Pygmy sperm whales are very difficult to detect, except in extremely calm seas. They have a shark-like head with a narrow underslung lower jaw. The flippers are set high on the sides near the head. The small sickle-shaped dorsal fin is usually set well behind the midpoint of the back and the blowhole is positioned more than 10% of the way down the back from the snout tip. Pygmy sperm whales are countershaded, ranging from dark gray on the back to white below. Often the belly has a pinkish tone. There is a light colored bracket mark, dubbed the "false gill," along the side between the eye and the flipper. The lower jaw generally contains 12-16 pairs of long, fang-like teeth that fit into sockets in the upper jaw, which usually has no teeth.
Adult pygmy sperm whales are 2.7-3.8 m long, and newborns are about 1.2 m. Adults may weigh as much as 450 kg.
Can be Confused With
Pygmy and dwarf sperm whales can be somewhat difficult to distinguish at sea. Pygmy sperm whales grow to somewhat greater lengths, and have smaller, more rounded dorsal fins, generally set farther back on the body. The position of the blowhole is another good indicator (more than 10% of the way back from the snout tip in pygmy sperm whales). There is some degree of overlap in most characteristics of these two species, and identifications must be made cautiously, even with a specimen “in hand.”
Pygmy sperm whales are found in deep waters in tropical to warm temperate zones of all oceans. They appear to be especially common over and near the continental slope.
Ecology and Behavior
Pygmy sperm whales inhabit oceanic waters. Most sightings of pygmy sperm whales are of small groups of less than five or six individuals. Almost nothing is known of the behavior and ecology of this species, other than what has been learned from brief sightings during research cruises. They are generally not commonly seen alive at sea, but they are among the most frequently stranded small whales in some areas. When seen at sea, they have usually appeared slow and sluggish, and often float at the surface with no visible blow. Very little is known of the reproductive biology of the pygmy sperm whale.
Feeding and Prey
Pygmy sperm whale diet is dominated by cephalopods.
Studies of feeding habits, based on stomach contents of stranded animals, suggest that this species feeds in deep water on cephalopods and, less often, on deep-sea fishes and shrimps. Pygmy sperm whales feed by seizing prey.
The pygmy sperm whale is not listed as threatened or endangered by either the IUCN or the United States government. Although they have never been taken in large numbers, either directly or incidentally in fisheries, pygmy sperm whales have been occasional victims of dolphin and small whale fisheries, as well as gillnet and purse seine operations. Other potential threats include plastic ingestion (as associated gut-blockage) and ship strikes.
The United States National Marine Fisheries Service considers animals in United States waters to be members of several distinct stocks, and assesses them separately. Delineations between stocks are often difficult to determine, therefore assessments should be considered ongoing processes. In the case of the pygmy sperm whale, concern that sightings may be confused with the cogener K. sima (the dwarf sperm whale) further complicates the estimation of abundance. Stocks are estimated as follows
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