Cornwall Mammal Group
Recognition:
Minke whale-(Balaenoptera acutorostra)
Order: Cetacea, Cornish Name: Morvil
Minke whales are the smallest of the baleen
whales, a group named after the plates of fine hairs that hang from the upper jaw and filter out food from the water. Fully grown minke whales may reach 10 m and weigh up
to 11 tonnes, while calves are 2.5 m long and weigh about 450 kg at birth.
They are streamlined creatures with a long,
pointed head, short arched dorsal fin two-thirds of the way down their back and they
have two short, pointed pectoral fins. Grey on top and white underneath, they are
difficult to spot at sea, despite their size. They can be easily confused with other
similar species such as sei, fin and Bryde’s whales. The one distinct physical difference
from these other whales is that the minke whale’s pectoral fins each have a white band across them, a feature found only in the northern hemisphere population. At sea a minke whale can be spotted by the spray of moisture it makes when it exhales from its blowhole at the surface, which are two openings on the top of the head. The blow is usually low and bushy, so is difficult to detect over a long distance, but on calm days it can be heard. When hunting, a typical pattern is 3 to 6 blows about 1 minute apart followed by a dive of 6 to 12 minutes.
When diving, the snout breaks the surface first followed by a blow and then the back
including the dorsal fin appear, after which the back arches and the dorsal fin rises as the entire animal sinks below the surfaces without showing the tail. They make loud, low-frequency vocalisations, which can be heard underwater over great distances, probably to communicate with each other.
Normally solitary, minke whales are rarely seen in groups of more than two or three, but in rich feeding grounds as many as 400 can gather in the same area. They can live for about 50 years, with calves becoming mature between 3 and 8 years. Females give birth to a single calf every 2 years, following a gestation period of 10 to 11 months, and the calf will remain with the mother up to 6 months old until it is weaned.
Minke whales are separated into three geographically isolated subspecies: Northern (found throughout the northern hemisphere and as far as the southern tropics), Dwarf (found in the southern hemisphere outside the polar region) and Antarctic (found in only the polar and temperate areas of the southern hemisphere). All of these migrate annually between warm breeding grounds and cold feeding grounds. Minke whales are a deep water, open ocean species and are rarely seen close inshore unless deep water occurs close to the coast. In Cornwall they have been recorded relatively regularly from St Ives around Land’s End to Fal Bay, and out to the Isles of Scilly. The northern minke whale population is thought to be around 185,000 individuals in the Atlantic, with unknown numbers in other areas. The dwarf subspecies population is unknown, while the Antarctic subspecies is anywhere between 0.5 and 1.4 million.
Minke whales feed mainly on plankton, krill and small fish. They will either slowly skim the surface to filter water through their baleen plates or take a massive mouthful as they lunge out of the water, expanding the throat pleats to maximise the volume they can scoop up and then strain the water out again through the baleen to gather food. Killer whales may gang up to separate a mother and calf, so that they can drown and prey upon the defenceless youngster. Otherwise, minke whales are too large to be vulnerable to any other natural predators. Humans now pose their greatest threat through whaling, but entanglement in nets is a problem too. Although rare, ship strikes are also a danger. It is possible that sonar can deafen whales close to the source of the device emitting the noise, while vocalisations may be drowned out, making it difficult for individuals to keep in contact.
Did you know?:
The minke whale has been known as the pikehead, pike whale, little finner, sharp-headed finner, lesser finback and, in
Cornwall, as the lesser rorqual.
© P Anderwald - Sea Watch Foundation
Survey Methods:
Land-based surveying can be used for Recording minke whales due to their greater abundance over other baleen-type whales. Boat-based surveys carried out from ships that cross areas of open ocean (e.g ferries) through programmes such as Organsiation Cetacea (ORCA) and Marinelife.
Recent strandings of minke whales include a 9 m animal at the Roseland in 2008 and a 7m whale near Padstow in 2007. A live stranded minke whale, 5 m long, was successfully re-floated from Long Rock, Marazion, in 2003.
Distribution:
Isolated sightings of minke whales have been reported from the north and south coasts of Cornwall. Gwennap Head and Gribba Point were hotspots between 1997 and 2002. Later sightings of were also reported from Lizard Point, Falmouth Bay, Lamorna Point and Lands End. Minke whales are more abundant in the north of the UK than the south but analysis of sightings have identified a concentration in the Bay of Biscay.
Records:
2007-2012: 278
2002-2007: 130
Pre-2001: 153
Total: 561
Conservation:
A UK BAP species, protected under the Wildlife and Countryside Act 1981 and Listed in Annex A of EU Council Regulation 338/97 and therefore treated by the EU as if they are on CITES Appendix I, thus prohibiting their commercial trade. Minke whales are currently classified as being of ‘least Concern’ in the IUCN Red List.
