Pygmy right whales’ feeding habits are no longer a secret

In the world of oceanic giants, the Pygmy right whales, or Caperea marginata, stand out as the smallest and arguably the most mysterious species of all baleen whales.

Despite their relatively minute size — measuring up to 6.5 meters in length and weighing up to 3.5 tons — and their discreet behavior compared to their louder cousins, like the humpback whales, these under-researched mammals continue to baffle and intrigue scientists.

Baleen whales, including the pygmy right whales, are unique for their ‘baleen plates’ that serve as nature’s equivalent of a sieve. Positioned inside the whale’s mouth, the baleen allows seawater to flow freely while trapping small prey items such as zooplankton and tiny fish. This provides the whales with their sustenance.

Studying the elusive pygmy right whale

Our understanding of these elusive pygmy right whales primarily derives from beached specimens, as their sparse distribution and subtle behavior make them hard to spot in the wild. Unlike their larger counterparts, pygmy right whales were seldom the targets of historical whale hunts due to their smaller size and comparatively low oil content.

Unlike most other baleen whales, pygmy right whales aren’t known for long-distance migrations. “They don’t make long cross-ocean migrations,” stated Dr. Tracey Rogers, professor of ecology and evolution at the University of New South Wales, Australia.

“Instead, they are homebodies, who remain near the coast of southern Australia year-round, where they breed and feed on krill and copepods.”

Dr. Rogers is the senior author of a recent study published in the journal Frontiers in Marine Science. The research indicates that these whales predominantly inhabit mid-latitude waters. One such area is the eastern Great Australian Bight and the area impacted by the Bonney Upwelling, stretching between Portland and Robe.

These regions are characterized by south-eastern winds that drive cold, nutrient-rich water to the surface from November to May. This seasonal upwelling triggers a food bonanza, attracting a plethora of seabirds and marine life, including the pygmy right whales.

Tracking the whales using isotopes

The scientists behind the study utilized an innovative approach to track the whales’ dietary patterns and habitats.

They analyzed the ratio of stable nitrogen isotopes (15N and 14N, denoted as the δ15N value) and stable carbon isotopes (13C and 12C, the δ13C value) found in the baleen plates of 14 adult pygmy right whales. The whales included both sexes and had been stranded between 1968 and 2019 along the Tasmanian or southern Australian coast.

“Baleen is made of keratin, like our fingernails, and grows throughout the life of the whale,” clarified lead author Adelaide Dedden, a doctoral student in Dr. Rogers’ research group. “As a stable tissue, baleen provides an ideal long-term signal to look at their diet and habitat use.”

Since animals acquire their nitrogen and carbon exclusively from their food, the isotope ratios in their tissues reflect their prey’s ratios. By matching the δ15N and δ13C values in the whale’s baleen with those in various potential prey, the researchers were able to deduce the pygmy right whales’ preferred food sources.

What they learned about pygmy right whales

The study revealed that the isotope ratios in the pygmy right whales’ baleen closely resembled those of copepods and krill species from zooplankton-rich regions off Australia. Notably, the whales’ isotope ratios did not align with those of Antarctic krill. This implies that unlike many other baleen whales, pygmy right whales do not embark on seasonal migrations to Antarctic waters.

The findings further indicated that these whales likely do not feed on pelagic fish. The isotope ratios did not match those of these fish species.

Despite their adaptability and resilience, the authors warned that the pygmy right whales’ specific dietary preferences and confined mid-latitude range could place them at risk.

“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,” cautioned Dr. Rogers.

This crucial study opens new avenues for further exploration and potential conservation efforts aimed at preserving these intriguing oceanic homebodies.

More about baleen whales

Baleen whales, belonging to the Mysticeti suborder, are one of the world’s largest and most magnificent marine creatures. Known for their distinguishing baleen plates and gargantuan sizes, these whales embody a diverse group. This group includes species such as blue whales, humpback whales, right whales, and the relatively smaller pygmy right whales.

Despite their sheer size, these gentle giants subsist predominantly on tiny sea organisms. They are a fascinating example of biological and ecological adaptation.

Physical characteristics

Baleen whales are easily distinguishable by their baleen plates – a series of flexible, comb-like filters in place of teeth. These plates, made of keratin, allow the whales to filter-feed by trapping small organisms while expelling seawater.

Baleen whales also display two blowholes on their upper bodies, enabling efficient respiration during their brief surface intervals. The size and shape of baleen whales vary considerably across different species. Their lengths range from 6 meters in pygmy right whales to over 30 meters in blue whales.

Behavior and habitat

Baleen whales populate all the world’s oceans, from polar to tropical waters. They exhibit diverse behaviors, including intricate songs, aerial acrobatics, and cross-ocean migrations. Most baleen whales undertake annual migrations between cold, food-rich waters for feeding in summer and warmer waters for breeding and birthing in winter.

Baleen whale diet

Despite their colossal size, baleen whales have a surprisingly modest diet comprising small marine organisms. Their food primarily includes krill, copepods, and small fish, sieved from seawater using their baleen plates.

The baleen acts as an efficient filter. It permits water to pass through while retaining food particles, which the whales then swallow.

Reproduction

Baleen whales have a gestation period of nearly a year, culminating in the birth of a single calf. The young whales, or calves, are born tail-first, and they can swim almost immediately. They feed on their mothers’ rich milk. It is very high in fat, and grow rapidly in the initial stages of their life.

Conservation status and threats

The conservation status of baleen whales varies by species. Some, like the humpback whale, are recovering due to extensive conservation efforts. Others, like the blue whale and North Atlantic right whale, are critically endangered.

Major threats to these whales include commercial whaling, ship strikes, entanglement in fishing gear, ocean noise, habitat degradation, and climate change.

Research and study

Baleen whales have been subjects of extensive research and study. This research contributes significantly to our understanding of marine biology, ecology, and evolution.

They have also played a pivotal role in highlighting conservation needs. Many scientific methods are employed for studying these whales. They include range from acoustic monitoring and aerial surveys, to genetic studies and isotopic analysis of their baleen.

Cultural significance

Baleen whales have considerable cultural and economic significance. They have been vital in the historical whaling industry, featured in indigenous folklore, and are now key attractions in the burgeoning whale-watching tourism sector.

As ambassadors of the ocean’s wonders and vulnerabilities, baleen whales are not merely a group of species but symbolize the complex interplay of life, evolution, and survival in the marine world. Their study and conservation continue to inspire awe and urgency in equal measure.