The surprising impact of whale pee on the health of ocean ecosystems

Baleen whales undertake some of the longest migrations of any mammal, traveling thousands of miles between nutrient-rich feeding grounds and tropical breeding areas.

Southern Hemisphere humpback whales make seasonal journeys of over 5,000 miles from Antarctic waters to the warm, shallow seas near Costa Rica. Gray whales travel nearly 7,000 miles between feeding areas off Russia and breeding sites along Baja California.

These migrations follow a common pattern: summers spent feasting in cold, food-rich waters, followed by long winters in tropical zones with little to eat. Yet, their movement serves a greater purpose beyond reproduction—whales act as a vital nutrient conveyor belt for marine ecosystems.

Most baleen whales are capital breeders, meaning they rely on stored energy for migration and reproduction. During summer, whales gorge on krill and fish, accumulating thick layers of blubber that sustain them through the winter.

North Pacific humpback whales, for example, gain about 30 pounds per day while feeding. By the time they leave for tropical breeding grounds, they carry massive reserves of stored fat.

Pregnant females, with the highest energy demands, store 25% more fat than nonpregnant ones and 37% more than males. Some species fast entirely during migration and calving, losing up to 200 pounds per day.

Whalers historically noted that whales killed at the end of breeding season weighed far less than those caught on feeding grounds. Their ability to travel such long distances and sustain prolonged fasting periods sets them apart from nearly all other mammals.

A widely accepted theory is that whales migrate to warm waters to protect their vulnerable newborns from predators like killer whales. Warmer temperatures may also help calves regulate their body heat before developing thick blubber. However, an emerging idea suggests that molting plays a role. Just like shedding skin, whales might migrate to warmer waters to help remove dead skin and fouling organisms like diatoms.

While whales are known for their vertical nutrient cycling—bringing nitrogen from deep waters to the surface through their feces—new research highlights their role in horizontal transport.

A University of Vermont study, published in Nature Communications, calculates that whales carry 4,000 tons of nitrogen annually to tropical regions. Before industrial whaling, this figure could have been three times larger.

Whale urine, feces, sloughed skin, placentas, and even carcasses provide an essential nutrient boost in otherwise low-nutrient waters. In areas like the Hawaiian Islands Humpback Whale National Marine Sanctuary, these contributions double the nutrient input from physical ocean forces.

“These coastal areas often have clear waters, a sign of low nitrogen,” says Joe Roman, a biologist at the University of Vermont and co-author of the study. “The movement of nitrogen and other nutrients can be important to the growth of phytoplankton, which fuels entire food chains, supporting fish, sharks, and invertebrates.”

Before industrial whaling decimated populations, whales played an even larger role in shaping ocean ecosystems. Blue whales, the largest animals to ever exist, remain poorly studied, with little known about their breeding areas. The impact of their nutrient transport is likely underestimated.

“We don’t often think of animals having an impact on a planetary scale, but whales do,” says oceanographer Andrew Pershing of Climate Central. “Nutrients are coming in from outside—not from a river, but by these migrating animals. It’s super-cool and changes how we think about ecosystems in the ocean.”

Seabirds are known to fertilize islands with nitrogen-rich guano, boosting plant growth. Similarly, whales act as the ocean’s circulatory system, moving nutrients across vast distances. Before commercial whaling reduced their populations by up to 90%, whales delivered nutrients that likely sustained entire coastal food webs. Today, conservation efforts are allowing some whale species to recover, slowly restoring this natural ocean fertilization system.

As scientists uncover more about these marine giants, it’s becoming clear that whales are more than just massive creatures roaming the seas. Their movements shape ocean productivity, and their survival benefits the entire marine food web.

Restoring whale populations could be a step toward reviving the nutrient cycles that once sustained vibrant ocean ecosystems.

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