Whales, Dolphins, and Porpoises: Cetaceans

Cetaceans are completely aquatic mammals: they feed, mate, calve, and suckle their young in the water. They are the most specialized mammalian swimmers. Some are capable of maintaining speeds up to 25 miles per hour, diving to depths of 10,000 feet, and remaining submerged up to 2 hours. The body is streamlined (limbs are tapered or lacking) and the tail is developed into horizontal flukes for propulsion. The smooth, supple, and hairless skin further reduces drag during swimming.

Cetaceans breathe through nostrils (blowhole) on top of the head. When surfacing after a dive, whales forcefully expel the previous lungful of air (blow) and inspire (breathe in) new air. Characteristics of the blow are useful for identification.

Cetaceans are grouped into two taxonomic suborders: the baleen whales (Mysticeti) and the toothed whales (Odontoceti). Mysticetes are filter feeders that forage for zooplankton and small fish by skimming or gulping huge amounts of prey and water. The water is then forced back out the mouth past hundreds of baleen plates that act as sieves to trap the prey, which is then swallowed.

Odontocetes have various numbers of identical conical or spade-shaped teeth that are used to strain or grasp prey, primarily fish and squid.

Taxonomic Relationships of Common Alaska Cetaceans

Family Characteristics of Alaska Cetaceans

Mysticetes (Baleen Whales)

All mysticetes have two nostrils. Females are generally larger than males but otherwise there is no sexual dimorphism. They are not known to echolocate prey. All three families are found in Alaska waters.

Balaenidae (right whales):

Robust body. Skim prey using hundreds of long baleen plates. High arching lower lip and massive head (makes up a third of body length) are needed to accommodate baleen plates. No dorsal fin or ventral throat grooves. Nostrils separated into two divergent blowholes, creates V-shaped blow.

Balaenopteridae (rorquals):

Numerous ventral throat grooves allow expansion for large-volume gulping of prey and water. Dorsal fin present. Single, straight blow.

Eschrichtiidae (gray whale):

Skim or dredge mud for crustaceans. Robust body with no dorsal fin or ventral throat grooves. Two to seven short, deep creases on throat. Baleen short and yellow.

Odontocetes (Toothed Whales)

All odontocetes have a single nostril blowhole. Sexual dimorphism is common—males are larger than females, and diagnostic secondary sex traits are present in some families (differences in dorsal fins, tooth pattern). Echolocation for prey is common. Five families are found in Alaska.

Physeteridae (sperm whale):