Pygmy killer Whale

Feresa attenuata Gray, 1874

English: Pygmy killer whale
German: Zwerggrindwal
Spanish: Orca pigmea
French: Orque pygmée

1. Description
Pygmy killer whales have a robust body that narrows towards the dorsal fin, hence the name “attenuata” (latin) meaning “thinning”. The head is round and blunt and lacks a beak typical of many dolphin species. The moderately long flippers are rounded at the tips with convex leading and concave trailing edges. Pygmy killer whales are mostly grey to black, with a subtle dark cape on the side, below the high, falcate dorsal fin. There is a paler grey area on each flank and an irregularly white patch on the ventral side between the flippers, around the genitals and occasionally the tail stock. The lips are also edged with white. Body size ranges from 2.1 to 2.6 m (Donahue and Perryman, 2002).

2. Distribution
This is a tropical and subtropical species that inhabits oceanic waters around the globe, generally not ranging north of 40°N or south of 35°S (Jefferson et al. 1993). It ranges north to the Gulf of Mexico, east coast of Florida, Senegal, Arabian Sea, Sri Lanka, Honshu, Hawaii, and Gulf of Tehuantepec, and south to Buenos Aires, Cape Province, Queensland, and Peru (Rice, 1998).

The distribution of F. attenuata is poorly known from sparse but widely distributed records worldwide. It is seen relatively frequently in the eastern tropical Pacific, Hawaii, and Japan, though it is not particularly abundant anywhere. Because it tends to avoid boats it may be more common than the records suggest (Carwardine, 1995).

It is notable that most of the records outside the tropics are associated with strong, warm western boundary currents which effectively extend tropical conditions into higher latitudes. Records of whales on the cool west coasts of southern Africa and Peru are exceptions, though these could well have originated in far warmer waters comparatively close by (Ross and Leatherwood, 1994 and ref. therein).

3. Population size
Nothing is known of population limits, size, or structure for this species (Ross and Leatherwood, 1994, and refs. therein).

4. Biology and Behaviour
Habitat: Occurs in deep, warm waters, rarely close to shore (except near oceanic islands). Mainly tropical, but occasionally strays into warm temperate regions (Carwardine, 1995).

Behaviour: F. attenuata may be difficult to approach and is known to avoid boats, though there are reports of bow- and wake-riding (Carwardine, 1995).

Schooling: Groups generally contain 50 or fewer individuals, although herds of up to several hundred have been seen. It is a slow and lethargic animal compared to the similar-appearing melon-headed whale (Jefferson et al. 1993; Ross and Leatherwood, 1994). Pods often swim abreast in perfectly co-ordinated “chorus lines” and, when alarmed, bunch together to rush away. Growling sounds may be heard above the surface. Herds often strand (Carwardine, 1995)., e.g. at Hawaii (Mazzuca et al. 1999) or in Brazil (Zerbini and de Oliveira 1997). A new record of a mass stranding of pygmy killer whales from the British Virgin Islands was documented by Mignucci-Giannoni et al. (2000), associating the stranding process with the meteorological and oceanographic disturbance of Hurricane Marilyn, which devastated the Virgin Islands a day prior to the stranding.

Food: Pygmy killer whales eat mostly fish and squid, although they occasionally attack other dolphins, at least when those dolphins are involved in tuna fishery interactions in the eastern tropical Pacific (Jefferson et al. 1993; Carwardine, 1995). Santos and Haimovici (1998) found mainly squids of the families Onychoteuthidae and especially Ommastrephidae in the stomach contents of Feresa attenuata.

5. Migration
No migrations are known (Carwardine, 1995). Incidental catches by Sri Lankan fishermen have been reported in monitored portions of the gillnet fisheries in all months except September, November and December, indicating that pygmy killer whales are present almost throughout the year in this region. Similarly, whalers of St Vincent, Lesser Antilles, indicated that they might encounter pygmy killer whales at any time of the year, implying residency. Though dated records for several other regions span several months of the year, they are at present too few to permit assessment of the migratory status of this species (Ross and Leatherwood, 1994).

