Whale of the Month - Fin Whale

Species fact file

Common names: fin whale, common rorqual, finback, fin-backed whale, razorback

Icelandic name: langreyður

Scientific name: Balaenoptera physalus

Family: Balaenopteridae (rorquals)

Max length: 27m (females), 25m (males) in the Southern Hemisphere, smaller in the Northern

Distribution: Global, but rarer in equatorial waters

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Fin whales are the second largest animal on Earth after blue whales. The genetic distance between these two species is similar to that between humans and chimpanzees; despite this, hybrids of blue and fin whales are relatively common and particularly well-documented in the north-eastern Atlantic. Currently, best-available knowledge is that humpback whales are more closely related to fin whales than blue whales are, but no hybridisation between these two species has ever been recorded.  

In the north-eastern Atlantic, fin whales seem to favour offshore waters between Iceland and Greenland. This region is one of the known summer feeding grounds for the North Atlantic population. Although fin whales are migratory, at present the North Atlantic breeding grounds and migration routes used by this population are still unknown. It has been theorised that some fin whales remain in colder waters year-round and their migration is therefore less dramatic than other baleen whales that may travel thousands of miles between sub-polar and tropical waters. Alternatively, wintering grounds may just be in remote offshore locations that we have yet to find!

Fin whales are just one of the many species of baleen whales which travel to Iceland every summer to take advantage of the vast abundance of food here. Life in polar and sub-polar seas is dictated by the ‘boom and bust’ cycle of the seasons. In summer, long hours of daylight combined with nutrient-rich cold water create the perfect conditions for phytoplankton – tiny, plant-like organisms which form the base of marine food chains. Phytoplankton grow in such abundance that they create huge phytoplankton blooms, turning the seas green and attracting a myriad of small, phytoplankton-munching animals called zooplankton. One such miniature marine grazer is krill. Krill is the main prey item of the four largest rorquals in Icelandic waters - blue, fin, humpback and sei whales.

So many large predators all feeding on the same thing should result in some intense competition for a meal! But a recent study found that baleen whales in Iceland have been able to reduce competition with one another enough that they can all coexist here. In ecology this is called ‘niche partitioning’. Niche partitioning is often as simple as each species hunting different prey, but can also involve feeding on the same prey in different places or at different times to one another, or even hunting different ages or sizes of the same prey species. In Iceland, for example, sei whales hunt in deeper waters far offshore, while humpback whales have a more coastal distribution and feed in shallower waters than the other species. Humpback whales also manage to reduce competition with other whales by feeding on a wide range of prey species, including many kinds of fish, in addition to krill.

Blue and fin whales, however, not only have a similar diet but also a similar distribution in Icelandic waters – so they probably do compete for food. These species are often seen in groups together, particularly in feeding grounds. It may be because they share many aspects of their ecology that hybridisation is more common between blue and fin whales than between other large rorquals.

Fin whales often travel in pairs or small groups, but these associations are transitory; like other baleen whales, strong social bonds are only between mothers and calves in the first few years of life.

Like most baleen whales, fin whales sing. Fin whale songs are some of the lowest-pitched noises made by any animal: their vocalisations can be as low as 20 Hz, with a wavelength of over 75 metres long! These sound waves are large enough to pass over almost any object, meaning they can travel unimpeded from one side of the world to the other.

Lunge-feeding is a common hunting technique used by rorqual whales, including fin whales. This is a very energetic way of hunting which involves swimming at high speeds through a dense shoal of their food. As the whale takes a gulp, all the grooves on the underside of its mouth expand and bulge out, encompassing almost the whole shoal!

Fin whales can dive to between 100 and 200m in depth while hunting, but most of their dives last less than 10 minutes. Given their huge size, fin whales are probably capable of diving for at least half an hour – it is speculated that lunge feeding is so energetically draining, they burn through their oxygen stores very rapidly and are forced to surface for air more frequently.

Fin whales have unusual asymmetric colouration: the right side of their head, including the baleen, is white, whereas the left side is dark. It has been suggested that because fin whales lunge on their right side while feeding, this asymmetry maintains the traditional countershading even while they are hunting.

Because of their size and speed, fin whales were among the last of the great whales to be targeted by whalers – it simply wasn't possible to hunt them on a commercial scale until the late 19th Century. However, with the rise of steam-powered ships and explosive harpoons, and the later introduction of factory ships, fin whale catches increased rapidly. In the first half of the 20th Century, the fin whale was the most heavily hunted species in the North Atlantic; in Antarctica, over 725,000 fin whales were taken by whalers between 1900 and 1985, when the global moratorium on whaling took effect. A recent review of whaling catches in the 20th Century found that, globally, more fin whales were killed than any other species.

Today, the IUCN Red List considered fin whales as Vulnerable: a recent improvement from the nearly 20 years this species had been listed as Endangered. Their global population does seem to be increasing, with fin whales returning to their Antarctic feeding grounds in greater numbers than have been seen for over 100 years.

Iceland is currently the only country in the world still hunting fin whales. But, with the ever-increasing rise of whale-watching and a steady decrease in demand for whale meat, whaling is becoming a financially inviable industry. Almost all of the fin whale meat caught in Iceland is exported to Japan, but interest in whale meat is dwindling there, too. Theoretically, the quotas for fin whale catches should prevent the North Atlantic population from being threatened by ongoing whaling: however, our oceans are changing, and the cumulative effect of many threats on an already vulnerable species is almost impossible to predict. Having been driven to near extinction within the last century, and now increasingly at risk from ship strikes, vessel noise, entanglements, and climate change, losing even a relatively small number of fin whales could well have a long-lasting impact on the species.

Once, whales were hunted throughout all the world's oceans. Most of the great whales have now been protected for 40 years or more – we hope that it won't be long before fin whales, like their cousins the blue and humpback whales, will be free to roam the waters around Iceland without the threat of encountering a whaling ship.

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New evidence that some North Atlantic fin whales spend winter in the Azores

How baleen whales in Iceland can limit competition for prey