The Great Whale Conveyor Belt: Earth's Largest Mammals Keep Oceans Thriving

Each year, the world’s largest mammals embark on epic journeys spanning thousands of miles across the planet’s oceans. However, large whales aren’t just impressive travelers – they’re also operating what scientists have called “the Great Whale Conveyor Belt,” the largest long-distance nutrient transport on Earth.

An exciting study just published in Nature Communications has quantified the massive nutrient transport mediated by baleen whales, revealing how these marine giants move tons of nitrogen and carbon from nutrient-rich polar feeding grounds to nutrient-poor tropical and subtropical breeding areas.

Researchers calculated that this “Great Whale Conveyor Belt” has diminished by approximately two-thirds since pre-whaling times. Perhaps most concerning, the study predicts that climate change could further reduce whale populations in coming decades, threatening what may be the largest long-distance nutrient subsidy on the planet. This, in turn, could disrupt marine ecosystem dynamics.

A gray whale mother-calf pair migrating along the central California coast from the wintering grounds in Mexico to the summer feeding grounds in the Arctic — Credit: NOAA

A Great Whale Conveyor Belt

Migrating baleen whales essentially function as living vessels, moving nutrients between ocean ecosystems that would otherwise remain disconnected. The mechanism is elegantly simple: baleen whales such as humpbacks, gray, and right whales spend their summers gorging in cold, food-rich waters near the poles. During this time, they build up enormous energy reserves in the form of blubber.

When winter approaches, they migrate to warmer waters near the equator where they fast for months while breeding or giving birth. During this time, they metabolize their fat stores and release nitrogen and other nutrients into these tropical waters through urine, placentas (after birth), and occasionally through the carcasses of whales that die during the journey.

The oceans’ fertilizers allow phytoplankton to bloom

The quantities involved are enormous. According to the study, just four species of baleen whales – gray, humpback, and North Atlantic and southern right whales – transport approximately:

46,500 tons of biomass
4,900 tons of carbon
3,800 tons of nitrogen

This nitrogen, primarily excreted as urea (the main component in urine), can stimulate the production of more than 18,000 tons of carbon through primary productivity. This means baleen whales are essentially fertilizing the base of the marine food web (phytoplankton) in regions where nutrients are typically scarce. In fact, in some locations, like Hawaii’s Humpback Whale National Marine Sanctuary, the nitrogen contribution from whales during the breeding season exceeds what’s naturally available through physical processes such as ocean currents.

An ecosystem service in peril

Perhaps the most striking finding of the study is its insight into our past impact on ocean ecosystems. Before industrial whaling decimated global whale populations, nutrient transport was approximately three times greater than it is today.

For centuries, humans hunted whales primarily for oil, unaware that we were simultaneously dismantling a global nutrient transport system. The study suggests that declining whale populations may have triggered cascading effects on marine ecosystems beyond the direct loss of the whales themselves.

Although some populations have partially recovered since the Moratorium on the ban of commercial whaling (1986), climate change now poses a new threat to these mobile ecosystem engineers. Models predict that Southern Hemisphere humpback and right whale populations will likely peak around 2050 before declining due to shifting ocean temperatures, sea ice patterns, and primary productivity—potentially disrupting one of Earth’s most significant biological nutrient transport systems just as we begin to grasp its full importance.

The lifelong impact of a single whale

Even at the individual level, whales make a remarkable difference. A single female humpback whale could produce 10 calves over her lifetime, requiring at least 20 return migrations. On each calving journey, she would transport approximately 77 kg of nitrogen to breeding grounds. This could stimulate the production of more than one whale’s worth of carbon on the breeding grounds over her lifetime. What a powerful illustration of how these animals contribute to marine ecosystems beyond their own biological needs.

Whales are not the only animals capable of moving nutrients within oceans

The researchers compared whale nutrient transport to that of seabirds, another important marine nutrient mover. While seabirds transport comparable amounts of nitrogen overall, whales move these nutrients much farther distances – across thousands of kilometers from polar regions to tropical waters – while seabirds typically operate over tens to hundreds of kilometers, with much of their nutrient deposition occurring on land rather than in ocean ecosystems.

Looking Forward

The study highlights how much we still have to learn about whale ecology and their role in global nutrient cycles. Researchers suggest that future studies should examine the migration patterns of other baleen whales such as minke whales, which could transport even more nutrients from their feeding to breeding grounds.

Better understanding of the “Great Whale Conveyor Belt” provides yet another compelling reason to protect the world’s remaining whale populations. Not only are these magnificent creatures worth saving for their intrinsic value, but they’re also maintaining critical connections between ocean ecosystems thousands of miles apart.

The findings underscore a fundamental ecological principle: in the interconnected web of life, the loss of one component can have far-reaching and unexpected consequences across the entire system.