Oceanology: To Catch a Tired Fish

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Why do swift and agile fish get caught in slow-moving nets? They simply get tired. This seaborne secret was documented recently when skindivers of the U.S. Bureau of Commercial Fisheries hung on the mouth of a big submerged trawl and took movies of fish as they were caught. The net moved through the water as slowly as 2 m.p.h., a pace that most fish can exceed with ease. But the skindivers learned that, fast as fish are, most of them are too lazy to take evasive measures. They swim languidly for a while to keep ahead of the net, but eventually they tire and drift back into its maw. After that, they are stuffed into its trailing "cod end," from which there is no escape.

Encouraged by these observations, the bureau's Seattle base designed a monster, bag-shaped trawl. The mouth, 117 ft. square, is kept open by floats and kitelike "otter boards"; it can be submerged at any depth. The great net is pulled through the water at less than 3 m.p.h. A few fish, including salmon, are smart enough to recognize danger and dart to safety, but most types do not take alarm until too late.

Armed with their slow, enormous net, the fisheries men have found an unexploited treasure in the North Pacific.

The midwaters between the surface and the bottom, a region usually neglected by commercial fishermen, swarm with great schools of hake. Often the giant net has caught them at the rate of a ton a minute. Pacific hake bring a low price because they are used to make fish meal, but the net has also caught ocean perch and other food fish. The bureau is looking forward to a time when fleets of supernets will comb the neglected mid-waters of the North Pacific, gulping shiploads of fish that are now almost untroubled by fishermen.