Sunday, July 31, 2016

Depletion is real, depletion is now, and if a jellyfish stings you, you know why.

My coworker, Ilaria Perissi (on the right in the picture), explaining the results of our works on fish depletion at the 34th conference of the System Dynamics society in Delft, Holland. We found that the same models that describe oil depletion can be applied to fish depletion, and that overexploitation is the main mechanism that leads to the decline of the world's fisheries. Should you want a copy of the paper, write me at ugo.bardi(thingything)

Just a few days ago, a friend of mine showed me three bright red stripes she had on her arm. It was the result of an unfortunate encounter with a jellyfish while swimming in the Mediterranean Sea. Today, this kind of encounters have become a normal occurrence; it seems to be normal that, when you swim in the sea, you have to maintain a paranoid attitude all the time and keep looking in all directions to avoid a painful brush with one of these creatures. It makes you envy the Australians who, after all, have only sharks to worry about when they swim. (actually, they also have highly poisonous jellyfish, but sharks are more spectacular, as you can understand from some recent Hollywood movies).

And yet, this invasion of alien jellyfish was not normal just a few decades ago. Surely, it was not normal a century ago, when the coast of the Mediterranean sea was the home of many local fishermen who would make a living with their catch. But, today, what would they be bringing back home? At best, a boatload of jellyfish, but their nutritive properties are not the top. So, there has been a change, a big change in the fish population in the sea. And this change has a cause: it is overexploitation that depleted the fisheries. The sea has been nearly emptied of fish, and that has generated a booming jellyfish population and of other invertebrates, such as crabs and lobsters, whose numbers, once, were kept in check by the fish.

So, I could have told to my friend that the painful red stripes on her arm were the result of the human tendency of overexploiting natural resources: oil, fish, or whatever. Always, our tendency to maximize our immediate profit leads to destroying the resources that make us live. However, wherever people still manage to make a living out of something, mentioning the depletion of that something is normally a no-no; you just don't say that word in a civilized conversation. It is a long story that started when whalers swore that the fact that the couldn't catch so many whales anymore was because the whales "had become shy" (as you can read in Starbuck's "History of the American whale fishery," 1876). In modern times, mentioning depletion and overexploitation is often met with scorn, especially from economists who remain convinced that the market mechanisms can optimize all economic activities. For instance, Daniel Pauly and others published already in 1998 a paper titled "Fishing down Marine Food Webs" describing exactly the phenomenon that leads the sea to become depleted in fish and rich in invertebrates. But, as you may expect, this was defined as a myth. You feel like telling these people to take a good swim in the Mediterranean sea and experience by themselves the abundance of invertebrates, there.

Eventually, anything and everything can be debated, discussed, supported, or denied. But I think that myself and my coworkers gave a non-negligible contribution to understanding the overexploitation of marine fisheries. We could do that by applying to fishing the same system dynamic models that are used for peak oil. And we found that the models work. The cycle of growth and decline of many fisheries can be described by a simple model that assumes that the main factor that affects productivity is the abundance of the fish stock. And the model shows that the fish stock declines; fish is removed from the sea faster than the stock can be replenished by reproduction. Here are the data for the Japanese fishery that we presented in Delft.

So, depletion is real, depletion is now, and if a jellyfish stings you, you know why.

If you like to have a copy of the paper presented at the Delft conference, just write me at ugo.bardi(zingything) The full paper is at present under review. I have also to thank my coworkers Ilaria Perissi, Alessandro Lavacchi and Toufic El Asmar.  


  1. Now EVERY year is L'année des méduses.

  2. I mentioned in my comment to your last essay the book 'Stung'. It is a very informative,excellent book by a jellyfish expert,Lisa-ann Gershwin.
    I am not sure if your comment about Australia not having a jellyfish problem
    was a joke or not. I live in North Queensland,Australia. Most lethal shark attacks in Australia are from the Great White Shark. It does not inhabit
    Northern Australia,but Irukandji and Box jellyfish (Chironex fleckeri) make
    swimming in the sea here between November and May a dangerous exercise,unless
    done within netted,jellyfish-proof enclosures.

  3. I have begun studying grazing, and the same sort of principle applies: if you allow the animals too much freedom to eat only their favorites, then you are pre-disposing for the ascendency of unpalatable species.

    1. Yes, it is a mammalian problem, hence the balance between predator and prey, else the prey would destroy their own food source and habitat. We think reason will afford mankind the ability to control this tendency, but Kapitalism puts Kaput to that hope as, far from discouraging rabid depletion, it ENcourages it. The destruction may be creative, as they claim, but it is Kapitalism's destruction that is touted by economists' paean for Kapitalism, calling it Creative Destruction, not the creative part (it's not called Destructive Creation, now, is it?), that, it is always assumed, has been supplied by something outside the Kapitalistic system.

