These whales have summer jobs as ocean fertilisers

Phytoplankton are the ‘grass of the sea’ – they are fundamental food for animals in the sea and in freshwater.

To truly bloom, phytoplankton need a steady supply of nutrients.

Baleen whales play an important role here, according to new findings.

Each summer, thousands of baleen whales, such as minke and fin whales, migrate north to feed in Arctic and sub-Arctic waters. There they do their part:

“By recycling nutrients in the ocean, these baleen whales can increase primary production by up to ten per cent,” says marine researcher Carla Freitas.

Researchers have long suspected that whales recycle nutrients, but now they have quantified how large their contribution is.

One nutrient mix in the poo, another in urine

Previous research has shown that the 15,000 minke whales feeding around Svalbard defecate about 600 tonnes each day.

Researchers have now also analysed their urine:

“Nitrogen is mainly excreted through urine. Phosphorus and other essential trace metals such as iron, zinc, copper, and manganese are mostly excreted through faeces,” says Freitas.

Nitrogen, phosphorus, and trace metals are key ingredients for phytoplankton. A lack of these nutrients limits production. Nitrogen is especially scarce in this region.

“Whale urine is not only a major source of nitrogen – it’s released in a form that phytoplankton can easily use,” says Freitas.

Up to 10 per cent

In the study, researchers focused on baleen whales feeding in the Barents Sea, Norwegian Sea, Greenland Sea, and Iceland Sea.

Baleen whales include minke, fin, sei, humpback, blue, and bowhead whales.

Researchers simulated primary production in two different scenarios: with and without nutrients from whales.

The contribution varied by time and place.

“We found the greatest effect in summer, when waters are stratified and nutrient levels are low – and in offshore areas far from other nutrient sources,” explains ocean researcher Morten Skogen.

Under such conditions, whale fertilisation can boost primary production by up to ten per cent. The yearly effect is more modest, up to four per cent.

More than top predators

The study suggests that increased primary production due to whale fertilisation creates ripple effects throughout the food web. There is up to ten per cent more zooplankton, which in turn feeds fish and other species.

“Whales are not just top predators – they are key species in the marine food web, recycling nutrients and contributing to a productive ecosystem,” says Carla Freitas.

Reference:

Freitas et al. Impact of baleen whales on ocean primary production across space and time, PNAS, 2025. DOI: 10.1073/pnas.2505563122

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