Melon-headed whale
The melon-headed whale (Peponocephala electra), also known less commonly as the electra dolphin, little killer whale, or many-toothed blackfish, is a toothed whale of the oceanic dolphin family (Delphinidae). The common name is derived from the head shape. Melon-headed whales are widely distributed throughout deep tropical and subtropical waters worldwide, but they are rarely encountered at sea. They are found near shore mostly around oceanic islands, such as Hawaii, French Polynesia, and the Philippines.
The melon-headed whale is the only member of the genus Peponocephala. First recorded from a specimen collected in Hawaiʻi in 1841, the species was originally described as a member of the dolphin family and named Lagenorhynchus electra by John Edward Gray in 1846. The melon-headed whale was later determined to be sufficiently distinct from other Lagenorhynchus species to be accorded its own genus.[3] A member of the subfamily Globicephalinae, melon-headed whales are closely related to long-finned and short-finned pilot whales (Globicephala melas and G. macrorhynchus, respectively) and the pygmy killer whale (Feresa attenuata).[4][5] Collectively, these species (including killer whales Orcinus orca, and false killer whales Pseudorca crassidens) are known by the common name ‘blackfish’. Melon-headed whales are one of the smallest species of cetacean (after pygmy killer whales) to have the word ‘whale’ in their common name.
Melon-headed whales have a robust, dolphin-like body, a tapering, conical head (head shape triangular when viewed from above) with no discernible beak and a relatively tall, falcate (sickle-shaped) dorsal fin located near the middle of the back. Body coloration is charcoal-gray to dark-gray body. A dark face ‘mask’ extends from around the eye to the front of the melon and larger animals have whitish lips. Melon-headed whales have a dark colored dorsal cape that starts narrowly at the front of the head and dips down at a steep angle below the dorsal fin. The boundary between the darker cape and coloration on the flanks is often faint or diffuse. Both the mask and dorsal cape are often only visible in good lighting conditions. Compared to females, adult males have more rounded heads, longer flippers, taller dorsal fins, broader tail flukes and some have a pronounced ventral keel posterior to the anus.[6][7][8]
Melon-headed whales grow up to 2.75 m (9.0 ft) in length, and weigh up to 225 kg (496 lb), adult males being slightly larger than females.[7][9] Length at birth is approximately 1 m (3.3 ft).[10][11] Melon-headed whales are physically mature at 13–15 years and live up to 45 years.[7]
At-sea, melon-headed whales can be confused with pygmy killer whales, which are very similar in appearance and share almost identical habitat and range.[12] The shape of the head, flippers and dorsal cape can be useful diagnostic features. Melon-headed whales have flippers with sharply pointed tips whereas pygmy killer whales have rounded flipper tips, and viewed from above, the head shape is more triangular than the rounded head of the pygmy killer whale.[8] The dorsal cape of melon-headed whales is rounded and dips much lower below the dorsal fin than that of pygmy killer whales, which dips at a relatively shallow angle and is more sharply demarcated in color between the dark cape and lighter flanks.[13] While both species have white around the mouth, in adult pygmy killer whales this can extend onto the face.[14]
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