  4. Surely you jest about Australia, which has some of the world's most venomous jellyfish floating in its waters, like the box jelly.
    Not to mention also saltwater crocodiles, largest reptile alive.

    1. Of course it was a joke. But I must also confess my ignorance about swimming in Australia's waters. I thought that if people were so worried about sharks (and crocodiles), maybe jellyfish was a minor problem (do sharks eat jellyfish?). But apparently its an additional problem!!

    2. Ugo

      Sharks do not eat jelly fish. To my knowledge the biggest predator of jellyfish is the sea turtle and their over hunting and egg collection have caused explosions in jellyfish population. Another big eater of jellyfish is the sunfish.

  5. Yes depletion is real and depletion is now and not only of fish. And there are many consequences already and not only jelly fish stings. Maybe it is a good thing that people are getting stung by jellyfish? It introduces a feedback loop into the system. But I think for most people the solution will be either to not go swimming at all or for some to go swimming in a hotel swimming pool instead and order fish for their lunch by the poolside. I don't think this is because people are stupid or bad or miinformed, though this too is true for some or maybe even many . It is because neither average people nor elites have a clue about what should be done. At best people will vote every few years for a political party that wants to (or says it wants to) put a stop to over exploitation of fishing grounds or maybe will support the EU. . And of course these "actions" too have a whole host of consequences too and not only good ones. And the depletion of fish and its consequences is probably one of the easier problems. It's true that some people are working on various solutions conceptually and a few also practically. But I think society as a whole is still far away from devising and implementing the multi dimensional and multi system and multi-actor (political, economic, cultural, behavioral, technical, institutional, legal, regulatory and etc.) solutions at various levels and places that will be required to address and hopefully eventually solve all kinds of depletion problems. Unfortunately by he time we are stung by jellyfish although it may not be "too late" it is already pretty late in "the game". To try to "win the game" I think "we" need to start to focus much more on solutions and their practical implementation.

  6. Living in Livorno (leghorn) I am familiar with another aspect of the problem (that I am sure Ugo included in the model).

    Being a fisherman is a hard job. You need money to buy your fishing ship and equipment, that you have to repay. You work hard, long working hours, out in the see, often by night. Being a fisherman is then a strong identity, is what you are, you cannot simply turn to be something else. Especially if there are not so many alternative jobs, due to the crisis. So the population of fishermen changes slowly with time, and if (when) the fish stock plummets down, you continue to fish, maybe asking some financial help from the government to face this "bad year".

    The same is happening with tuna fishermen in southern Italy. in a small sea like the Mediterraneum the induced delay steepens the descending curve.

  7. Depletion is a consequence of overpopulation, the so-called elephant in the living room that is being overlooked by many analysts who only look at one problem at a time.

    It has been said by some that religion is a cause of much suffering among people. That is debatable. What isn't debatable is that the ideology of classical economics, without being modified by the addition of key concepts from ecological economics or bio-physical economics, is highly destructive because it attempts to sweep the phenomenon of depletion under the rug. The longer society goes without dealing realistically with depletion, the steeper will be the Seneca cliff of societal decline.

  8. We are in the trap efficiency. With additional enegía abundant exosomatic, we can take a renewable energy source such as fish beyond recovery. Their energy niches are being replaced by species of no commercial interest. For example jellyfish. We are getting by "natural selection" a hostile and toxic ecosystem for us

  9. Our biggest problems are:
    1. Going after Southern Ocean krill, and
    2. Using small pelagic fish species for fish farming.
    The Chinese are setting up a base in Tasmania to attack krill. There are already populations of penguins in some areas going extinct due to the inability to get food within range of their it will be seals and whales.

  10. Felt motivated to do a bit of googlin by this really nice post: european fishery ministers have a habit to more or less ignore scientific recommendations about catch quotes. This is leading to de-facto nonapplication of the (otherwise good) european fishery legislation. Thus, they are acting not only against common sense and against the spirit of law, but also against the overwhelming opinion of the europeans.

    Another example, where a small group of people is able to push through their short sighted interests because of a dysfunctional media - they love more to focus on school shootings 5000 km away in the us of a and similar things...

    1. I reply to myself, to add an interesting article in the "Guardian" supporting the stance about the media i expressed in the last paragraph:



Ugo Bardi is a member of the Club of Rome and the author of "Extracted: how the quest for mineral resources is plundering the Planet" (Chelsea Green 2014)