Tuna hooked by pole and line fishing makes easy prey for an opportunistic shark.

Besides man, killer whales are major predators pursuing tuna.

Artist's conception of pole and line fishing. When one fish is hooked, the rest of the school tends to follow the hooked fish to the side of the fishing vessel .

Scientist tagging a juvenile tuna.

Preparing to tag a large yellowfin tuna caught on longline gear by the Bureau of Commercial Fisheries Ship OREGON in the Caribbean Sea.

Diagram illustrating concept of selectivity of mesh size on size of fish captured during trawling operations.

Scientists measuring dimensions of tuna caught in Hawaii area of Pacific.

Modern tuna purse seiners in port.

French tuna purse seiner F/V KERGUELEN at Mahe, Seychelles. Note helicopter on flying bridge. It is used to visually search for schools of tuna.

The Spanish tuna purse seiner F/V TXORI-EDER in the western Indian Ocean. Smaller vessel on the stern is secured to purse seine and when a school of tuna is encountered, the small boat is launched and it helps ship encircle it.

Tuna purse seiner fishing in the eastern Atlantic Ocean.

Observation helicopter operating off tuna purse seiner.

Spotters looking for signs of tuna such as logs on surface or agitated water. Tuna tend to congregate around floating logs or other floating objects on the surface.

Spotter using large binoculars to look for signs of tuna.

School of tuna agitating the surface while pursuing smaller fish.

Tuna purse seiner is headed towards school of tuna to encircle with net. Workboat that helps hold net during deployment is still on starboard stern. Smaller vessel in water is used to make noise to scare tuna into staying within confines of net prior to ship and workboat deploying and closing the net.

Tuna purse seiner is deploying net with assistance of workboat which is seen at far end of net. The workboat will pull the net in a circle to capture the tuna.

Tuna purse seiner is deploying net with assistance of workboat which is seen at far end of net near horizon on upper right of picture. The boat appears as a small rectangle behind a vertical rope.

Workboat holding net prior to ship encircling school of tuna.

Helicopter eye view of ship pulling net in circle to capture tuna. Workboat is in lower center of photo and is holding the end of the net.

Ship is finishing deployment of purse seine net. Almost all of the net is now in the water and the ship will continue to encircle the school of tuna while the workboat (not shown) holds the other end of the net.

Ship has finished deploying net which is still attached by a cable. Prior to net closing, the small boat in photo makes noise to keep tuna herded into net.

Encircling the school of tuna is now complete. The workboat is bringing the end of the net back to the ship so that hauling in can proceed.

The net is now closing in a nearly perfect circle. The purse seiner is now starting to pull the net back on board. The workboat is seen to the left and is secured to the ship. It is now acting like a tugboat and is pulling the purse seiner away from the net so that it does not become entangled.

The winch operator is hauling in the cables to close the net. This closes the bottom of the net such that it is now like a purse. The fish no longer have any way to escape.

Another view of hauling on the cables to close the net.

A view of tuna agitating the surface as the net is drawing closed.

A view of the tuna that are captured inside the net.

After closing the net and trapping the fish, the net is now brought on board. This is a view of the net being run through the powerblock and then laid back on the stern of the fishing vessel.

After closing the net and trapping the fish, the net is now brought on board. This is a view from the pilothouse of the fishing vessel looking aft as the net is brought through the powerblock and laid on the stern.

Once the purse has been completed, the net is brought on board. This is the first stage of bringing the net through the power block prior to laying it on the stern.

A view of the power block as the net is coming on board.

A view of the power block as the net is coming on board.

A view of the power block as the net is coming on board. The tremendous power of the winches hauling the net through the powerblock rips apart fish entangled in the net.

An aerial view of a purse seiner after the purse has been closed and the net is being hauled aboard.

Power block operator monitors the net as it comes aboard. If need be, he will stop the net in case of a problem.

The net is now on board and the operation of collecting the fish has begun. The large basket in the upper left is dipped repeatedly into the water to bring the fish on to the boat.

The net is now on board and the operation of collecting the fish has begun. The large basket is dipped repeatedly into the water to bring the fish on to the boat.

The net is now on board and the operation of collecting the fish has begun. The large basket is dipped repeatedly into the water to bring the fish on to the boat.

The net is now on board and the operation of collecting the fish has begun.

The net is now on board and the operation of collecting the fish has begun. The large basket is dipped repeatedly into the water to bring the fish on to the boat.

A basket load of fish on board.

The basket load of fish is being brought out of the water and will be placed directly over the hole in the foreground. The fish will be deposited in the hole which has a chute that leads directly to the freezer compartments.

The basket load of fish is now directly over the hole that leads to the freezer compartments.

After the basket is unloaded, the fish are channeled into a chute that leads to a freezer compartment. Here the fish are dropping into it.

A basket load of fish being emptied on deck.

Peruvian purse seiners.

Peruvian purse seiner fishing for small pelagic fish.

Peruvian purse seiner fishing for small pelagic fish.

Peruvian purse seiner fishing for small pelagic fish.