Whale of the Month - Long-Finned Pilot Whale

Species fact file

Common names: long-finned pilot whale, blackfish

Icelandic name: grindhvalur

Scientific name: Globicephala melas

Family: Delphinidae (dolphins)

Max length: 6m (females), 8m (males)

Distribution: temperate to sub-polar in the Atlantic and Southern Oceans, and parts of the Mediterranean

‍

Long-finned pilot whales are the second-largest member of the dolphin family. They are one of two pilot whale species. Short-finned pilot whales are generally found in more tropical areas, but the two species overlap in some parts of the world, such as in the warm temperate North Atlantic, the east coast of Australia, and around South America and South Africa. As their names suggest, the species can be told apart by the length of their pectoral fins. Long-finned pilot whales can have fins measuring up to 27% of their body length!

Pilot whales are a very sociable species. They form large social groups that typically consist of 20 to 150 individuals, but aggregations as large as thousands have been observed. These large groups form when multiple smaller family units temporarily join together. Social bonds within these family units are very strong and may persist for years or even decades. Studies of long-finned pilot whale social structure suggests a matrilineal structure, similar to that observed in north-eastern Pacific killer whales. Both male and female pilot whales remain in their mother’s family unit for life.

Calves are raised cooperatively by the whole family, not just the mother. Adult pilot whales often ‘babysit’ calves, even those that they are not so closely related to; these babysitters are often male. Alloparental care – where adults temporarily take care of calves that are not their own – has been observed in a few cetacean species and is particularly well-documented in sperm whales, where it is generally females who act as babysitter. These females are either close relatives or close social companions of the mother. Alloparental care in pilot whales is thought to be almost a by-product of their close-knit social structure: because family units periodically merge into larger groups, pilot whales of all ages will socialise with many other individuals, not all of whom are close relatives.

Long-finned pilot whales feed mainly on cephalopods – particularly squid. There has been limited research on the diving and foraging behaviour of this species, but it is thought to be somewhat similar to short-finned pilot whales. They are amongst the deepest-diving of the dolphin family; short-finned pilot whales have been recorded reaching depths of over 1000m. They have characteristic V-shaped dives, like other deep-diving dolphins such as Risso’s dolphins, with a very steep ascent and descent. They swim so fast that their foraging dives normally only last about 10 minutes.

Pilot whales frequently beach themselves in mass strandings. What might initially trigger a whale to beach itself is still poorly understood, but it is thought that the strong social bonds between pilot whales is why these events are so massive in scale – once one of their group has stranded itself ashore, the others are unwilling to leave it and inevitably follow. In 2019, two of the largest mass strandings in Icelandic history occurred within just three weeks of one another.

In Iceland, long-finned pilot whales seem to have an unusual antagonistic relationship with killer whales. Large groups of pilot whales are frequently observed harassing and mobbing killer whales, often resulting in a high-speed chase as the pilot whales try to drive them out of the area. The reason for this strange behaviour is still unknown. It may be an anti-predator response, as killer whales are certainly capable of killing young pilot whales, but there are no records of Icelandic orcas hunting pilot whales and this population is thought to favour fish over marine mammals. Alternatively, if there is competition for prey between the two species, pilot whales may be driving killer whales away to ensure more food for themselves. But pilot whales are believed to mainly hunt squid, whereas Icelandic killer whales most commonly feed on herring.

Another layer of complexity has recently been added to this perplexing story. In the past few years, there have been sightings of female killer whales accompanied by a newborn pilot whale calf. These females may have ‘adopted’ pilot whale calves as a replacement for their own. In both documented observations of this behaviour, the calves were already malnourished and don’t appear to have survived for long; when the adoptive mothers were next spotted, they were without a calf. This fascinating behaviour has not been recorded anywhere else in the world so far!

‍

Learn more about...

The role of babysitting in pilot whale society

How tagging can reveal the deep-water hunting behaviours of pilot whales

The interactions between killer whales and pilot whales in Iceland