Order Cetacea • Family Delpinidae
Status: Protected Species
Melon-headed whales look much like false killer whales, and especially pygmy killer whales. Melon-headed whales are dark grey overall, with a dark saddle patch, or a ‘cape’, around the dorsal fin. They have a lighter grey or white patch below, and the lips are light grey or white. Melon-headed whales range from 1.7 to 2.7 meters in length.
Times of Occurrence
Melon-headed whales were found in the Gulf of Mexico during the spring, summer and winter (Jefferson and Schiro 1997). The lack of fall sightings was probably due to the low numbers of sightings. Melon-headed whales probably occur in Hawai’i throughout the year.
Melon-headed whales are found in the tropical and sub-tropical regions throughout the world (Leatherwood and Reeves 1983). Locally, they have been observed off Hawai’i, Lanai and O’ahu (Shallenberger 1981).
Little data exists on the abundance of melon-headed whales. One survey in the Eastern Tropical Pacific estimated that there were 45,000 melon-headed whales in that area (Wade and Gerrodette 1993). They are frequently seen in Hawai’i (Shallenberger 1981). Pod sizes are usually large, up to 500 animals, so there are probably several thousand melon-headed whales in the State.
Melon-headed whales form large groups, ranging from 150-500 animals (Shallenberger 1981; Wade and Gerrodette 1993). Melon-headed whales are reported to associate with Fraser’s dolphins in other areas. In Hawai’i, they have occasionally been observed with humpback whales (personal observation).
Based on their prey species, these whales probably dive to hundreds of meters.
Watkins et al. (1997) found that the calls of melon-headed whales were relatively low in amplitude, 155 dB re 1 µPa at 1 m for whistles and 165 dB re 1 µPa at 1 m for click burst sounds. Clicks lasted 0.1 to 0.2 seconds with repetition rates of up to 1200/second. The dominant frequencies of the whistles were between 8 and 12 kHz and had both upward and downward frequency modulation. In general, the number and amplitude of clicks increased with the activity level of the whales.
There are no studies on the hearing ability of melon-headed whales. However, given their vocalization range, it is likely that they hear well from 4-8 kHz up into the echolocation frequencies of 50-60 kHz.
Stomach contents of melon-headed whales from the Caribbean and South Africa included evidence of both squid and fish (Best and Shaughnessy 1981; Caldwell et al. 1976) One melon-headed whale recovered in Hawai’i had 11 otoliths (fish parts) and six upper and lower squid beaks, confirming reports from other areas (Clarke and Young 1998).
Melon-headed whales are sometimes taken in fisheries in other countries (Perryman et al. 1994). There are no reports of heavy metal or organochlorine contamination, but it is likely that they are susceptible to this form of pollution.