By: Christian Lydersen, Heidi Ahonen and Kit M Kovacs // Norwegian Polar Institute. Nils Øien // Institute of Marine Research. Jade Vacquié-Garcia and Christophe Guinet // CNRS La Rochelle University. Mads Peter Heide-Jørgensen // Greenland Institute of Natural Resources
Fin whales are among the largest animals to ever have lived on our planet. They can grow to 25 m long and weigh 80 tonnes. Only the blue whale can become longer, and only the shorter, stockier bowhead whale can weigh more. Fin whales are true cosmopolitans and are found in all the world’s large oceans, from tropical to polar areas. Like all the large baleen whales, fin whales were hunted excessively during commercial whaling, mainly in the 20th century, that reduced their numbers to close to extinction. Fin whales are now protected throughout most of their range and in the North Atlantic they seem to have recovered from earlier whaling operations. An estimated 80 000 individuals of this species can be found in this region today.
Fin whales are often observed in the Svalbard area, especially at the shelf-break along the west coast of Spitsbergen, but also inside the fjords and north of Spitsbergen up to the summer ice edge. We don’t know how many fin whales spend the summer around Svalbard, but surveys covering the waters south, west and north of Spitsbergen indicate that several thousand are likely seasonally resident each year.
Fin whales, together with blue, minke and humpback whales, forage around the Svalbard archipelago during the productive summer season. Humpback whales migrate in winter to the Caribbean or Cabo Verde, where they are commonly observed and have been photo-identified. But the wintering grounds for blue, fin and minke whales remain a mystery, although it has been assumed that the whales must be offshore and away from major shipping routes or people would have seen them.
We wanted to shed light on the migration paths of the fin whales that summer in Svalbard. The most obvious method to do this is to deploy satellite tracking devices on the whales. Because fin whales are the fastest swimming of the larger whales it is hard to get tracking devices to stay on the animals; the drag on the tags becomes too large and the tags normally fall off after a month or two. Thus, we conducted fieldwork as late as possible (late September) in the hope that some tags would stay in place long enough to give us the information we wanted. The tags, which transmit location, consist of a small cylindric unit (30 × 22 mm) that is anchored into the whale’s blubber and sits at the skin surface, with a stop plate beneath it. They are deployed using a specially designed air gun.
We instrumented 25 fin whales with satellite tags on the west coast of Svalbard; two were tagged from a small boat, and the rest were tagged from a helicopter. In 2019, we located a large concentration of fin whales east of Hornsund and tagged 19 whales in just three hours (including refueling of the helicopter and the crew).
Ten of the 25 whales did not leave Svalbard during the timespan when their tags reported locations. These individuals could obviously have migrated southward later in the year, but based on data from a passive acoustic monitoring array we operate in the Svalbard area, we believe that many fin whales do overwinter in the High Arctic. It is unknown whether this is a response to reduced sea ice over recent decades, but we do hear fin whale calls north of Svalbard until November, and throughout the winter in the Fram Strait.
The 15 whales that left Svalbard all travelled southwest, with the longest track ending up off the coast of Africa – a journey of more than 5000 km. The whales moved quickly during their migrations; one maintained an average horizontal speed of 9.3 km/h (traveling 223 km per day) for a period of a week. However, contrary to what was previously thought, many of the whales stopped “en route” to feed as they moved southward. The whale that was tracked for the longest time (96 days) ended up some 200 km west of Casablanca in Morocco and spent about a month in deep warm waters between there and southern Portugal. We believe that this is one of several possible breeding areas for the fin whales that summer in the North Atlantic.
Lydersen C, Vacquié-Garcia J, Heide-Jørgensen MP, Øien N, Guinet C, Kovacs KM (2020) Autumn movements of fin whales (Balaenoptera physalus) from Svalbard, Norway, revealed by satellite tracking. Scientific Reports 10, 16966: 1-13, doi:10.1038/s41598-020-73996-z
Ahonen H, Stafford KM, Lydersen C, Berchok C, Moore S, Kovacs KM (2021) Inter-annual variability in acoustic detection of blue and fin whale calls in the Northwest Atlantic High Arctic between 2008-2018. Endangered Species Research, Forthcoming