In the north-east Atlantic, Blue Whales are primarily distributed in deeper waters seaward of the continental shelf (Sigurjónsson 1995, Pike et al. 2019). There is evidence that their occurrence is highest in very deep offshore waters. For example, acoustic monitoring along the Atlantic Frontier between Spain and the Faroe Islands recorded higher numbers of detections at the sites located furthest west into deeper water in the Atlantic basin (Charif and Clark 2009). Large-scale sighting surveys also suggest that Blue Whale occurrence is higher in more central parts of the European assessment area than it is along the European shelf edge (e.g., Waring et al. 2008, Hammond et al. 2011, Rogan et al. 2018, Pike et al. 2019). However, Blue Whales do also utilise coastal shelf feeding areas in Iceland (Akamatsu et al. 2014), and approach the coast of volcanic islands while on migration (e.g. in the Azores: Silva et al. 2014). In the northernmost parts of their range, they may be found in coastal habitats and among loose pack ice (Storrie et al. 2018).

Blue Whales are generally a migratory species, although animals may be found throughout their range at most times of year. While the summer feeding areas at the northern end of their north-east Atlantic migration route are reasonably well documented, their wintering areas in the (sub)tropics are poorly known. Recent sightings off Mauritania in winter support one wintering area off north-west Africa (Baines and Reichelt 2014). Photo-identification matches between the Azores and Svalbard, and between Mauritania and Iceland (Sears et al. 2015), shows linkage between low, mid and high latitude areas in the eastern North Atlantic. Animals likely travel along, or west of, the Atlantic margins of the Iberian Peninsula, Ireland and the UK. Tracking of vocalising Blue Whales using acoustic arrays in that region, evidenced a northward movement from April to June, and a southward movement in autumn and winter (Charif and Clark 2009). Peak Blue Whale numbers in the Azores occur in spring and summer, particularly February to June, concurrent with a northward movement from a wintering area located further to the south (Visser et al. 2011, Silva et al. 2014).

Although a migratory species, the Blue Whale appears to forage year-round, including at low and mid latitudes as well as at the better documented high latitude feeding grounds. For example, Mauritania and the Azores are both used as foraging areas by eastern North Atlantic Blue Whales (Visser et al. 2011, Silva et al. 2013, Baines and Reichelt 2014), and isotope analysis of whales sampled in the Azores during spring indicated that they had fed during winter or early spring in (sub)tropical waters further south (Silva et al. 2019). Feeding has also been observed along presumed migration routes, for example in deep water west of Ireland (Wall et al. 2009, Baines et al. 2017). The species is a lunge-feeder, targeting shoals of small crustaceans both at the surface and subsurface to depths exceeding 300 m (Calambokidis et al. 2008, Goldbogen et al. 2011). Most foraging dives are <10 min in duration and reach average depths of around 200 m (Goldbogen et al. 2011). In the North Atlantic, it feeds almost exclusively on euphausiid krill, comprising Meganyctiphanes norvegica and Thysanoessa spp. (Visser et al. 2011, Silva et al. 2013).

Little is known of Blue Whale social structure in European waters. They are usually sighted alone or in small groups of up to 3 animals in the region (Silva et al. 2014, Baines et al. 2017, Vacquié-Garcia et al. 2017, Storrie et al. 2018, Pike et al. 2019), although larger aggregations can form in productive foraging areas. Hybrids have been documented in Spain and Iceland, arising from mating between Fin Whales (Balaenoptera physalus) and Blue Whales, where in the majority of cases the Blue Whale was the female (Pampoulie et al. 2020, Aguilar and Borrell 2022).

No defined calving grounds have yet been identified for the species in the eastern North Atlantic, but mother-calf pairs have been seen in the Azores and off the west coast of Ireland (Sears et al. 2015).

Globally, Blue Whales are cosmopolitan and are distributed from the tropics to the pack ice in both hemispheres, although they are relatively scarce in equatorial waters. They migrate seasonally between summer feeding areas located at mid and high latitudes, and wintering grounds located at lower latitudes. Within the North Atlantic, their core distribution extends from the Virginia coast of the USA (Lesage et al. 2017, Engelhaupt et al. 2020), the Azores (Silva et al. 2013, 2014), and Mauritania (Sears et al. 2005, Baines and Reichelt 2014) northwards to Greenland (Heide-Jørgensen et al. 2007) and Svalbard (Storrie et al. 2018).

In Europe, knowledge of Blue Whale distribution originates primarily from whaling catches, along with contemporary sightings. Whaling data support a historical distribution across northern parts of the European assessment area, including the waters around Svalbard, Jan Mayen, Norway, the Murman coast of the Russian Federation, Iceland, the Faroe Islands, Scotland (UK), and Ireland (Jonsgård 1977, Sigurjónsson and Gunnlaugsson 1990, Allison 2020, Evans 2020). Catches were highest in the northern part of this area, around Norway, Svalbard and Iceland. Comparatively small numbers were landed at Faroese, Scottish and Irish shore stations, mostly in summer (Evans 1980, Cooke 2018). A small number of animals were also caught off the Iberian Peninsula coasts of Spain and Portugal and in a whaling ground located off the Strait of Gibraltar (Aguilar and Borrell 2022).

