The habitat of the spotted dolphin is clear, deep tropical ocean. Its home waters are warm, lovely to look at, sparse of life - a marine desert. Spotted dolphins roam that country like Bedouins. Their oases are the plumes of upwelling and nutrients in the lee of islands; their uluations are cries rising high above the hearing range of human beings; their dunes are the blue swells. They gather occasionally in herds of a thousand or more - several schools in a temporary federation - but more often they are seen in bands of a few hundred. Like many of the ocean's hosts, they are fewer than they once were.

Awaiting a tribe of spotters in their element is a peculiar experience. You hang from the surface by your snorkel, marking time with a slow churning of your fins. The swell lifts you by the hair , drops you, lifts you again. Beneath you lie two miles of ocean - a bottomlessness, for all practical purposes, an infinity of blue. When you are new to it, the blue void has a pull. It wants you, tries to call you down. A thousand coruscating shafts of sunlight probe it, illuminating nothing. Nothing is there to illuminate, nothing to establish scale or distance. A tiny gelatinous fragment of salpa, drifting up ten inches from your faceplate, startles you. For an instant it could be anything - a strange man, a whale, a shark.

From that lambent blue field, featureless yet somehow forever shifting, empty yet pulsing with all the imagined sharp-toothed things that might come out of it, come the spots indeed. You blink behind your faceplate, but the spots remain. They are real, not hallucinations. Around each white dot a gray dolphin materializes. Five or six quick strokes of the flukes and they are upon you, sleek, fast, graceful legions. They come a little larger than life, for water magnifies. They animate the void. With barrages of clicks and choruses of high-pitched whistling, with speed and hydrodynamic perfection, with curiosity, mission, agenda, and something like humor, they fill up the empty blue.

The first rank of dolphins race past. Behind them a second rank of dots appear, doubtful at first, like the first stars of twilight. The dots jiggle oddly as the beaks cast about for you, and then hold steady when they have fixed on you. Another rank of dots, and then another: the society of Stenella attenuata sprints by in waves, the squads of adult males, the gangs of juveniles, the nurseries of females and calves.

The squads of adult males execute close, synchronized flybys and pummel you with sound - loud bursts of echolocation that are both a threat and a piercing sonic look at you. The males acoustically "see" the air spaces of your lungs, watch your skeleton articulate. The clicks of their echo-sounding proceed from the amplifier in the "melon" - the dolphin's bulbous forehead - but the beak tip is so white and prominent that the sound seems to come from that. The beak is the Geiger counter; you are the uranium. As the white tip swings in line with you, the clicks come louder and faster, reach crescendo as the beak draws its bead, and then recede as the beak swings away again.

When a squad of males sounds you out in unison, the sensation is like equatorial rain on a tin roof; first a few scattered drops, then the downpour. You don't hear the echolocation so much as feel it. Your whole body becomes a tympanic membrane. You really are, for once, all ears.

The gangs of juveniles are curious but don't come so close. They fake boldness. The nurseries keep their distance, small calves nursing on the move or swimming at their mothers' backs, stroke for stroke in perfect synchrony, holding position just above and behind the maternal dorsal fin. Occasionally a larger calf strays off to swim with a rhythm of its own. Now and again a whistling dolphin emits a long, thin stream of bubbles from its blow-hole. This seems to signify mild distress, or a low-grade warning. Now and again a dolphin defecates, a slightly grayer streams of bubbles. From a distance the two sorts of contrail are hard to tell apart. If the dolphin is gliding at the moment of emission, the bubbles run out straight behind. If the dolphin is swimming, the action of the flukes beats the contrail into a wavy line.

Dolphins have no shame. They have no private moments. In courtship, foreplay, and sex they are public, and as they pass you see snatches of dolphin intimacy, if that's the word. One dolphin in a pair will yaw sideways, its pectoral fin pointing to the surface, and then, slowing to let its partner pass above, will allow the tip of its pectoral to trace delicately the length of the partner's belly, past the genital slit. Sometimes the romance is cruder. The amorous dolphin will jam its pectoral into the vicinity of the genital slit and impatiently, with stiff-shoulder jerks, work that area over hard. Mock fights occur, irritations, moments of play. You see only fragments, bits of behavior, for the school never lingers. To the sirens of their whistling (inaudible in the higher ranges even to dogs), to the klaxons of their clicks, they race for that distant fire that oceanic dolphins are forever chasing.