Thanks a lot, Sheyka!
|Blue whale earplug, extracted from a dead individual. Credit: Michelle Berman- Kowalewskic, Santa Barbara Museum of Natural History, Santa Barbara, nationalgeographic.com|
Biography Of A Blue Whale, Told Through Ear Wax
by Ed Yong
A few years ago, Stephen Trumble contacted the Santa Barbara Museum of Natural History and asked if they had some earwax from a blue whale.
In 2007, a large ship travelling off the coast of California collided with a male blue whale, ending its life at the tender age of 12. It was one of three similar strikes that year. The animal’s 21 metre carcass washed up on the beach, and scientists from the local museum examined and dissected it with machetes and excavators. They collected several tissues and organs, including a 25-centimetre tube of earwax.
Earplugs are common to blues and other large whales like fins and humpbacks. They are similar to the ones in your ears, although obviously much bigger. Each is an oily build-up of wax and fats that accumulates through the whale’s life. “It looks like a long candlestick that’s been beat up a bit,” says Sascha Usenko, Trumble’s colleague at Baylor University. “It’s not appealing-looking.”
A whale produces a lighter-coloured wax during the time of year when it’s feeding, and a dark-coloured version when it migrates. If you cut through the earplug, you can see these varieties as alternating light and dark bands. They’re like tree rings. And just like tree rings, you can use them to estimate a whale’s age. That’s why scientists often collect and store the wax from dead whales.
But Trumble and Usenko have shown that the wax can reveal much more. It also preserves a chemical biography of a whale’s life, from its birth to its untimely ship-inflicted death. It records some of the hormones that surged through its body and the pollutants that it absorbed.
The duo previously measured environmental contaminants in whale blubber, but they realised that the same chemicals also ought to build up in earwax, which is made of similar fatty substances. “It was really an ‘A-ha!’ moment,” says Usenko. To find fresh whale wax, they contacted Michelle Berman-Kowalewskic from the Santa Barbara Museum of Natural History, who handed over the earplug from the dead blue whale they had dissected in 2007.
The plug showed that the whale’s testosterone levels rose during its first three years of life, fell until it was nine, and then shot up by around 200 times. That’s almost certainly the point when it became sexually mature. When other scientists have tried to work out this age using body length, ovaries or blubber, they’ve come up with estimates ranging from 5 to 15 years. “We didn’t really know,” says Udenko. “Now, we’ve nailed that down with tight resolution for one animal, and it’ll be really exciting to do a bunch more.”
Meanwhile, the whale’s levels of cortisol—a stress-related hormone— rose steadily over the course of its life and peaked a year after its testosterone spike. This might reflect the need to compete for mates, or to interact with other mature whales. “I think about what I was like at that age,” says Udenko. “A raging bull, trying to figure out my place in the social order… I was pretty stressed out.”
In the earplug, the team also found traces of several contaminants. There were 16 pesticides, flame retardants and other pollutants that tend to persist in the environment for a long time, such as the long-banned insecticide DDT. These were most concentrated during the first six months of the whale’s life, suggesting that they were inherited from its mother, either through the womb or from her milk.
There was also a fair amount of mercury, which gradually accumulated over the whale’s life and peaked twice, once when it was five years old and again when it was ten. Human industries like gold-mining can release large amounts of mercury into the oceans. Perhaps this whale was caught in a few such surges during its travels past California.
The chemical contents of the whale’s blubber matched those within its wax, which assured Trumble and Usenko that their readings were accurate. But blubber has no rings, so it can only give you an overall picture of the whales’ life. Earwax can tell you what happened every six months. Blubber gives the sum of the whale’s chemical bill; the earplug shows the individual lines.
“I was surprised at how well [the technique] worked, not only for persistent chemicals but for hormones that typically rapidly degrade,” says Usenko. “It allows us to ask more complex questions that are difficult to get at, like: What are the impacts of contaminants or stress on these animals?”
To get the same sorts of readings, Usenko says that he would need to follow a blue whale around for years, and take tissue sample from it every six months. “You couldn’t do it,” he says. “People have tried, but it’s difficult and you have to be committed for 30 years. Here, we can go to a lab and reconstruct the same effort in a month.”
|Blue whale earplug, whole (top) and in cross-section (bottom). Credit: Trumble et al, 2013. PNAS.|
But the earplugs have several limitations, says John Wise, a toxicologist at the University of Southern Maine who specialised on marine mammals. They only capture certain pollutants that accumulate in fat, they don’t tell us how those pollutants affect the animal’s health, and they can only be extracted from a dead whale. “Nevertheless, it’s a new and useful part of our whale conservation toolbox as we seek to better understand ocean pollution,” he says.
And, of course, the team have only looked at one earplug from one whale. Usenko acknowledges this, and says the study is meant to be a proof-of-principle. “We want to encourage museums to keep and collect these samples,” he says.
Existing earplugs should already provide a trove of data. The Smithsonian Institute alone has hundreds of plugs in its collection, many of which have been traced back to specific whales. They’re not in pristine condition, but they could be useful. Charles Potter, who manages the institute’s marine mammal collection and is a co-author on the paper, is now thinking about how to preserve these waxy treasures.
Reference: Trumble, Robinson, Berman-Kowalewski, Potterd & Usenko. 2013. Blue whale earplug reveals lifetime contaminant exposure and hormone profiles. PNAS http://dx.doi.org/10.1073/pnas.1311418110
PS: In case anyone was wondering, it doesn’t seem that the earplugs prevent the whales from hearing. In fact, some scientists have suggested that the plugs might actually help to channel sound towards the eardrum.
And finally, this is a good chance to reprise my blue whale facts:
- Blue whales are so big that each one can grow as large as a fully grown blue whale. That’s huge!
- If you take all the blue whales in the world and put them on a giant weighing scale, you are on drugs.
- A blue whale’s main artery is so big that a human could swim through it, but it’s generally not advised.
- A blue whale’s heart is the size of a Volkswagen beetle, but its steering is rubbish.
- If you take a blue whale’s intestines and lay them in a line, the whale will die. Also, what’s wrong with you, you sick bastard?