In a recent fishing magazine that I read a few days ago, a top-notch journalist had written an article about white marlin.
The author had interviewed and quoted several highly regarded sport fishing captains. One of them, Captain John Bayliss, is considered to be among the best of the best by both his peers and his competitors.
Bayliss told the author that he always liked to keep an eye out for sea birds. He specifically mentioned looking for terns and shearwaters, "Either working bait or sitting on the water. Sometimes they’ll lie to you, but for the most part the birds are pretty reliable" I agree fully with Bayliss. Terns especially, have great vision. They can spot bait as small as minnows and the predators that chase them. These birds dive down beneath the surface to grab the minnows that the tuna chase into a compact ball of food.
In fact, the day before reading that article, I had told a friend who wanted to try to catch a blue marlin from his center console boat "if you find 2 or more terns flying together do NOT lose sight of them!" Terns are a good indicator of small baitfish in the area. This almost always attracts tuna, which are usually but not always small. Tuna are the sheep for which the blue marlin, a wolf of the sea, is hunting! Terns can see fish, even very small bait fish, well below the surface. When the bait the tuna are feeding on runs away, dives deeply or have all been eaten the tuna leave and so do the marlin. A lone tern will fly miles looking for bait fish and often finds them by finding tuna or other terns feeding.
Many avian predators and scavengers searching for food tend to fly in a line but as far apart as they can possibly be and still see a bird of their own species on either side of them.
If the bird to either side of them suddenly disappears, the avian equivalent of "HEY WHERE DID MIKE GO?" flashes through their brain. The bird promptly alters course to go in the direction of the mysteriously missing bird, where he very quickly finds Mike and a bunch of other terns chowing down. A chain reaction occurs and more and more terns quickly arrive at the feast. When all the food has been eaten or dives deep beneath the surface, the terns once more spread out and search for another food fight to join in on. As long as the last two terns have not split up there may be a tuna or two and there is still a good chance for a marlin in the area. Don’t leave until the last few terns are gone.
This is when "Run and Gun" fishing is a good idea, especially if a modern, open scan radar is available on one or more boats that fish as a team. North Carolina charter boats are a prime example of a fleet that excels in a team approach to finding fish for their customers. There are many charter fleets in both the Atlantic and Pacific, with huge expanses of ocean and conditions changing daily that use these tactics. Some knowledgeable groups of amateurs do as well.
Unfortunately, instead of terns or shearwaters, the photograph in the magazine showed a small group of Frigate birds, also called Man-o-War birds, and stated that these birds also indicate schools of small baitfish below the surface. This is an inaccurate statement.
Finding a single Man-o-War bird is generally a sign of the presence of a large predatory fish, one that is likely to feed on flying fish.
The fish most often found under a single Man-0-War is a dolphin fish, also referred to as Mahi Mahi or Dorado. Man-o War birds do not dive below the surface. They swoop down on flying fish, squid or half beaks that are trying to escape from a dolphin or a billfish by jumping into the air and flying away from the subsurface predators. This is an aerial show, taking place above the surface of the water and can be seen at a long distance by the naked eye, with binoculars or on a radar screen.
Frigates hover over dolphin fish and billfish near the surface but are not good indicators of bait that is below the surface.