Peponocephala electra (Gray, 1846)

Russell A. Mittermeier & Don E. Wilson, 2014, Delphinidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 410-526 : 519-520

29.

Melon-headed Whale

Peponocephala electra

French: Péponocéphale / German: Breitschnabeldelfin / Spanish: Delfin de cabeza de melon

Other common names: Electra Dolphin, Little Killer Whale, Many-toothed Blackfish

Taxonomy. Lagenorhynchus electra Gray, 1846 ,

type locality unknown.

This species is monotypic.

Distribution. Worldwide in tropical and subtropical waters from c.40° N to ¢.35° §, including the Gulf of Mexico, Arabian Sea, Bay of Bengal, South China Sea, and Timor Sea.

Descriptive notes. Total length up to 280 cm; weight up to 275 kg. Neonates may be up to 100 cm long and weigh 15-20 kg. Male Melon-headed Whales tend to be slightly larger than females. The Melon-headed Whale is very similar in appearance to the Pygmy Killer Whale ( Feresa attenuata ). It is moderately robust in stature, with bulbous, although not overly round, head with barely visible beak, tall falcate dorsal fin, and sickle-shaped flippers. More triangularshaped head and more sharply pointed flippers distinguish it from the Pygmy Killer Whale. Skin is dark gray, but darker colored cape may be discernable along back, dipping below dorsal fin. Lips are usually white, and white—to—pale-gray patches are often present on throat and extend along ventral body to urogenital region. Dark band may also extend from blowhole anteriorly along melon, and dark eye patches may extend from eyes up and forward toward front of melon, resulting in a mask-like appearance. Males tend to have longer dorsal fins and flippers, more distinct post-anal humpjust anteriorto tail flukes, and more bulbous melon than females. Young Melonheaded Whales may have more sloping melon than adults. There are 20-25 pairs of small, slender teeth in each jaw.

Habitat. Prefer tropical and subtropical waters, and occasional sightings from higher latitudes usually associated with extended warm water currents. The Melon-headed Whale is most abundant in deep, offshore waters and is only found in coastal regions if continental shelf is close to shore, resulting in near-shore deep waters (e.g. around oceanic islands). Populations of Melon-headed Whales seem to be drawn to regions of equatorial upwelling, likely for foraging.

Food and Feeding. Mesopelagic squid are the preferred prey of the Melon-headed Whale, but small fish and crustaceans also may be suitable alternatives. The Melonheaded Whale also may prey opportunistically on common dolphins ( Delphinus spp. ) escaping from or injured in the purse-seine fisheries for yellowfin tuna ( Thunnus albacares) in eastern tropical Pacific Ocean. A recent study suggested that offshore eddies off Hawaii may be preferred foraging habitat for local populations of Melon-headed Whales.

Breeding. There is no specific information available for this species, but inconclusive evidence suggests that peak breeding of Melon-headed Whales occurs in July-August, and sexual maturity occurs at c.11-5 years for females and c.15 years for males.

Activity patterns. Little is currently known about the behavior of the Melon-headed Whale. Prior to the 1960s,it was only known from skeletal remains. Sightings of Melonheaded Whales at sea indicate that individuals “porpoise” or shallowly leap out of the water when traveling fast and may occasionally breach, spy-hop, and bow ride. Off the Philippines, large groups raft close together while resting.

Movements, Home range and Social organization. The Melon-headed Whale, unlike the similar Pygmy Killer Whale, is often observed in large groups of 100-500 individuals (maximum of 2000). Mixed-species groups are also common and usually include Fraser’s Dolphin ( Lagenodelphis hosei ), the Spinner Dolphin ( Stenella longuostris), the Atlantic Spotted Dolphin ( Stenella frontalis ), the Common Bottlenose Dolphin ( Tursiops truncatus ), and the Rough-toothed Dolphin ( Steno bredanensis ). The Melon-headed Whale is also known for mass strandings, which are increasing in frequency in the North Pacific Ocean. Reports from two strandings—one from Japan and the other from Brazil—revealed high parasite loads in stranded specimens. This may have physically impaired navigation of a few individuals in the groups, causing the other individuals to follow suite due to the species’ strong sociality. In several mass strandings, sex ratio has been female biased (c.1:2), which also implicates socially related behavioral segregation and strong female—female association. No migrations are currently known for the Melon-headed Whale, and little data exists on movement and residency patterns. Sightings at higher latitudes suggest that they follow warm-water currents. Repeated resightings of individuals off the Hawaiian Islands suggest some site fidelity, and more recent work shows evidence that there are two resident, demographically independent, populations: one limited to the north-western area of the Hawaiian Islands and the other ranging throughout the main archipelago.

Status and Conservation. CITES Appendix II. Classified as Least Concern on The [UCN Red List. Global abundance of the Melon-headed Whale is estimated at more than 50,000 individuals, but there are currently no estimates of global population trends. High global abundance, a large distribution, and mostly localized threats mean that a 30% reduction in abundance during the next three generations is unlikely. There are an estimated 45,400 individuals in the eastern tropical Pacific Ocean, 3451 individuals in the Gulf of Mexico, 2947 individuals off Hawaii, and ¢.2200 individuals around the Philippines. The Melon-headed Whale is taken as direct catch in subsistence fisheries in the Caribbean and off Indonesia, Sri Lanka, Taiwan, and Philippines, mostly for human consumption and for use as bait in other fisheries. They also are taken occasionally in the infamous Taiji drive fishery ofJapan, and individuals caught live there sometimes have been sold for captive display in aquaria, although the Melon-headed Whale is notorious for being aggressive and difficult to train. The Melon-headed Whale is also sometimes incidentally caught in driftnet fisheries throughout the tropical Pacific Ocean and yellowfin tuna purse-seine fisheries. None of these fisheries, where the Melon-headed Whale is either directly or indirectly caught, is extensively monitored, so their effect on local populations is unknown. Examination of stranded specimens from Japanese coasts has showed high concentrations of heavy metals (e.g. cadmium, and mercury) and high, although decreasing (over the last ¢.30 years), levels of PCBs and DDT. Concentrations of PBDEs have been increasing over the last 20 years. The Melon-headed Whale is also vulnerable to loud anthropogenic noise. Military training exercises around the Hawaiian Islands were implicated in anomalous movements or “near stranding” of a group of 150-200 Melon-headed Whales into a shallow, confined bay in Kauai, Hawaii; they stayed for more than 28 hours, presumably to avoid the noise. Stranded specimens have also been found to have swallowed various plastic items, which may have been partly responsible for their deaths.

Bibliography. Aschettino et al. (2012), Barlow (2006), Dolar et al. (2006), Endo et al. (2008), Jefferson & Barros (1997), Jefferson, Fertl et al. (2006), Jefferson, Webber & Pitman (2008), Kajiwara et al. (2008), Miyazaki et al. (1998), Perryman (2009), Perryman et al. (1994), Taylor et al. (2008e), Wang & Yang Shihchu (2007), Woodworth etal. (2012).

Figures

On following pages: 33. Commerson’s Dolphin (Cephalorhynchus commersonii); 34. Chilean Dolphin (Cephalorhynchus eutropia); 35. Heaviside's Dolphin (Cephalorhynchus heavisidii); 36. Hector’s Dolphin (Cephalorhynchus hector).

Distribution. Worldwide in tropical and subtropical waters from c.40° N to ¢.35° §, including the Gulf of Mexico, Arabian Sea, Bay of Bengal, South China Sea, and Timor Sea.