Balaenoptera physalus, Linnaeus, 1758

Russell A. Mittermeier & Don E. Wilson, 2014, Balaenopteridae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 242-299 : 295-297

7.

Fin Whale

Balaenoptera physalus

French: Rorqual commun / German: Finnwal / Spanish: Rorcual comun

Other common names: Common Rorqual, Finback, Fin-backed Whale, Finner, Herring Whale, Razorback; Northern Fin Whale (physalus); Southern Fin Whale (quoyi)

Taxonomy. Balaena physalus Linnaeus, 1758 ,

“Habitat in Oceano Europao.” Restricted by Thomas in 1911 to “ Norway, near Svalbard , Spitsbergen Sea.”

Genetic support for recognition of subspecies of B. physalus is weak at the moment, although preliminary studies of mitochondrial and nuclear markers suggest distinct differentiation among populations in different ocean basins. Morphological support for separate northern and southern subspecies primarily relies on size differences (larger in Southern Hemisphere), although it also appears that northern populations have shorter and broader flippers than southern populations. A possible third subspecies, patachonica , named by Burmeister in 1865, is included in the list of Marine Mammal Species and subspecies. However, this form is not currently recognized by IUCN. Two subspecies recognized.

Subspecies and Distribution.

B.p.physalusLinnaeus,1758—oceansoftheNorthernHemisphere.

B. p. quoyi Fischer, 1829 — oceans of the Southern Hemisphere.

Descriptive notes. Total length 2200-2700 cm; weight 60,000-90,000 kg. Adult female Fin Whales can be 5-10% longer than males. Total body length estimates are 2500 cm and 2700 cm for male and female “Southern Fin Whales” (B. b. quoyi ) and 2200 cm and 2400 cm for male and female “Northern Fin Whales” (B. b. physalus ). The Fin Whale is the most slender species of rorquals and is only exceeded in maximum body length by the Blue Whale ( B. musculus ). Color of adult Fin Whales is a uniform dark gray to brownish-black on back and sides, grading into white on belly. Undersides of pectoral flippers and caudal flukes are also white. Perhaps the most distinctive coloration feature of the Fin Whale is its asymmetric head coloration; left side of head including lower lip is uniformly dark gray like body, while right lower lip and right inside of mouth are white. White coloration can extend onto right upperlip and neck. The recently described Omura’s Whale ( B. omurai ) has a somewhat similar color asymmetry of head, although dark-gray pigmentation of left side of head extends past lower lip nearly to midline of throat, instead of typically covering only lower lip, as in Fin Whales. Fin Whales typically lack mottled coloration of Blue Whales and extensive scarring of Sei Whales ( B. borealis ). On Fin Whales, there is often a grayish white, chevron-shaped patch on upper back behind blowholes, with apex of chevron pointing forward. Head makes up ¢.20-25% of total body length. External surface of rostrum has a median ridge that extends from blowholes to tip of snout. Median ridge of Fin Whales is not as sharply defined as in Sei Whales or Bryde’s Whales ( B. edeni ). Viewed from above, rostrum of the Fin Whale has straight lateral margins, even more so than in Sei Whales. Like most species of rorquals, head of the Fin Whale is relatively flattened in lateral view. Dorsal fin is distinct, up to 60 cm tall, and positioned about three-quarters the distance from tip of rostrum to tail. Behind dorsal fin, peduncle is marked by distinct dorsal and ventral keel-like ridges, features that give Fin Whales their nickname of “razorback.” Tetradactyl (four-fingered) pectoral flippers of Fin Whales are relatively small and slender compared with pectoral flippers of Blue Whales and measure only 8-10% of total body length. Width of caudal flukes measures 20-24% of total body length and can be up to 500 cm across from tip-to-tip in a 2000cm individual. As with most species of rorquals, smooth trailing edge of caudal flukes is marked by a deep median notch. Ventral grove blubber has 50-100 pleats that extend from tip of rostrum to umbilicus and slightly beyond. Baleen apparatus reflects coloration asymmetry of rest of head, with entire left baleen rack and posterior two-thirds of right baleen rack composed of dark blue-gray baleen laminae with vertical streaks of white or yellow. In contrast, baleen laminae in front of right baleen rack are white or yellow. Fringing baleen bristles are generally yellowish white and somewhatfiner (averaging 0-35-0-4 mm in diameter) than coarse, black baleen bristles of Blue Whales. Baleen laminae are relatively broad, with average length-to-width ratio c.2:1. Largest main baleen plates are 70-90 cm in length. Number of baleen laminae varies widely, with Southern Fin Whales possessing an average of 356-365 laminae and Northern Fin Whales in the North Pacific Ocean averaging 360-390 laminae. Greatest number of laminae reported approaches 470/rack. Fin Whales are relatively fast swimmers and can reach speeds of 28 km/h for short periods. Normal cruising speed is 9-15 km/h. Fin Whales can forage at depths as great as 300 m, much deeper than foraging Blue Whales or Sei Whales. As a consequence, Fin Whales often rise to the surface at a steep angle, blow, submerge their massive heads, and then dive again with a distinctly arched back and well-exposed dorsal fin. While diving, they almost neverlift their caudal flukes above the water’s surface. A typical surface blow is cone-shaped and can reach up to 6 m. Fin Whales, unlike other large species of rorquals, occasionally breach and, when doing so, collide with the water surface with a tremendous splash.

