Balaenoptera physalus

Balaenoptera physalus

The fin whale or finback whale, common rorqual, herring whale, razorback whale (Balaenoptera physalus Linnaeus, 1758) is a cetacean belonging to the Balaenopteridae family.

Systematics –
From a systematic point of view it belongs to:
Eukaryota domain,
Kingdom Animalia,
Phylum Chordata,
Mammalia class,
Order Cetartiodactyla,
Infraorder Cetacea,
Family Balaenopteridae,
Genus Balaenoptera,
Species B. physalus.
The terms are synonyms:
– Balaena antipodarum Tomilin, 1957;
– Balaena maximus subsp. borealis Knox, 1838;
– Balaena mysticetus subsp. major Kerr, 1792;
– Balaena physalis Kerr, 1792;
– Balaena physalus Linnaeus, 1758;
– Balaena rostrata subsp. australis Desmoulins, 1822;
– Balaena sulcata Neill, 1811;
– Balaena tschudii (Reichenbach, 1846);
– Balaenoptera antarctica Gray, 1846;
– Balaenoptera antiquorum Gray, 1846;
– Balaenoptera aragous Farines & Carcasonne, 1829;
– Balaenoptera australis Gray, 1846;
– Balaenoptera blythii Anderson, 1879;
– Balaenoptera brasiliensis Gray, 1846;
– Balaenoptera copei (Elliot, 1901);
– Balaenoptera mediterraneensis Lesson, 1828;
– Balaenoptera mediterranensis Cabrera, 1961;
– Balaenoptera patachonica Lahille, 1905;
– Balaenoptera patachonicha subsp. tschudii (Reichenbach, 1846);
– Balaenoptera patagonica Dabbene, 1902;
– Balaenoptera physalis (Linnaeus, 1758);
– Balaenoptera rorqual Lacépède, 1804;
– Balaenoptera schlegeli subsp. swinhoei (Gray, 1866);
– Balaenoptera sulcata;
– Balaenoptera sulcata subsp. arctica Schlegel, 1841;
– Balaenoptera swinhoii Gray, 1866;
– Balaenoptera tenuirostris Sweeting, 1840;
– Balaenoptera velifera subsp. copei Elliot, 1901;
– Balaenopteris guibusdam Tomilin, 1957;
– Benedenia knoxii Gray, 1864;
– Dubertus rhodinsulensis Tomilin, 1957;
– Physalis vulgaris Fleming, 1828;
– Physalus antarcticus Gray, 1850;
– Physalus australis Gray, 1850;
– Physalus brasiliensis Gray, 1850;
– Physalus duguidii Gray, 1864;
– Physalus dugundii Heddle, 1856;
– Physalus fasciatus Gray, 1850;
– Physalus patachonicus Burmeister, 1866;
– Physalus verus Billberg, 1828;
– Pterobalaena communis Van Beneden, 1857;
– Pterobalaena gigantea;
– Pterobalaena gigantea subsp. michrochira Barkos, 1862;
– Sibbaldius tectirostris Cope, 1869;
– Sibbaldius tuberosus Cope, 1869;
– Swinhoia chinensis Gray, 1868.
Within this species the following subspecies are recognised:
– Balaenoptera physalus subsp. patachonica Burmeister, 1865;
– Balaenoptera physalus subsp. physalus (Linnaeus, 1758);
– Balaenoptera physalus subsp. quoyi (Fischer, 1829).

