; use a straightedge to connect the water temperature and DO.  Read the % saturation at the intersection of this line with the middle line.

Dissolved Oxygen % Saturation Nomogram

 ·         at 10 meters, with a temperature of 10°C, at surface pressure would hold (at 100% saturation) 10.92 mg, but you may find 15 mg/l.; compared to the surface it would be supersaturated, but at the depth and pressure it’s at, it may be less than saturated.

o       How can water be supersaturated?

§         intense photosynthesis

§         entrainment of air falling over a dam or spillway; high pressure of impact drives gases into solution; may lead to gas bubble disease, a problem in TVA dams

§         affects fish if subjected for a few hours to >115% saturation; bubbles form in tissues; emboli collect in gills causing anoxia and death; also affects cladocerans.  Other biota, e.g., crayfish and stoneflies are hardier.

So, too much oxygen is also a problem. But what really piqued my interest wad the statement of “intense photosynthesis” as a cause. That made me wonder if photosynthetic algae and diatoms would respond to increased temperature, so I went looking and found this paperProduction and fate of extracellular polymeric substances produced by benthic diatoms and bacteria: A laboratory study by Lundkvist et al.

And the graph showing how photosynthetic oxygen production changes with temperature, again hard data from observation:

Fig. 7. Dose-response curve on light intensity and photosynthesis measured as oxygen production by benthic algae population.

So, it seems to me that the ocean already has this worked out. If O2 can be supersaturated, and “intense photosynthesis” can be a cause, it would seem that warmer water that normally would get oxygen from air-sea interaction and entrainment might be supplemented from increased algal photosynthesis.

Besides, broad differences in oxygen content by latitude are well known:

Image: Wikipedia

And fish aren’t static entities…they move. So I suppose I’m not too worried about global warming shrinking fish. Overfishing is likely a far greater problem for reduced fish size, as are oxygen deprived dead zones due to fertilizer runoff as we’ve seen in the Gulf of Mexico:

Dead zones occur throughout the world and are caused primarily from excess fertilizer and animal manure run-off, as well as, emissions from sewage treatment plants, urban and suburban run-off, and air emissions from vehicles. The largest dead zone in the country occurs at the mouth of the Mississippi River in the Gulf of Mexico each spring. In past years, the dead zone (pictured in the satellite image as the red coastal areas around Texas, Louisiana, Mississippi, Alabama, and Florida) has encompassed some 5,000 square miles. –


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Chris B

The model would be better used as a video game App for your smart phone.

Sounds fishy to me 😉


Whilst individual modeled fish may shrink, the piscine collective will grow with more food available?


OH Boy! I smell grant money!


Fish always shrink when you cook ’em!

Tim Walker

It made me wonder why the warm seas of today have any large fish in them. Somebody better tell the big fish, ‘the models say they can’t grow that big in warm water’. Then there are the epocs of the past when the seas and oceans were warmer. The large fish fossils of those times must be fake.

overfishing has NOTHING to do with this. never before in the history of the earth has their been any warmer state where life has thirved!!!!!!
oh wait…


More and more, the papers in Nature Climate Change sound like conversations overheard in the patients day room of a mental hospital.


Did I see that dreaded term ‘computer modelling’ again?? They were then ‘surprised’ to see the fish shrinking (on the computer screen that is). Well that ‘proves’ it then, whatever the computer said must be true.

george e smith

That’s why Whale sharks and basking sharks are found mostly in the tropics, as also are the big marlins and tuna species. Can’t think of a fish that is particularly big found in the Arctic ocean.

Jeff D

We were just told that the human population will be decreasing by 300,000,000 due to CAGW. Looks like our demise will keep the balance to fish size in check and there will still be plenty to eat.


Sorry, but I don’t know where else to put this. Here’s a book review of “Prize Fight: The Race and the Rivalry to be the First in Science”.
Down And Dirty Science –
An exploration of the lengths some scientists will go to for credit, fame, and glory

It’s very interesting. I might just pick up the book. It describes cronyism and conflicts of interest in the world of science funding and publication. Just thought it would be interesting to people here.

Gary Hladik

We’re all supposed to drive compact cars instead of SUVs, right? So what’s wrong with compact fish? 🙂


But the unexpectedly big effect that climate change could have on body size suggests that we may be missing a big piece of the puzzle of understanding climate change effects in the ocean.
Not even a hint of suspicion that their model might reflect their lack of understanding of reality. PlayStation “scientist.”


“we may be missing a big piece of the puzzle”

Two fish quotes seem apropiate….first to the Darth Mega-warmists and Luke Mini-warmists on the Orwellian group think of Carbon climate forcing:
“We don’t know who discovered water….but we are pretty sure it wasn’t the fish”.
Second, from the seldom quotable Sarah Palin….here directed at ‘consensus science’
“Only dead fish go with the flow”.
Obi “No Warm Kanobi


Why are green bureaucrats and academics listed as separate groups?