Habitat. Temperate and colder waters, with a cosmopolitan geographical distribution in all ocean basins from equatorial to polar regions. As is the case with most species of rorquals, Fin Whales have a seasonal migratory pattern that generally involves moving between high-latitude feeding grounds and low-latitude breeding and birthing grounds. Important habitats are primarily associated with topographic and oceanographic conditions on feeding grounds and along parts of their migration route. Locations of summer, polar feeding grounds are more easily defined and predictable for Fin Whales than locations of their winter breeding and birthing grounds, which are more diffuse across broad spans of longitude. In the central and eastern North Atlantic Ocean, Northern Fin Whales are most common during boreal summer in waters over the continental slope and continental shelf seaward of the 200m isobath (line demarking the same depths underwater), whereas along the Eastern Seaboard of the USA, they tend to be most abundant in waters over the continental shelf centered on the 100 m isobath but extending into shallower and deeper waters. Northern Fin Whales are locally common in continental shelf waters of the Gulf of Saint Lawrence and the adjacent Saint Lawrence Estuary, where their distribution appears to be associated with areas of high productivity that are driven by conditions of tidal and current mixing aligned along steep contours of the drowned Laurentian Channel. Formation of pack ice in winter forces Northern Fin Whales offshore, while breakup of sea ice in spring allows whales to move back inshore. Concentrations of Northern Fin Whales in the North Pacific Ocean and Bering Sea generally occur along the shelfsslope break (¢.200 m isobath) where frontal boundaries or mixing zones between coastal and pelagic waters result in high primary productivity during boreal summer. In waters off British Columbia, Canada, Northern Fin Whales also frequent continental shelf waters of the Hecate Strait and Queen Charlotte Sound, where topographic and oceanographic conditions again appear to concentrate zooplankton. In the Southern Ocean, Southern Fin Whales typically do not range to the edge of the Antarctic pack ice during austral summer like Blue Whales and Antarctic Minke Whales ( B. bonaerensis ). Southern Fin Whales tend to migrate in pelagic waters, and whaling records documentthis migration as occurring along coasts of South America as far north as Peru in the South Pacific Ocean and north-eastern Brazil in the South Atlantic Ocean, along coasts of Africa north of South Africa in the South Atlantic and Indian oceans, and in waters north of Australia and New Zealand. Whaling recordsalso indicate that Southern Fin Whales formerly occurred during austral winter in warm oceanic waters of the central South Atlantic and South Pacific oceans far from land. These general migratory patterns are more complex in some parts of the Southern Hemisphere and Northern Hemisphere, with resident or semi-resident subpopulations reported in areas with more year-round abundance of prey (e.g. Gulf of California and the Mediterranean Sea).

