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October 25, 2001

Sunning Swords

Swordfish are actually heating themselves with the warmer surface water, not the sunlight.

Q: While fishing for giant bluefin tuna in the canyons off Montauk, I sometimes see swordfish sunning themselves at the surface to keep warm. I know swordfish are deepwater fish because they have huge eyes, and I also know that bluefin are warm-blooded so they can dive deep into cold waters as well. My question: Which fish swims deeper, swordfish or bluefin? - Robert Johnson, New York, New York

A: Swordfish swim much deeper. Found at temperatures ranging from 41 to 81 degrees Fahrenheit, swordfish prefer waters between 64 and 72 degrees. They generally stay above the thermocline, but may dive deep, feeding anywhere from the surface to the bottom, often on deepwater squids and crustaceans. Swordfish may dive to depths of over 2,000 feet, where specialized brain and eye heating organs help them hunt. Bluefin tuna, by comparison, spend most of their time near the surface. Although bluefin can tolerate a wide range of water temperatures, thanks to their warm body temperature, they prefer feeding on small schooling fishes and generally stay within 300 feet of the surface.