Minke Whale – Balaenoptera acutorostrata
Habitat: Mainly over continental shelf of temperate and subartic regions, often very close to land, may enter estuaries, bays, or inlets. Often feeds around banks and in areas of upwelling or strong currents around headlands and small islands, primarily during summer.
Description: Smallest baleen whale around British Isles, general form similar to fin and sei whales but with sharply pointed snout. Body is dark grey to black on back, white on belly and underside of flippers. Light chevrons across dorsal surface; one just above and behind flippers, the other more diffuse, between flippers and dorsal fin. Flippers are narrow, with distinctive white band on upper surface. 50 – 70 throat grooves. Short baleen plates (30 cm long x 12 cm wide), yellowish white, 230 – 342 on each side of upper jaw. Plates sometimes with black streaking, fringed with fine white bristles.
Size: 8 – 8.5 m, females larger. Northern hemisphere individuals smaller.
Weight: 5,000 – 14,000 kg.
Lifespan: 40 – 50 years.
Distribution: Commonest baleen whale in North Atlantic and British Isles, mainly in temperate and polar regions. Widely distributed along Atlantic seaboard of Great Britain and Ireland, west and north Norway, Faroes, and Iceland, often seen close to the coast. Also in north and central North Sea, regularly south to Yorkshire coast. Small numbers in Irish Sea; rare in south North Sea, Channel, and Bay of Biscay. Most sightings July – September but can be seen any time May – October, and some remain in coastal waters year-round.
Diet & Feeding: Takes more fish (such as sandeels, herring, sprat, cod, capelin, haddock, saithe, whiting) than other northern hemisphere rorquals; euphausiids and pteropods also taken, especially in higher latitudes. Uses variety of feeding methods depending on prey, including side- and lunge- feeding, and engulfing prey with open mouth from behind.
Breeding: Births occur mainly around December, probably in temperate offshore waters, possibly in subtropics. Gestation lasts for 10 months; lactation <6 months; calving interval of at least 1 – 2 years. Sexual maturity reached at 7 – 10 years in Antarctic populations; aging Atlantic populations more difficult due to indistinct layering of ear plugs, which are usually used to gauge the age of an individual.
Conservation Status & Population: Listed by IUCN as lower risk / near threatened. Threats include whaling, sometimes entanglement in fishing fear (mainly salmon gillnets and creel lines). Relatively high pollutant levels of PCBs. May suffer from sounds from vessels, particularly whale-watching; it is the focus of British whale-watching industry. Seismic testing for oil and gas exploration, collisions with vessels, and use of active sonar by military also has impacts.
Because of small size, not a target of Scottish and Irish whale fisheries in early 20th century. Exploited more reecntly when stocks of larger rorquals depleted (and in some cases, protected). Whaling taking place since the late 1920s has reduced stocks by 45 – 70% compared to pre-exploitation abundance.
Smallest and most common baleen whale around British Isles, and most likely to be observed from land. Low blow (2 m) not always visible, typically seen at same time as 30 cm recurved dorsal fin 2/3 along back. Flippers have diagonal white band on upper surface. Head slender, triangular, with straight rather than curved borders to rostrum. Usually seen singly or in pairs, sometimes aggregates into groups of 10 – 20 when feeding. Frequently approaches vessels.
Vocalisations: Intense low-frequency broadband (0.5 – 1 kHz bandwidth) and harmonic downsweeps. These include short broadband downsweeps (mainly 0.13 – 0.06 kHz lasting 200 – 300 ms), grunts (mainly 0.08 – 0.14 kHz, but up to 2 kHz, lasting 165 – 320 ms), and thumps (often downsweeps, mainly 0.1 – 0.2 kHz and lasting 50 – 70 ms).