It was an unusual, eerie encounter. In cold, greenish water, clouded by plankton blooms and the tiny pulsing invertebrate salps feeding on them, the sperm whales were milling round. Slowly, some were sinking head-first and disappearing into the haze beneath me. Others were rising from the depths, rejoining those on the surface, then dissolving away into the distance. Two drifted in from behind me, so close that their sudden bulks appearing at my shoulder startled me. Constant chattering – strings of clicks and creaks – passed between the whales. One phrase, if such a human term is appropriate for describing sperm whale communication, seemed to be recurring: Zizzzzz tuc tuc tuc. Louder and more sharply defined, it was, perhaps, emanating from the largest whale, a cow close to 36 feet in length. This cow appeared to be the center of attention. The others, females and adolescents of both sexes, began aggregating around it.

Earlier, from the boat, we had observed a single large cow lobtailing; raising its flukes to the sky and repeatedly bringing them down to bash the surface of the sea. On a whale this size, those flukes can weigh around two metric tons - about as much as a large four-wheel-drive SUV. And so, each impact of flukes on water generated a resounding whooomp that would have been audible for long distances underwater and sent shockwaves of white spray flying into the air.

We watched through the morning as small groups of whales congregated on the surface of the water off the Azores. Sperm whales typically spend 10 to 15 minutes on the surface between foraging dives. On this day in calm seas and under low cloud, numbers of them were laying on the surface for hours, side by side – logging as this behavior is called. At one time, we could count 17 whales in one group.

Now, snorkeling in the water, I could see the flukes of this largest whale clearly. It was the same cow we had observed from the boat. After swimming past me, it sank quite quickly, head first, until it almost disappeared.

This was not a dive. There had been no final head-raised breath that characteristically signals the beginning of a sperm whale’s profoundly deep descent. They’ve been recorded reaching depths of around 9,800 feet in their hunts for squids, octopuses and fish.

We don’t know how they regulate their buoyancy. There’s certainly no gush of bubbles issuing from their blowholes as there is when a scuba diver sinks by dumping air from a buoyancy vest. Nor do they have the scuba diver’s reserve of compressed air for reinflation. But by some means, they seem to be able to control their orientation in the water with ease, and, as I watched, the large cow arrested its descent.

Other whales began to cluster around it. They remained in this formation for some minutes. Two or three individuals peeled away. Others moved in.

Eventually the assemblage sank further than I could follow by free diving and disappeared from view. The water around me, more than 3,000 feet deep, was empty. Only the distinct static that is the so-far unbroken code of sperm whale conversation — if that’s what it is — continued unabated.

Later in the afternoon, with the clouds now lifted, a group of whales wallowed on the surface, up sun, not far from the boat. In water clouded by those dense blooms of plankton and salps, and against the strong light, it was difficult to identify individual whales. But one unmistakable feature was visible; the curled and floppy flukes of an infant whale, recently emerged from the womb of its mother.

So, was this what the day had been all about? Had we witnessed some form of ritual surrounding the birth of a sperm whale? Had the lobtailing cow been summoning the clan for the event? Had far-flung individuals gathered to greet the newcomer? Were they now dispersing to relay the news?

We don’t know.

We had observed comparable events some years previously: some 250 nautical miles west of this latest encounter a large lobtailing cow whale; a brief but intense gathering of whales; new-born whales in the area within hours of the lobtailing.

Writing in the late 1700s, French scientist René Lesson ruefully said “What an impenetrable veil covers our knowledge of cetacea! Groping in the dark, we advance in a field strewn with thorns.”

It is still true today. The observations described above might be connected. They might not. In providing us glimpses of their lives, these enigmatic animals, the world’s largest toothed predators, leave swirling in their wakes, not just sheets of sloughed skin and detritus, but hosts of unanswered questions.

Photographs taken under permit issued by Secretaria Regional do Mar, Ciência e Tecnologia with precautions taken to avoid disturbance to the animals. Swimming with whales is forbidden in the Azores without written permission of the Secretaria.

For more information about their photography and research and to request access to their images, write to [email protected].