No specific information is available on habitat use in European waters as the species is vagrant.

Globally, the Pygmy Killer Whale occurs in deep, warm waters, generally beyond the continental shelf, and rarely close to shore (except near some oceanic islands where the water is deep and clear). This species is mainly tropical and occasionally strays into warm temperate regions (Williams et al. 2002).

A long-term study at Hawai’i Island suggested that there is a small resident population with long-term site fidelity to the island (McSweeney et al. 2009). Around Hawai’i group sizes ranged from 4 to 33 individuals, sightings were in depths ranging from 113 to 2,862 m, and they were located 2.8 to 16 km from shore (McSweeney et al. 2009). Long-term associations have been documented in Hawai’i both between adult females and males (Baird, 2016). No detailed information is available anywhere else globally.

Little is known of the feeding habits of the Pygmy Killer Whale, although cephalopods (squid and octopus) and small fish are part of their diet as shown by stomach content analysis of stranded and bycaught animals (Elorriaga-Verplancken et al. 2016, O’Dwyer et al. 2015). The stomach contents of two stranded individuals in Cabo Verde showed 95% of the prey items identified were from the Deepbody Boarfish Antigonia capros and the Lanternfish (Myctophidae) (O’Dwyer et al. 2015).

Given the absence of feeding observations in over 72 encounters with Pygmy Killer Whale, McSweeney et al. (2009) suggested that feeding likely takes place at great depth or at night on prey species that move closer to the surface associated with the deep-scattering layer, which includes Myctophidae. They have occasionally been recorded attacking dolphins associated with tuna in the eastern tropical Pacific (Perryman and Foster 1980), although feeding on other mammals seems to be more opportunistic than a regular source of diet (Baird 2018a).

Pygmy Killer Whales are distributed in tropical and subtropical oceanic waters worldwide, generally between 40°N and 35°S. They generally do not move close to shore, except in some areas where deep, clear water is near the coast, such as around oceanic archipelagos like Hawai’i (Baird 2018) where there is a regular presence (McSweeney et al. 2009) or Madeira Islands in the subtropical Atlantic Ocean (Freitas et al. 2012). Little information is available about the presence of this species worldwide (Jeyabaskaran et al. 2011).

The species has not been regularly reported in European waters. The four northernmost sightings occurred in the Bay of Biscay in April-May 1997-1999 (Williams et al. 2002). However, there is no known record in the French Atlantic, the Iberian Peninsula or the Azores archipelago (Prieto and Silva 2010, Silva et al. 2014). No confirmed record exists in the Mediterranean and Black Seas, and a previous doubtful stranding record from Algeria was found to be a misidentified Risso’s Dolphin calf (ACCOBAMS 2021).

The Pygmy Killer Whale was recorded for the first time in the Madeira Archipelago in May 2009, as a group of 12 animals with two calves (Freitas et al. 2012). They have been sighted sporadically since then and confirmed occurrences through photo-documentation from whale-watching companies and Madeira Whale Museum surveys remain rare in the area, including about 10 observations, including one with calves (Madeira Whale Museum, unpublished data). In the Canary Islands, two sightings of Pygmy Killer Whales were recorded in the Eastern islands in 2009, one in September off Lanzarote and the other in October off Fuerteventura (Martín et al. 2011). No stranding of the species has ever been reported in any of the seven islands, although the Canary stranding network has recorded 938 strandings of 25 species since 2000 (Gobierno de Canarias 2018).

The Pygmy Killer Whale seems to be overall rare in European subtropical waters, although the low research effort in offshore waters may not be sufficient to detect a more regular presence of the species. The few high-latitude sightings are thought to represent extra-limital records associated with incursions of warm water. However, these could increase in the future due to climate change. The species seems to be naturally rare over its global range as well (Braulik 2018).

Even in tropical waters of the eastern Atlantic, their presence is very limited close to shore and unknown for offshore waters. Off Cabo Verde islands, Pygmy Killer Whales were recorded only four times. The first time was a mass live stranding involving seven animals (six adults and one juvenile) in February 2012, on the northern coast of Boa Vista Island (López-Suárez et al. 2012). Out of the seven individuals, two lactating females ended up dead. The first confirmed sighting occurred in June 2018 but was only published later; four individuals were observed in shallow waters (~50 m) off São Nicolau Island (Legrand and Monticelli 2020). Another sighting occurred in September 2019, when a group of approximately 30 animals, including two calves, was photographed in shallow waters (~150 m) off São Filipe, Fogo Island (Berrow et al. 2020). The two most recent confirmed sightings occurred in September 2022, with ~9 individuals observed on the 9^th and ~15 individuals on the 11^th south of São Nicolau Island, both including young calves (L. Freitas pers. comm. 2022).

Pygmy Killer Whales are expected to be found in most regions of western Africa, with the possible exception of northern Morocco. A stranding was recorded in Mauritania in January 1995 (Robineau and Vely 1998) and two individuals were captured, one in Senegal (Cadenat 1958, Fraser 1960) and another off Ghana (Van Waerebeek et al. 2009). Several years of extensive cetacean surveys in potentially suitable deep-water habitats between the Gulf of Guinea, Gabon and Angola did not conclusively record Pygmy Killer Whales, indicating that the species might be genuinely scarce in the eastern tropical Atlantic (de Boer 2010, Weir 2011). The only verified sighting in the African eastern tropical Atlantic occurred ~47 km off Côte d’Ivoire in November 2011, with ~10 individuals (Weir et al. 2013).

The species is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES). Pygmy Killer Whales are protected from deliberate disturbance, capture or killing under the EU Habitat Directive as all other cetacean species within EU27 waters. Although not listed on either appendix of the Convention on Migratory Species, Pygmy Killer Whales are protected by some instruments of this convention, such as the Agreements of ASCOBANS (Baltic, North East Atlantic, Irish and North Seas) and ACCOBAMS (Mediterranean and Black Sea and the adjacent Atlantic area), and the Memorandum of Understanding of Western African Aquatic Mammals (Western Africa and Macaronesia, www.cms.int/aquatic-mammals).

Research is needed to determine the distribution and the impact of potential threats on this species in offshore waters of European Mammal Assessment region.