Oceans Get Hotter, Fish Shrink

It could soon be much, much harder to find Nemo according to a new study in Nature about how fish size is affected by changes in temperature, lower oxygen content and other ocean biogeochemical properties (including rising acidification). Specifically, fish could shrink in size by as much as 14 to 20 percent from now until 2050 due to the warming of the ocean.

Indeed, a 2011 study already showed that the size of haddock in the North Sea is declining.

The Ocean’s Fish Are Getting Smaller and Smaller

Researchers from the University of British Columbia used computer modeling to study the effects of changes in the ocean and climate systems on 600 species of fish. The study’s lead author, William Cheung, emphasized that he and his colleagues were “surprised to see such a large decrease in fish size.” Fish in the tropics, who are smaller-bodied, are especially affected by warmer ocean temperatures and will migrate to regions that are now temperate or even to polar ones.

Cheung’s co-author, Daniel Pauly, explained why warmer ocean temperatures can lead to smaller fish:

It’s a constant challenge for fish to get enough oxygen from water to grow, and the situation gets worse as fish get bigger. 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.

In warmer waters, the metabolic rate of fish increases so they need more oxygen. But, because warm water holds less oxygen, the fishes’ growth will be limited.

A University of York professor, Callum Roberts, who was not a participant in the study, said that Cheung’s and Pauly’s findings were the “most comprehensive to date.” He also suggested that fish size could shrink even more, with deep ramifications not only for marine ecosystems but also for global food supplies as currently “one billion people rely on fish for primary animal protein and that is going to increase, especially in developing countries” and as overfishing is already reducing the amount of fish.

Climate change is already proving detrimental to marine life, it goes without saying. Roberts also points out that, with overall ocean temperature higher, the warmer waters at the surface mix less with the colder ones below. The result is fewer nutrients for fish as the colder waters contain most of the nutrients. “We are already seeing some evidence of this, as oceanic ‘deserts’ are getting larger,” he tells the Guardian.

Sea Levels To Keep Rising Due to Global Warming

If shrinking fish are not reason enough to cut greenhouse gas emissions, another just-published study offers more evidence to do so. According to this study, an ”irreversible warming” of earth has been “triggered” by greenhouse gases and will lead to sea levels rising for thousands of years.

European scientists used computer modeling to predict changes in sea levels over millennia as the result of reductions in land ice in Greenland and Antarctica and the warming of the oceans. One researcher, Professor Philippe Huybrechts, made the dire statement that, should climate change be “severe and long-lasting,” it is not only that the oceans will heat up and fish will shrink but “all ice will eventually melt.”

Get ready for a hotter future world with tinier and tinier fish, unless we do even more to cut down on greenhouse gases.


Related Care2 Coverage

6 Things You Need To Know About the Ocean: Care2 Exclusive With Ocean Pioneers

5 Reasons There Will Soon Be No More Fish in Our Seas

Skin Cancer Found in Wild Fish for First Time


Photo by Marko D Photography


Loesje vB
Loesje Najoan3 years ago

Kristina Chew you are right, I saw it on tv due to climate change and global warming oceans get hotter and Fish Shrink said a fisherman in India. So sad.....let's do something for our terrifying planet!

Carrie Anne Brown

thanks for sharing :)

Katherine Wright
Katherine Wright3 years ago

I'm not the least bit surprised to read this. Humans have managed to decimate every species, destroy our environment and we don't seem to give a damn.

Polar bears and penguins are losing their habitats at record rates, mountain lions have to find shelter in suburbia and being shot for it, humans want to cull badgers, poison prairie dogs, kill rhinos for their horns, eat shark fin soup, overfish our oceans, kill our bears, our wolves, our community cats, the dolphins, whales, raccoons, turtles, slaughter the seals, pit bulls, elephants, tigers, lions, chimps and the list goes on and on.

When will the destruction cease??? My guess is when it's too late, if it's not too late already.
This is shameful and scares the $h!t out of me. And it should scare everyone.....

Cheryl I.
Past Member 3 years ago

We are destroying our planet and it seems like we wont stop until there is nothing left.

Jennifer C.
Past Member 3 years ago


Diane L.
Diane L.3 years ago

Whoops, sticky keyboard. I meant read your "Marine Fishes" handbook.

Diane L.
Diane L.3 years ago

"Instead of seeing Damselfish "clown" fish getting up to 3", we may soon be seeing 2.25"-2.5" as the upper length in the wild instead...."..........Thaddeus, sounds like you know your fish. However, I "got" the writer's point, just don't agree with the use of the species and the analogy of "Nemo" to demonstrate the effects of global warming on reef fish in particular, nor is the TITLE appropriate or accurate. The "Nemo" species CAN grow to 3" in the wild, but rarely does. Read your Marne Fishes handbook, the one by Scott Michael, considered "The Bible". I have a clown species, a "Maroon Clown" which, according to Michael's book CAN get to 6 - 6-1/2" in ideal conditions. Mine is over 7" and the water is warmer than I'd like but it's been very warm here and the heater is not even plugged in and I've had to actually add ice cubes on hotter days to keep things cooler. I have no additional aeration besides the power filter and one additional pump at the opposite end of the aquarium.

Carla van der Meer

With everything we know, why are we not doing more to prevent further damage and to try and repair what we have already done?

Diane L.
Diane L.3 years ago

Ken G., unless the writer is so narrow-minded she can't stand being criticized and had my post deleted, it's a mystery. I said nothing against the C.O.C., just found fault with the facts as written. Obviously my comment showed up or our resident expert here, James K. who so eloquently called me names, strictly against Care.2's C.O.C. wouldn't have read what I'd said.

"Indeed, a 2011 study already showed that the size of haddock in the North Sea is declining." ....you probably have a good point. We used to routinely be able to go salmon fishing and bag our limit in a few hours, often catching 20- 30 lbers. These days, if one can afford to go in the first place, they're lucky to catch ONE, and if they do, it's probably less than 10 lbs. The fish aren't becoming smaller, just fewer there to be caught and those that are caught are not as mature as before WHEN caught.

Diane L.
Diane L.3 years ago

James, you are out of line and your post is being flagged for name-calling. I didn't just "once have a fish tank". I've had tropical fish for decades and have done my research on the topic. May I suggest you do the same before going off criticizing an experienced "hobbyist" and the writer here is not one. So you "scuba dived" yet assume I never have? The writer lists no education or experience as a marine biologist or even as someone who has had a "fish tank", so the wording used is misleading and meant to "shock" readers, nothing more. "Oscellaris Anemonefish" (Nemo) is not shrinking in size. The numbers of specimens could be "shrinking" due to loss of habitat, but warmer waters is not a factor in "fish size" in that regard.