Fried fish? – Life/Ecosystems

Fried fish? – Life/Ecosystems – management of fisheries

Libby Tucker

Fifty years ago, Earth’s oceans were one gigantic aquarium, teeming with billions of huge fish like marlin, swordfish, and tuna. Now 90 percent of all large ocean fish have vanished, says a new study by biologist Boris Worm of Germany’s Institute of Marine Science. What happened?

“Fisheries scrape the corners of the ocean to catch every last big fish,” Worm says. No wonder, since 1 billion people rely on fish as their main source of protein, an essential nutrient. Responsible fisheries limit their hauls–so fish populations can recover to their original numbers before the next fishing season. But some fisheries overfish to the point of devastating ocean ecosystems (communities of diverse organisms). Result: Some species’ survival is endangered.

Decades of overfishing have also caused the average size of some fish species to shrink along with the population count. Example: Early last century, swordfish commonly weighed up to 300 pounds. Today, fishermen are lucky to reel in a 90-pounder. Why? In order to keep up with soaring demand, fisheries catch fish before they reach full size.

Overfishing also disrupts the ocean’s age-old food chain (path of food consumption in an ecosystem). When large fish like saithe, for example, disappear, they no longer feed on smaller fish like cod (see diagram, above). Then cod populations skyrocket, changing the once balanced ocean food chain–maybe for good.

The good news: Fish populations can bounce back if protected. That means capping the number of fish that fisheries can catch. And governments have created no-fishing zones where fish populations can fully recover. Says Worm: “It’s important to save the world’s big fish. They’re the lions and tigers of the sea.”

BROKEN FOOD CHAIN

A food chain is a path that links predator and prey. One example in the European North Sea: Large fish called saithe (top) feed on smaller cod, which in turn eat whiting, and so on down to phytoplankton (microscopic organisms). But decades of overfishing have nearly wiped out the largest saithe. Result: The remaining small saithe aren’t strong enough to prey on cod; instead, they eat herring. This shatters the natural food chain–and fisheries move on to catch smaller saithe and cod.

It’s called “fishing down the food web.”

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