6 to
100 and extending at least to the navel. (_Photo by L. Rigley._)]

SEI WHALE (B)

_Balaenoptera borealis_ Lesson 1828

Other Common Names

Pollack whale, sardine whale, Rudolphi's rorqual.

Description

Sei (pronounced "say") whales have been reported to reach 62 feet (19
m).

The snout is less acutely pointed than that of the fin whale but when
viewed from the side appears slightly arched. In general, the head is
intermediate in shape between that of the blue whale and that of the fin
whale. The dorsal fin, which is from 10 to 24 inches (25.4 to 61 cm)
tall and strongly falcate in adult animals, is located about two-thirds
of the way back on the back, farther forward than that of the blue or
fin whales. Sei whales are dark steel gray on the back and sides, and on
the posterior portion of the ventral surface. The body often has a
galvanized appearance due to scars possibly resulting from lamprey bites
inflicted during migrations into warmer waters. These scars may be dark
gray to almost white in color. On the belly there is a region of grayish
white that is confined to the area of the ventral grooves. Neither the
flippers nor the tail flukes are white underneath. The right lower lip
and the mouth cavity, unlike those of the fin whale, are uniformly gray.
The baleen plates are uniformly grayish black with fine grayish-white
fringes. (A small number of sei whales have been noted to have a few
half-white plates near the front of the mouth, a feature which might
result in their confusion with fin whales.)

Natural History Notes

The blow of sei whales is an inverted cone rarely taller than 15 feet
(4.6 m).

Sei whales are generally skimmer feeders and do not usually dive very
deeply. For that reason they usually surface at a shallower angle than
fin whales. The head rarely emerges at a steep angle (except when the
whales are chased). Instead, the blowholes and a major portion of the
back, including the dorsal fin, become visible almost simultaneously and
remain visible for relatively long periods of time. In this species it
can be generally stated that the amount of the back in the area of the
dorsal fin which is exposed above the surface as the animal sounds is
approximately the same height as the dorsal fin. When they begin another
dive, sei whales do not arch the tail stock or flukes high. Instead,
they normally submerge by slipping quietly below the surface, often
remaining in view only a