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A Basking Shark?

Was the Stronsay Monster the incorrectly identified remains of a decayed basking shark?

Sir Everard Home was the first proponent of this theory. He was a member of the Royal Society in London and the expert on basking sharks at the time. He said that the witnesses were ignorant fishermen and, although he had not seen the remains, he said that it had not measured 55 feet (16.8 metres) at all. He thought 35 feet was much more realistic.

pic 1 (sir everard home (1756-1832), after a painting by w. beechey, 1810

PIC 1 (Sir Everard Home (1756-1832), after a painting by W. Beechey, 1810

The picture below gives an impression of the size that basking sharks reach. The largest basking shark measured 11.5 metres. The Stronsay Monster was measured to be 16.8 m. A mathematician called Holden calculated that the maximum size that they would probably reach is 12-15 m.

The distribution of the basking shark is shown in red. The basking shark is found around the Orkney coast, and fishermen of the time would have been quite familiar with its appearance while the creature was alive. The decayed basking shark looks quite different.


The basking shark decays in an odd way. The huge gill apparatus is very poorly supported and this rots off, leaving the appearance of a small head with a long neck and flippers (very Nessie-like!). People have been fooled by this before. The identification of the Stronsay Monster as a decayed basking shark, therefore, depends upon the carcass being decayed enough to make the fishermen unable to recognize it as a basking shark (which they would have been familiar with).

how a basking shark decays

image of decayed basking shark 

The pictures above are of a decayed basking shark. The gills have rotted away. You can clearly see how the spine looks like a long, thin neck and the pectoral fins look like large flippers. The decayed muscle fibre looks like a hairy mane. The spine of the shark only extends into the top lobe of the tail so when the lower lobe rots away this gives the appearance of a long, thin tail. 

A Japanese fishing boat trawled up the specimen below. See the clear appearance of a small head on the end of a long, thin neck with flippers. It was thought to be a sea monster. Subsequent studies of the amino acid composition of the creature showed that it was a decayed shark.


Back to the Stronsay Monster ...

What about the other comments the eyewitnesses made? Could these be explained by the shark theory? Let's see.

Question 1 - Was the carcass in a state of decay?

The contents of the stomach emitted a 'fetid smell', according to William Folsetter. However, the stomach contents quickly putrify after death due to the action of gut bacteria etc. It would be possible for the stomach contents to be rotting while the rest of the carcass was in good shape.

Below: Internal anatomy of a shark

Notes on the Stronsay Monster skin

Thomas Fotheringhame said he stroked the skin. This indicated it had not rotted off. He said that if brushed from the head to the tail it was smooth, but rough if brushed from the tail to the head. Shark skin is covered in scale-like objects called dentricles. They would certainly be rough if stroked in the wrong direction. Would they be smooth if brushed in the correct way?

Denticles of a Porbeagle shark magnified

Above are two close-ups of the skin of a shark. The tanned skin is rough and referred to as shagreen. The 'scales' are called dentricles and are actually more like teeth. Top is a diagram of dentricles. Basking shark skin also has a smelly mucous and some fishermen claim to be able to smell them coming. Had this all washed off? If not, the fishermen would have recognized this characteristic shark odour if it was a basking shark?

Question 2 - What were the bristles and why did they glow in the dark when wet?

Below is a picture of the Japanese catch - a decayed shark. The Stronsay Monster had bristles around the fins and down the back. The only creatures with hair are mammals, and sharks are not mammals. It is possible that the decayed muscle fibres of a shark could be mistaken for hair - see the fibres fringing the fin in the picture again.

Some bacteria glow - perhaps bacteria on the carcass glowed while wet. Many sea creatures glow - plankton clinging to the carcass may have glowed while wet.

Question 3 - How do you account for the 3 pairs of 'legs' or 'wings'?

The only creatures with 3 pairs of legs are insects. I think we can assume the Stronsay Monster was not a huge insect. The way that proponents of the decayed basking shark theory account for the three pairs of appendages is as follows:

1st pair nearest the head = the pectoral fins

2nd pair = the pelvic fins

3rd pair = a male shark's claspers. Sharks have organs called claspers which they use during reproduction. You can see them in the photograph on the left. Look at the shark morphology diagrams below. The claspers are right behind the pelvic fins. This is not how the appendages on the drawing of the Stronsay Monster by Mr Petrie are arranged, and the witness were happy with the likeness.


Claspers have been mistaken for legs before - see picture below of a 'huge fish' washed ashore, and see how the artist has turned the claspers into legs with clawed feet.



Basking Shark claspers

 diagram of basking shark claspers

So, in summary:

Points which favour the decayed basking shark as a candidate for the Stronsay Monster

  • It is the right colour - grey
  • It is found around the coast of Orkney
  • It has not got bones but cartilage
  • It is big
  • It looks like a sea monster when decayed
  • It could have 'bristles' when decayed
  • It could have 3 pairs of appendages

Points which go against the theory

  • The basking shark does not grow large enough
  • The spacing of the appendages wouldn't fit with the artist's drawing and the witnesses did not criticise that point
  • The witnesses did not say the carcass was very decayed and described being able to examine the throat. (The only bones they mentioned were the one visible where part of the tail was missing and part of the jaw.)
  • The witnesses did not mention any odour of basking shark (just a minor point)
  • The witnesses would probably have been familiar with basking sharks and did not identify the carcass as being one (this argument depends upon how decayed the carcass was)
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