Study first to explore combined impacts of fishing and ocean warming on fish populations

Warming and fishing affecting survival of small fish


Research News


The combined effect of rapid ocean warming and the practice of targeting big fish is affecting the viability of wild populations and global fish stock says new research by the University of Melbourne and the University of Tasmania.

Unlike earlier studies that traditionally considered fishing and climate in isolation, the research found that ocean warming and fishing combined to impact on fish recruitment, and that this took four generations to manifest.

“We found a strong decline in recruitment (the process of getting new young fish into a population) in all populations that had been exposed to warming, and this effect was highest where all the largest individuals were fished out,” said lead author and PhD candidate, Henry Wootton, from the University of Melbourne.

Mr Wootton and his team established 18 independent populations of fish in their lab and exposed these to either control or elevated temperatures, and to one of three fisheries harvest regimes. They then followed the fate of each population for seven generations, which equates to nearly three years of lab time.

“Our study is the first to experimentally explore the joint impact of fishing and ocean warming on fish populations,” Mr Wootton said.

The research is released today in the journal PNAS with researchers saying the solution is less selective fishing, which will help ensure balanced sex ratios and the persistence of valuable bigger females.

Co-author Dr John Morrongiello said: “Wild fisheries provide food for billions of people worldwide, particularly in our Pacific region where fish is the major source of animal-based protein. Past fishing practices have caused spectacular fishery crashes and so it is important that we adopt management approaches that will ensure our oceans continue to maintain sustainable fisheries.”

He added: “Sustainable fisheries management in the face of rapid environmental change is a real challenge. Getting it right will not only provide food and economic security for millions of people worldwide but will also help protect our ocean’s valuable biodiversity for generations to come.”

Dr Asta Audzijonyte, co-author from University of Tasmania and Pew Fellow in Marine Conservation, said it was surprising to find such strong and delayed negative impact of warming on small fish survival.

“We still do not fully understand why this happens, but our findings clearly show that protecting fish size diversity and large fish can increase their resilience to climate change. While reversing climate change is hard, restoring and protecting fish size diversity is one thing that we certainly can do, and we need to do it fast,” she said.

Dr Audzijonyte added: “Most experimental research on climate change impacts is done on relatively short timescales, where fish are studied for two or three generations at best. We found that strong negative impacts of warming only became apparent after four generations. This suggests that we might be underestimating the possible impacts of climate change on some fisheries stocks.”


From EurekAlert!

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April 28, 2021 2:24 am

The only place where oceans are warming is in models. Hard to get the fish into the models!

Paul C
Reply to  RickWill
April 28, 2021 2:45 am

However, due to ocean currents, and oscillations, localised warming can take place. This can affect the zones in which some fish species proliferate in different years, so some of their research may actually be useful.
At least they tried to perform experiments. Though, rather than generational effect, I think it more likely that the reduced viability of fish they observed would be due to biological contamination (bacteria/algae/fungus) which I would expect to grow more concentrated at raised temperatures over the three year life of the experiment.

Reply to  RickWill
April 28, 2021 4:05 am

I wonder which country has the largest fleet of super trawlers. Which country is the greatest emitter of greenhouse gases?

Reply to  Scissor
April 28, 2021 6:02 am

CO2 is welcome…nothing can be done about H2O. 25,000 barrels of DDT have been discovered 3000 feet down between Catalina Island and the California coast – that’s pollution, no? Marine life has high cancer rate.

Reply to  Anti_griff
April 28, 2021 8:49 am

All statements I saw said suspected. No one has actually gone down to test any contents.

But: If it is DDT, and still good, it should be recovered and taken to those areas of the US and the world were it can save millions of lives and prevent untold suffering from the diseases spread by the insects DDT k!lls.

BTW. When I was a child, living in tidewater Virginia adjacent to Langley AFB, the bug spraying USAF planes were stationed at Langley. In the spring, since the area was home to MANY high ranking military of the AF, Navy and Army, they would spray the area where we lived. Usually in the afternoon, early evening when it was very calm. They would fly so low that at times they hit the tops of the tallest trees. For the 3 or so years the panes were based at Langley, the mosquito problem was miniscule. After they were transferred to, I was told, Egypt, we had to live with NATURE and the regular spring to summer mosquito infestations, greatly limiting our outdoor fun in the evenings.