Rick Bradford

Perhaps if today’s climate ‘consensus scientists’ had to use nomograms instead of fast computers, they would have more time to consider whether they were making complete idiots of themselves.


I think I’ve figured it out,
Someone changed their 24′ screen to a 22″ screen !!

David Falkner

Can I say that I think you missed the 100,000,000 will die from global warming story?


24″ ……. darn typo agian

Dr Burns

There’s also an evolutionary effect that makes fish grow smaller.


Personally, I think this is less likely due to too little oxygen and more likely due to the temperatures they kept the fish at along with their methodology. If you look, they kept the fish at the same temperatures all the time. Some fish don’t like to be at certain temperatures and 18 C is really at the upper limit of species tolerance here as evidenced by the highest mortality numbers and simple check of species preferred temperature; just because they can tolerate a temperature doesn’t mean they like it. One would think that these guys would likely seek cooler water if given the chance.
Something else to consider is that higher temperatures will do two things to your tank: 1.) It will reduce oxygen solubility. Given that they made sure that all tanks had at least 80% oxygen saturation in their outflows, this should not have been a concern. 2.) It will increase the metabolism of your inhabitants increasing the amount of biological waste they produce reducing your water quality. This does affect your tank life’s growth rates because less pristine/healthy water is less conducive to rapid growth. This would make your tank inhabitants smaller at higher temperatures. However, in the ocean, this would not be a problem because you do not have the closed environment issues that all tank environments suffer from.
Had they kept the higher temperature fish in a cleaner environement, they might have closed the growth deficit. This is why you raise aquarium fry in a bare bottom tank, feed them three times daily and vacuum that bottom once daily before doing a massive water change of at least 2/3 water volume to maximize your fry growth. It’s about as close as you can get to simulating a lake type environment in the home aquarium.
But that’s what my untutored hobbyist insticts tell me from looking at their methods. There are just some things they don’t say.


Anyway, small Nemo are REALLY cute !!!


george e smith says:
Can’t think of a fish that is particularly big found in the Arctic ocean.
Do you count whales as a fish ? 🙂
Down here, the whales choose WARMER northern waters in the winter and head back south during summer.
Must be just about time to watch a few heading south past Newcastle. Great sight they are too :-))


@Dr Burns says:
That report was going along nicely until….
“It took scientists a long time to reach a consensus on climate change, and acceptance of this phenomenon might require a long time, too,”
obligitory climate change mention !!!

Mike McMillan

My experience with fishermen is that the fish seem to grow larger as time goes by.

John F. Hultquist

The standing world record largemouth bass was caught in 1932. To this day it has not officially been broken. There is a sign to commemorate this massive fish. Here is a picture and the caption:
This story is from the State of Georgia, USA and the fish was caught in a slough off the Ocmulgee River in the south-central part of the State. It is a bit hard to believe that this water was either cool or oxygen rich. At least not on June 2nd – the date of the catch.
About other large bass and why they have not been certified as breaking the 1932 record:


Never was so little owed by so many to so few…..

old engineer

It appears that the academic culture has produced a generation of persons with science degrees to whom computer outputs are data. Does not bode well for the future of science or our world.

But people will be genetically modified to be smaller in the future to combat climate change so the shrinking fish will be proportionately the same. They’ll just have to make-up less batter.


Another “could” paper

Now ” Shoulda woulda coulda,” means I’m out of time
Coz “Shoulda woulda coulda”, can’t change your mind
And I wonder, wonder, wonder what I’m gonna do
“Shoulda woulda coulda” are the last words of a fool

~Beverley Hknight


Give a university professor a fish and he eats for a day.
Teach a university professor to make fishy alarmist predictions and he is on the gravy train for life!


Well of course. The people living in the Alps are also only half as tall as they should be because of the thinner air and less oxygen up there. Awesome, another climate prediction, the truth of which I can check within my life-time.

george e smith

“””””…..AndyG55 says:
September 30, 2012 at 9:01 pm
george e smith says:
Can’t think of a fish that is particularly big found in the Arctic ocean.
Do you count whales as a fish ? :-)…..”””””
WUWT is a science site; well no, it is actually THE science site, and Dr Judith Curry notwithstanding, I do consider myself to be a scientist. Actually my business cards, when I have had them, always said Engineer/Scientist.
And I can spell Botany, so even I know that whales are mammals, and not fish.
But it does terrify me to think how big whale sharks, and great whites would get, if they ever discovered how nice it is to live up in the arctic ocean; think of all the sea bears the GWs could eat; and all those Walrussters too.

