How does an 18-foot-long, 2,000-pound carcass simply vanish?
This question has intrigued many divers and photographers who frequently explore the waters off San Diego.
It began earlier this spring when Doug Bonhaus seized the opportunity of calm weather to scuba dive in Scripps Canyon. As he descended, a massive form became visible beneath him.
At a remarkably shallow depth of 115 feet, he discovered the remains of a baby gray whale.
Whale falls are typically not encountered by human divers, as they are usually found by remotely operated vehicles at depths beyond 3,000 feet.
Marine biologists speculated about the origins of the gray whale calf. An animal resembling the one found on the ocean floor had been seen swimming near La Jolla Shores, desperately seeking its mother. In its last moments, it had approached boats, seemingly pleading for help that never came.
Since this was the first time a fall was so easily accessible, other divers made their way to the site. Among them was Jules Jacobs, an underwater photojournalist who has documented his explorations for The New York Times.
At that time in late January, the carcass’s location was in a trough in the canyon that required precise navigation to reach. Thus, Mr. Jacobs prepared himself for a challenging and risky dive.
Swimming through the dim light with a team of five other divers, their dive lights suddenly revealed what he had come for: the emaciated calf with its mottled skin. Its eyes, already surrendered to the elements, seemed to wear an expression of sorrow.
“It’s humbling to dive among a whale fall where the tail is as large as your own body,” Mr. Jacobs remarked.
Mr. Jacobs planned more dives to study the carcass. During his second visit a week later, he noticed a portion of the tail was missing, likely taken by scavenger sharks such as the seven-gilled or the mako.
After a series of spring storms, Mr. Jacobs descended into the cold darkness for a third time in late February. Clutching his camera gear so tightly that his knuckles turned pale, he awaited the sight of the decaying body.
Yet, what he discovered was only the barren ocean floor.
The calf had vanished.
Gray whales, which can reach lengths of about 45 feet as adults, undertake one of the longest migrations of any mammal. They journey from the warm waters of Baja California to feeding areas in the frigid Arctic Oceans. The missing calf and its mother were likely headed north when they became separated. At this stage in their migration, they would have been particularly vulnerable, with the mother having fasted for six months.
Gray whale populations exhibit a boom-and-bust cycle, experiencing crashes and recoveries, occasionally losing up to a quarter of their numbers in just a few years.
However, in the past six years, the population has not rebounded as it has after previous die-offs. Scientists blame this decline on climate change, which hastens Arctic warming and disrupts the food sources for gray whales. Additionally, ship strikes and entanglement in fishing gear exacerbate losses due to starvation.
“We’re unlikely to see a return to a population that can sustain 25,000 gray whales anytime soon,” said Joshua Stewart, an assistant professor at the Oregon State University Marine Mammal Institute. Dr. Stewart anticipates many more whales will perish along the West Coast.
Nevertheless, in the natural course of events, a whale’s death doesn’t always signal an end. Instead, it can herald new beginnings.
A flourishing ecosystem arises from a whale carcass, even from that of a calf. Scavengers consume the flesh, while microbes and worms colonize the bones, creating new pathways for budding reefs.
“A whale fall is an incredible bounty, potentially offering as much sustenance as what normally accumulates on the ocean floor over the span of 200 years,” noted Craig Smith, professor emeritus of oceanography at the University of Hawaii. “Ironically, we understand more about whale-fall communities in deeper waters than in shallower environments.”
The decomposition of a whale occurs in three distinct ecological phases. Initially, scavengers such as sharks, crabs, and hagfish arrive to consume the soft tissues. Next, hordes of worms appear in “massive, writhing clusters in the nutrient-rich ooze surrounding the carcass,” explained Dr. Smith. This phase can last up to seven years, which scientists refer to as the enrichment-opportunist stage.
Finally, bacteria deep within the bones generate hydrogen sulfide, supporting chemosynthetic bacteria on the surface of the bones and those that live in symbiosis with animal hosts. This stage can endure for decades, with over 200 marine species thriving on a single whale fall.
However, this young whale and its remains had disappeared. Did something or someone take it, halting the life-giving process of the whale fall?
Gregory Rouse, a marine biology professor at the Scripps Institution of Oceanography, argues that the explanation is less enigmatic. He noted that during whale falls, the decomposition of the body cavity produces gas, which can cause the carcass to rise after initially sinking, then float before finally coming to rest on the sea floor.
Strong winds and fluctuating currents likely pushed the body deeper into the canyon, which extends as far as 1,600 feet.
“This animal could have grown into a giant, yet its life was cut short in its infancy,” Mr. Jacobs remarked.
Yet, where it now lies in the shadows, new life may emerge and thrive.