Mysterious behavior of Pygmy right whales (Caperea marginata) – the smallest, ‘most enigmatic’, and probably least studied of all baleen whales.
Pygmy right whales (Caperea marginata) hold the title as the smallest, most mysterious, and least explored among all baleen whales. Baleen, acting like sieves in their mouths, allows seawater to flow through while capturing small prey like zooplankton and small fish.
These elusive creatures are rarely spotted in their natural habitat, primarily due to their relatively small size (6.5 meters long and weighing up to 3.5 tons), scattered distribution, and inconspicuous behavior, which sets them apart from the more conspicuous humpback whales.
Historically, these creatures have eluded the attention of whalers, and our limited understanding of them primarily comes from studying stranded specimens.
A recent study, led by Dr. Tracey Rogers, a professor of ecology and evolution at the University of New South Wales, reveals that the behaviors of pygmy right whales are unlike other baleen whales.
How are Pygmy Right Whales different from other baleen whales?
Rogers adds, “Here we show that pygmy right whales don’t behave like most other baleen whales: they don’t make long cross-ocean migrations.”
The study, published in Frontiers in Marine Science, suggests that these whales are confined to mid-latitude waters, frequently inhabiting regions such as the eastern Great Australian Bight and the area influenced by the Bonney Upwelling.
In these regions, southeastern winds bring nutrient-dense, cold water to the surface from November to May, resulting in a feast for marine life and seabirds.
In this study, they analyzed the ratio of stable nitrogen isotopes 15N to 14N (the δ15N value), and stable carbon isotopes 13C to 12C (the δ13C value) in the baleen plates of 14 adult pygmy right whales.
This analysis was performed to understand their dietary preferences and habitat use. The whales studied included both genders that were stranded on the Tasmanian or southern Australian coast between 1968 and 2019.
The baleen plates, borrowed from the South Australian Museum in Adelaide, serve as an ideal long-term indicator of their dietary habits and habitat use, as explained by the lead author Adelaide Dedden, a doctoral student in Dr. Rogers’ research group.
“Baleen is made of keratin, like our fingernails, and grows throughout the life of the whale,” as explained by lead author Adelaide Dedden, a doctoral student in Rogers’ research group. “As a stable tissue, baleen provides an ideal long-term signal to look at their diet and habitat use.”
Isotope ratios in animals’ tissues mirror those of their food since animals get their nitrogen and carbon exclusively from their diet. As one moves up the food chain, these isotope ratios increase regularly, with the lowest in phytoplankton and the highest in top predators. Dedden and her team could deduce the pygmy right whale’s diet by comparing the δ15N and δ13C values in the baleen to those of potential prey.
The findings revealed a close match between the isotope ratios in the pygmy right whales’ baleen and those of copepods and krill from zooplankton-rich regions off Australia.
Contrarily, there was no match with the isotope ratios of Antarctic krill, indicating that, unlike other baleen whales, pygmy right whales do not migrate seasonally to the Antarctic. Similarly, the isotope ratios did not match those of pelagic fish, suggesting these smaller whales do not feed on fish, unlike their larger relatives.
The research team warns that the limited range and specific dietary preferences of the pygmy right whales could pose a threat to their survival.
Rogers says, “As large-bodied mammals who feed on tiny prey, pygmy right whales need to consume vast quantities of food. This makes them vulnerable to changes in their local environment. Their home, the temperate oceans of the southern hemisphere, is warming at an alarming rate. We plan to study next how they will respond to this change.”
Image Credit: Henry Cordell