The story hidden in their mouths — ScienceDaily

UNSW Sydney scientists have uncovered the secrets locked in the jaws of humpback whales and southern right whales. Baleen — the characteristic hair-like device that toothless whales use to feed — reveals how these large aquatic mammals adapt to environmental changes over time.

Filter-feeding whale baleen — the hair-like structures that humpback and southern right whales rely on for food — contain a chemical record of their feeding habits, which can help researchers understand changes in whale movements and behaviors over time.

Researchers have now shown how changes in whale feeding habits over nearly 60 years correspond to changing climate cycles. The research, published in Marine Science Frontiersshows that it is possible to link feeding habits to climatic conditions using whalebone, which could help us understand how these large aquatic mammals might react to climatic events in the future.

“What’s amazing is that all of this information about food and spatial patterns was unlocked just by analyzing plates in their mouths,” says Adelaide Dedden, lead author of the study and a PhD student at UNSW Science.

In the study, the researchers compared information stored in the baleen of humpback and right whales in the Pacific and Indian Ocean with environmental data to see if their behaviors reflected changes in climatic conditions over time.

“We have found that the same conditions – La Niña events – that bring us to these devastating floods are also not good for the humpback whales that migrate along the east coast of Australia,” says the professor. UNSW Tracey Rogers, marine ecologist and lead author of the study.

Using baleen samples from museum archives, strandings and previously published data from other studies, they found that humpback whales migrating along the east coast of Australia showed signs of poorer foraging opportunities during La Niña phases – a large-scale climate cycle that determines food availability in the Southern Ocean.

“Baleen whales are huge and need huge amounts of food. This makes them vulnerable to changes in the environment, but it’s also made worse by their survival strategy,” says Professor Rogers. “They fast for long periods of time when they leave their productive feeding grounds to breed. This is why they are extremely sensitive to changes in ocean-atmosphere cycles as they can result in food availability.”

Whale Bone Whispers

A whale-sized animal isn’t exactly easy to analyze in a lab environment. Instead, researchers can examine smaller hard tissues that keep a more detailed record of the animal’s activity.

For filter-feeding whales, the long, thin plates of keratin that hang from their upper jaws, called baleen, allow them to capture many small prey at once – but they also deposit chemical clues called stable isotopes that give clues to their eating habits.

“As the baleen grow, the biochemical signals from their food are trapped. Like the information on the pages of a book, they don’t change over time,” says Professor Rogers. “These signals allow us to piece together the behavior of whales over time – what they ate and the general area where they were at the time.”

The study found that stable isotope variability in humpback whale baleen correlated with changes in climate cycles, implying that whale feeding habits change with climate-dependent resource availability.

“Oscillation patterns in assimilated isotopes along their baleen are known to reflect changes in whale physiology, but we have also found links between this isotopic variability and changes in the environment that occur at the time,” Ms Dedden said.

Feast or Famine

Humpback whales spend their winter months in warm tropical waters to breed before returning to southern Antarctic waters during the summer to feed. In the midst of this migration to the tropics, they are far from reliable food sources and must depend on their body reserves and opportunistic prey off Australia to survive.

“As filter-feeding organisms, they depend on large aggregations of krill because it is energetically expensive for them to feed,” says Dedden.

Antarctic krill need sea ice to thrive. After the La Niña phases, further research has shown that there is less concentration of sea ice where these whales feed, which means there is less krill for the whales to consume. and support them during their months of migration.

“[With] humpback whales off the east coast of Australia showing signs of reduced feeding after La Niña periods, this means they are potentially struggling to build up the necessary energy reserves during the summer,” explains Ms. Dedden.

Previous research has found links to increased whale strandings on the Australian coast after La Niña years, which the researchers say can be attributed to lower feeding success.

“Our colleagues have shown that humpback whales are leaner – a sign that they are experiencing poor foraging conditions – and are more likely to become stranded in the years following La Niña events,” says the Professor Rogers.

“With La Niña events expected to increase in intensity and frequency, this unfortunately means that these whales may continue to have more of these poorer feeding prospects, and we may see more strandings in the future. “

Hopes for the future

Although not clear waters for east coast humpback whales, the study found that Australian west coast humpback whales that feed in the Indian Ocean have showed increased feeding success during La Niña periods. In promising signs, the researchers also say their east coast counterparts are developing alternative feeding strategies in more temperate waters.

“East coast humpback whales have shown signs of adapting to different feeding strategies in other known productive regions along their migration route…something that future research could examine,” said Ms. Dedden.

The researchers hope to use the study results to develop models that can help predict whale behavior in the future.

“We’ve built models from historical trends in the past, and now we can use those models to make predictions into the future to see what that might look like for our whales,” says Professor Rogers.

“The information from the study will also be useful to managers now, to know in advance those years when whales are likely to be more vulnerable so that they can be prepared and, if necessary, modify their management strategies regarding entanglement and stranding of whales.”

Although humpback whales are no longer listed as endangered, climate change still poses a significant long-term threat to the species.

Professor Rogers says our actions today to tackle climate change will make a big difference for whale populations now and in the future, just as they will for us.

“We need to act now while we still can,” she said.

“Acting now on climate change is good for the whales but also for all of us.”