I was outside MANY times when they sprayed, felt the mist, am 65 now and as far as I can tell have had no ill effects from those applications of DDT.

Rick C
Reply to  Drake
April 28, 2021 9:57 am

No one has actually gone down to test any contents.”

What contents? Those barrels are 3,000 feet down and would have been crushed under 1350 psi when they were dumped decades ago. There might be traces of their contents left, but the pollution disaster occurred long ago and apparently went unnoticed.

Michael S. Kelly
Reply to  Rick C
April 28, 2021 12:15 pm

“…and apparently went unnoticed.”

Probably because, even if the channel between the island and coast were closed at both ends (making it the Lake – as opposed to Gulf – of Santa Catalina), 25,000 barrels of DDT would constitute around 7 parts per billion by volume. And it isn’t closed…

Reply to  Drake
April 28, 2021 3:17 pm

My dad and his 5 siblings grew up on a dairy. During summer they would close all the doors of the milk barn and fog it with DDT, everyday!
They are all now in their 80’s and their father lived to 85 and died of heart disease.

I believe there were impacts from DDT use but are almost always overstated. Todays society doesn’t under how to value costs and benefits.

But I am confident in stating thet DDT saved more lives than the COVID-19 vaccine ever will!

Capn Mike
Reply to  Drake
April 28, 2021 5:57 pm

Exactly my story. I’m 73 and still kickin’

Richard Page
Reply to  Anti_griff
April 28, 2021 10:59 am

DDT has a far lower rate of cancer causation than coffee. So yes, dumping any foreign substance at sea can be considered pollution. Harmful pollution though? Probably not.

Reply to  RickWill
April 28, 2021 4:48 am

This report smells fishy. As the oceans rise and warm, more corals with grow and more fish will grow because the oceans will be larger. Bottom line: global warming is making the oceans great again.

Paul C
April 28, 2021 2:25 am

So their conclusions do support marine conservation/reserve areas where no commercial fishing effort takes place, and the big old fish produce thousands of eggs to spread future generations into surrounding seas. Pity the EU supports the Dutch pulse trawlers (illegal under the Common Fisheries Policy, but given exemptions) which, similar to dynamite fishing, leaves a lifeless wasteland behind. The fishermen around here seem to know what the researchers conclude. That the big old fish (particularly females) are key to producing future generations, so release them and you can catch their offspring in later years. Same with lobsters.

Jay Willis
Reply to  Paul C
April 28, 2021 2:43 am

Yes I agree the EU fisheries policy is a disgrace. The amazing thing is that everybody knows it’s a disgrace but are powerless to change it. One good reason for Brexit.

The larger older fish also swim further to deposit their eggs far from their usual feeding areas, so as to give their offspring a size advantage. Iceland run a well managed fishery, so I buy my cod from there.

Paul C
Reply to  Jay Willis
April 28, 2021 3:10 am

The pillaging of UK waters by EU boats towards the end of the transition period was a particularly bad example of the CFP in operation. The withdrawal agreement is extremely poor in not taking back full control of British waters. The EU destroyed the majority of the British fishing fleet, though the British government were probably best described as incompetent rather than malicious in handling of EU rules and in the Icelandic fishing negotiations in which the UK fleet could have continued with its historic catch.
At least we now know that the EU is open to altering rules which affect elements agreed in the withdrawal agreement, as it has already done that itself. A simple rule change requiring all fish caught in British waters to be landed in British ports would allow some scrutiny of the illegal fishing being done by EU boats. Simple penalty for non-compliance – boat excluded entirely from fishing in British waters, with seizure as the appropriate penalty. No chance with the current government, but we can always hope for a better one in the future.

Capn Mike
Reply to  Paul C
April 28, 2021 6:01 pm

I’ve observed “no take” zones in the Caribbean and The Bahamas. It took a while to get the locals to agree to it, but man, the take in the areas surrounding those zones skyrocketed. The locals are now on board.

