A pod of orcas grabbed the headlines in late March 2019. Researchers performing their annual dolphin and whale surveys off the southwestern coast of Australia stumbled across an orca attack on a healthy, adult blue whale. They recorded the event, which had never been documented before. Just two weeks later, a blue whale calf was taken by many of the same individuals. Another blue whale calf predation was witnessed in 2021.
Around the world, orcas had been known to predate on the calves of large whales, such as those of humpback whales and gray whales. However, until recently, it was unknown whether they hunt and kill the largest animal to have ever lived on Earth: the blue whale.
But for all the attention that the orcas received for their deeds, they aren’t the only species to kill blue whales. Considered extremely valuable due to their large size and quantities of baleen, blubber and meat, blue whales were hunted extensively by human whalers before the practice was banned in 1986. By the 1960s, though, the species was nearly extinct. And as recently as 2018, an Icelandic whaling company killed a blue whale.
Despite decades of protection, blue whale populations have yet to recover from the impacts of commercial whaling. And the endangered mammals now face new threats, such as entanglement in fishing gear and ocean pollution.
Unlike orcas, the giant, peaceful blue whales have no teeth. Instead, they sport baleens made of a hornlike, keratinous material; arranged in two rows of transverse plates, which hang down from their upper jaws. After taking a mouthful of seawater, baleen whales—such as blue whales—squeeze the water back out, leaving food, mostly krill, behind in these “curtains.”
Baleens, though, act not only as strainers. They’re a kind of history book, telling stories of climate change adaptation, ecosystem engineering and epic travel journeys.
Baleens as history books
In December 2021, researchers from the Royal Netherlands Institute for Sea Research reported in the journal Royal Society Open Science that they had found a novel way to analyze baleens and create “history books” for whales. By taking samples from the baleens of beached whales or other whales that had died, they found that they could chemically analyze the amino acids that had been laid down across the length of a baleen, essentially reconstructing the history of the animal’s diet and migration routes.
Baleens allow filter-feeding whales to take in many small prey at one time, but they also collect chemical clues, known as stable isotopes, that hint at a whale’s eating habits. As the baleens grow, biochemical signals from their food are trapped. Like the information in the pages of a book, they don’t change with time. These signals allow scientists to reconstruct the behavior of the whales through the years—what they ate and the general area where they were at the time.
For their study, one of the things the scientists looked at was the various isotopes of nitrogen. Nitrogen-14 is the most abundant, but there is also a heavier version, nitrogen-15, that has an extra neutron. When an animal digests plankton, part of the protein from the plankton is used to create the animal’s own proteins. In this process, the concentration of the heavy nitrogen increases a little at each step on the food chain. As a result, animals higher up on the food chain contain more and more nitrogen-15.
But even in different places on Earth, the concentrations of nitrogen-15 are not equal: the higher north in the Atlantic Ocean you go, the heavier nitrogen becomes in the water and thus in plankton.
To distinguish the potential effects of position on the food chain from the latitude of the foraging area, the researchers applied a new trick: they analyzed the different nitrogen forms in individual amino acids.
Certain amino acids (the building blocks of protein) cannot be made by the body. As a result, those essential or source amino acids remain mostly intact throughout the food chain. Other, so-called trophic amino acids are reworked and do change. Thus, the difference in nitrogen composition between source and trophic amino acids is a measure of how high up on the food chain an animal is.
In the whales, the trophic versus source amino acid difference appeared to be constant across the baleens, meaning that these individuals ate at the same food chain level during the whole period their baleens were being formed. Thus, the differences in nitrogen isotopes in the baleens had to be a “geographic effect,” recording the presence of the whales in waters with different nitrogen compositions. By looking at the concentrations of nitrogen-15 in the baleen layers, the scientists were able to determine the whales’ annual migration patterns between the Arctic and North Atlantic Oceans.
The scientists say that knowing not only what a beached whale has eaten but also where it has been swimming in recent months can help to identify migration pathways for threatened populations. Such information can even still be extracted from whales in museum collections, which could be useful in identifying long-term changes in diets and migrations due to human impacts.
Baleens as climate-change barometers
Baleens can tell another story: how whales adapt to environmental changes over time.
Researchers from the University of New South Wales, Sydney, have now shown how modifications in the dietary habits of whales going back almost 60 years correspond with changing climate cycles. The research, published in Frontiers in Marine Science, demonstrates that it’s possible to link feeding patterns with climate conditions using whale baleens—which we know from the previously mentioned study hold a chemical record of their diets—helping us understand how these large aquatic mammals may react to climate events in the future.
