25 March 2026: A new study on the baleen plates of Balaenopterid whales

A study by Marc Ruiz-Sagalés and colleagues, titled “Multielement Stable Isotope Ratios in the Baleen of Maternal and Fetal Fin Whales Provide Evidence for the Most Recently Formed Segment of Balaenopterid Baleen”, was published in the Marine Mammal Science journal in December 2025.

Baleen whales do not have teeth. Instead, they have keratin plates inside their mouth, known as baleen plates, which they use to filter small prey. These plates are commonly used for studying the life cycle of baleen whales through Stable Isotope Analysis (SIA). SIA examines the chemical composition of animal tissue, allowing us to understand the animal’s diet and habitat (as the diet is influenced by the habitat and the food sources available in it). However, as baleen grows, different parts of the plate will reflect the whale’s diet at different parts of its life, so correctly interpreting the results of an SIA can be tricky.

This study identified the baleen segment reflecting the most recent stable isotopes by analysing samples from a deceased pregnant fin whale and her foetus. The authors hypothesised that the stable isotope values in the foetus’s baleen plates would match the mother’s most recent values, as the foetal baleen was newly formed. They analysed the stable isotope values along the baleen plates of both animals to identify which baleen segments were simultaneously deposited in both individuals. The results show that the base of the baleen plate, hidden below the gums, is likely to best reflect a fin whale’s most recent diet and habitat use.

The authors recommend that, when using baleen plate SIA and other similar chemical analyses, the baleen plate should be removed and analysed in its entirety, as the base of the plate below the gum line represents where the whale last fed.

Read the full article by Marc Ruiz-Sagalés et al HERE.

Photo credit: Kjell Arne Fagerheim