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Whales are important for healthy oceans. They move tons of deep-water nutrients to the surface when they poop, and, according to new research, they also transport massive amounts of nutrients from Alaska to Hawaii in their urine.
Fifteen years ago, scientists discovered that whale poop provided a crucial resource for the growth of plankton, contributing to ocean productivity, a press release from the University of Vermont (UVM) said.
Now, a new UVM-led study has found that whales carry large amounts of nutrients across entire ocean basins — from the cold waters of their feeding grounds to the warm seas where they mate and birth their calves near the equator. Most of the nutrients are transported through their urine, with carcasses, sloughed skin, placentas and calf feces also contributing.
“These coastal areas often have clear waters, a sign of low nitrogen, and many have coral reef ecosystems,” said co-author of the study Joe Roman, a biologist at UVM, in the press release. “The movement of nitrogen and other nutrients can be important to the growth of phytoplankton, or microscopic algae, and provide food for sharks and other fish and many invertebrates.”
The researchers calculated that, throughout the world’s oceans, great whales — including gray whales, humpbacks and right whales — move roughly 4,000 tons of nitrogen annually to tropical and subtropical low-nutrient coastal areas.
These massive whales also bring over 45,000 tons of biomass. Before whaling by humans decimated whale populations, at least three times more nutrients might have been transported these incredible distances.
“We call it the ‘great whale conveyor belt,’” Roman said, “or it can also be thought of as a funnel because whales feed over large areas, but they need to be in a relatively confined space to find a mate, breed, and give birth. At first, the calves don’t have the energy to travel long distances like the moms can.”
The whales also likely stay in sandy, shallow waters to muffle their sounds.
“Moms and newborns are calling all the time, staying in communication, and they don’t want predators, like killer whales, or breeding humpback males, to pick up on that,” Roman said.
This means the nutrients that are spread throughout the ocean are concentrated in much smaller coral and coastal ecosystems, “like collecting leaves to make compost for your garden,” Roman said.
During the summer months, adult whales feed in northern latitudes like Iceland, Alaska and Antarctica, eating herring and krill to put on tons of fat. Recent research has found that North Pacific humpbacks gain approximately 30 pounds a day from spring to fall.
“They need this energy for an amazing journey: baleen whales migrate thousands of miles to their winter breeding grounds in the tropics — without eating. For example, gray whales travel nearly 7000 miles between feeding grounds off Russia and breeding areas along Baja California. And humpback whales in the Southern Hemisphere migrate more than 5000 miles from foraging areas near Antarctica to mating sites off Costa Rica, where they burn off about 200 pounds each day, while urinating vast amounts of nitrogen-rich urea,” the press release said. “One study in Iceland suggests that fin whales produce more than 250 gallons of urine per day when they are feeding. Humans pee less than half a gallon daily.”
Whale migrations are the longest of any mammal on the planet.
“Because of their size, whales are able to do things that no other animal does. They’re living life on a different scale,” said co-author of the study Andrew Pershing, an oceanographer at nonprofit Climate Central, in the press release. “Nutrients are coming in from outside — and not from a river, but by these migrating animals. It’s super-cool, and changes how we think about ecosystems in the ocean. We don’t think of animals other than humans having an impact on a planetary scale, but the whales really do.”
Before industrial whaling in the 19th century, whales’ nutrient inputs would have “been much bigger and this effect would’ve been much bigger,” Pershing added.
Nutrient inputs for Earth’s largest animal ever, the blue whale, are unknown, so they were not included in the study’s primary calculations. Population numbers for blue whales who live in the Southern Ocean are still much lower than they once were after being decimated by hunting in the 20th century.
“There’s basic things that we don’t know about them, like where their breeding areas are,’’ Pershing said, “so that’s an effect that’s harder for us to capture.”
Humpbacks and blue whales were both depleted by whaling, but some humpback populations are rebounding after decades of conservation efforts.
“Lots of people think of plants as the lungs of the planet, taking in carbon dioxide, and expelling oxygen,” Roman said. “For their part, animals play an important role in moving nutrients. Seabirds transport nitrogen and phosphorus from the ocean to the land in their poop, increasing the density of plants on islands. Animals form the circulatory system of the planet — and whales are the extreme example.”
The study, “Migrating baleen whales transport high-latitude nutrients to tropical and subtropical ecosystems,” was published in the journal Nature Communications.
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