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, it has become a normal occurrence; it seems to be normal that, when you swim in the sea, you have to maintain a nearly paranoid attitude 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.
And yet, this invasion of alien jellyfish it was not normal just a few decades ago. And, surely, it was not normal a century ago when the sea 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? Only 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 which has 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, 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. 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 when we applied to the available data 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.bard(zingything)unifi.it. The full paper is at present under review. And I have also to thank my coworkers Ilaria Perissi, Alessandro Lavacchi and Toufic El Asmar.