Sei whales – distribution, abundance and ecology

Sei whales (Balaenoptera borealis) are currently classified as globally endangered by the International Union for Conservation of Nature, due to heavy exploitation by commercial whaling operations in the 1900s. Little is understood about the modern-day distribution and ecology of this species worldwide, due to its occurrence in predominantly offshore habitats (making it challenging to study) and the unpredictable fluctuations in its distribution between years.

In the Falkland Islands, Southern Hemisphere sei whales have been increasingly observed in nearshore waters since the 1990s, providing a rare opportunity to initiate a coastal field study on the species. Caroline has worked for Falklands Conservation (FC) since 2016, implementing several consecutive field projects on sei whales around the Islands:

• An EU BEST 2.0 Small Grants project titled “Developing a site-based conservation approach for sei whales Balaenoptera borealis at Berkeley Sound, Falkland Islands.” The project aimed to investigate the distribution, population size and ecology of sei whales at Berkeley Sound in East Falkland during 2017;
• A Royal Society for the Protection of Birds (RSPB) funded project investigating the genetic diversity of Falkland sei whales via biopsy sampling in 2017;
• A survey of sei whales on the west coast of West Falkland during the 2018 field season, funded by FC, the RSPB, and the Falkland Islands Government. The project collected information on the distribution, behaviour, abundance and ecology of sei whales;
• A Darwin Plus funded project (DPLUS082) at two sites (Berkeley Sound and Falkland Sound) between 2019 and 2021, focused on photo-identification, genetics and ecology of sei whales and of the southern right whale (Eubalaena australis).
• A Darwin Plus funded project (DPLUS126) in the north-east Falklands in 2022 and 2023, focused on the satellite-tracking of sei whales and southern right whales, and ongoing work on their photo-identification, genetics and ecology.

The work carried out during the projects to date has included:

• Visual surveys of the spatio-temporal distribution and abundance of sei whales, southern right whales, and coastal dolphins from shore, vessel and aerial platforms;
• Photo-identification work to identify individual whales and investigate their movements, minimum population size, and associations;
• Satellite tracking to collect data on movements, habitat use, and foraging ecology;
• Faecal sampling to examine diet, parasites and extract whale DNA;
• Biopsy sampling to collect small tissue samples to carry out genetic and stable isotope analysis;
• Acoustic monitoring to identify the calls and song of sei whales in the Falkland Islands, which will be relevant to global monitoring of the species;
• Behavioural work to assess the dive times and surfacing characteristics of sei whales around the Falkland Islands.

In combination, the projects are providing a large amount of novel systematic information on sei whale occurrence in the Falklands, which will feed into the development of conservation and management plans. The work has already been used to successfully confirm the Falkland Islands Inner Shelf Waters as a KBA for sei whales, highlighting the global significance of the area for the species. Outputs from the ongoing work, including scientific papers, will be listed below as they become available.