Fin Whale

Fin Whale: Balaenoptera physalus

IUCN status: Endangered

Status and distribution summary:

Global population is estimated to be c65,000, a tiny proportion of what there were prior to whaling. Fin Whales occur in all oceans of the world, and most populations are at least partially migratory, moving from warmer wintering grounds to cooler high latitude waters (but usually below 600) such as the Bay of Biscay to feed in summer. Fin Whales are one of the most numerous of large cetaceans, having recovered from the ravages of commercial whaling. The animals encountered in the eastern parts of the Bay appear to be part of a larger population living in the eastern Atlantic Ocean, which may number over 5000 individuals.

Exploitation:

Although not heavily hunted before steam power and exploding harpoons were introduced due to its high swimming speed, it was very heavily targeted in the 20thC. Precise data is lacking but somewhere approaching 1,000,000 Fin Whales were taken, 75% of these were in the southern hemisphere.

Since protection was introduced in the latter part of the 20thC there has been some recovery in numbers in some populations. However, Iceland and Japan resumed killing Fin Whales in 2005/6, albeit in small numbers thus far.

Other threats:

Collision with shipping is significant in several areas of their range with heavy shipping routes. Impacts of climate change on the oceans are not fully understood but may have significant effect on their prey.

Where it is seen:

Almost invariably associated with the deep waters of the continental shelf slope and the Abyssal Plain in the Bay of Biscay. Only rarely seen over shallow water. However the are regularly seen feeding off southern Ireland.

Frequency of sightings:

The commonest large whale occurring in Biscay, Fin Whales are seen on almost every crossing from May through to October, and to see over 20 animals on a mid summer crossing is normal in most years. However, in 2010 they were very scarce until September. They are recorded at other times of the year, but with less frequency, suggesting that there is seasonal migration into the eastern part of Biscay.

Recognition:

Fin Whales are the second largest animals on the planet (adults reach up to 25 metres in length) and relatively slender.

In regular surfacing they usually show the following features:

  • Upperparts appear black in dull light, though in good light they appear a dark grey or brown
  • The asymmetrical colouration on the lower lip (the right hand side is pale to white and the left hand side is dark) is diagnostic and can be seen on animals when subsurface in good light
  • The dorsal fin is small, usually swept back and falcate (though variable), and is set well back on the body (more than 2/3 to the tail), so is not visible at the surface until after the blow has finished
  • The blow is strong, tall, columnar and lingers for several seconds

Care should be exercised as blows later in a sequence tend to be lower and more bushy.

Behaviour:

Usually occurs as singles or in groups of 2-7, though occasionally in bigger numbers spread over a large area of sea.

Blow sequence is usually 4-5 blows 10-20 seconds apart, followed by a deep dive lasting 5-15 minutes, the tail stock is strongly arched on the last dive, though flukes almost never show.

Usually undemonstrative, but is occasionally seen to breach, when ca 2/3 of the animal appears at around a 45° angle, causing a huge splash on re-entering the water. Is seen to feed at the surface, when they lunge through prey concentrations often on their side with large disturbance of the sea surface.

Ignores ships, leading to occasional very close views.

Confusion species:

  • Sei Whale; is very similar in appearance at sea, but with a tall more erect dorsal fin set much further forward, that shows at the same times as the blow, which is generally lower and bushier, it lacks asymmetrical pattern on lip
  • Blue Whale; is huge, bluey grey, and has a tiny (barely visible) dorsal fin which shows only late in the roll
  • Humpback Whales; rare in Biscay, they show a hump in front of the dorsal fin, and have a very bushy blow
  • Minke Whale: is similar in shape and colour but much smaller (but compare with Fin Whale calves), rarely has visible blow, shows white patches on pectoral fins