Basking shark

Latin: Cetorhinus maximus 
Manx: Gobbag Vooar 
IUCN Red List Status (March 2022): Endangered  

As of April 2022, MWDW have taken on the sole public sightings scheme for basking sharks in Manx waters. Manx Basking Shark Watch (2004-2022) has ceased operating, and all tagging/DNA sampling has stopped in Manx waters. Unused tags have been given to Irish scientists.  

Every summer, from mid-May to mid-August, mighty basking sharks descend upon the Isle of Man. 
Most basking shark sightings are reported within 1km of land along a 40km stretch of easily accessible coastline on the west and southwest of the Island. 

When the seas are calm and the weather is settled and sunny, the plankton concentrates at the surface of the sea and the basking sharks feed on this plankton close inshore. You may even be lucky enough to see basking shark courtship activity from the coast with the naked eye or binoculars.   

Over the past decade, basking shark sightings have been in steep decline. It is vital that the monitoring of shark sightings in Manx waters continues each year in order to further understand this decline. If you have seen a shark please report it via the ‘report a basking shark’ sightings form.

Physical description: 

Basking sharks can reach 11m (36m) but typically average 6m (19ft), making them the second largest of all sharks. Their huge triangular dorsal fin can be easily spotted at the surface, sometimes along with tip of the tail fin and bulbous nose. Colour is dark grey/brownish. Huge mouth is usually agape as they spend the majority of their time feeding when near the surface. 

Behaviour:  

Basking sharks are huge, slow moving fish, maintaining a steady course as they allow tidal currents to filter water and plankton through their gills. The huge triangular dorsal fin is seen moving slowly, steadily, and often in a straight line, sometimes with tail and nose at the surface at an equal distance either side of the dorsal fin. They do not possess any bones making them extremely bendy creatures. Sometimes you will see triangular shaped dorsal fin glinting at the surface as the animal bends its body in line with the current, and the sun catches off it. If a shark decides to dive, it does so by slowly sinking lower in the water. 

Other behaviours 

When basking sharks come together to court, as they do in Manx waters, they can be seen displaying some really interesting behaviour. Incredibly for such a massive but typically slow animal, basking sharks are able propel themselves out of the waters and full body breach. This is assumed to be a male courtship signal, displaying to the females that they are fit and strong. It may also be effective in removing lice and other parasites that reside on shark skin.  

Parallel swimming (side by side swimming) 

Echelon swimming (formation swimming in sets of twos or threes one in front of the other) 

Nose to tail following (literally, one shark touching its nose to the tail of the animal infront, using its slip stream to feed more efficiently)  

Close following (similar to above, but with a gap between sharks) 

Close flank approach (slowly approaching another shark the side, often touching flanks) 

Abundance in Manx waters: 

Pre-2010, basking sharks were in such abundance in Manx waters that fishermen from the time used the descriptive example of being able to ‘step across sharks to walk back to land’. Literally hundreds aggregated along our west coast each summer, putting the Isle of Man on the map as a basking shark hotspot. 

Sadly, over the course of the last decade, there has been a huge decline in basking shark numbers. To put it into perspective, back in 2009 there were around 500 sightings submitted, and by 2019 that had fallen to 50. Since then, year on year, numbers have dropped again, with only 8 sharks reported in 2020, and 8 in 2021. There are many theories as to why this is the case but there is still no conclusive evidence. More research needs to be done into plankton levels and underwater electronic signals. 

Previous tagging work conducted by Manx Basking Shark Watch between 2007 and 2017 show where our sharks have travelled to and from. Interestingly, they appear to have no fixed destination, with some simply hopping across the water to the Hebrides or Cornwall, whilst one individual crossed the Atlantic to Newfoundland, and another went down to Morocco.  

Abundance worldwide: 

Basking sharks are found in temperate and tropical waters. In temperate climates they are seen feeding near to the surface, giving them their name as they appear to bask at the surface. In tropical waters they are found at greater depths, below the thermocline (Ebert et al. 2013, Dewar et al. 2018). The species vertically migrates to depths of 1,26m (Gore et al. 2008) and are known for their long migrations.  

Photo: Anders Salesjo

The ‘3 points’ of a basking shark; Bulbous nose, dorsal fin and tail fin, are sometimes seen if the shark feeds very close to the surface. Photo: Anna Bunney

Basking sharks can be seen in close proximity to the shore like this one at Niarbyl, on our west coast. Photo: Anna Bunney

At least 3 sharks engaging in courtship behaviour. Photo: Anna Bunney

The dorsal fin often possess nicks and spots, making each fin unique and identifiable to researchers 

Contrary to popular belief, a basking shark CAN close its mouth. Photo: Anders Salesjo