Pygmy Killer Whale (Feresa attenuata)
Description & Ecology
Pygmy killer whales, Feresa attenuata (Gray, 1874), are very similar in appearance to melon-headed whales and to juvenile false killer whales. From a distance it is very difficult to tell these three apart. The shape of the head, the dorsal fin and the flippers of pygmy killer whales are different from the other two. The head of Feresa attenuata is rounded and lacks a beak. They have an under slung jaw and white lips, and usually a white patch on the tip of the lower jaw. The skull is asymmetrical and the right jaw is smaller and usually has one less tooth than the left jaw. The teeth are large and conical. There are usually 8-11 pairs of teeth in the upper jaw and 11-13 pairs of teeth in the lower jaw. Pygmy killer whales have a sub-triangular, long based, high dorsal fin with a tip that points backward. The dorsal fin is located near the centre of the body and lacks rigidity, often inclining to the side. The flippers of pygmy killer whales are moderate in length and have rounded tips. The body of Feresa attenuata is slender, though the midsection forward is slightly more robust than the midsection back. Pygmy killer whales are not whale-sized at all; rather, they are average-sized dolphins and part of the Family Delphinidae. An adult ranges in length from 2.1-2.6 m and weighs between 110-170 kg. The colouring is dark gray to black with some paler markings on the underside, as well as some white on the belly. Feresa attenuata has a groove on the skin of its belly that extends from up front to their umbilicus (navel) to their anus. In both males and females this groove contains the umbilicus, the anus and the genitals. Longevity in this species is poorly understood. Pygmy killer whales are described as aggressive animals that have been seen snapping their jaws, beating their flippers and flukes on the surface of the water, and growling. In captivity they elicit fear reactions from other cetaceans. They will charge, bite, and snap their jaws at other cetaceans as well as their trainers. They will often kill all other cetaceans that are in the tank with them. Though aggressive toward other animals pygmy killer whales are shy of vessels. At the water's surface, pygmy killer whales are quite acrobatic. They are often seen leaping, spy hopping, tail slapping, and occasionally bow riding. Social groups of this species are usually made up of approximately 25 individuals. In areas where they are more frequently sighted, such at the Hawaiian Islands, herds contain up to 50 individuals and on rare occasions a few hundred. The pygmy killer whale occurs in deep, warm waters, generally beyond the edge of the continental shelf, and rarely close to shore (except near some oceanic island groups where the water is deep and clear). This species is mainly tropical, but occasionally strays into warm temperate regions. Little is known of the diet of this species, although it is known to eat fish and squid. It has occasionally been recorded attacking dolphins, at least those involved in tuna fishery interactions in the eastern tropical Pacific (Perryman and Foster 1980). Reproductive biology is poorly known in this species. Pygmy killer whales usually occur in groups of 50 or less. Both sexes may remain in their birth groups. They are generally less active than other oceanic dolphins; frequently they are seen "logging"--resting in groups at the surface with all animals oriented the same way.
This is a tropical/subtropical species that inhabits oceanic
waters around the globe generally between 40°N and 35°S. It does not generally
approach close to shore, except in some areas where deep, clear waters are very
close to the coast (such as around oceanic archipelagos like Hawaii). Reports of
its occurrence in the Mediterranean Sea, while common in the literature, are not
supported by authenticated records. It is also doubtful whether it occurs
regularly in the Red Sea or Persian Gulf (Leatherwood et al. 1991). A few
high-latitude strandings and sightings are thought to be extralimital records,
and are generally associated with incursions of warm water (Ross and Leatherwood
1994; Donohue and Perryman 2002; Williams et al. 2002).
