It’s March on the Antarctic Peninsula, at the tail end of the expedition cruising season. Winter is in the air, with the days getting shorter in a blaze of terrific sunsets. On shore, the penguins are undergoing their annual moult in anticipation of spending the next few months at sea, and everywhere it seems, there are whales.
Whale watching in Antarctica at this time of year is a very special experience. The hunger of the summer months, when the newly-arrived whales must feed almost 24 hours a day after months without a meal in their tropical breeding grounds, has been replaced by something far more leisurely. Humpbacks ‘log’ – snoozing at the surface – and even approach groups of kayakers out of curiosity.
But like their visitors, these whales will soon be turning their flippers north to migrate back to warmer climes. And as they do, they’ll play a key role in keeping the world’s oceans healthy and productive. Moving vast amounts of carbon and nitrogen from the rich productive polar waters to the nutrient-poor tropics allows ecosystems there to thrive. This is the largest single long-distance nutrient transport system on Earth, and scientists are only just beginning to unravel its secrets.
The Great Whale Conveyor Belt
The way that whales move nutrients from high latitudes like Antarctica to tropical and subtropical ecosystems is known as the Great Whale Conveyor Belt, and recently published research has lifted the lid on the vast scale of the enterprise.
The humpback whales, seen along the Antarctic Peninsula, spend their summers feeding on massive quantities of krill. They squeeze the entire year’s feeding cycle into the few short months they’re in polar waters, building up the blubber that will sustain them through their long migration to warmer waters before they breed and give birth.
The distances each whale swims each year are truly vast. One humpback whale spotted last year by a member of the Swoop team in Antarctica had previously been seen off the Panama’s Pacific coast, a massive 5,100 miles (8,200 km) away. During this migration, it would have released essential nutrients like nitrogen back into the waters along the way. Believe it or not, whale pee makes for great marine fertiliser, along with the placentas after giving birth and their carcasses when they die.
If you’ve ever snorkelled on a Hawaiian reef and marvelled at the sea life there, thank a humpback whale.
Warm tropical waters aren’t as productive as cold polar waters, but the nutrients provided by whales, brought all the way from Antarctica, play a vital role in stimulating the growth of the phytoplankton that fuels the entire ecosystem.
How whales cycle nitrogen and carbon
For the first time, researchers have been able to quantify just how many nutrients these whales are transporting across the oceans. By studying migrating humpbacks from Antarctica and Alaska, as well as grey whales in the Pacific, North Atlantic and Southern right whales, it’s estimated that more than 46,500 tons of biomass, 4,900 tons of carbon and 3,800 tons are moved every year from polar latitudes to less productive warmer waters. This isn’t a drop in the ocean either: it’s believed that in some areas such as Hawaii, home of the Humpback Whale National Marine Sanctuary, the nitrogen they import each year is greater than anything that would be naturally available from the ocean. And all that nitrogen is fertilizer for phytoplankton. If you’ve ever snorkelled on a Hawaiian reef and marvelled at the sea life there, thank a humpback whale.
What makes this even more extraordinary is that while they’re in polar waters, whales effectively act as farmers for the ecosystem where they feed. They dive deeply to feed, then release nutrients from the bottom of the water column at the surface. Whale poop is bright pink thanks to their steady diet of krill (it’s unmissable if you see it during a cruise!), and is wildly rich not just in nitrogen but also in iron. This ‘whale pump’ allows phytoplankton to bloom, creating a food source for the krill eaten by whales as well as fish, penguins and seals.
Whales aren’t just redistributing nutrients across the oceans on conveyor belts, they’re acting as climate engineers.
This whale pump isn’t just a virtuous circle for a nice seafood buffet. The phytoplankton draw vast amounts of carbon from the atmosphere, and then krill store this in their calcium carbonate shells. When krill die, this carbon sinks in solid form to the ocean floor. In this way, the Southern Ocean acts as a vast carbon sink. In their own way, whales aren’t just redistributing nutrients across the oceans on conveyor belts, they’re acting as climate engineers.
The human impact of whale hunting
This outsized role that whales play in keeping our oceans, and even our climate, healthy begs an uncomfortable question: what happened in the 20th Century, when we hunted whales to the very point of extinction to turn them into oil and margarine?
The new study estimates that before industrial whaling, the amount of nutrients transported by whales was approximately three times greater than it is today. The large-scale removal of whales from the ecosystem almost certainly did untold damage to marine ecosystems by dismantling one of its key components.
The effects of that devastation can still be felt today. A sighting of a blue whale in Antarctic waters attracts such excitement, because their numbers are perhaps just a single percentage of what they were before whaling, and even nearly 40 years after the ending of commercial whaling, conservationists have observed only the slowest growth in their populations. Blue whales are the largest creatures ever to live on this planet, and they were killed in their tens of thousands before we knew anything about the vital role they played keeping our oceans healthy and productive.
The picture of other species is more hopeful however. Fin whales, bested in size only by blue whales, are now a common sight in Antarctic waters and are increasingly seen feeding in huge congregations as they return to their historic feeding grounds.
Better yet, the global population of humpback whales has largely recovered to its pre-whaling numbers. Humpbacks are relatively fast breeders – a female might produce ten calves in her lifetime, each time returning to and from the rich polar waters, helping to move their nutrients to warmer waters.
The future of the conveyor belt
Research on the Great Whale Conveyor Belt continues to unpack how these amazing creatures shape the environment they live in. Neither fin whales nor minke whales (another common Antarctic species) were included in the study, as their migrations are less understood and their offshore breeding grounds are harder to observe than species like humpbacks. Further studies will surely shed light on the role they play.
As the world’s ecosystems and climate come under increasing pressure from human activity, the discovery of the crucial role played by whales comes at an important time. In the dying days of commercial whaling, environmental campaigns like Save the Whale concentrated on larger charismatic species, but today it’s better understood that protections only work when they are centered on entire ecosystems. Studies like those on the Great Whale Conveyor Belt and the Whale Pump show the role that whales play in immense natural systems that sustain life across vast distances.
It’s March on the Antarctic Peninsula. Winter is in the air and the humpback whales are fat with krill and feeling playful. If you’re out in a zodiac, one might approach and even swim under you, before surfacing to cover you with a great cloud of fishy breath. When it does, it momentarily places you at the centre of a vast web. The carbon and nitrogen in the atmosphere connect to the depths of the ocean, and the freezing waters of the Antarctic join warmer seas thousands of miles to the north. It’s a reminder that the health of our whale populations is inextricably linked to the health of the oceans – and they need our help to continue their journey.
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