Finner

Balaenoptera physalus is a rorqual of the family Balaenopteridae, described by Linnaeus in 1758 ^[1]. It is the second-largest whale, after the blue whale, and lives mostly in deep, open waters from temperate to polar latitudes ^[2]. In Peru, the 2026 master plan of the Mar Tropical de Grau National Reserve calls it «rorcual común» and lists it among the cetaceans seen in the Cabo Blanco – El Ñuro sector ^[3]. Its global IUCN Red List category is Vulnerable ^[4].

It is a slender, streamlined whale with a V-shaped head and a tall dorsal fin that curves backwards, set about two-thirds of the way along the body ^[2]. The back and flanks are black or brownish grey and the belly is white; many animals have pale grey V-shaped chevrons behind the head, and the underside of the tail is often white with a grey edge ^[2].

Its most distinctive feature is the asymmetric colour of the head: the lower jaw is dark on the left side and white on the right, and the tongue is the reverse ^[2]. It measures 75 to 85 feet in length (roughly 23 to 26 m) ^[2]. The maximum body length of fin whales in the Antarctic exceeds 23 m, 3 to 4 m more than in the Northern Hemisphere ^[5]. An adult skeleton from the South Atlantic, taken in 1952, measured 19.54 m when reconstructed ^[6]. Newborns are about 18 feet long ^[2].

Similar species

• Balaenoptera musculus: The blue whale is the only species larger than the fin whale, which ranks second in size among all whales ^[2].

It lives in the deep waters of all the major oceans, mainly at temperate to polar latitudes, and is less common in the tropics ^[2]. A review of records from 1980 to 2012 found an equatorial gap, between about 20° N and 20° S, supported by many line-transect surveys and by the scarcity of sightings and acoustic detections in that band ^[7]. In 34 cetacean presence studies carried out between 23° N and 12° S the species was not reported ^[7].

In the whaling era there were a few catch records off Ecuador (near 0°) and off Peru (near 15° S), but they were infrequent and did not sustain a fishery for this species ^[7]. Among the post-1980 sightings are some west of Chile, near 30° S ^[7]. The 2026 master plan of the Mar Tropical de Grau National Reserve lists the rorcual común among the cetaceans seen in the Cabo Blanco – El Ñuro sector, in northern Peru ^[3].

Three subspecies are recognised: a Northern Hemisphere one, a Southern Hemisphere one and a pygmy form; a genetic analysis suggests that North Pacific and North Atlantic whales should not be treated as one subspecies ^[5].

Males reach sexual maturity at 6 to 10 years and females at 7 to 12; physical maturity comes at about 25 years and maximum lifespan is estimated at about 90 years ^[2]. Gestation lasts 11 to 12 months and a single calf is born, in tropical or subtropical waters in midwinter ^[2].

It feeds by lunging into schools of prey with its mouth open, and filters the water through 260 to 480 baleen plates per side ^[2]. According to estimates cited in a study of animals from Iceland, a single lunge can engulf 60 to 82 m3 of water with prey, and a 20 m whale needs about 901 kg of krill a day ^[8]. That study describes a narrow but strongly muscular oesophagus and proposes that it pushes the mixture to the stomach as a continuous stream ^[8].

It produces pulses at about 20 Hz, lasting roughly 1 s, that sweep down from about 28 Hz to about 15 Hz and reach 160 to 186 dB re 1 μPa at 1 m ^[9]. These pulses are often accompanied by a higher-frequency component that varies by region ^[9].

In summer it feeds on krill, on small schooling fish (such as herring, capelin and sand lance) and on squid, and in winter it fasts during migration ^[2]. Most migrate from polar feeding areas in summer to tropical breeding areas in winter ^[2]. However, its seasonal movements are not as clear-cut as those of the blue or humpback whale: some animals stay at latitudes of 50° to 60° even in the cold months ^[7].

The ecology of south-eastern Pacific populations could not be documented with verifiable sources for this account. Acoustics offers a clue about population structure: in the Weddell Sea, the 99 Hz high-frequency component was detected at 7 of 10 recording positions, whereas the 86 Hz one appeared only in the west, near the western Antarctic Peninsula, which suggests two distinct acoustic populations ^[9].

The species' global IUCN Red List category is Vulnerable ^[4]. Between 1890 and 1980 commercial whaling removed more than 900000 fin whales and cut their abundance by more than 70 % ^[7]. The International Whaling Commission moratorium set catch limits to zero in 1982, and the species is in CITES Appendix I ^[7].

Current threats are vessel strikes, entanglement in fishing gear, ocean noise and changing climate ^[2]. In a study of 11 whale species cited by Edwards and colleagues, fin whale strikes were the most frequent ^[7]. A 1952 skeleton preserves healed fractures from a collision with a ship that the whale survived, which is evidence that the problem is old ^[6]. Outside a few areas, its recovery status is uncertain ^[7].

It was one of the species most heavily hunted by twentieth-century commercial whaling, with more than 900000 animals removed between 1890 and 1980 ^[7]. The few catch records off Peru (near 15° S) were infrequent and did not lead to a sustained fishery for the species ^[7].

According to a 2015 synthesis, limited hunting persisted near Greenland, near Iceland and in the Antarctic ^[7]. Animals from a commercial catch in Iceland were used in 2015 and 2018 to study the anatomy of their oesophagus ^[8].

The 2026 master plan of the Mar Tropical de Grau National Reserve records 13 of the 32 cetacean species cited for Peruvian waters in the Cabo Blanco – El Ñuro sector, among them the rorcual común, alongside the humpback whale, Bryde's whale and the blue whale ^[3].

The plan gives no dates, precise places or number of sightings for the rorcual común ^[3]. Because the species lives mostly in deep water and is less common in the tropics, these sources do not allow a sighting on an outing to be promised ^[2],[7].