Geographic Distribution and Habitat –
Balaenoptera physalus is a cosmopolitan species that lives in all major oceans of the world and in waters ranging from polar to tropical. It is absent only in waters close to pack ice at both the northern and southern ends and in relatively small areas outside large oceans, such as the Red Sea, although they may reach the Baltic Sea.
In the North Atlantic it has a wide distribution, ranging from the Gulf of Mexico and the Mediterranean Sea northward to Baffin Bay and Spitsbergen. In general these cetaceans are most common north of about 30°N latitude, but considerable confusion arises about their occurrence south of 30°N latitude because of the difficulty in distinguishing this species from others.
Extensive ship surveys led the researchers to conclude that the summer feeding range of Balaenoptera physalus in the western North Atlantic is mainly between 41°20’N and 51°00’N, from coast seaward to the outline of 1,800 m.
The North Pacific summer distribution is found in close offshore waters from central Baja California to Japan and up to the Chukchi Sea bordering the Arctic Ocean.
High densities occur in the northern Gulf of Alaska and southeastern Bering Sea between May and October, with some movement through the Aleutian Passage into and out of the Bering Sea.
Several whales tagged in November and January off Southern California were killed during the summer off central California, Oregon, British Columbia, and in the Gulf of Alaska. In addition, specimens of this species have been observed feeding 250 miles south of Hawaii in mid-May, and several winter sightings have been made there. Some researchers have suggested that whales migrate to Hawaiian waters primarily in the fall and winter.
In general, therefore, Balaenoptera physalus is more common in the southern hemisphere, less common in the tropics. It arrives in polar waters, but less frequently than the blue or minke whale. In the Mediterranean it is the most present species.
There are probably three isolated populations: in the North Atlantic, North Pacific, and Southern Hemisphere. Some populations migrate to low latitudes, with relatively warm waters, in winter and to higher latitudes, with colder waters, in summer, although the movements are less predictable than in other large cetaceans. Certain low-latitude populations, such as those in the Gulf of California (Bay of Cortez), Mexico, appear to be sedentary.
In Italian seas this species has been observed in areas where the average depth was greater than 2200 m, at a distance of about 44 km from the coast (although it is not uncommon to spot it in coastal waters or even in bays and channels between islands). It is particularly frequent in summer in the western Ligurian Sea, in the Corsican Sea and in the northern portion of the Sardinian Sea. It is present, but less frequent, in the Tyrrhenian and Ionian.
Its marine habitat is linked to its habits, as it is a pelagic species, typical of open seas and deep waters both on platforms and continental slopes, where it feeds on plankton. Its distribution is often associated both with the presence of plankton and with the chlorophyll present in the water (this is directly related to phytoplankton).
The distribution of the species shows important annual variations but, as mentioned, is considered mainly pelagic and generally observed in the waters beyond the continental shelf, at depths between 400 and 2500 m.
It can also go to shallow coastal waters to feed.
The highest population density occurs in temperate and cold waters.

Description –
The Balaenoptera physalus is the second largest animal on the planet, after the Balaenoptera musculus.
This cetacean can reach and exceed 26 m (on average between 18 and 25 m) for a weight of 30-80 tons.
The animals of the northern hemisphere are normally 1-1.5 m shorter than those of the southern hemisphere and some authors believe that they are distinct subspecies. It is easily confused with other fin whales but an essential element for recognizing it at close range is the asymmetrical pigmentation of the head: on the right side, the lower lip, the oral cavity and some of the baleen are white, while the left side is uniform gray.
Also, when swimming just below the surface, the white lip is often clearly visible, however it can be confused with the white pectoral fin of a humpback whale. Once one of the most common fin whales, today its populations are seriously compromised by whaling.
Like other whales, males make long, loud, low-pitched sounds. The vocalizations of Balaenoptera musculus and Balaenoptera physalus are the lowest frequency sounds produced by any animal. Most sounds are downward frequency modulated (FM) infrasonic pulses of 16 to 40 hertz in frequency (the frequency of sounds that most humans can hear ranges from 20 hertz to 20 kilohertz). Each sound lasts one to two seconds, and various combinations of sounds occur in patterned sequences lasting from 7 to 15 minutes each. The whale then repeats the sequences in bouts lasting up to many days. Speech sequences have source levels up to 184-186 decibels relative to 1 micropascal at a reference distance of one meter and can be detected hundreds of miles from their source.
When the sounds of Balaenoptera physalus were first recorded by US biologists, they did not realize that these unusually loud, long, pure and regular sounds were made by whales. They first investigated the possibilities that the sounds were due to equipment malfunctions, geophysical phenomena, or even part of a Soviet Union plan to detect enemy submarines. Eventually, biologists proved that the sounds were the vocalizations of these cetaceans.
The songs of this whale can penetrate more than 2,500 m below the sea floor and seismologists can use those song waves to carry out underwater surveys.
Their water jet is also characteristic. When feeding, they blow five to seven times in rapid succession, but when traveling or resting, they blow once every minute or two. On their last dive they arch their backs out of the water, but rarely lift flukes out of the water. Then they dive to depths of up to 470m when feeding or not when resting or traveling. For example the average feed dive off California and Baja lasts 6 minutes, with a maximum of 17 minutes; when traveling or resting, they usually only dive for a few minutes at a time.

Biology –
As far as reproduction is concerned, conception takes place in the winter.
After a summer spent in cold waters to feed and stock up on energy reserves, the future mother returns to the heat, to the mating site and gives birth after about 11-12 months of gestation. Weaning takes place around 6 months: the young grow at the dizzying rate of 60 kg in weight and 3 cm in length per day.
The emissions of the sounds of the Balaenoptera physalus and their vocalizations have a link with the reproductive season of the species and that only the males make the sounds indicate these vocalizations as possible reproductive manifestations.
Unfortunately, over the last 100 years, the dramatic increase in ocean noise caused by shipping and naval activity may have slowed the recovery of the population of these cetaceans, preventing communication between males and receptive females.
The life expectancy of this species is believed to be up to 100 years.