April 28, 2021 2:47 am

Well yes – fish will be more resilient to climate change if they still – umm – exist?

Ron Long
April 28, 2021 2:59 am

You could substitute “polar bears” for fish in this fishy story. Forty years ago it was recognized that polar bear populations were in dramatic decline, so the Greenies adopted the polar bear as a marker for CAGW. Then hunting polar bears was halted and, presto chango, polar bear populations increased dramatically (h/t Dr. Susan). So for the same results for fish change the rules and support more fish farming instead of over-fishing wild stocks.

M Courtney
April 28, 2021 3:12 am

“We still do not fully understand why this happens, but our findings clearly show that protecting fish size diversity and large fish can increase their resilience to climate change. While reversing climate change is hard, restoring and protecting fish size diversity is one thing that we certainly can do, and we need to do it fast,” she said.

You know this makes exactly as much sense, probably for the same reason, if you replace “fish” with “the economy”.

OK the grammar is off but the meaning is the same.

Peta of Newark
April 28, 2021 3:12 am

Quote:this effect was highest where all the largest individuals were fished out,

Errr, how to put this delicately….

Don’t you need ‘adults’ to make babies?

Reply to  Peta of Newark
April 28, 2021 3:45 am

Thanks, Peta of Newark. That made me smile.


Reply to  Peta of Newark
April 28, 2021 5:50 am

Well, according to our enlightened betters, the idea that only women can get pregnant is outdated and anybody who says otherwise is evil and must be silenced at all costs. What other teachings in biology have we gotten wrong after all these years? The BBC told schoolchildren that there are over 100 genders, so obviously our thinking on that has been wrong for thousands of years. Since the new biology shows that you don’t need to be a woman to have a baby, who is to say that only adults can make babies? In fact, how dare you say only adults can make babies!

(/end sarcasm)

April 28, 2021 3:17 am

There was a very significant rise at Greenland’s east coast in cod fishing due to warmer water since about  1920 (Carruthers, 1941) Fig:,  after the start of  Early Arctic Warming in winter 1918/19. The trend change in the early 1930s is remarkable as well.

April 28, 2021 3:27 am

We then explored whether our observed recruitment decline could be explained by changes in egg size, early egg and larval survival, population sex ratio, and developmental costs.

They didn’t check to see how many fish were transgender, did they. There’s probably a model for that.

Climate believer
April 28, 2021 4:08 am

Heat (however slight) = bad.

According to recent Australian fish stocks reports I can’t see a problem. Over 90% of their stock is categorised as sustainable, and they have recovery management plans for other depleting or depleted stock in place.

Looks like a very well managed system despite their boiling seas.

Pamela Matlack-Klein
April 28, 2021 4:10 am

Fish have been around for a very long time. And we can be fairly confident that the warming patterns these folks are claiming have probably also been happening for a very long time. This is like the rapid SL rise we are told is happening, also something the planet has experienced in the past.

Over-fishing, however is new. And not a good thing. But it is also something that can be reversed as in the case of the polly bears and whales. Stop killing them and the populations will recover.

April 28, 2021 4:45 am

In real life fish are not bound to a tank. Fish would just move to colder areas, of which there is plenty.

Reply to  Rudi
April 28, 2021 10:58 pm

Rudi, as a pond owner & fisherman I concur 100 percent. Sorry that I didn’t see your comment before I made mine.

Coach Springer
April 28, 2021 5:08 am

Curious about the control group(s). Where did they find oceans that had not warmed and those that had warmed rapidly for 4 generations? Those that were over fished and those that were not? Those that were both not overfished and not warmed, those that were overfished and not warmed, …

Tim Gorman
April 28, 2021 5:33 am

It’s called “catch and release” by sport fishermen. Been known about for more than a generation. It applies in small ponds and large lakes. There is no doubt it also applies in the ocean as well.

Nothing to do with climate change.

April 28, 2021 5:36 am

I suppose that it takes a particular kind of politically correct thought to label reproduction as recruitment.
Perhaps that is why they call the journal PNAS?

Joseph Zorzin
Reply to  dk_
April 28, 2021 5:42 am

It sounds more sciencey.