In this study, the researchers compared the information stored in the baleens of humpback and right whales in the Indian and Pacific Oceans with environmental data to see whether their behaviors reflected changes in climate conditions over time.
Humpbacks spend their winter months in warm, tropical waters to breed before traveling back to southern Antarctic waters during the summer to feed. Amid their migration to the tropics, they’re away from reliable food sources and must depend on their body’s reserves and opportunistic prey off Australia to survive.
Using baleen samples from museum archives, strandings and previously published data, the researchers discovered humpback whales migrating along the east coast of Australia showed signs of poorer feeding opportunities during La Nina years, which are characterized by unusually cold ocean temperatures in the Equatorial Pacific. El Nino years, in contrast, are defined by unusually warm ocean temperatures in the Equatorial Pacific.
As filter feeders, baleen whales rely on big aggregations of krill. Antarctic krill need sea ice to thrive. Following La Ninas, there is less sea ice where the whales feed, meaning that there are fewer krill for them to consume and to sustain them through their migration months. With the humpbacks from Australia’s east coast showing signs of reduced feeding following La Nina periods, it means that they’re struggling to build up their required energy reserves.
Previous research found links between increased whale strandings on the Australian coast following La Nina years, which the researchers say can be attributed to less feeding success. With La Nina events predicted to increase in intensity and frequency, these whales may continue to have poorer feeding prospects, and we could see more strandings in the future.
On the other hand, the study found that humpbacks from the west coast of Australia who feed in the Indian Ocean showed increased feeding success during La Nina periods. And the east coast whales are showing promising signs that they are adapting by developing different feeding strategies in other, known productive regions on their migration route. Hopefully, the information from this study will be useful for determining ahead of time those years when whales are likely to be more vulnerable so that management strategies around whale entanglements and strandings can be altered.
Baleens as backstories
From 1910 to 1970, humans killed an estimated 1.5 million baleen whales in the waters encircling Antarctica. You’d think that for krill, this would be a boon. But new research published in the science journal Nature suggests the opposite: that the decline of baleen whales in the Southern Ocean has led to a decline of krill.
For this study, researchers looked at baleen whales: blue, fin, humpback and minke. They employed several high-tech tagging devices that recorded the animals’ movements and sounds. Drones measured the length of individual, tagged whales, which helped the researchers estimate the size of their gulps. Underwater devices called echo-sounders measured how much prey was around.
The data revealed that whales in the Southern Ocean eat about twice as much krill as former estimates suggested, and that krill-feeding blue and humpback whales off the coast of California eat two to three times as much as once thought. Fish-feeding humpback whales, however, were found to eat the previously estimated amount or less.
With these new consumption figures, the researchers calculated that in the early 20th-century, the abundance of krill in the Southern Ocean had to be about five times what it is today to feed the pre-whaling cetacean population. This implies that whales play a complex role in their ecosystems, where their decline or recovery is strongly tied to overall ecosystem functioning and productivity.
The Southern Ocean is among the most productive ecosystems on Earth, largely due to the abundance of microscopic algae, called phytoplankton. Phytoplankton are a vital food source for crustaceans, krill and small fish; which, in turn, are consumed by larger animals, including birds, other fish and whales. But whales also help sustain phytoplankton. Through eating krill and then defecating, whales release the iron that is locked within krill back into the water, making that iron available to phytoplankton, which need it to survive.
In essence, then, large whales are mobile krill-processing factories. Each blue whale or fin whale is the size of a commercial airplane. So, in the first half of the 20th century, before whaling, there were at least an additional 1 million of these 737-sized, krill-processing plants moving around the Southern Ocean, eating and fertilizing.
The researchers say that their results are a sign of just how much the precipitous decline of large marine mammals has negatively impacted the health and productivity of ocean ecosystems.
Baleens as ways for becoming better
I believe we have no grounds to blame the orcas. We killed a staggering 360,000 blue whales in the 20th century in Antarctic waters alone, before the International Whaling Commission effectively banned commercial whaling in the mid 1980s.
When whales were very numerous, they played a gigantic role in bolstering the Earth’s ocean ecosystem. Almost four decades after we stopped hunting whales, we’re still learning what impact that had. Perhaps, now, the stories to be found in baleens will inspire us to seriously consider the planet-wide repercussions our actions can cause.
Here’s to finding your true places and natural habitats,