Blog & PodcastDealing with the Climate Crisis

Anthony Day helps you plan a sustainable future with expert guests and reports on green technologies from across a warming world.

Do you like fish?  I’ve just been reading a book which made me think very hard about whether I wanted to eat any fish ever again. And I'm certainly no vegetarian and have no plans to become one. The book I read is called What a Fish Knows by Jonathan Balcombe. I decided to put the whole thing in context so I’ve studied the topic from Greenpeace, Oceana, WWF, Global Fishing Watch and Fishcount to the UN Food and Agriculture Organisation, academic articles, press reports and the latest book by Sir David Attenborough.

3-Second Memory

There’s a popular belief that goldfish, and maybe all fish, have a memory span of just 3 seconds. Jonathan Balcombe cites research studies which have shown that fish can remember not just for minutes, but in many cases for months or years. Fish don't have eyelids, eyebrows or facial muscles so they have no means of making expressions which could betray emotions. They can make noises, but only when they’re in water. So it’s easy to think that they are pretty low-grade organisms with little awareness of the environment around them. Far from the truth. Studies have demonstrated their intelligence in various different ways. In the lab it's been shown that they can be conditioned and trained like rats or birds. For a food reward they will jump through hoops or find their way out of a maze, and they can remember the route months later. Fish can remember pain and fish are known to be “hook shy” which means that once they have been caught by an angler they will remember not to be caught again. 


In the wild, the Frill-fin goby memorises a map of the sea bed at high tide so it can jump from rock pool to rock pool when the tide goes out. Some fish are pretty close to being tool users. They will use blasts of water from their gills to blow the sand away from the clams they are looking for. Then they will pick up the clams and smash them against rocks in order to get to the animal inside. Archerfish will knock insects out of trees above the water with a well-aimed jet from their mouths. Tiger fish have been seen to capture birds skimming across the water by leaping up and snatching them. No mean feat when the refractive index of the water makes it difficult to determine the exact position of the bird, and it has to be done in a split second.


Then there is the symbiosis between fish, such as between cleaner fish and their very much larger clients. Cleaners may clean the skin or may swim into the larger fish’s mouth to clean between its teeth on the clear understanding that it will be in no danger. The relationship is beneficial to both. The cleaner gets a meal and the client fish is relieved of parasites and other debris. The cleaners are also smart enough to discriminate between visiting clients and their regulars. They will give priority to fish passing through because they know that if they don’t, the opportunity will be lost, while their regulars will be back again soon. 

The grouper, a species of large fish which includes sea bass, has been observed to hunt in some cases with the moray eel. With different speeds and sizes they make a powerful  hunting combination and they share the prey between them. Not the behaviour of  low-grade organisms with little awareness of their environment. Fish can remember, they can learn, they can solve problems, they experience pain.

Let’s look now at the big picture. 

World population is growing and in China and India the per capita consumption of fish is growing but the quantity taken from the sea has peaked. According to the FAO the global catch of wild fish has averaged 90m tonnes over the seven years to 2017, the latest data available. This despite the immense technical resources invested in the fishing industry, with global subsidies estimated at $35 billion.

Factory Ships

There are some 23,000 factory ships larger than 100 tons supported by sonar, satellites, GPS, depth sensors, ocean floor maps, spotter planes and helicopters. Some use mile-long purse seine nets to entrap complete shoals. Others trail lines up to 60 miles long with thousands of baited hooks. Bottom trawlers rake everything from the sea bed for shrimps, cockles or clams, but destroying the habitat for everything else. The old adage, “There’s plenty more fish in the sea,” no longer rings true. The limit to fishing is not how many we can catch but how many are left to be taken.


A crucial problem is bycatch. Bycatch is loosely defined so it’s difficult to determine whether the proportion is rising or falling. Bycatch is the proportion of the catch which contains species which were not targeted. This may include unwanted fish but also includes turtles, seabirds, whales and living corals which get tangled up in the fishing gear. Much of this is dumped, dead, back into the sea. Global Fishing Watch reports that 100,000 albatross are killed by the fishing industry each year and 15 of 22 species are facing extinction. 

