Pygmy right whales swim in the same waters all year round 鈥� a behaviour rarely seen in baleen whales, which typically migrate thousands of kilometres to look for food and mates. The finding offers a rare insight into the behaviour of a whale species we still know very little about, and might inform conservation efforts.
The pygmy right whale (Caperea marginata) is the smallest filter-feeding whale on Earth at just 6.5 metres long. The species is so secretive and rare that it was thought to be extinct until a decade ago. Researchers still aren鈥檛 sure how large the global population is, or where pygmy right whales live and what they eat.
Finding and tracking these whales is challenging, so at the University of New South Wales in Australia and her colleagues chose a different approach. They analysed samples taken from the bristle-like baleen plates in the jaws of 14 already deceased pygmy right whales, which were loaned to them by a local museum. 鈥淏aleen is made of keratin, like our fingernails, and grows continuously throughout the life of the whale,鈥� says Dedden.
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Because the chemical composition of the food a whale eats gets trapped in its growing baleen, isotope analysis can reveal useful long-term information about the whale鈥檚 diet and, by implication, where it roamed. Each baleen plate had up to four years鈥� worth of information, making this the most extensive study of the pygmy right whale diet and movement to date.
By matching the ratio of carbon and nitrogen isotopes in the whales鈥� baleen to known food sources, Dedden and her team found that the whales ate a diet rich in Australian krill and other crustaceans all year round. Most baleen whales are highly migratory, travelling between polar feeding areas in the summer and tropical calving areas in the winter, but there were no indications from the analysis that these pygmy right whales ate Antarctic species. Instead, they seem to spend all of their time hanging around Australia鈥檚 temperate waters.
One reason pygmy right whales might forgo long-distance migrations is their relatively small size. 鈥淏eing the smallest of the baleen whales, they may not need to rely on the greater abundance of krill in Antarctica to support their body size like their larger relatives,鈥� says Dedden. During their peak feeding season, baleen whales like the blue whale take in around 3600 kilograms of Antarctic krill per day 鈥� roughly the weight of a single pygmy right whale.
As climate change continues to influence ocean temperatures, currents and acidity, Dedden hopes the new analysis will help experts better anticipate how to protect the pygmy right whale, which is currently classified as 鈥渄ata deficient鈥� by the .
Frontiers in Marine Science
