It started as a day on the water and turned into a count that reached 299.

Wildlife photographer Chris Fallows and author-naturalist Monique Fallows spotted an enormous feeding aggregation of humpback whales off South Africa’s west coast in December, according to the AP. Scientists call this kind of gathering a whale “supergroup.”

“It was extraordinary,” Chris Fallows told the AP. “Quite quickly we realized that there must be several hundred whales coming together in one particular area.”

To avoid double-counting, the South African couple used photographs of each whale’s uniquely patterned tail to identify individuals. After reviewing the images and data, Alex Vogel, Africa coordinator for whale-tracking organisation Happywhale, said the sighting appears to be the largest of its kind.

Chris Fallows described the blow plumes as a “Manhattan skyline” of whale breath, the AP reported. Humpbacks are more commonly seen alone or in much smaller pods.

For scientists, the gathering points to a major conservation success. The AP reported that Southern Hemisphere humpbacks rose from fewer than 10,000 during the height of commercial whaling to more than 100,000 after the 1986 international moratorium.

Not every whale population has recovered the same way. The International Union for Conservation of Nature lists seven of the 14 great whale species as endangered or vulnerable.

Researchers and citizen scientists are helping track whale recovery. Happywhale uses public submissions of whale photos to help verify sightings and identify individual animals.

Scientists are also watching for threats. Els Vermeulen, chief scientist at the University of Pretoria’s Whale Unit, told the AP that ship traffic around the southern tip of Africa has risen sharply as vessels reroute away from conflict zones in the Red Sea and growing instability around the Strait of Hormuz.

Gregg Oelofse, Cape Town’s coastal and environmental manager, said that heavier traffic through whale habitat increases the risk of deadly collisions.

“We’ll see the propellor strike often through the whale’s body,” Oelofse told the AP. “So, it’s like these big cuts in the whale’s body.”

Vermeulen said she and others are pushing for formal ship speed limits near the South African coast. “In general, the moratorium on whaling can be classified as one of the strongest conservation success stories in the marine environment,” Vermeulen concluded to the AP.

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