The Billfish Story: Swordfish, Sailfish, Marlin, and Other Gladiators of the Sea

CHAPTER 1 The Rise of Billfish

5 The Rise of Billfish 1 An eighty-pound female sailfish, large for her species, slowly cruises the cobalt-blue waters around the island of Bermuda in search of her next meal. She has ridden the powerful Gulf Stream to this ancient island, which plunges thousands of feet to the ocean floor. As the result of a complex interplay of Bermuda’s underwater topography and current flow, nutrient-enriched water has welled up from the depths to initiate a food chain. As if out of nowhere, microscopic plants and animals appear—a meadow of life spreads across the ocean surface—and baitfish move in to partake of this cornucopia of organisms. But the sailfish is also ready to assume her role as the apex predator. Using her large eyes, she searches the dim reaches of the water column for her prey, looking for any tell-tale sign of life. Subtle movements below catch her attention, and she is now on full alert. The school of herring also senses her presence and assumes a defensive posture, instinctively congregating into a bait ball—a whirling mass of panic-stricken fish, a living tornado counting on safety in numbers. The sailfish slowly circles the bait ball, herding her prey into an evertightening circle. Usually the denser the clustering of prey, the safer are the individuals in it, since most predators have difficulty singling out an individual, isolating it from its neighbors. But by all accounts, the sailfish is a finely attuned predator, who will turn this defensive posture against the prey. She is adorned for the battle. Like the hoisting of the Jolly Roger banner, she has raised her saillike dorsal fin to its maximum vertical extent, giving the impression of a much larger organism. Her body 6 chapter one flashes with color, often in silvery blue stripes. The color bursts serve to further unsettle the skittish prey. But this outward display of prowess is short-lived; it is time for her to feed. She retracts her pelvic fins into a pair of grooves along the ventral side of her body. Propelled by her powerful, sickle-shaped tail, she darts into the outer “wall” of the bait ball, her now streamlined form allowing her to reach eye-blurring speeds. The bait ball starts to break down as individual members scatter , seeking to avoid the oncoming attack. But to no avail. With each sharp turn she makes in the bait ball, her swordlike bill hits and stuns numerous prey. She then turns and consumes her victims headfirst, feeding until she is satiated. All that remains from this onslaught are photo 1. Sailfish and bait ball. Copyright Istockphoto.com / Amanda Cotton. the rise of billfish 7 the silvery scales of the herring slowly sinking into the depths. This primal act has been played out over the centuries in a watery arena, tens of millions of years old, which she shares with other billfish: white marlin and blue marlin, spearfish and swordfish. Stirrings within an Old Earth The evolution of these gladiators of the sea over the eons is inextricably linked to shifting continents, the opening of new seaways, and the birth of new land forms, changes that have provided the impetus for the rise of new life forms and the demise of long-established ones. This evolutionary story is an old tale—one much older than any billfish. Through the accumulation and analysis of interlocking lines of evidence , geologists tell us with considerable confidence that the earth is 4.6 billion years old. Yet the geography of the planet only 200 million years ago was markedly different than it is today. Landmasses were locked together in the supercontinent Pangaea and surrounded by the vast ocean Panthalassa. The breakup of Pangaea, which came to be known as continental drift, did not occur uniformly over time; most of the continents broke away sporadically. The earliest new ocean was the southern North Atlantic, an embryonic seaway formed about 165 million years ago. By the late Cretaceous Period, 94 million years ago, the breakup of Pangaea was complete, but it was not until another 60 million years passed that the Atlantic Ocean took on a shape and appearance that would be recognizable today, stretching unimpeded from almost pole to pole—a new niche for the life to come. Though continental drift is powered by immense plumes of molten material that rise from great depths within the earth...