Fin whale (Balaenoptera physalus) COSEWIC assessment and status report: chapter 3

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Species Information

Name and classification

The fin whale was originally referred to as Balaenoptera musculus (the blue whale was referred to as Balanoptera sibbaldii) until True’s (1899) evaluation of Linnaeus’ Systema Naturae. Subsequently, this species was classified as Balaenoptera physalus (L. 1758) (Rice 1998).

Southern and northern hemisphere fin whales are considered geographically separate subspecies: B. p. physalus for the northern hemisphere and B. p. quoyi (Fischer 1829) for the southern hemisphere. This is based on morphological differences and suspected reproductive isolation due to alternating migratory schedules in each hemisphere(Rice 1998, Aguilar 2002, Notarbartolo-Di-Sciara et al. 2003).

English common names for this species include finback and finner.French common names include rorqual commun, baleine à nageoires and baleinoptère commune (Gambell 1985, Jefferson et al. 1993).

Hershkovitz (1966) listed a number of names supposedly applied to the fin whale by Aboriginal people.

Description

The fin whale is the second largest member of the family Balaenopteridae, after the blue whale (B. musculus). It has been characterized as the “greyhound of the sea” due to its fast swimming speed and streamlined body (Reeves et al.2002). In dorsal view, the head is narrow, measuring about 20-25% of the total body length, with the rostrum particularly pointed, prominent splash guards around the double nares (i.e., nostrils) and a single median head ridge. The eyes lie just above the corners of the mouth. The lower jaw is laterally convex and juts 10-20 cm beyond the tip of the rostrum when the mouth is shut. The dorsal fin is set about three quarters of the way back along the dorsal surface, is falcate or pointed, and can be 60 cm high. Behind the dorsal fin, the caudal peduncle has a sharp, prominent ridge.

The bodies of fin whales are dark grey or brownish-grey dorsally and on the sides, shading to white ventrally. Some individuals have a V-shaped chevron on the dorsal side, behind the head. The colour of the lower jaw is asymmetrical – dark on the left and light on the right. This pigment asymmetry continues in the baleen plates, where the right front third are yellowish-white, and the remainder of the right and all of the left baleen plates are a dark blue-grey. This colouration pattern is diagnostic for the species(Agler et al. 1990). The ventral surfaces of the flippers and flukes are also white. The lighter ventral side of the animal may acquire a yellowish tinge in colder waters generally attributed to diatom presence (Gambell 1985, Aguilar 2002). Some adults show scarring indicative of lamprey or remora attachment or nicks and scars on the fins or body that may stem from interactions with fishing gear or other animals(Seipt et al. 1990, Notarbartolo-Di-Sciara et al. 2003).

Adult females reach lengths 5-10% greater than adult males(Aguilar 2002, Ralls and Mesnick 2002). Adult fin whales in the southern hemisphere are up to 4 m longer than their northern hemisphere counterparts (Bannister 2002), and have longer, narrower flippers (Nemoto 1962).

Fin whales can be confused with blue (B. musculus), sei (B. borealis) and Bryde’s (B. brydei) whales (Jefferson et al. 1993), and with the recently described Balaenoptera omurai (Wada et al. 2003). However, Bryde’s whales tend to be restricted to warmer latitudes (below 40ºN) (Omura 1959), and B. omurai is much smaller, and has to date only been found in the western North Pacific. Confusion with these two species in Canadian waters is therefore unlikely.

Morphologically, the fin whale is similar in overall size to the blue whale, but the head is more pointed. Upon close examination, the fin whale has only a single prominent head ridge compared with three in Bryde’s whales (Leatherwood et al. 1988). The dorsal fin is larger than the blue whale’s, and is set farther back and has a shallower rise than those of the sei and Bryde’s whales. When a fin whale surfaces, the blowholes are seen first followed by the dorsal fin. In sei and Bryde’s whales, the blowholes and dorsal fin usually appear almost simultaneously (Leatherwood et al. 1988). The blue whale is the only member of the genus Balaenoptera to regularly “fluke up” (i.e., lift its flukes above the surface when starting a deep dive).

On both coasts, there is considerable overlap in body size, colouration, dorsal fin shape, and distribution between fin and sei whales (Kate Wynne, personal communication. University of Alaska Fairbanks, School of Fisheries and Ocean Sciences, 118 Trident Way, Kodiak, AK 99615; Hal Whitehead, personal communication. Department of Biology, Dalhousie University, Halifax, NS, B3H 4J1). This makes the sei whale the species most likely to be confused with fin whales in Canadian waters.

Individual animals can be identified by means of scarring, pigmentation patterns, dorsal fin shapes and nicks(Agler et al. 1990). Slight variations in size and pigmentation are documented for different regions in the Northern hemisphere (Aguilar 2002).