Basking sharks can be found worldwide in temperate waters, typically between 6-16 degrees C (42-60 degrees F). In the northern Atlantic, they are most frequently sighted during the months of April – September, often in shallow coastal habitats. Aggregations (groups) of individuals can be observed during this time in highly frequented locations known as basking shark "hotspots", which include Inishowen waters (Martin & Clark, 2008, CSAS 2008). In the Pacific, basking sharks are mainly reported during the winter months, between October – May. Historically, frequent sightings occurred on the coast of California, especially near the Santa Barbara Channel Islands, although sightings have declined in recent decades without a clear reason (McInturf et al. 2022). Though rare, basking sharks are also still spotted off the coast of California (a significant range) and have been tagged in the Pacific (Dewar et al., 2018; Squire, 1990). Sharks tagged off the coast of California travelled to Mexico and Hawaii, and some appeared to follow the diel vertical migration of deep sea zooplankton (Dewar et al., 2018).

 

Similarly, until the late 1960’s basking sharks were also commonly sighted and encountered in the northern end of their eastern Pacific range, especially in British Columbia. Observations of this species on the California and Canadian coast have dramatically reduced in number since that time (CSAS, 2008; McInturf et al. 2022). this following historic hunting pressures and local Government eradication programs in the 1950s and 60s, which are suggested to have removed 90% of the regional basking shark population.

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MIGRATION​

Research in the UK estimates that basking sharks spend up 36% of their time on the surface during their seasonal hotpot residence (Sims et al, 2003), though areas of high shark activity may not always be characterised by visible feeding behaviour (Southall et al, 2005). Significantly less is known about basking shark overwintering behaviour because these organisms tend to move away from coastal areas following the summer season in the northeastern Atlantic (Sims et al., 2003; Gore et al, 2008). Early hypotheses suggested that basking sharks hibernate offshore (Parker and Boseman, 1954), however, tagging studies suggest sharks undergo extensive migrations from September to May (Gore et al., 2008; Skomal et al., 2009; Doherty et al., 2017). The current accepted migratory theory for sharks in the North East Atlantic is that they move from west to east, moving from deep-water to coastal Europe waters in April, then gradually moving northward following the increases in sea surface temperature and copepod density until late August. This is when the sharks are believed to return to deeper waters in the west. 

 

Basking sharks are capable of traversing entire ocean basins with tagging data revealing large-scale movements of over 17,000 km (longest continual tracking to date, from Cape Cod to southern Brazil, with winter residency in New England; Braun et al. 2018) , however, their migratory strategies vary widely. For example, sharks tagged off the coast of Scotland have been observed to travel anywhere from the Bay of Biscay in Europe to the northern coast of Africa (Doherty et al., 2017). Others in this region have also been known to travel across the Atlantic Ocean (Gore et al., 2008) and have also been found in the Mediterranean (Ali et al., 2012; Fossi et al., 2014). 

 

There is little data regarding basking shark movements in the Southern Hemisphere, with the majority of research on this species having been conducted in the North East Atlantic (Lucifora et al., 2015). Basking sharks are seasonally found in Chile and Southern Africa and there is historical documentation of basking sharks in Brazil (Lucifora et al., 2015). 

​Potential drivers of movement  are thought to include thermoregulation, feeding at deeper ocean layers, or travel to mating grounds. While it is not entirely clear, the North Atlantic Oscillation (NAO) may share correlation with basking shark migrations. The NAO impacts sea surface temperature, which may in turn impact phyto- and zooplankton abundance (Cotton et al., 2005), and more recent research has found that basking sharks appear to have a preference for sea surface temperatures between 13 and 20 degrees Celsius (Crowe et al., 2018).

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HOTSPOTS, MIGRATION AND CONSERVATION​

Generally, basking sharks have been recorded to be somewhat habitual in their choice of feeding areas and timing of their return to coastal hotspot locations. Unfortunately, such localised population groups have historically been vulnerable and may continue to be highly susceptible to target fishing and bycatch (Sims & Reid, 2002). Previously targeted by fisheries in Norway, Ireland, the United Kingdom, the United States, Canada, Japan and New Zealand, the basking shark is currently listed on the IUCN Red List as globally endangered (IUCN, 2018). Furthermore, studies that have observed trans-Atlantic migrations (Gore et al., 2008) have led to considerable debate on the possibility of a single genetic population in the North Atlantic. This would have significant implications for conservation bodies and the scale on which protective measures are implemented.

 

Satellite tagging does indicate that, when in Europe, basking sharks spend the majority of their time in the exclusive economic zones of several nations, along the continental shelf where waters are most productive (Southall et al., 2006). 

 

In 2020, Scotland declared four new MPAs, including the Inner Sea of Hebrides, which would encompass key basking shark habitat (Nature Scot, 2020). The importance of Hebrides to basking shark courtship was cited as one reason for the placement of the MPA (Marine Scotland, 2020).  Ireland is currently looking to expand their marine protected area networks (Marine Protected Area Advisory Group, 2020) and have listed basking sharks under the Wildlife Act, which protects basking sharks from harassment while feeding or participating in reproductive activities.