Information from Colin Speedie (Cornish Wildlife Trust)
 

In May 1998 literally hundreds of Basking Sharks were seen off the Lizard Peninsula, southern Cornwall.

The whole sea was covered with sharks from close inshore to the horizon.

The sharks first arrived about 12 May 1998, and a they were still around at the beginning of June.  In Kennack Bay on the southern coast of the Lizard the numbers at their peak were estimated to exceed 200 and some reliable reports put the number closer to 500. There were so many sharks that it was impossible to count them and hard to estimate their abundance.

The Basking Shark, Cetorhinus maximus, is the largest fish found in the seas around the British Isles and is regularly seen off the south-western coasts but usually in ones or twos and only very rarely in such large congregations.

In UK waters it is believed that the preferred prey of Basking Sharks is the reddish copepod Calanus finmarchicus, which is around 5 mm long. This is reported from examination of stomach contents. A recent study in the Plymouth area discovered that the dominant (and thus preferred) species was Calanus helgolandicus. In other parts of the world, different calanoid species may fulfil the same role.

Fish eggs and various larvae may also be taken because of the indiscriminate way that the shark feeds.

From:  Colin Speedie <Colin.Speedie@btinternet.com>

Calonoid copepods and the most numerous of the copepods in the oceans of the world and this is certainly true in British seas where they form the bulk of the prey of the Herring. Calanus finmarchicus and Calanus helgolandicus are almost identical and can only be separated by examination of the basipodite in the fifth swimming leg under a microscope. (Ref: Marine Plankton: A Practical Guide, by GE & RC Newell, Hutchinson Educational 1963).
 

A large plankton bloom is likely to be responsible for this spectacular occurrence that attracted crowds of spectators. The best vantage point were the cliffs overlooking Kennack Bay. The plankton front is carried by  the wind, ocean currents and tides into the bay where it remained trapped by the land. The sharks are likely to remain on the surface until the weather breaks. This occurred in the first week of June.

Large Sharks

Basking Sharks are present every year off the south-west of Britain and are also well known visitors to the Isle of Man shores. I have seen a huge specimen in the entrance to Shoreham Harbour, Sussex, and in the last century there is a report of the largest recorded Basking Shark stranded on Brighton beach. It measured 11.12 metres long.

Large carnivorous sharks like the Shortfin Mako, Isurus oxyrinchus, and the Porbeagle Shark, Lamna nasus, visit British seas in the summer but these fish rarely exceed 3 metres in length. There are no records of shark attacks on bathers.

The Basking Shark has full protection under the Wildlife and Countryside Act 1981 in British territorial waters.

(There was a EC Quota for 100 tonnes of shark livers.)

Killer Whales

Such a huge congregation of Basking Sharks attracted the attention of one of the fiercest and most powerful predators of the oceans. Killer Whales, Orcinus orca, were seen with the whales. It is unlikely to have been a happy coexistence. Killer Whales are armed with a formidable array of teeth and they are known to attack Basking Sharks which must be a rather brutal sight with pods of Orcas tearing into the larger sharks. A large expanse of the sea would have been covered in blood.
 

Whales on the Attack  from the Cornish One-List Bulletin 345  (18 March 2000) for the Full Report.

by Richard Shimell

Strong evidence that killer whales visit Cornish waters to feast on basking sharks has been presented by the Cornwall Wildlife TrustŒs marine group.

Information gathered by volunteer members of Seaquest South West shows an almost identical seasonal pattern to the presence of the two species off our coasts.

Observers in Cornwall have long suspected that the killer whales, also known as Orcas, which are regularly seen in spring and summer in Cornish waters, were here to pursue basking sharks.

But the only evidence to back this up had been an account by a West Cornwall fisherman who saw a frenzied attack by a Killer Whale on a large shark off Porthcurno more than 50 years ago.

Vince Smith's One-List/Cornish Wildlife
Seaquest SW (Cornwall Wildlife Trust web pages)

Weight of the Basking Shark

My best guess for a shark around 9-10 metres long is 7 tonnes.

An estimate was worked out for a 29 ft (8.8 metres) basking shark at Gavin Maxwell's shark factory on the island of Soay as follows:

Head        1 ton
Liver        18 cwt
Fins         1 ton
Tail          0.5 ton
Skin        1 ton
Meat and backbone 1.5 ton
Guts       0.5 ton

This gives a total of nearly 6.5 tons, to which may be added 0.5 ton for stomach and intestine contents.

I have historical records of very large sharks by-caught off Cornwall weighed on local harbour cranes at over 6.5 tons
 

Colin Speedie

24 May 2010 onwards
Some of the first Basking Sharks, Cetorhinus maximus, of the year are spotted off Land's End, Cornwall. "I heard a brief splash as three of the twelve sharks breached the surface"

Other Basking Shark reports from off the coast of Cornwall came from Pendeen and Praa Sands and the odd one off the Lizard. Later reports on 18 May 2010 saw the sharks off Porthcurno and Sennen, Cornwall.

September 2007
I was also told about a sighting at St Abbs Head, SE Scotland. A party of the ranger staff were snorkelling at Pettico Wick and had close encounter with a smaller Basking Shark, Cetorhinus maximus, of about 3 to 4 metres in length.

5 September 2007
An astonishing 462+ Basking Sharks, Cetorhinus maximus, were seen in the morning between Longships and The Brisons, off the west of the Cornish mainland!  Accompanying the sharks were many Gannets, suggesting that fish and plankton would have been present. Also, in much the same place (10 km sq. SW 33) between 20 and 24 Risso’s Dolphins, Grampus griseus, and 35 Common Dolphins Delphinus delphis, were recorded.

21 April 2007
A Basking Shark, Cetorhinus maximus, was seen near the Lizard, Cornwall, swimming out to the Point.

19 April 2007
A small (3 – 4 metres long) Basking Shark, Cetorhinus maximus, was seen by Edward Murray off Picklecombe Fort at the western entrance to Plymouth Sound around 2:30 pm. It was circling, apparently feeding.

This is the first recorded Basking Shark with location details this year. An earlier 3 metres long Basking Shark was seen off Cornwall on 10 May 2007, but the details are not available.
BMLSS Basking Sharks

4 February 2007
A 7.5 metres (TL) long Basking Shark, Cetorhinus maximus, 2.3 tons gutted, was landed by a Dutch trawer in Denmark. The liver weighed 400 kg.

Largest One from the English Channel on record

I have a record of a Basking Shark which was 970 cm (29 ft 9 in) total length from the English Channel.
It was cited by Parker & Stott (1965) in Zoologische Medelingen 40: 305-319..

Philip Vas

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Basking Sharks in the Bristol Channel  1999
Basking Sharks off Wexford, Ireland

Pelagic Shark Research Foundation:  Basking Sharks