Common Names: Sperm whale; Cachalot
Irish Name: An chaisealoíd
Body Size: Large; average length 15m. for males with a max. of 20m; average female, 11m. to a max. of 17m. Calves are 4m. at birth . Weight averages 40 tons for males, 22 tons for females.
Head Shape: Profile is unmistakable; enormous head with a blunt snout with relatively small underslung jaw; head forms 1/3 of overall body length and considerably more than 1/3 of body mass.
Dorsal Fin & tail Stock: No true dorsal fin but 2/3 way down the back flesh and fibre are raised into distinct dorsal hump resembling a low, fatty fin. Beyond this are a series of knuckles , usually 4 or 5. Flippers are short and stubby, but the tail flukes are broad and powerful; their surface area being the largest of all whales, providing rapid acceleration.
Colouration: Normally steely dark grey with light brownish underlay. The skin around the lips is usually white and there are often white blotches on other parts of the head, at the navel, alongside the hump, or splashed in random streaks along the flank and tail.
Additional Body Markings: Frequency of white patches increases with age. Skin on head is patterned with circular scars formed by suckers on tentacles of giant squid, some of which have measured 5 in. in diameter, making the tentacles over 2ft. in diameter.
Long, blunt head first to appear above surface, often at an angle, to expose blowhole. Head is highly asymmetrical and the single nostril is situated well to the left of the midline, producing a forward angled and left leaning blow, unlike that of any other whale. The blow shoots up 3-5 m. at a forward angle of 45 deg. First exhalation after deep dive is like a blast that is audible from up to 1km, with each subsequent breath lasting about 3 sec. on exhalation and 1 sec. for the next air intake.
The whale usually spends 10 minutes at the surface, breathing very deeply every 10-15 seconds before diving. After the final blow of a series at the surface, the whale draws its head under and a cloud of vapour persists as the long back bends down to expose the hump and the knuckles along the spine. The dive is almost vertical and the broad tail flukes are always thrown well up in the air.
When seen diving from a distance, the sperm whale can be mistaken for a humpback, which may also arch its back and lift its flukes before diving. Humpback whales have very distinct, white markings underneath flukes.
Usual surface speed is less than 6 kph. but are capable of 40kph. in certain circumstances. Time spent at the surface is normally devoted to breathing, but sometimes they will float motionless as they rest. They have been observed drifting, tail down, with their noses sticking out of the water, or lying on their sides with one flipper and one fluke showing above the surface. When resting on the surface they are vulnerable, as they can be approached, almost to the point of touching them, before they take fright and dive. As a rule, it is more difficult to approach solitary males, but groups of females with young are less wary and can be approached with small boats.
Best estimates suggest populations of 350,000 in the southern hemisphere and 175,000 in the northern hemisphere; figures are based on approximation only. Since the early 1700's this species has been the mainstay of whaling and up to 1963, as many as 30,000 Sperm whales were taken annually. This species favours the edges of ocean trenches and points where strong currents flow in opposite directions. Both sexes migrate, moving in autumn towards the equator and in spring towards the poles. Males tend to travel further and faster than females and young. In theory, the population in each hemisphere is distinct, but logic suggests that there is considerable mixing in equatorial areas such as the Galapagos, where cold-water currents and abundant food exist year round.
Sperm whales are occasionally observed in Irish waters in very deep water off the continental shelf. Their near absence from the IWDG sightings database, simply reflects their offshore distribution. But the Irish Air Corp has as part of a collaboration with the IWDG, taken aerial photographs of sperm whales passing offshore along the northwest coast. While only occasionally visually detected, they are regularly detected acoustically by towed hydrophones or during passive acoustic monitoring.
Adults can eat up to 1 ton of squid daily. They specialize in large deepwater species, but at least one specimen's stomach is reported to have held 28,000 tiny surface squid. Over 40 species of cephalopods are known to be eaten, along with a variety of fish species such as: long nose skate, snappers, lobsters, angler fish and ocean perch.