Artist's conception of tuna trolling operation.

Fishing vessel trolling for tuna in the Pacific.

Fishing vessel trolling for tuna in the Atlantic.

Pole and line fishing boat above a school of tuna. The jets of water facilitate fishing as they prevent the tuna from noticing activity on the deck. This technique uses live bait.

Pole and line fishing vessel with live bait container on the foredeck.

Tuna caught by pole and line method on the Bay of Biscay.

Tuna caught with rod and reel and live bait. Rod and reel as opposed to pole and line method is used when fish are far from boat instead of directly under or near the boat. The rod and reel allows casting live bait to the fish.

Tuna caught with rod and reel and live bait. Man with rod and reel is out of picture to right; man on left is helping pull in the fish; man on right is waiting to gaff the fish.

Using live bait to bait the hook for tuna fishing with pole and line fishing.

Tuna caught with rod and reel and live bait. Man with rod and reel is out of picture to left; men in foreground are helping pull the fish in.

Tuna caught with rod and reel and live bait.

Tuna caught with rod and reel and live bait.

Fisherman preparing rod and reel for tuna fishing.

Pole and line fishing. Man in foreground is throwing live bait in water to keep school of tuna around the boat. Man with hose is spraying water to keep tuna from noticing boat. Lines in upper left lead to pulley system. When large fish is hooked, a man pulls on rope to pull fishing pole vertical which brings fish to side of boat for gaffing.

Boat rigged for pole and line fishing. Note live bait tanks on deck fore and aft of pilot house. Poles of varying size are secured in vertical position ready for fishing. The largest poles are rigged to the pulley system that can be seen approximately 5 meters above the deck.

Seining for bait fish for pole and line tuna fishing. Boat in right center is rigged for pole and line fishing, but searching for schools of bait fish.

Tuna coming to side of boat during pole and line fishing operation.

Large tuna brought to side of boat for gaffing during pole and line fishing operation. Man in left foreground is throwing bait into waters around the fishing vessel.

Relatively small tuna being caught during pole and line fishing operations.

The CAPE BEVERLY, one of the first commercial tuna vessels outfitted for purse seining operations. This photo was taken on its maiden voyage. Published in: "Purse Seine Revolution in Tuna Fishing", by Richard McNeely, Pacific Fisherman, June 1961.

Pole and line fishing with two poles working in unison. Big tunas like this are often landed on two poles in the Hawaiian fishery.

Photo #3 of sequence. Pole and line fishing with six poles working in unison. The fish has been pulled on deck through the combined effort of all six fishermen.

Photo #2 of sequence. Pole and line fishing with six poles working in unison.

Photo #1 of sequence. Pole and line fishing with six poles working in unison.

Fishermen catching yellowfin tuna by pole and line fishing. They are standing in the racks on the Bureau of Commercial Fisheries Vessel HUGH M. SMITH.

Fishermen catching yellowfin tuna by pole and line fishing. They are standing in the racks on the Bureau of Commercial Fisheries Vessel HUGH M. SMITH.

Measuring the length of a bluefin tuna.

Pole and line tuna fishing boat from Fuenterrabia, Northern Spain.

Pole and line tuna fishing boat from Fuenterrabia, Northern Spain.

Scientists tagging bluefin tuna in the Bay of Biscay with traditional tagging method.

After tagging, the bluefin tuna are returned to the sea. The tag is visible on the back of the tuna.

Man on left is holding tuna while man on right prepares to insert tag.

Fisherman bringing tuna to tagging table while pole and line fishing for additional tuna continues. Scientists were conducting the tagging operation on a chartered commercial fishing vessel. All tuna caught were tagged and returned to the sea.

After tagging, the bluefin tuna are returned to the sea.

Pole and line fishing on a chartered vessel to catch tuna for tagging. Scientists tagged each fish caught and returned it to the sea.

After tagging, the bluefin tuna are returned to the sea.

Scientist preparing to tag albacore tuna - Thunnus alalunga.

Pole and line fishing on a chartered vessel to catch tuna for tagging. Scientists tagged each fish caught and returned it to the sea.

Scientist displaying pop-off electronic tag. This tag is inserted into a fish's flesh and pops off when it has been programmed to do so. It transmits a signal to an ARGOS satellite for tracking large pelagic fish species.

Scientists measuring a bluefin tuna - Thunnus thynnus.

A bluefin tuna caught in the trap at Stintino.

Bluefin tuna male sexual glands.

Bluefin tuna female sexual glands. Also, note heart in upper right of container .

A bluefin tuna attacked by a shark while being brought aboard during pole and line fishing operations. This tuna was attacked during a scientific tagging cruise on a chartered vessel.

Photo #1.Cross-section of first spine of dorsal fin of young bluefin tuna showing annual growth rings. These rings are similar to tree growth rings. The wide (brown) areas represent summer growth during periods of high food intake. The narrow (white) bands represent periods of less fast growth during the winter when the fish's metabolism slows.

Photo #2. Compare this cross-section to the previous image. Notice the greater width of the outer band. This is because the first cross-section was from a bluefin tuna caught in June while the second was from a tuna caught in November. The wider area represents a long period of high food intake during summer/ autumn months. These images are greatly magnified.

Cross-section of first spine of dorsal fin of a one-year old bluefin tuna. This image is greatly magnified.

A fin whale - Balaenoptera physalus -on the Bay of Biscay.

A pod of killer whales on the Bay of Biscay.

Artist's conception of school of tuna pursuing a school of bait fish while pole and line fishing is being conducted from fishing vessel.