Food and Feeding. The Fin Whale is relatively euryphagous (compared with the Blue Whale) and consumes a variety of prey depending on availability and season, sometimes feeding exclusively on pelagic crustaceans and other times consuming only schooling fish. This opportunistic feeding strategy is well illustrated by the resident population of Northern Fin Whales in the Gulf of California, where they feed on krill in protected waters of Bahia de Loreto in winter but move farther north in the Gulf to feed on schooling fish in summer. In other regions of the Northern Hemisphere, the preferred invertebrate prey is krill (Meganyctiphanes spp., Euphausia spp., and Thysanoessa spp.), although copepods (Calanus spp.) are also consumed in abundance and occasionally squid (Ommastrephes spp. and Gonatus spp.). Schooling fish preferred by foraging Northern Fin Whales occur in dense aggregations depending on location and time of year and include herring (Clupea spp.), cod (Gadus spp.), mackerel (Scomber spp.), pollock (Pollachius spp.), and capelin (Mallotus villosus). In the Southern Ocean, Southern Fin Whales feed almost exclusively on krill (Euphausia spp.), as do Blue Whales, and the widespread distribution of this abundant prey near the Antarctic Convergence means that the two species of rorquals are broadly sympatric in large mixed groups on austral summer feeding grounds. This pattern of sympatry combined with the close phylogenetic relationship between Fin Whales and Blue Whales helps explain the common occurrence of Fin Whale x Blue Whale hybrids, including at least one reported hybrid female that was pregnant. During winter, most populations of Southern Fin Whale undergo some form of migration to breeding and birthing grounds in lower latitudes, where they are said to fast, although it may be more accurate to say that they simply consume less food. Whaling records indicate that toward the end of winter, Southern Fin Whales are distinctly thinner and more emaciated than when they first arrive on breeding grounds in spring. Butchered carcasses of wintering whales yielded less oil and their stomachs typically were empty. It is not until Southern Fin Whales arrive again on high-latitude feeding grounds that they begin to rebuild their energy stores of blubber. Recent research using various digital instrument packages temporarily attached to backs of foraging Fin Whales has greatly expanded our knowledge of their feeding behavior. A typical foraging event involves a series of dives, some as deep as 300 m. Although the start of a dive begins with powerful fluking, much of the descent is in the form of a glide. At the bottom of each dive, an individual performs a series of lunges, each involving an initial burst of speed (up to 3 m/s) followed by a rapid deceleration (less than 1 m/s) during which lower jaws gape to almost 90° and ventral throat pouch inflates somewhat like a parachute. Estimates suggest that pouch fills at the rate of ¢.20 m?/s and mouth begins to close three seconds into the lunge and is completely closed after a lapse of only six seconds. At this point, the throat pouch has greatly expanded to occupy up to 60% of total body length and contain as much as 70,000 1 of sea water weighing as much as 60,000 kg. Surprisingly, in less than a minute, all of the engulfed water passes out through the baleen apparatus as the pouch steadily deflates trapping as much as 10 kg of krill in the mouth. Foraging Fin Whales perform an average of 4-4 lunges/dive and return to the surface powered by steady and powerful fluking. After several hours of foraging dives, an adult Fin Whale can ingest more than 1000 kg ofkrill, providing enough energy to sustain it for an entire day, while also building up energy stores for the coming winter.

Breeding. As with most species of rorquals, reproductive biology of Fin Whales is poorly known, with the majority of available information provided by postmortem whaling records. These data suggest that females in the Northern Hemisphere formerly reached sexual maturity at 10-12 years of age but that age of sexual maturity has now been developmentally accelerated due to density-dependent factors related to low population size. Current estimates for the onset of sexual maturity in northern waters are down to 6-7 years of age. Estimates of body length at sexual maturity have not changed for female Northern Fin Whales and remain at ¢.1850 cm. Males show a similar pattern of developmental acceleration, and although formerly reaching sexual maturity at c.11 years of age, it is now estimated at only c.5 years of age and a body length of ¢.1750 cm. Sexual maturity of female and male Southern Fin Whales formerly occurred at c.12 years and c.11 years, respectively, but it has now fallen to c.6 years and c.4 years. Related body length measurements at sexual maturity for female and male Southern Fin Whales have remained at ¢.2000 cm and ¢.1900 cm, respectively. Reproductive cycle of Fin Whales is closely tied to their seasonal migration between high-latitude feeding grounds and low-latitude breeding and birthing grounds. In general, pregnant females give birth in the same temperate waters where conception occurred during the prior winter. Gestation is usually c.11 months, with a single young typically born in the respective austral or boreal winter. Although rare, twin births have been reported. Young are ¢.640 cm in length at birth and weigh 1000-1500 kg. Young are weaned at 6-7 months at a length of 1100-1300 cm. Whaling statistics suggest a neonatal growth rate of 50-60 kg/day and up to 3 cm/day, while consuming 72 kg/day of milk. After weaning, growth rate slows to an average of 26 cm/month up to sexual maturity at c.2-3 years of age. Sex ratio of neonates is essentially 1:1, which probably holds for much of the year except for periods when differential segregation of sexes or sexual classes occurs on or at the ends of the seasonal migrations. Females are reported to reproduce on a 2year cycle, suggesting an interbirth interval of ¢.6 months. There is some evidence that at least some populations of Fin Whales have mating systems involving male—male competition to monopolize females. Limited observational sampling seems to show that mating sometimes involves a group of 3—4 individuals, with two whales involved in copulation and attendant males as bystanders. One study of Northern Fin Whales in the Gulf of California also has documented singing males that produce long, low-frequency vocalizations that may attract females to dense patches of food, where mating then may occur. Conception typically occurs in respective austral and boreal winters, with peaks in December—January in the Northern Hemisphere and June-July in the Southern Hemisphere. Nevertheless, whaling statistics correlating embryo size with geographical location and time of year suggest that mating may take place throughout the year in some areas. Studies of growth layers formed in wax plugs from ear canals of butchered whales suggest that Fin Whales live for 90-100 years.

