Post-recovery numbers of the southern subspecies are predicted to be less than 50% of the pre-whaling population, even by 2100, due to long-lasting impacts of whaling and slow recovery rates.

[10] In 1804, Bernard Germain de Lacépède reclassified the species as Balaenoptera rorqual, based on a specimen that had stranded on Île Sainte-Marguerite (Cannes, France) in 1798.

In 1865, German naturalist Hermann Burmeister described a roughly 15 m (49 ft) specimen found near Buenos Aires about 30 years earlier as Balaenoptera patachonicus.

[19] Most experts consider the fin whales of the North Pacific to be a third subspecies—this was supported by a 2013 study, which found that the Northern Hemisphere B. p. physalus was not composed of a single subspecies.

[20] A 2019 genetic study concluded that the North Pacific fin whales should be considered a subspecies, suggesting the name B. p. velifera (Scammon 1869).

[23] The genetic distance between blue and fin whales has been compared to that between a chimpanzee and human[24] (3.5 million years on the evolutionary tree.

[39] The penis size of fin whales typically reaches a length of 1.3 m (4 ft 3 in); the testes usually weigh 1–3 kg (2.2–6.6 lb) in mature individuals.

They first investigated the possibilities that the sounds were due to equipment malfunction, geophysical phenomena, or even part of a Soviet Union scheme for detecting enemy submarines.

[52][53] Over the past 100 years, the dramatic increase in ocean noise from shipping and naval activity may have slowed the recovery of the fin whale population, by impeding communications between males and receptive females.

[61] The North Atlantic fin whale has an extensive distribution, occurring from the Gulf of Mexico and Mediterranean Sea, northward to Baffin Bay and Spitsbergen.

[61] Extensive ship surveys have led researchers to conclude that the summer feeding range of fin whales in the western North Atlantic is mainly between 41°20'N and 51°00'N, from shore seaward to the 1,000 fathoms (6,000 ft; 1,800 m) contour.

Acoustic readings from passive-listening hydrophone arrays indicate a southward migration of the North Atlantic fin whale occurs in the autumn from the Labrador-Newfoundland region, south past Bermuda, and into the West Indies.

[67] One or more populations of fin whales are thought to remain year-round in high latitudes, moving offshore, but not southward in late autumn.

Although some fin whales are apparently present year-round in the Gulf of California, there is a significant increase in their numbers in the winter and spring.

[68] Southern fin whales migrate seasonally from relatively high-latitude Antarctic feeding grounds in the summer to low-latitude breeding and calving areas in the winter.

[69] It has been shown that populations of fin whales within the Mediterranean have preferred feeding locations that partially overlap with high concentrations of plastic pollution and microplastic debris.

[73] Fin whales might have started returning to the coastal waters off British Columbia (a sighting occurred in Johnstone Strait in 2011[74]) and Kodiak Island.

Year-round confirmations indicate possible residents off pelagic north eastern to central Chile such as around coastal Caleta Chañaral and Pingüino de Humboldt National Reserve, east of Juan Fernández Islands, and northeast of Easter Island and possible wintering ground exist for eastern south Pacific population.

[81] Among Northern Indian Ocean and Bay of Bengal, such as along Sri Lanka, India, and Malaysia, sightings and older records of fin whales exist.

In January 1984, seven were seen from the air circling, holding the flippers, and ramming a fin whale in the Gulf of California, but the observation ended at nightfall.

Of the 1,609 fin whale stomachs examined at the Hvalfjörður whaling station in southwestern Iceland from 1967 to 1989 (caught between June and September), 96% contained only krill, 2.5% krill and fish, 0.8% some fish remains, 0.7% capelin (M. villosus), and 0.1% sandeel (family Ammodytidae); a small proportion of (mainly juvenile) blue whiting (Micromesistius poutassou) were also found.

[91] Off West Greenland, 75% of the fin whales caught between July and October had consumed krill (family Euphausiidae), 17% capelin (Mallotus) and 8% sand lance (Ammodytes sp.).

[93] In the Southern Hemisphere, they feed almost exclusively on euphausiids (mainly the genera Euphausia and Thysanoessa), as well as taking small amounts of amphipods (e.g. Themisto gaudichaudii) and various species of fish.

If prey patches are not sufficiently dense, or are located too deep in the water, the whale has to spend a larger portion of its day searching for food.

Therefore, the implication can be made that the feeding migration of fin whales every year in circumpolar waters can be associated with pathologic risk.

[103] An emaciated 13 m (43 ft) female fin whale, which stranded along the Belgian coast in 1997, was found to be infected with lesions of Morbillivirus.

[104] In January 2011, a 16.7 m (55 ft) emaciated adult male fin whale stranded dead on the Tyrrhenian coastline of Italy was found to be infected with Morbillivirus and the protozoa Toxoplasma gondii, as well as carrying heavy loads of organochlorine pollutants.

However, the later introduction of steam-powered boats and harpoons that exploded on impact made it possible to kill and secure them along with blue and sei whales on an industrial scale.

In response the Japanese Coast Guard has started a surveillance program to monitor large cetacean activity in Tsushima Strait to inform operating vessels in the area.

In Monterey Bay and the Southern California Bight, fin whales are encountered year-round, with the best sightings between November and March.