A Killer Whale Killing Spree on the West Coast Is Actually Good News
Natural whale deaths benefit the whole ocean ecosystem. Human-caused ones, though, are another story.
A killer whale tries to drown a gray whale calf as the calf mother defends it. Image: Jodi Frediani
This past 4/20, while marijuana merrymakers gathered on the UC Santa Cruz campus to celebrate, just a few miles away on the shores of Monterey Bay, whale watchers boarded boats to see killer whales. One of them was California-based wildlife photographer Jodi Frediani, who counted more than 30 of the iconic black-and-white cetaceans. That day, she witnessed them begin what many experts consider to be an unprecedented gray-whale killing spree.
Over the course of the next two weeks, Frediani and other observers watched more than 30 killer whales (led by a pod of nine) attack eight gray whale calves, killing six. The massacre was so unusual it made the local news. Many who heard about or saw the event expressed their shock and sadness that the killer whales nabbed so many young gray whales.
To Frediani, the killings of the gray whales, which in the eastern Pacific were once an endangered species—while disturbing to watch—are examples of nature taking its course. Like all animals, killer whales need to eat, Frediani told me, and it just so happens they have a taste for other whales' blubber.
The natural deaths of gray whales and other large whale species, as a result of predation or old age (as opposed to human-caused deaths such as fishing gear entanglements or boat collisions), is beneficial for not just the killer whales that consume their flesh, but the entire ocean ecosystem.
"There are likely hundreds of species that use whale carcasses," said Joe Roman, a conservation biologist and researcher at the Gund Institute for Ecological Economics at the University of Vermont and a Hrdy Visiting Fellow at Harvard University.
Roman, who has studied the ways that whales affect marine ecosystems, told me that the living animals transport nutrients through oceans vertically and horizontally. Whales dive deep to feed and then rise back to the surface to take in air and excrete nutrient-rich feces. This process, called "the whale pump," helps fertilize the marine ecosystem from above.
Whales also help spread nutrients as they migrate, excreting feces containing the nutrients from krill, small fish, crustaceans and other types of tiny plankton they've consumed in high-latitude feeding areas, to low-latitude breeding areas where fewer nutrients circulate.
"Whales are not just passengers in the oceans, dependent on bottom-up forces such as phytoplankton blooms," said Roman. "They can also help drive marine ecosystems by redistributing nutrients, such as iron, phosphorous, and nitrogen, providing food for predators such as killer whales, and habitat for deep sea species."
Whales nourish the sea when they die. Sometimes they wash ashore, where seabirds and scavenger animals consume them. When a whale goes down in the middle of the ocean, it sinks to the bottom in what's called a "whale fall." Scavenger species such as seabirds and great white sharks will nibble away at the flesh when the whale is freshly deceased and floating at the ocean's surface.
As more advanced stages of decomposition set in, the body sinks to the ocean floor, where specialist species such as the carpet worm and various types of bone-eating worms further break down the whale's body. A whale fall sequesters a large amount of carbon in the deep sea.
"That whale falls harbor unique communities, enhancing species diversity and evolutionary novelty in the deep sea," said Craig Smith, professor of oceanography at the University of Hawaii at Manoa. He told me that dead whales, which emit large amounts of sulfur as they decompose, may have created a habitat to which some marine species learned to adapt to survive in the highly sulfuric conditions of deep-sea vents and cold seeps.
Experts stress that there is a big difference between human-caused whale deaths and natural ones. Since January 2016, there has been an enormous, and to-date unexplainable, die-off of humpback whales, two times the historical average, off the Atlantic coast. The groups tasked with overseeing these incidents, the Greater Atlantic Regional Marine Mammal Stranding Network and National Oceanic and Atmospheric Administration Fisheries Service, haven't been able to determine the cause. But they suspect the 43 humpback whales they've found dead could have succumbed to disease, biotoxin poisoning, or due to human activities.
Whaling caused an enormous depletion in populations worldwide. While it's less prevalent today, we now kill large numbers by hitting them with our boats, poisoning them, performing military sonar exercises, blasting undersea air-guns, and entangling them in fishing gear. Experts say more unnatural whale deaths could change the ocean ecosystem—in fact, they probably already have.
"It is quite possible that the first marine species extinctions caused by humans were species dependent on whale falls in the North Atlantic, where large whales were depleted in the early 1800," Smith said.
Because humans have taken over so much of the seas, whale mortality events like the killer whale killing spree in Monterey Bay are rare instances where human activities are not to blame for the mass deaths of large whales.
Subscribe to Science Solved It, Motherboard's new show about the greatest mysteries that were solved by science.