Reply to  Joseph Zorzin
April 28, 2021 5:58 am

More like someone spent too much time in HR and gender studies and not enough in studying biology. More political “science,” studying new ways to regulate food production, when arbitrary regulation, based on feelings, is what they admit has caused their perceived problem.

jim hogg
Reply to  dk_
April 28, 2021 6:25 am

Reproduction and recruitment rates can differ for many reasons. In the case of lobsters for example, the proportion of the larvae total (resulting from reproduction) that survive (recruitment) depends on many factors, including the pelagic fish population that feed on them when they’re in the water column, and also on the benthic substrate they find themselves in during the next stage.

Joao Martins
April 28, 2021 6:02 am

Mr Wootton said:

“Our study is the first to experimentally explore the joint impact of fishing and ocean warming on fish populations”

Most certainly, he is candidate to a PhD in Expertology:

1. He says he has studied the impact of fishing, but the only thing he has done is take some fish out of his aquarium, not the “real thing” (captures in fishing boats, fish schools moving everywhere, etc.)

2. He sya he has studied the the impact of ocean warming, but what he did was lookat an aquarium with thermostats, not at the “real thing” (the ocean).

Mr Wootton, after finishing his work and being granted his doctoral degree, will know a lot of useless anecdotal information about aquaria and nothing about the real life outside, in the oceans, in the fishing boats.

Reply to  Joao Martins
April 28, 2021 8:13 am


This more of a study of preserving the fisheries than effects of Gorebull warming.

The fish will move if they are not caught! Duhhhh…

Too many examples of over harvesting, just like the bears, and the jury is still out on a few species… our Gulf red drum in the Panhandle have still not recovered twenty years after we stopped the slaughter of the spawning adults, and I have not seen a lotta cod in the market.

About the only time I like to see the word “sustainable” is for game and fish management. Without great management, you would not be able to get a lobster today. And Alaska has good, fair management practices. About the only seafood product here in Florida that depends more on the ecology than the netters is shrimp. They only live a few years and a few netting restrictions do not significantly affect the supply, considering most shrimp in the store is raised on a farm outside the U S . Being spoiled, I get mine right off the dock in the bayou.

Gums sends…

Joao Martins
April 28, 2021 6:10 am

“The combined effect of rapid ocean warming…”

A rapid warming of fish in water usually ends in fish soup. Some people prefer fish after a rapid warming in a pan with oil.

April 28, 2021 7:02 am

How large are those Chinese fishing fleets again? Does a doubling of the Chinese fishing fleet and resupply tankers matter to Mr. Model?

April 28, 2021 7:12 am

Fishing and ocean warming?
Study the effects of two entirely different things at the same time?
Seems like a poor approach to me.

Sweet Old Bob
April 28, 2021 9:40 am

“the research found that ocean warming and fishing combined to impact on fish recruitment, and that this took four generations to manifest. ”

“fish recruitment ” just another acadumbic bit of word twisting .

What kind of rewards do they offer to entice “recruits ” ?
Do the “recruits ” have to pass a physical exam ?

Are the “recruits” smarter than these authors ?

Where is the bootcamp ?

How many weeks does it last ?

Is there a graduation ceremony ?

H. D. Hoese
April 28, 2021 9:52 am

Seems as if warming may be good, turns out 3X as many snapper as models predicted. Those catching them sort of knew that decades ago. They do put in the error bars.

Stunz, G. W., and 17 other authors 2021. Estimating the Absolute Abundance of Age-2+ Red Snapper (Lutjanus campechanus) in the U.S. Gulf of Mexico. Mississippi-Alabama Sea Grant Consortium, NOAA Sea Grant. 439 pages.

Also North Atlantic, among others, not so bad. “While biomass was reduced to about 95 percent of optimal levels in the 2000s, biomass of the average stock is now greater than MSY-related levels and is increasing.” Melnychuk M. C. et al., 2020. Global trends in status and management of assessed stocks: achieving sustainable fisheries through effective management. FAO Fisheries and Aquaculture Technical Paper No. 665.