The FAO suggests that the proportion of bycatch is falling, and if it is calculated as solely the tonnage discarded that may be true. However unwanted species are now being retained to be made into fish meal for fertiliser or animal food. If we add this to the quantity dumped the proportion of the total catch which is bycatch is 40%. The consequence of this is to unbalance the food chain and the ecosystem within the ocean. It’s recognised that if too many large fish are taken then there are fewer to breed the next generation. If too many small fish are taken by mistake there are fewer to become the next generation or to be food for the next generation and fisheries collapse.

See the link below to a WWF paper on defining bycatch.


In a press release last week announcing its UK Fisheries Audit report Oceana said that 6 out of 10 UK fish were being overfished or were in a “critical” state. Prof. Mark Flaherty of the Department of Geography, University of Victoria, Canada invites contributions for a special issue on aquaculture of the Sustainability journal, to be published later this year. He says,

“There is compelling evidence that wild harvests of fish, crustaceans and other aquatic species will not be able to keep up with the demands of a global population that is expected to reach 9.7 billion by 2050. Around 90% of the world’s stocks are now fully fished or overfished, while habitat degradation and human-induced climate change are placing increased stress on all aquatic life. Higher incomes and greater consumer awareness of the nutritional benefits of aquatic products are pushing global per capita consumption to record highs.


“It is widely acknowledged that sustainable aquaculture development is critical for meeting global food needs… This Special Issue aims to investigate the contribution of aquaculture to community development, and the challenges associated with local resource use, from a variety of perspectives.”

Marine Protected Areas

In his book, A Life on Our Planet, Sir David Attenborough’s theme is rewilding, restoring nature to restore the ecological balance, to bring all forms of harvesting, including fishing, back to sustainable levels. Among other things this will significantly reduce excess CO2 in the atmosphere. He quotes Professor Callum Roberts. You may remember him, he spoke to the Sustainable Futures Report in October 2015 about Marine Protected Areas. (MPAs) Attenborough describes these as areas of the oceans where fishing is generally not allowed. The fish can develop unhindered and recreate a natural balance. Populations grow and begin to spread outside the protected area where fishing is permitted. The stocks are never totally depleted because the fish can breed in these protected areas. I say that fishing is generally not allowed in MPAs because I find that the latest campaign from Greenpeace is to urge to UK government to keep super-trawlers out of its MPAs. It seems to defeat the whole object of a protected area if super trawlers are freely allowed to operate within it. Attenborough believes that a whole third of the oceans should be designated as MPAs, either the open oceans or maybe the coastal regions. These coastal areas would include mangroves and kelp forests both of which can act as nurseries for small fish and both of which sequester carbon. It's a benign sort of geo-engineering. 


While I'm on the topic of geo-engineering, I attended a lecture recently by Professor Wil Burns from the Institute for Carbon Removal Law and Policy at the American University about ocean-based CO2 removal. He looked at a number of techniques to increase CO2 absorption. The first was ocean iron fertilisation. This would stimulate the development of phytoplankton which would absorb carbon, die and sink to the ocean bed taking the carbon with them. Some believe that this could lead to a reduction of up to 25% of atmospheric CO2, but experiments on small areas have indicated that 10% is more realistic. There are risks of course. The marine ecosystem contains multiple phytoplankton and if growth of the wrong sort is stimulated the zooplankton which prey on them would starve and so would the fish which rely on them, with implications for the whole food chain. Too much phytoplankton could block the light and release toxins and generate that powerful greenhouse gas methane, which would negate the original objective. 

