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Disappearing Fish

Disappearing Fish School of Tuna
Photo Credit: By Danilo Cedrone (United Nations Food and Agriculture Organization) [Public domain], via Wikimedia Commons

In the nineteenth and early twentieth centuries, authors like Herman Melville, Jules Verne, and Ernest Hemingway pitted grizzled adventurers against the mightiest creatures of the ocean. Today, the struggle of man-versus-nature is quite a different contest. Science reporter Bob Hirshon tells us that the world's biggest fish are now in serious jeopardy.


Transcript

Why the catch of the day is getting skimpy. I'm Bob Hirshon and this is Science Update.

If your grandfather ever told you about the gigantic fish he used to catch, he probably wasn't exaggerating. Because in his day, big fish like marlin, tuna, cod, and grouper were in fact much bigger—and far more plentiful to boot.

That's been confirmed by biologist Ransom Myers and marine scientist Boris Worm at Dalhousie University in Nova Scotia. They studied worldwide fish populations from 1950 to the present.

Myers:

And basically what we found all over the ocean, wherever we had data, is that the abundance of large fish, in terms of numbers and weight, were ten times higher originally than they are now. That is, that what we're left is one-tenth of the original number and weight of large, large fish.

And because many of these fish are top predators, their disappearance is also throwing ocean ecosystems off balance. Myers says only drastic cutbacks in industrial fishing can save the big species.

Myers:

And you have to remember that with the great whales, that we as humanity stopped whaling. In fact, arguably, the first collective act of humanity was to save the great whales.

Myers recently testified before Congress to alert them to the problem. For the American Association for the Advancement of Science, I'm Bob Hirshon.


Making Sense of the Research

As you can tell from the story, fishing isn't what it used to be. Early in the 20th century, fish were plentiful, cheap, and often very big. Ironically, the full-throttle industrial fishing efforts that were meant to capitalize on this bumper crop have made fish rarer, smaller, and as a result, more expensive.

What's the difference between "industrial" fishing and the kind of fishing that humans have practiced for thousands of years? There's no hard and fast answer, but basically once you start using advanced machinery and technology to catch many, many fish at once, you move into the territory of "industrial" fishing. Industrial fishing has been practiced in some parts of the world for centuries. But it was around 1950 that it began to take over a large percentage of the world's waters.

Along with the advent of industrial fishing came the advent of detailed record-keeping. That's where Myers and his colleagues step in. By tracking the sizes and quantities of catches from the time an industrial fishery casts its first line into virgin waters, and following them up to the present day, they can get an idea of how the fish population has changed over time. Every species has a slightly different rate of decline, but on average, it looks like large fish today are down to a tenth of their original numbers. And because they're being caught before they've had a chance to fully grow, they're also substantially smaller.

Myers says that he's met with some resistance from commercial fisheries. They argue that we haven't caught most of the fish; we've only caught most of the fish that are easy to catch. However, Myers points out that our techniques for finding fish have become much more sophisticated over the years. And even if only the cleverest fish remain, it won't be long until we outsmart them too—and in doing so, shortchange not only ourselves but the world's oceans as well.

Now try and answer these questions:

  1. How did Myers and his colleagues track fish populations?
  2. Suppose an area had been commercially fished since 1800 but had records going back only to 1950. Would this be a useful area for Myers' study? Why or why not?
  3. What obstacles stand in the way of conserving large fish populations?
  4. How else might the disappearance of large fish affect ocean ecosystems?

For Educators

In What's Wrong With the Oceans? Can Photography Help?, from National Geographic's Xpeditions, students research environmental problems facing the world's oceans and think about how the art of photography can help solve these problems. (Grades 9-12)

The Seafood Choices Alliance is a non-profit group that connects chefs, commercial fisheries, supermarkets, and consumers to conservationists in order to promote environmentally sustainable fishing practices.


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