Antarctic minke whale

The Antarctic minke whale (Balaenoptera bonaerensis) is a small rorqual of the Southern Hemisphere, described by Burmeister in 1867 and accepted as a valid species in the world register of cetaceans ^[1]. It lives tied to the sea ice of the Southern Ocean and is the only baleen whale that consistently inhabits ice-covered waters ^[2].

In 1998 two species of minke whale were recognised, this one and the common minke, and its abundance was estimated at 515000 individuals from surveys run from 1992 to 2004 ^[3]. The International Union for Conservation of Nature rates it globally as near threatened ^[4]. Peru's marine wildlife watching manual lists it among the larger cetaceans (cetáceos mayores) under the name ballena minke antártica ^[5].

It is a rorqual of modest size: on the western side of the Antarctic Peninsula, 68 individuals measured by photogrammetry from drones had a mean length of 8.04 m ^[6]. That figure comes from one particular population and does not summarise the whole species ^[6].

At sea it is hard to separate from the dwarf form of the common minke whale, with which it shares part of the Southern Hemisphere, and knowledge of its distribution at low and mid latitudes is very limited owing to little research effort and low detectability at sea ^[3]. The most practical clue is geographic: the Antarctic minke is relatively more frequent south of 65° S ^[3].

Similar species

• Balaenoptera acutorostrata: At sea it can be mistaken for the dwarf form of this species; the Antarctic minke is relatively more frequent south of 65° S ^[3].

It has a circumpolar distribution and probably breeds between 7° and 35° S ^[6]. It is thought to breed in subtropical waters of the South Atlantic, South Pacific and Indian Oceans during the austral winter and to migrate south in summer to feed on krill, although direct evidence for that link is scarce ^[3].

Within the ice, the highest densities are predicted at the ice edge and at medium concentrations, and medium densities were recorded up to 500 km into the ice ^[2]. By contrast, very few animals were counted in ice-free waters west of the Antarctic Peninsula, which supports its dependence on sea ice ^[2]. Populations of the Indo-Pacific sector seem to separate into at least 2 stocks ^[3].

On the western side of the Antarctic Peninsula, DNA profiling of 82 biopsies taken between 2013 and 2020 identified 29 distinct males and 40 distinct females ^[6]. Blubber progesterone levels indicated that 59 % of the sampled females were pregnant, and after adjusting for sexual maturity the median pregnancy rate came to 92.3 %, so most mature females are pregnant in a given year ^[6].

Its repertoire of sounds includes the already known downsweep and, from tags carrying video and a hydrophone, 3 further new calls; all 4 have peak frequencies of 90 to 175 Hz and last 0.2 to 0.8 s ^[7]. Each call type was associated with behavioural and environmental variables measured by the tags ^[7].

It feeds on krill under the ice, a niche that it has been proposed not to share with other krill-feeding whales of the Southern Ocean ^[2]. The ice may also help it avoid type A killer whales, which do not enter it ^[2].

It is among the most abundant yet most poorly understood cetacean species, because of the difficulty of working in its sea-ice habitat ^[7]. The video and sound tags of that study were deployed in 2 bays beside the Gerlache Strait, in February and March of 2018 and 2019 ^[7]. Among 333 examined animals, 7 species of epibionts were found, and 125 of the whales carried at least one; the authors propose that detecting coronulid barnacles could evince seasonal migration, since their occurrence drops markedly where the minimum sea surface temperature is below 12 °C ^[3].

The current global assessment on the IUCN Red List classes it as near threatened ^[4]. An analysis of circumpolar ship-based surveys suggests a possible 30 % drop in abundance, and the authors stress that conservation measures and further study of its status are needed ^[2].

Its dependence on ice makes it vulnerable to climate: a general decrease in sea-ice cover would narrow its available habitat, and the forecast ice changes could affect it heavily ^[2]. West of the Antarctic Peninsula, where ice is changing fast, the pregnancy rates measured there serve as a baseline against which to detect future change ^[6].

Part of what is known about the species comes from captured animals. The 333 animals used to study its epibionts came from whales taken on the most recent NEWREP-A Antarctic cruise ^[3]. In a 2022 study, the length at which females mature was taken from commercial catch data ^[6].

In Peru it appears among the larger cetaceans (cetáceos mayores) covered by the good-practice manual for marine wildlife watching, which also sets minimum approach distances for cetaceans: 100 m for those longer than 5 m and 300 m when they are feeding or socialising ^[5].

The literature consulted documents no specific sightings of the species in Peru: the official marine wildlife watching manual (2026 edition) only names it in its list of larger cetaceans (cetáceos mayores), without giving sites ^[5]. It is thought to breed in subtropical waters in winter, but direct evidence for those migrations is limited, so it should not be counted on in any outing ^[3].