The Surprising Role of Whales in Ocean Carbon Capture

[By Jessica Aldred]

Saving the whales may be more important than planting trees when it comes to tackling climate change and keeping our oceans healthy. The world’s biggest animals play a crucial role, helping fertilise the phytoplankton that absorbs 40% of the world’s CO2. They also capture vast amounts of carbon in their bodies before sinking to the bottom of the ocean when they die and locking it away, sometimes for centuries.

Last year, the International Monetary Fund (IMF) valued the role of whales in carbon sequestration and healthy ocean functions at more than US$1 trillion. It estimated a single great whale to be worth more than US$2 million, based on its contribution to carbon capture, fisheries enhancement and tourism.

But populations of whales in the world’s oceans have been decimated in the last two centuries, falling from 5 million to 1.5 million today. More than 30 years after commercial whaling was largely banned in a bid to protect them, whales continue to suffer from human impacts in the form of plastic and noise pollution, injuries from ships, entanglement in fishing gear and changes to the ocean due to global warming.

Whales and carbon capture

A whale accumulates carbon through feeding and stores it in its body during its long lifetime. Some whales weigh up to 200 tonnes, with an average lifespan of 70 years. One species, the bowhead whale, is estimated to have a lifespan of 268 years.

When a whale dies, it sinks to the bottom of the ocean, where the carbon in its body is sequestered. The IMF estimates that each great whale sequesters 33 tonnes of CO2 on average, and that a tree absorbs only up to 22kg of CO2 a year. Tree-planting schemes are being seen as the cheapest and fastest method of taking CO2 out of the atmosphere, but the evidence suggests conserving and boosting whale populations also has great carbon-capturing potential.

Sunken whale carcasses take decades to decompose, and become an entire ecosystem in themselves, supporting deep-sea species from large scavengers to microscopic bacteria with a huge and immediate source of food.

Priceless poo

Whales do more for carbon capture when they are alive, however, thanks to their jumbo-sized poo. These “faecal plumes” contain enormous amounts of nutrients – including phosphorus, iron and nitrogen – that are essential for the growth of microscopic organisms known as phytoplankton. When these plants photosynthesise, they consume carbon dioxide and produce oxygen. The IMF calculates that phytoplankton are responsible for capturing about 37 billion tonnes of CO2, the same as 1.7 trillion trees, or four Amazon forests’ worth. They also contribute as much as 50-85% of the oxygen in the Earth’s atmosphere. The famous National Geographic ocean explorer Sylvia Earle has estimated that they provide the oxygen for one in every five breaths we take.

Scientific research shows that whales have a “multiplier effect”, increasing phytoplankton production wherever they are found. As well as bringing nutrients from the ocean’s depths to the surface through their vertical movement, called the “whale pump”, whales also distribute them laterally on their vast migrations, a phenomenon named the “whale conveyor belt”.

Whale behaviour

Humans have always found the behaviour of whales intriguing and endearing, perhaps because we have so much in common. Whales and dolphins live in tightly knit groups known as “pods”, have complex relationships and talk to each other. A 2017 study compiled a list of behaviours that are similar to humans and primates including: working together for mutual benefit; teaching young how to hunt and use tools; using regional “dialects”; identifying individuals with unique sounds; looking after young that aren’t their own; and social play.

Ship strikes and entanglement

Many of the world’s busiest cargo and ferry lanes and ports directly overlap with areas where whales feed and breed or travel along migratory routes. Ship strikes have become a leading cause of death, with whales often simply unable to get out of the way in time. Noise from boats also interferes with their ability to navigate and communicate.

As fisheries respond to a growing global appetite for seafood, entanglement in fishing gear is also an increasing threat for many whale species. Particularly affected is the North Atlantic right whale, found along the east coast of North America from Florida to Canada, a region also home to lucrative lobster and crab fisheries. The long vertical ropes or “lines” used to connect traps on the ocean floor to floats on the water’s surface pose a lethal threat to right whales. The ropes can constrict body parts and cut into their flesh and bone, causing abrasion, infection and sometimes severance. Often whales can drag the heavy gear around for months, struggling to eat, swim, dive, breathe and reproduce. They lose energy and weight gradually, sometimes taking years to die.

Studies show that nearly three-quarters (72%) of diagnosed deaths of this species between 2010-18 occurred because of entanglements, and that 85% have been caught in fishing gear at least once. There are now just 409 remaining individuals, with less than 100 females of breeding age. Without intervention, they may be functionally extinct by 2040.

As well as live fishing gear, whales are also being killed in their thousands by “ghost gear”: abandoned, lost or discarded plastic fishing nets, ropes and lines in which they become trapped.

Climate change

Warmer ocean temperatures and melting sea ice pose serious threats to the survival of the world’s great whales. The reduction of sea ice cover is likely to impact belugas, narwhal and bowhead species for whom the Arctic provides habitat and feeding grounds. In the Antarctic, sea ice is also decreasing in certain areas, resulting in massive declines in krill, a primary food source for many species including whales.

The krill and plankton that form the foundation of the marine ecosystem are also being affected by the increasing acidification of the ocean. More CO2 being absorbed by the ocean means that some of these species will be unable to form and maintain their protective calcium carbonate shells, threatening key species further up the food chain. Studies show that plankton populations could decrease by as much as 40% by 2050. Coral reefs and polar regions are on the frontline of the acidification crisis, with North Pacific salmon, mackerel, herring, cod and baleen whales among the species under the most immediate threat.

Warmer seas will also affect the distribution of whales. If their prey moves as a result of climate change, they will likely follow. Mass movement of species to different habitats will result in increased competition for diminishing amounts of prey.

Pollution

Toxic chemicals banned decades ago could kill off more than half of the world’s killer whale population in 30-50 years, scientists believe. PCBs (polychlorinated biphenyls) are man-made organic compounds once used in electrical equipment, flame retardants and paints until they were found to be so dangerous to human health that they were banned in the US in the 1970s and Europe in 1987. Resistant to heat, chemicals and natural degradation, the same things that made PCBs so attractive also makes them hard to destroy, and so they remain in the ecosystem decades later. Some were improperly stored or disposed of, or even directly discharged into soils, rivers, wetlands and the ocean. Entering the food chain, they have worked their way up to concentrate in top predators, causing cancers, altering behaviour, damaging immune systems and harming reproduction. European killer whale populations, along with dolphins and porpoises, are the most contaminated in the world, and some of the most heavily exposed populations are not expected to survive the next few decades.

Jessica Aldred is special projects editor for chinadialogue, focusing on globally important environment themes including the ocean and biodiversity. She spent 10 years as deputy environment editor at the Guardian, and has nearly 20 years' experience working in the newsrooms of major media organisations in London, Sydney and Melbourne. 

This article appears courtesy of China Dialogue Ocean and may be found in its original form - including a series of stunning photographs by Wade and Robyn Hughes - by clicking here. Their new book Looking for Whales is now available to order online.