Activity patterns. Daily activity patterns of Fin Whales have been described on summer feeding grounds in both hemispheres and consist of foraging individuals generally following the diel movement cycle of their prey species (deep water during the day and shallow water at night). Like most species of rorquals, annual activity patterns of Fin Whales are primarily related to migration between summer feeding grounds and winter breeding and birthing grounds.

Movements, Home range and Social organization. The Fin Whale has a cosmopolitan geographical distribution like most species of rorquals and occurs in all ocean basins from equatorial to polar regions. They are the only rorqual that regularly occurs in the Mediterranean Sea but are absent from most tropical regions. Although Fin Whales exhibit the general annual migration cycle of other rorquals, moving from polar feeding grounds to temperate breeding and birthing grounds, certain populations undergo considerably longer migrations than others. In the North Pacific Ocean, Northern Fin Whales are distributed mainly north of 30° N during boreal summer, extending into the Gulf of Alaska and later in summer into the Bering Sea and even the Chuckchi Sea. In the western North Pacific Ocean, summer distribution of Northern Fin Whales extends from waters around Japan northward into the Sea of Okhotsk. Winter grounds are less well known but appear to include waters from California south to the tip of Baja California in the east and offshore well into the central Pacific Ocean. In the western North Pacific Ocean, Northern Fin Whales are reported during winter from the Sea ofJapan, the Yellow Sea, and the East China Sea through the Philippine Sea. This general seasonal pattern breaks down in areas where prey abundance is more stable throughout the year, such as in waters off central and southern California (35° N). In addition, a resident subpopulation in the Gulf of California is known to live year-round throughout this oceanographically complex body of water. Northern Fin Whales occur throughout the North Atlantic Ocean, generally north of 30° N where the Gulf Stream appears to moderate their annual migration cycles. During boreal summer, Northern Fin Whales in the east penetrate as far north as waters around Svalbard in the Arctic Ocean, but rarely north of the Barents Sea, while in the western North Atlantic Ocean, they summer in Baffin Bay, the Davis Strait, and waters off Labrador and Newfoundland south to Cape Hatteras. These occurrences may represent separate northern and southern subpopulations. During boreal winter, Northern Fin Whales in the North Atlantic Ocean typically leave their northern feeding grounds and migrate into warmer, southern waters of the West Indies in the west and from the Bay of Biscay and Spain to the Canary Islands in the east. Migration typically occurs in open ocean making it difficult to determine migration routes and actual destinations. Northern Fin Whales have been reported to overwinter in the North Sea and adjacent waters during mild winters, generally moving offshore to avoid pack ice. A resident subpopulation of Northern Fin Whales, genetically distinct from those in the North Atlantic Ocean, is reported to occur in the central and western Mediterranean Sea. Southern Fin Whales in the Southern Hemisphere occur throughout the Southern Ocean during austral summer, mainly between 40° S and 60° S, except in the South Pacific Ocean region where they may penetrate nearly to the Antarctic Circle. The anti-tropical distribution of Fin Whales is centered at temperate latitudes and the 6month, out-of-phase nature of the migration cycle, with Southern Hemisphere populations at low latitudes at the same time that Northern Hemisphere populations are at high latitudes and vice versa, means that there are little if any instances of sympatry and thus limited opportunities for interbreeding among populations in the two hemispheres. Migrations typically are segregated by sexes and sex classes, with pregnant females usually preceding other individuals, soon followed by adult males and anestrous females, and finally by lactating females, their young, and juveniles. On winter grounds where births occur, sex ratio of neonates from whaling records is 1:1. Fin Whales are not gregarious, and the only consistent social bond is the ephemeral mother—offspring pairing that lasts from birth to weaning. During migrations, group size typically is small, with groups of 2-7 individuals. Solitary individuals, however, are the norm. On summer feeding grounds, groups of considerably more individuals have been reported, but these aggregations lack any obvious social organization and instead generally reflect high abundance of prey in these high productivity polar waters. In the North Pacific Ocean, these feeding aggregations often form along shelf edge where oceanic frontal boundaries or zones of mixing between shelf and oceanic waters occur. No accounts of cooperative feeding behavior have been reported for Fin Whales.