Yet another painful-to-read “study” press release.
1. A finding is put forth.
2. It is derived from a model
3. The results are discussed as if they were data.
4. The authors express surprise that these findings might ‘exist’
5. The “data” is used to “predict” something, while the findings as declared as “important” for the understanding of how things “might” change with “a warming climate”
Are there any computer-savvy fellers out there that could write a model to model a climate change press release? Then we could be surprised every day! We could find importance in a myriad of suggested problems, from what Mr. Snofgrass had for supper or whether his Ice cream melts more quickly in August.
The cumbersentence below is a perfect example of word-count padding and precious little else.
“But the unexpectedly big effect that climate change could have on body size suggests that we may be missing a big piece of the puzzle of understanding climate change effects in the ocean.”
You sure are missing a big piece of something! I feel ill.

george e smith

“””””…..John F. Hultquist says:
September 30, 2012 at 9:27 pm
The standing world record largemouth bass was caught in 1932. To this day it has not officially been broken. There is a sign to commemorate this massive fish. Here is a picture and the caption:
This story is from the State of Georgia, USA and the fish was caught in a slough off the Ocmulgee River in the south-central part of the State. It is a bit hard to believe that this water was either cool or oxygen rich. At least not on June 2nd – the date of the catch.
About other large bass and why they have not been certified as breaking the 1932 record:…..”””””
Well the only reason a larger record LMB hasn’t been caught, is that Ray Scott decreed that only registered paying members of B.A.S.S were aloud to be recognized as having caught a record Large Mouth Bass, and preferrably in the BASSMaster’s Classic; and furthermore, flyrod catches were not eligible to be recognized as catching a large LMB.
Other than that, California has plenty of large LMBs specially around San Diego.

george e smith

“””””…..SteveC says:
September 30, 2012 at 7:52 pm
Fish always shrink when you cook ‘em!…..”””””
And when you eat ’em.

“We were surprised to see such a large decrease in fish size”, in our computer. This saved us days or weeks of cold and wet work at sea actually looking at what was happening in reality, It also avoids the danger caused by us being unable to manipulate field observations as we would like to receive ongoing funding.


This is another shingle for the WUWT Science Paper Wall of Shame.

Steve Tabor

Quick! Somebody send this to the Warmlist before it disappears!




That’s it. I will from now on use Starcraft 2 to do any research with. Apparently it’s valid to do so and it’s science.


News flash! Alien life confirmed! Aliens exist and come to Earth!
Proof: the game Half Life.


tried posting this on the climate news thread, but the comment failed to go thru. it’s more relevant here anyway:
1 Oct: The Conversation: Guy Pearse: What about your carbon pawprint?
(The Conversation is funded by CSIRO, Melbourne, Monash, RMIT, UTS, UWA, Canberra, CDU, Deakin, Flinders, Griffith, La Trobe, Murdoch, QUT, Swinburne, UniSA, UTAS, UWS and VU)
(Guy Pearse receives funding from UQ for his fellowship.)
The ecological consequences of pets are significant when you consider the land needed to produce the energy and resources required for a large dog are equivalent to that of a four-wheel drive Land Rover; a medium dog is equivalent­ to a VW Golf. Or so say Brenda and Robert Vale, authors of the provocatively titled Time to Eat the Dog. Among many reason­able observations they note that we face real problems “when everyone starts to have a big car, big house, big family and a big dog”…
Guy Pearse
A former political adviser, lobbyist and speechwriter, Guy grew up in Townsville and was educated at James Cook University (BA Hons), Harvard (MPP), and the ANU (PhD). He was a member of the Liberal Party for 19 years and worked for various Liberal politicians including former environment minister, Robert Hill. He has been government relations and policy adviser for numerous industries and environmental organisations, and a consultant to the Australian Greenhouse Office. While studying at the Kennedy School of Government and Harvard Business School in the mid 1990s, Pearse also worked on the advance staff of then US Vice President, Al Gore…
His thesis became the basis for the “Greenhouse Mafia” episode of ABC’s Four Corners in February 2006…
australia’s partly taxpayer-funded SBS knows a good story when it sees one:
1 Oct: SBS: What about your ‘carbon pawprint?’
Guy Pearse from the University of Queensland asks.


OMG, does this mean mermaids will have smaller titties

son of mulder

I bet if one did a profile of fish size by latitude the biggest fish would live in warmer water. There is more food, more energy to be absorbed. Am I right?


where i am the bigger fish are in warmer water.
When i go on fishing trips to the tropics the size of the fish is not tiny. what a load of crap this is embarrassing. If they have degrees they need stripping.


And I was under the impression that increase in Temperature would increase the size of fish
Rypel, A.L. 2009. Climate–growth relationships for largemouth bass (Micropterus salmoides) across three southeastern USA states. Ecology of Freshwater Fish, 18, 620–628.

F. Ross

So… great white and tiger sharks will become like minnow size? What’s not to like?