Members of an enormous social gathering of hundreds of sperm whales, which spread across many square kilometers. (All photos: Tony Wu)

A version of this story originally appeared on bioGraphic.com.

“Hundreds of sperm whales swam to and fro, their huge bodies elegantly twirling and twisting through the water as they socialized. I felt like a gatecrasher at a wedding, so obvious was their delight in each other’s company.”

So began photographer Tony Wu’s experience of being underwater with a superpod of sperm whales. It was a rare opportunity to observe an elusive animal: Sperm whales dive to depths of up to 3,000 feet to feed, and they spend a large proportion of their time in the deep ocean, away from the surface.

The photographs that Wu captured show the distinctive social activities of a family group of sperm whales. Amid the sounds of whale communication, Wu noticed particular behaviors. The whales jostled close together to rub dead skin from their bodies. In addition to the en masse exfoliation, the superpod also defecated, which is believed to aid the nutrients in the water.

Currently, there is no accurate estimate for how many of them exist. After centuries of commercial whaling, which was only banned in the 1980s, they are still classified as vulnerable by the IUCN Red List. Ocean pollutants, and dangers of swallowing plastic, are continued threats.

Here is a selection of Wu’s remarkable photographs of this underwater gathering.

An adult sperm whale just below the ocean surface, with two other members of her family group visible in the background.

An adult female sperm whale—the dominant member of this group—carrying a large piece of a giant squid brought up from the deep trench below. Says Wu, “Members of the family played with leftover bits of squid, shredding their meal, perhaps part of the process of weaning the calf pictured swimming alongside the female.”

An inquisitive sperm whale calf approaches photographer Tony Wu, buzzing him with biosonar.

The prominent white stripes on the surface of the adult in the foreground made it relatively easy for photographer Tony Wu to distinguish this family unit from the many dozens of others gathered in the area.

During the gathering, the sperm whales defecate clouding the water.

A large cluster of sperm whales, part of an enormous “superpod” gathering of hundreds, if not thousands, of individuals.

In this photo, the whales’ sloughed-off skin is visible. Shedding skin is thought to be a mechanism by which whales rid themselves of parasites.

The sperm whales engaged in social activities like physical contact and biosonar communication.

The sperm whale gathering lasted for two days.