Status and Conservation. CITES Appendix I. Classified as Endangered on The IUCN Red List, with the subpopulation in the Mediterranean Sea listed as Vulnerable. The Fin Whale has been listed as endangered in the USA since 1970. Causes of population decline are obvious and well documented in kill records kept by the whaling industry. Commercial whaling of Northern Fin Whales began in the late 19" century in the North Atlantic Ocean, and an estimated 45,000 individuals were killed in this region (Canada to Svalbard) in 1876-1915. An additional 55,000 Northern Fin Whales are estimated to have been killed in commercial whaling operations in 1915-1986, after which the International Whaling Commission (IWC) set catch limits for all whales at zero (commercial whaling moratorium). A similar record of intense hunting is documented for commercial whaling activities in the North Pacific Ocean, where ¢.74,000 Northern Fin Whales were killed in 1910-1975. This figure does not include thousands of unspecified whales documented in 1900-1930 whaling statistics. These numbers, however, pale compared with whaling records from the Southern Hemisphere, which document more 725,000 Southern Fin Whales killed in 1905-1976. The majority of these whales (703,693) were killed in the Southern Ocean, where hunting of Southern Fin Whales intensified in the 1930s as populations of Blue Whales declined because of overhunting. During the peak of commercial exploitation (1935-1970), c.30,000 Southern Fin Whales were killed annually. By 1974, whaling operations were killing less than 1000 Southern Fin Whales/year, a decline that underscored the unsustainability ofthis level of hunting. Commercial whaling of the Fin Whale ended in 1976 in the North Pacific Ocean, after the 1976-1977 season in the Southern Ocean, and in 1987 in the North Atlantic Ocean. Northern Fin Whales are hunted still in waters off Greenland, with up to 20 individuals killed annually under the IWC’s “aboriginal subsistence whaling” scheme. Iceland resumed commercial whaling of Northern Fin Whales in 2006 under a formal objection to the IWC’s ban on commercial whaling, and Japan starting killing Fin Whales in the 2005-2006 season as part of its “scientific whaling” program. Protected from intense commercial whaling since 1985, populations of Fin Whales in both hemispheres have started to increase, although rate of increase and population trends have not been calculated. Estimates placed the cumulative North Atlantic population of the Northern Fin Whale at ¢.52,000 individuals in 2001 and the Mediterranean population at 3583 individuals in 1991. In 1975 the cumulative North Pacific population of Northern Fin Whales was estimated at ¢.17,000 individuals. Estimates for Southern Hemisphere populations of Southern Fin Whales are of questionable reliability and varied from a low of ¢.15,000 individuals in 1983 to a high of ¢.85,200 individuals in 1979. As with other species of rorquals, the international moratorium on commercial whaling that began in 1986 represents the primary conservation measure for insuring survival of the Fin Whale. Ongoing threats are essentially the same as for other whale species and include entanglement in fishing gear (bycatch), fatal encounters with vessels (ship strikes), anthropogenic impacts (whale watching harassment), habitat decline and interference, aboriginal whaling, and “scientific research.” Additional threats posed by climate change and potential loss of prey base and shifts in critical habitat are of unknown impact to the recovery of the Fin Whale.

Bibliography. Aguilar (2009), Bérubé et al. (2002), Burmeister (1865), Gambell (1985b), Goldbogen (2010), Goldbogen et al. (2006), Gregr & Trites (2001), Moore et al. (1999), NMFS (2010a), Panigada et al. (1999), Reilly et al. (2008g), Rice (1998), Sergeant (1977), Thomas (1911), Tomilin (1957), Vikingsson (1997).

Figures

5. Blue Whale (Balaenoptera musculus), 6. Omura’s Whale (Balaenoptera omurai), 7. Fin Whale (Balaenoptera physalus), 8. Humpback Whale (Megaptera novaeangliae)

Subspecies and Distribution. B.p.physalusLinnaeus,1758—oceansoftheNorthernHemisphere. B. p. quoyi Fischer, 1829 — oceans of the Southern Hemisphere.