Algeria; Anguilla; Antigua and Barbuda; Aruba; Australia; Bahamas; Bangladesh; Barbados; Belize; Benin; Brazil; Brunei Darussalam; Cambodia; Cameroon; Cayman Islands; China; Cocos (Keeling) Islands; Colombia; Comoros; Congo; Congo, The Democratic Republic of the; Cook Islands; Costa Rica; Côte d'Ivoire; Cuba; Djibouti; Dominica; Dominican Republic; Ecuador; El Salvador; Equatorial Guinea; Fiji; France; French Guiana; French Polynesia; Gabon; Gambia; Ghana; Grenada; Guam; Guatemala; Guinea; Guinea-Bissau; Guyana; Haiti; Honduras; India; Indonesia; Iran, Islamic Republic of; Italy; Jamaica; Japan; Kenya; Kiribati; Korea, Republic of; Liberia; Madagascar; Malaysia (Peninsular Malaysia, Sabah, Sarawak); Maldives; Marshall Islands; Mauritania; Mayotte; Mexico; Micronesia, Federated States of; Morocco; Mozambique; Myanmar; Nauru; Netherlands Antilles (Bonaire, Curaçao, Netherlands Leeward Is.); New Caledonia; Nicaragua; Nigeria; Niue; Northern Mariana Islands; Oman; Pakistan; Palau; Panama; Papua New Guinea; Peru; Philippines; Pitcairn; Portugal; Puerto Rico; Saint Kitts and Nevis; Saint Vincent and the Grenadines; Samoa; Senegal; Sierra Leone; Singapore; Solomon Islands; Somalia; South Africa; Spain; Sri Lanka; Suriname; Taiwan, Province of China; Tanzania, Thailand; Timor-Leste; Togo; Tokelau; Tonga; Trinidad and Tobago; United States; Venezuela, Bolivarian Republic of; Vietnam; Virgin Islands, British; Virgin Islands, U.S.; Wallis and Futuna; Western Sahara; Yemen
Although there is little information on the population biology
of this species, the pygmy killer whale appears to be naturally uncommon. Wade
and Gerrodette (1993) estimated that there were about 38,900 (CV=31%) of these
whales in the eastern tropical Pacific. There are estimated to be 817 (CV=112%)
in the Hawaiian portion of the US EEZ, and 408 (CV=60%) in the northern Gulf of
Mexico (Barlow 2006; Mullin and Fulling 2004).
Population Trend: Unknown
Because of their relatively low abundance, even small takes in localized areas could be significant. Although there is considerable controversy regarding the absolute level of declines, there is good evidence of large-scale reductions in many predatory fish populations (e.g., Baum et al. 2003, 2005; Sibert et al. 2006; Polacheck 2006) and over-fishing and collapse of several important “prey” fish stocks world-wide (e.g., Jackson et al. 2001). The effects of such fish population reductions and subsequent ecosystem changes on world-wide populations of pygmy killer whales are unknown but could result in population declines. Predicted impacts of global climate change on the marine environment may affect pygmy killer whales, although the nature of impacts is unclear (Learmonth et al. 2006). This species, like beaked whales, is likely to be vulnerable to loud anthropogenic sounds, such as those generated by navy sonar and seismic exploration (Cox et al. 2006) and have been a part of multi-species unusual stranding events in Taiwan (Wang and Yang, 2006). Pygmy killer whales have been killed directly in both harpoon and driftnet fisheries (Caribbean islands, Sri Lanka, Taiwan and Indonesia) and incidentally in various types of fishing gear (most areas of the species’ range). A few individuals are known to be taken in drives and in driftnets in various regions, most notably Japan and Sri Lanka (Ross and Leatherwood 1994). Reports on the small-cetacean fisheries of St Vincent and Lamalera suggest that pygmy killer whales form a very small proportion of the catch and that catches probably have little impact on the subpopulations in those areas. In Sri Lanka, there is mortality of this species due to harpooning of dolphins for use as bait on long-lines for sharks, billfish, and other oceanic fishes (Ross and Leatherwood 1994). Although they comprise less than 2% of all cetaceans in monitored by-catches in gillnet fisheries in Trincomalee, Sri Lanka and in villages on the south-west coast of Sri Lanka, this may amount to 300 - 900 pygmy killer whales each year (Ross and Leatherwood 1994). The numbers of animals killed incidentally in net fisheries, such as those in Sri Lanka, may be much higher than is so far documented, because monitoring of these widespread activities is incomplete. In the long term, such takes may have a significant impact on pygmy killer whales where their distribution overlaps with extensive gillnetting operations (Ross and Leatherwood 1994). Small incidental catches are known in fisheries in other areas including the Philippines and Taiwan (Ross and Leatherwood 1994, Dolar 1994, J. Wang pers. comm. 2007). Evidence from stranded individuals of several similar species indicates that they have swallowed discarded plastic items, which may eventually lead to death (e.g. Scott et al. 2001); this species may also be at risk. This species does not appear to be particularly abundant anywhere that it has been sighted. In Hawaii, subpopulations appear to be small, and this, along with their limited movements, suggests the species may be particularly vulnerable to human impacts regionally.
The species is listed on Appendix II of CITES. Research is needed to determine the impact of potential threats on this species.