April 28, 2021 11:07 am

Well, knowledge is slowly increasing but still woefully incomplete IMJ. Research continues, in the past few years a Russian ship has spent weeks in the North Pacific in a multinational effort that observes and sometimes catches fish. (They’ve had surprises, such as Pink salmon not being where they expected one year. Durn critters refuse to report for human census.)

There are many factors, populations have always fluctuated. For example, tribal people on the Seward Peninsula of AK were in trouble for food over a century ago when salmon population plummeted at the same time as caribou herds moved away (as they occasionally do), and over-harvesting reduced whale population (a ‘tragedy of the commons situation – when everyone is responsible no one takes responsibility).

Fish populations move around with ocean water temperature, for example the Pacific Decadal Oscillation – a good year for salmon near AK is a poor year near OR, in between BC sees variation with specific variety of salmon. (I doubt the fish migrate a great distance after getting to their destination to find more food, survival rate may be higher in certain water, although fish from the Columbia have been tracked heading north of Vancouver Island which is a long journey.)

Precipitation is key, as it affects river flow . Larger salmon are considered more capable of leaping up through tough water – shown on the Fraser after a huge rock slide created a 15 foot high waterfall, but some tributaries produce tougher variants of small salmon varieties (one in the Caribou was noteworthy.) Eco-activists are of varying mind as to whether or not warmer means less precipitation – I point to tropical jungles versus north Africa in challenging the claim that more evaporation will stay in the air.

Reply to  Keith Sketchley
April 28, 2021 11:27 am

There’s the factor of fish waiting until water is cooler before heading upstream, observed with the might Fraser. (They are reported to return to the Strait of Georgia if they find water warmer than they want, I expect that is their way of knowing that water flows may be low, some people also are concerned that they are not as strong in warm water. )

Salmon returning to the small Goldstream river will actually move on to try to find a better river, amount of time they wait varies with type of salmon. Of course moving on takes more energy thus survival rate is probably lower.

Herring switch waterways if there seems to be a crowd headed toward the estuary of their birth.

Salmon and other migrating fish such as the Steelhead and Cutthroat versions of trout change from fresh to salty water then back again – they stooge in the Strait of Georgia for a couple of weeks as the water there is less salty due river outflow mixing with ocean water.

Gordon A. Dressler
April 28, 2021 1:04 pm

We still do not fully understand why this happens, but our findings clearly show that protecting fish size diversity and large fish can increase their resilience to climate change.”

 A billion years of evolution over climate-induced wide variations in ocean physical and chemical parameters just might have something to do with it.

April 28, 2021 2:44 pm

Every year, except 2021 :-(, I spend days fishing for tuna off the California and Mexico coasts. I have learned that tuna follow the water temperature instead of dying in water either too hot or too cold. Funny how that works.

Reply to  markl
April 28, 2021 6:21 pm

Thanks for that info, they are not stupid for their lives.

There are anecdotes of fish varieties normally only seen at the Columbia and south showing up at the Strait of Juan de Fuca when water near the coast is warmer than usual (the ‘Blob’ phenomenon).

Fish eat smaller creatures like shrimp, herring get eaten by salmon. So the movement phenomenon may come from what suits plankton at the bottom of the food chain. Such factors may motivate shifts in location of population, IIRC some small creatures moved away from the coast of Antarctica, eco-ignorants flapped that the species was in danger but they were too ignorant/lazy to look around.

Other critters move around – Transient Killer Whales come and go around Vancouver Island, whereas the Southern Resident Killer Whales do not move as much (though have been seen off California and Alaska).

April 28, 2021 10:05 pm

In the ocean, fish can move deeper when temps warm to the point where they aren’t comfortable. Ponds, too — I own one. But tanks in a lab not so much. Sounds bogus to me, just another attempt to gain grant money & status by running with the CAGW narrative.

Tim Gorman
Reply to  anthropic
April 29, 2021 2:21 pm

You didn’t *really* expect these academics with no real world experience to know what you know merely by living in the real world?

Matthew Sykes
April 29, 2021 12:52 am

Fish like it warm. Fish move into British waters in the summer.

April 29, 2021 7:02 am

No-one asked the obvious question do the hotter global warmed fish take less energy to cook and therefore help save the planet 🙂

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