Ecological role –
Although the Balaenoptera physalus is a species, their migratory attitude is known, moving seasonally in and out of the high latitude feeding areas, yet their overall migratory pattern is not well understood. Acoustic readings from passive listening hydrophone arrays indicate that a southward migration of this species into the North Atlantic occurs in the fall from the Labrador-Newfoundland region, south past Bermuda and into the West Indies. One or more populations are thought to remain year-round in high latitudes, moving offshore, but not southward in late autumn. A study based on the re-sighting of specimens identified in Massachusetts Bay indicates that pups often learn migration routes from their mothers and return to their mother’s feeding area in subsequent years.
In the Pacific, migration patterns are poorly characterized. Although some specimens are apparently present year-round in the Gulf of California, there is a significant increase in their numbers in the winter and spring.
Southern individuals migrate seasonally from relatively high-latitude Antarctic feeding grounds in summer to low-latitude breeding areas in winter. The location of their winter breeding areas is still unknown, as these whales tend to migrate to the open ocean.
As mentioned, it is present in the western and central Mediterranean and documented in North Africa. In summer it is frequent in the Gulf of Lion and in the Corsican-Ligurian-Provençal Basin where it feeds on krill; in the Balearic Sea its presence seems constant all year round. The species moves from north to south by making migrations. In Italy it has been widely documented in the Ligurian Sea and in the central-northern Tyrrhenian Sea. In Sicily it is sighted regularly in the Strait of Messina and in the autumn and spring around the Pelagie Islands.
As far as nutrition is concerned, the Balaenoptera physalus has a very varied diet, but the main components are Euphasiacea (planktonic crustaceans known as krill), fish and small cephalopods.
The hunting technique is particular: it approaches a school of fish at considerable speed to throw itself at the point where it is thickest. Then, by dilating the throat region, which can also double the diameter of the anterior part of the body, it swallows water and fish.
Furthermore, this cetacean does not avoid or approach boats. It’s nearly impossible to gauge when it will emerge or move away—it can be difficult to observe closely. She is a fast swimmer, capable of reaching speeds of 30 km/h. It is seen more often than other fin whales in small groups.
However, its large size can play against it in the event of collisions with ships and ferries, a very common cause of mortality in Italian seas.
As far as its predation is concerned, with the exception of some cases, in which they have been attacked by the Orcas, the large size of the Balaenoptera physalus seems to shelter them from the annoyance of the predation.
Currently, according to the Zoological Society of London, based on criteria of evolutionary uniqueness and population scarcity, it considers the Balaenoptera physalus one of the 100 species of mammals at greatest risk of extinction.
At present, thanks to the moratorium announced by the IWC, this cetacean is not hunted, but it was hunted in the 20th century and its numbers are so low that in the IUCN Red Data Book the species is still listed in the Endagered category ( threatened). It is in fact still a species subjected to various pressures and seems to be in a state of decline in the adult population.
Given its migratory nature and its etho-ecological characteristics, the main dangers to its conservation are attributable to: accidental catches (F02) from pelagic nets deriving from and pollution of marine waters (H03), such as chemical and plastic contaminants, from excess energy (H06) such as noise disturbance. Numerous studies consider the danger of collision with large vessels as the main threat (G05).
The population in the area between the Ligurian Sea and the central Tyrrhenian Sea is also decreasing; there is a minimum estimate of 500 individuals. In Pelagos Sanctuary, comparisons between 1992 and 2009 data seem to indicate a decline in population size, although results need to be compared with caution due to differences between study platforms, the size of the investigated areas, and the time elapsed
For this reason, some international protection and guardianship programs have been undertaken.
The species is included in Annex IV of the Habitats Directive (92/43/EEC) and in Annex II of the Bern Convention, in Annex II of the SPA/BIO Protocol of the Barcelona Convention and in Annexes I and II of the Convention of Bonn. The species is included in the CITES Convention and in the ACCOBAMS Agreement.
It has also been legally protected both in Italy since the 1980s and internationally and included in numerous protected areas.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Facilidad Global de Información sobre Biodiversidad.
– Gordon Corbet, Denys Ovenden, 2012. Guide to mammals of Europe. Franco Muzzio Publisher.
– John Woodward, Kim Dennis-Bryan, 2018. The Great Encyclopedia of Animals. Gribaudo Publisher.

Photo source:
– https://dannykesslerphotography.com/portfolio/fin-whales-mediterranean/