Whale pee carries nutrients across the world

A study has found that whales play a massive and previously unrecognised role in moving thousands of tonnes of nutrients - foremost among them nitrogen and phosphorus, which are essential in sparking plankton blooms - over thousands of miles of ocean. This creates a nutrient cycle on an epic scale as they feed in one place and later relieve themselves - as well as reproduce and die - in another. The University of Vermont’s Joe Roman has made the discovery by studying the habits of humpback, right, and grey whales. And don’t be under any illusion about how much urine we’re talking about…

Joe - So a typical human, we make about two litres of urine a day. Fin whales are much larger. So that's the only species that's actually been studied. And this is from whaling data in Iceland. Estimates are maybe a thousand litres or 250 gallons per day and similar amounts for other large whale species. And that is rich in nitrogen. It's also rich in other nutrients like phosphorus. And then it also has chlorine and sodium. And for your listeners to realise, that's pretty common, right? In the ocean. So we really looked at the nutrients that are limiting, that are going to spark growth in those areas.

Chris - And so to what extent might they therefore be moving nitrogen around rather than just pick up nitrogen in their food from a local area and then they just pee in that local area. So they just cycle what's already around. Have you got evidence they're actually actively moving the nitrogen from A to B?

Joe - Whales are what's known as capital breeders. What does that mean? It means they feed for part of the year and they breed at a different part of a year, unlike humans, which have to feed while they're having offspring. So they're travelling a thousand, two thousand kilometres to places like the Caribbean or Hawaii. And the females, in order to give birth and in order to lactate and to gestate, they need enormous amounts of energy. Where do they get that from? They're breaking down the fats and the proteins that they stored in the summer. And in the process, they have to release excess nitrogen, excess phosphorus. Other pathways include placentas. So whale placentas can be hundreds of pounds. Infant mortality in whales can be fairly high. So when a calf dies, that brings a lot of nutrients. And then the whales themselves can also, you know, they can die on the breeding grounds as well. So those four pathways are how they bring nutrients. But because whales are peeing all the time, that's the main source by far, is the urine, is the main source for nitrogen and other nutrients.

Chris - So how much nitrogen are they moving and other nutrients around the planet when they go from A to B in this way?

Joe - About 4,000 tonnes of nitrogen per year. So what we did is we looked at one particular system, whales that feed in Alaska and breed in Hawaii because that system is well studied. There, they bring as much nitrogen from Alaska to Hawaii as the local processes of wind and upwelling transport into these systems. So this is a biotic or a biological form of bringing these new nutrients, these external nutrients, into the system. And then we start to get an idea of what the impact might be on phytoplankton. Hawaii, about 4,000 tonnes of biomass or just body are transported there every year. And that's comparable to like 10 million Big Macs. I mean, they're bringing a lot of food into the system. So it's not just the nutrients, but sharks feed on the carcasses or the placentas, fish feed on it. These nutrients can get into the coral reef systems. So it's two processes, one sort of daily in the urine and the other in, you know, at the end of an animal's life is the other big pulse of nutrients or biomass food.

Chris - Did we see an impact then when there were fewer whales? Luckily, numbers are climbing across many species because of international bans on whaling. Wasn't always like that. And some animals were close to the point of jeopardy. They have rebounded. So are we now seeing a change in that nitrogen flux and what impact is having?

Joe - That's exactly right. So historically, whales were, it depends on the species. We haven't talked about blue whales and fin whales, but blue whales, for example, were reduced to about 1%. Largest animals ever existed on the planet, down to 1% of their population in the Southern Hemisphere. So basically they had no ecological role. And that still sadly remains for some species like the North Atlantic right whale, only 350, 400 whales on the planet. Their ecological role is pretty small. Let's look at some better news though. Right whales in the Southern Ocean, as well as humpback whales in the North Pacific and gray whale populations have all increased. They're rarely up to historical numbers, but that has allowed us to really examine what the impact of these whales could be. I think 50 years ago, 60 years ago, oceanographers overlooked the role of whales. They were so rare. Of course they weren't important. We had basically eradicated them. But keep in mind, Chris, that we still have a long way to go here. One study that we mentioned is that 4% of the biomass of mammals on the planet is wild biomass. The vast majority are humans and cows and sheep. That 4% includes all the whales, all the great whales. So it's not surprising that we haven't considered animals as being an important part of what I describe as the circulatory system of the planet because we really sort of clogged up those arteries. And now we're just starting to see in places like Hawaii and the Caribbean what the restoration of these species can mean for local ecosystems and for global nutrient transport.