The second technique is ocean alkalinity enhancement or ocean liming. By pouring lime into the ocean and reducing its alkalinity the ocean would be able to absorb more CO2 from the air. Again, some say that this could remove 25% of all CO2. However the cost is estimated at $3 trillion per annum and risks include damage to wildlife and reefs and the release of heavy metals. Like iron fertilisation, more research is needed here.

Finally, artificial upwelling was considered, which involves pumping water from the depths of the ocean to the surface and restructuring ocean ecosystems. Costs, benefits and risks are not yet fully understood. 

All these techniques have risks. Nonetheless Professor Burns believes action of this nature must be taken on a worldwide scale if we are to fulfil the objectives of the Paris agreement.

Fish Farming

Returning to fish. Given that fishing wild fish from the sea has peaked, the shortfall is made up by aquaculture. This is a term which covers a wide range of activities but the largest portion is fish farming. Farmed fish now make up about 40% of the fish supply. On the face of it, keeping fish in pens close to the shore with no need to go out on the high seas to harvest them seems like an excellent idea. In practice there are many downsides. First of all the primary food for captive fish is fish meal. Some fish, notably the Menhaden, is caught specifically for use as food for farmed fish, pigs or chickens. Some of the bycatch that we spoke about is also used for this. More than half the fish oil produced is fed to farmed salmon.

Farmed fish are typically kept in very high concentrations which become breeding grounds for parasites and diseases.  Farmers have become used to losses of 10% - 30%. The fish waste, itself polluted with the pharmaceuticals used to keep these diseases under control, pollutes the surrounding water and affects the local fish. Sea lice infect the fish in great numbers and there is very little that they can do about it. The sea lice eggs escape from the nets and infect wild fish populations. The decline in these populations can have a knock-on effect among bears, eagles and orcas. Sometimes the nets are torn and the captive fish escape. Farmed fish have never had to hunt for food and therefore have no idea what to look for and have never learnt to escape from predators. Secondly they may mate with local populations and weaken the strain.

David Attenborough points out that in some parts of the world mangroves are cleared to allow fish farms to be installed, but he does explain that some techniques of fish farming can be sustainable. Some farmers are siting their pens out at sea where the stronger currents improve hygiene. The fish are vaccinated rather than dosed in pharmaceuticals which can drift away and pollute other parts of the sea. They are kept at lower densities and they are fed on a plant-based diet. Some farms are constructed in multiple layers so that the waste from the fish drops down to feed other seafood like sea cucumbers, urchins, mussels, clams and edible seaweed. Farms managed in this way, he believes, could hold opportunities for coastal communities and for the billion people who rely on fish as their primary source of protein.

There are things that can be done to manage our oceans sustainably, but can only be done by international consensus and regulation. It’s another situation where urgent action is needed.

No More Fish Suppers?

So why am I concerned about whether I should continue to eat fish? As I’ve said, I’m no vegetarian but I eat meat in the knowledge that regulations ensure that the animals I eat have been humanely slaughtered. Compare this with the way we treat wild fish, which we now know are sentient beings with a degree of intelligence and an awareness of pain. Dragged on board fishing boats, many are crushed to death while the rest asphyxiate. If they are packed in ice they die more slowly. Some fish are gutted alive and can take an hour or more to die. Line-caught fish may be on the line for days and may be attacked by predators with no means of escape. They’ll die once they’re hauled on to the ship. Deep sea fish die of decompression as their swim bladders explode.

Jonathan Balcombe says, “When we eat fishes we fund their capture.”


The other scandalous process is hunting sharks for their fins for shark fin soup. The sharks are hauled on board, the fins are hacked off and they are thrown back into the sea to die. They cannot swim, they cannot hunt, they cannot feed. They just drift to the bottom of the ocean and death. Millions of sharks are treated in this way each year, to the extent that some species are endangered.

Of course sharks attack humans, but it’s been calculated that the ratio of shark attacks on humans to human attacks on sharks is about 1 to 5,000,000.