In the northernmost part of the European assessment area, Blue Whales are regularly sighted in steep coastal habitats located to the north and west of Svalbard to over 80ºN (Vacquié-Garcia et al. 2017, Storrie et al. 2018). Acoustic work in the Fram Strait (79 ºN) has evidenced high presence of Blue Whales in summer and autumn (Moore et al. 2012, Ahonen et al. 2021), and its distribution extends westwards to the east coast of Greenland (Heide-Jørgensen et al. 2007). It is rarely observed in the shallow Barents Sea and eastern Norwegian Sea (Christiansen et al. 1992, Leonard and Øien 2020, Mishin 2021). Some sightings have been recorded from around Jan Mayen (Christiansen et al. 1992). The waters around Iceland appear to be a particular stronghold for Blue Whales in the European assessment area. The species is regularly observed in deep waters to the north and west of Iceland, including the Denmark Strait (Sigurjónsson 1995, Pike et al. 2019, Leonard and Øien 2020). It also feeds close to shore in Iceland during summer, particularly along the north coast (Akamatsu et al. 2014).

Blue Whales are rare around the Faroe Islands and in the deep-water Faroe-Shetland Channel that extends between the Faroes and Scotland; they have not been recorded during several extensive surveys of that region (e.g., Weir et al. 2001, Skov et al. 2002, Hammond et al. 2011). That area also had the lowest number of Blue Whale acoustic detections during 10 years of year-round monitoring carried out along the entire Atlantic Frontier from the Faroes to north-west Spain (Charif and Clark 2009). In contrast, acoustic detections increased to the south of the Wyville-Thomson Ridge and through the Rockall Trough, peaking west of the Porcupine Bank to the west of Ireland (Charif and Clark 2009). While not confirmed during systematic visual surveys west of Ireland (Rogan et al. 2018), Blue Whales were sighted multiple times during a geophysical survey of the Porcupine Seabight in summer and autumn (Baines et al. 2017). The species appears to be distributed solely over deep waters in the Atlantic Frontier region, and only very rare strandings have been recorded in semi-enclosed shelf areas such as the North Sea coasts of Belgium, Denmark and Scotland (Harmer 1927, de Smet 1974, Kinze 2007). The Irish Sea, North Sea, Baltic Sea and English Channel are not therefore considered to be part of the usual distribution range.

Blue Whales were likely never abundant in warm temperate regions of the eastern North Atlantic (Aguilar and Borrell 2022). There have been a small number of sightings in deep waters in the Bay of Biscay, including in the English, French and Spanish EEZs (Weir 2001, National Oceanography Centre 2015, Laran et al. 2017). A few sightings have also been recorded during recent surveys off the Atlantic coast of Galicia in north-west Spain (Díaz López and Methion 2019), and off Portugal (Bencatel et al. 2019). Low numbers of acoustic detections occur to the north-west of Spain, particularly during the autumn (Charif and Clark 2009). The species has not been documented in the Mediterranean Sea (ACCOBAMS 2021). While some Blue Whales were landed at shore stations situated in the Strait of Gibraltar (Aguilar and Borrell 2022), those whaling grounds were located in Atlantic waters west of the Strait and the species has not been documented off Gibraltar itself.

The Blue Whale is rarely reported in the Macaronesian region of the southernmost part of the European assessment area, despite significant coverage around the archipelagos from whale-watching boats. The exception is around the Azores, where it is frequently encountered throughout the deeper waters of the archipelago during spring and summer (Silva et al. 2014) and detected acoustically in autumn, winter and spring (Romagosa et al. 2020). Only scarce sightings have been documented in the Madeira (Freitas et al. 2012, Alves et al. 2018) and Canary (Ritter and Brederlau 1998) archipelagos, and the species does not appear to be common in those areas. The wintering grounds are poorly known, but some winter occurrence has been documented off Mauritania in north-west Africa (20ºN: Baines and Reichelt 2014).

Sightings of the species have also been recorded during occasional surveys in the far west of the European assessment area, over the mid-Atlantic Ridge (Waring et al. 2008). Acoustic monitoring in southern parts of the mid-Atlantic ridge also detected Blue Whales west of Madeira and the Canary Islands (Nieukirk et al. 2004).

The species has been protected by the general moratorium on commercial whaling since 1986, although this does not cover catches taken under scientific permit.

It is listed on Appendix I (endangered migratory species) of the Convention on the Conservation of Migratory Species of Wild Animals (Bonn Convention, 1979), and on Appendix II (strictly protected species) of the Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention). It is included on Annex IV Council Directive 92/43/EEC on the Conservation of Natural Habitats and of Wild Fauna and Flora (the Habitats Directive) as a species requiring strict protection across its entire natural range within the EU. It is listed in Appendix I (species threatened with extinction) of the Convention on International Trade in Endangered Species (CITES), which prohibits international trade.

Blue Whales are included in the Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and contiguous Atlantic area (ACCOBAMS), which was concluded under the auspices of the Bonn Convention. The agreement aims to maintain favourable conservation status of cetacean species within its defined area, managing threats and working towards the long-term sustainability of populations.