In 2015, scientists discovered a grizzly scene in a remote fjord of Patagonia, Chile: a mass die-off of 337 baleen whales. Later investigation revealed that they were sei whales, an endangered species of baleen whale.
At the time the cause of death was unknown, but the event—the largest beaching of baleen whales ever observed—is now attributed to a harmful algal bloom, also called a red tide for its often rusty-red colouration.
Katie McConnell, a marine biologist at Oregon State University, was working on a research team to identify and catalogue marine invertebrate species in Golfo de Penas when they discovered the dead whales.
They decided to change course and document the beaching event, including setting up 16 time-lapse cameras to film the whale carcasses as they decayed over a period of up to two years.
Solving a mystery
“In the deep sea, a single whale carcass is a huge event”, McConnell says. “They can ignite these flourishes of life and feed a diverse array of species for a long time, but nobody really knows what happens on beaches”.
Whales that wash up on coastlines where humans live don’t tend to sit undisturbed for very long, so this offered a rare opportunity to study hundreds of carcasses over a long period of time.
While the public’s attention was focused on what caused the die-off, not many people were thinking about the effects on Patagonian ecology, says McConnell.
“I started thinking what happens now, who might benefit from this, are these whales really lost, or are they somewhat recycled?”
A lively show
The cameras reveal that flocks of birds soon descended on the carcasses to feed. Microbial activity on the skin of the whales gave a surprising amount of movement. During high tides, some of the bodies were partly submerged, allowing snails, urchins, and other invertebrates to pick the bones clean. That made room for algae to grow.
“That’s on single carcasses, so it’s difficult to think of the magnitude of the impact of hundreds of them in a region”, says McConnell.
Analysis of the footage revealed five phases of decomposition. The first three; fresh, bloated, and active decomposition are the most rapid, while the remaining two, advanced decomposition and dry remains can last years, until the bones eventually wash away.
McConnell hopes the footage will create a forensic reference for future stranding events by documenting the various stages of decomposition, giving a frame of reference for being able to devise a time of death, and ultimately, a cause.