6. Threats
Direct catch: A few individuals are known to be taken in drives and in driftnets in various regions, most notably Japan and Sri Lanka (Jefferson et al. 1993). Reports on the small cetacean fisheries of St Vincent and Lamelera suggest that pygmy killer whales form a very small proportion of the catch, and that catches probably have little impact on the populations in those areas. In Sri Lanka, there is additional mortality of this and other species due to harpooning of dolphins for use as bait on long-lines for sharks, billfish, and other oceanic fishes (Ross and Leatherwood, 1994 and refs. therein).

Incidental catch: 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 of the 15 000 - 45 000 dolphins estimated to die each year in such fisheries (Ross and Leatherwood, 1994, and refs. therein). 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 stocks resident in areas where pygmy killer whales (and other small cetaceans) and extensive gillnetting operations overlap (Ross and Leatherwood, 1994). Small incidental catches are known in fisheries in other areas (Jefferson et al. 1993), e.g. the Philippines (Dolar et al. 1999).

Pollution: There are reports on the presence of hydrocarbon residues, including DDT, Dieldrin and PCBs in various tissues of three pygmy killer whales from the Gulf and Atlantic coasts of Florida (Ross and Leatherwood, 1994 and refs. therein).

7. Remarks
There is very little knowledge about this species, its abundance, migratory behaviour or by-catch rates in offshore fisheries. For South American populations, see recommendations in Hucke-Gaete (2000). General recommendations on Southeast Asian stocks can be found in Perrin et al. (1996).

8. Sources
- Carwardine M (1995) Whales, Dolphins and Porpoises. Dorling Kindersley, London, UK, 257 pp.
- Carwardine M, Hoyt E, Fordyce RE, Gill P (2000) Wale Delphine und Tümmler. Könemann-Verlag, Köln, Germany
- Dolar M L L, Suarez P, Ponganis P J, Kooyman G L (1999) Myoglobin in pelagic small cetaceans. Journal of Experimental Biology 202 (3): 227 - 236
- Donahue MA, Perryman WL (2002) Pygmy Killer Whale - Feresa attenuata. In: Encyclopedia of marine mammals (Perrin WF, Würsig B, Thewissen JGM, eds.) Academic Press, San Diego, 1009-1010.
- Hucke-Gaete R ed. (2000) Review on the conservation status of small cetaceans in southern South America. UNEP/CMS Secretariat, Bonn, Germany, 24 pp.
- Jefferson TA, Leatherwood S, Webber MA (1993) FAO Species identification guide. Marine mammals of the world. UNEP / FAO, Rome, 320 pp.
- Mazzuca L, Atkinson S, Keating B, Nitta E (1999) Cetacean mass strandings in the Hawaiian Archipelago, 1957-1998. Aquatic Mammals 25 (2): 105-114
- Mignucci-Giannoni AA, Toyos-Gonzalez GM, Perez-Padilla J, Rodriguez-Lopez MA, Overing J. (2000) Mass stranding of pygmy killer whales (Feresa attenuata) in the British Virgin Islands. J Mar Biol Assoc U.K. 80: 759-760.
- Perrin WF, Dolar MLL, Alava MNR (1996) Report of the workshop on the biology and conservation of small cetaceans and dugongs of Southeast Asia. East Asia Seas Action Plan. UNEP(W)/EAS WG. 1/2, Bangkok, Thailand.101 pp.
- Rice DW (1998) Marine mammals of the world: systematics and distribution. Society for Marine Mammalogy, Special Publication Number 4 (Wartzok D, Ed.), Lawrence, KS. USA.
- Ross GJB, Leatherwood S (1994) Pygmy killer whale - Feresa attenuata. In: Handbook of Marine Mammals (Ridgway SH, Harrison SR eds.) Vol. 5: The first book of dolphins. Academic Pres, London, pp. 387 - 404.
- Santos RA, Haimovici M (1998) Cephalopods in the diet of marine mammals stranded or incidentally caught along Southeast and Southern Brazil (21° to 34° S). Copenhagen Denmark Ices 15 pp
- Zerbini AN, De Oliveira Santos MC (1997) First record of the pygmy killer whale Feresa attenuata (Gray, 1874) for the Brazilian coast. Aquat Mamm 23 (2):105-109