Abandoned Gear

Another consequence of commercial fishing is the 650,000 tons of gear which is abandoned or lost each year. Ghost nets drifting across the ocean trap all sorts of fish and marine animals, and often their predators seeking an easy meal get trapped as well. They all slowly die together and sink to the depths.

Inhumane slaughter

The way wild fish die is a cause for concern and it is receiving increasing attention. Many fish farms have systems for humanely slaughtering their fish and there is pressure to introduce humane slaughter to commercial fisheries. Given the conditions and the quantities of fish involved, the logistics of this will be complex and probably expensive as well. There are links below to detailed analyses of the problem by and the Humane Slaughter Association.

Poisoned Food

The other reason for my concern about continuing to eat fish is based on this quotation from Jonathan Balcombe's book.

“Fish flesh is the most contaminated of all foods. Water flows downstream. Effluents find their way into organisms at the base of the food chains, which in turn get concentrated through bio-accumulation as they move up food chains, ending up in the tissues of apex predators. Of 125,000 new chemicals developed since the industrial revolution, 85,000 have been found in fishes. It is well established that certain human demographics – most notably pregnant and nursing women and young children – are advised to limit consumption of fishes to avoid risk of exposure to mercury and other harmful chemicals… among the undesirable effects these contaminants can have on us are lower intelligence; lower sperm counts; more symptoms of depression anxiety and stress; and earlier puberty.”

Maybe I’ll just eat the chips.

UK Fishing

Before I close this episode of the Sustainable Futures Report I’ll comment on British fishing, particularly post-Brexit. Fisherman generally voted for the United Kingdom to leave the European Union without realising that they would prejudice their access to European markets where the majority of fish caught by the British fleet is sold. The agreement finalised at the end of last year which featured much debate on fishing even though it represents a minute proportion of UK GDP, provided that there would be no tariff barriers. What was not well understood was that by leaving the single market we had opened ourselves up to non tariff barriers. 

Taking Back Control

So by taking back control of regulations including those governing our fisheries the United Kingdom is now able to set different standards from those in Europe. However, anything sold in Europe must meet European standards and since the 1st January fishermen have needed to fill out customs declarations and to obtain veterinary certification of the standard of the fish. This has led to both delays and extra costs. Fish have a very short shelf-life and some consignments have spoiled before reaching their destination. European customers are looking for other sources of supply. Some Scottish fishermen are landing their catches in Denmark in the EU, instead of selling them in the UK. The government’s reaction is that these are teething problems which will all be sorted out, but there is no doubt that customs forms and veterinary certificates will be required indefinitely. It’s an ongoing cost. Scottish fishermen marched on Westminster in protest. They were unimpressed by the fisheries minister who admitted that she had not read the new agreement with Europe on fishing because she was too busy preparing for Christmas. They were more than angry at this comment from Jacob Rees Mogg MP, the leader of the House of Commons:

“We’ve got our fish back. They’re now British fish and they are better and happier fish for it.”

With such intellectual giants in charge what could possibly go wrong?

And that's it,

For another week. Many thanks for listening and special thanks as always to my patrons for their continuing support. You too can be a patron - you just need to go to  and sign up.

That will be another edition of the Sustainable Futures Report next week, another tying up of loose ends; many stories which I've not been able to use over the last few weeks. Then we can look forward to a story about coal and the episode after that looks at green investment.

For the moment that was the Sustainable Futures Report 

I’m Anthony Day

Bye for now.




What a Fish Knows by Jonathan Balcombe 

A Life on Our Planet by Sir David Attenborough 

Statistics - FAO 




Global Fishing Watch 

Humane Slaughter

Fishing post Brexit

Tory MPs from fishing areas criticise government over red tape 

Rees Mogg comment 

Minister did not read deal 



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A weekly podcast and blog brought to you by Anthony Day. A selection of stories and interviews aiming to be sustainable, topical and interesting.
And also, I do address conferences.

Anthony Day

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