Slender and elongated, fin whales are sleek and streamlined with a flat V-shaped head and up to 100 ventral grooves (pleats) extending to the navel. Fin whales have a distinctly ridged back from dorsal fin to flukes, earning them the name razorback. Fin whales are the only cetacean to have asymmetric coloration. While the right side, including the lower jaw, throat and tongue are white, the left side is gray. This asymmetry may simply be a characteristic that does not confer any special advantage and no one knows for sure if the asymmetry has some special adaptive purpose. Fin whales appear to prefer shallow, coastal waters with uneven sea floors, from 100 to 200 meters deep. Fin whales are deep divers that may reach depths of 750 feet. As well, they are fast swimmers capable of reaching speeds exceeding 20 mph. Fin whales can attain lengths of 88 feet and weights of 70 tons, although the average weight is 50 tons and the average length is 65 feet.
Fin whale diets are generally dominated by euphausids ( since 70 percent of the diet consists of krill ) and copepods ( 25 percent of the diet consists of copepods ) with some fish and squid comprising the remainder of the diet ( 5 percent of the diet consists of fish and squid ). In the waters off eastern Canada the fin whale diet consists primarily of euphausids ( krill ) and capelin. Sand lance, cod, herring and pollack are also consumed by fin whales. Fin whales possess 260 to 480 baleen plates ( each about 2 feet long ) per side and each plate is edged with grey bristles. Fin whales are gulp feeders that swallow vast quantities of water and krill into their expandable gular pouches and then strain out the krill between the baleen plates using force generated by their tongue and gular pouch. Fin whales can live to be seventy years of age.
Male fin whales attain sexual maturity between 8 and 12 years of age and female fin whales attain sexual maturity between 6 and 10 years of age. Mating usually happens in December and January and female fin whales carry the baby whale in their womb for 11 to 12 months ( gestation period ). Calving transpires from November to January and nursing lasts from six to seven months. Female fin whales give birth every three years and female fin whales undergo a six month resting period after giving birth. Female fin whales have pregnancy rates of between 38 percent and 50 percent. Gross annual reproduction rates of 8 percent have been estimated for global fin whale populations.
Altogether there may be 200 thousand fin whales on the planet with most being located in the southern ocean. In the North Atlantic alone, there are estimated to be 56 thousand fin whales and in the Gulf of St. Lawrence there are an estimated 380 fin whales. Entanglement in fishing gear may be the biggest threat to baleen whales. Seven fin whales were found entangled in lobster gear on the edge of the Scotian Shelf in 2003. Ship strikes occur with ships 80 meters or longer that travel at 14 knots or faster and such collisions pose a big threat to fin whales. In a 13 year period about 26 percent of stranded fin whales in the Mediterranean could be linked to ship strikes. Not all ship strikes are fatal however about 4 percent of fin whales in the North Atlantic bear scars from such encounters. Concentrations of organochlorines sufficient to cause concern were found in fin whales from samples taken in the Gulf of St. Lawrence. Climate change and commercial fishing may reduce prey for fin whales and this is a major issue of concern. Their vocalizations are usually at low frequencies below the 120 Hz range and and their repetoire is dominated by short, pulsing sounds at 23 Hz.