Could Loch Ness Monster be a sturgeon or catfish?
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It is 90 years since the first modern-day sighting of something large swimming in Loch Ness that sparked the global phenomenon of the "monster "that today shows no sign of waning.
But it is also an important anniversary for a man who for decades has featured prominently in the fascinating story, and became a figurehead in the search and research of the world famous waters and its denizens.
It is 50 years since Adrian Shine (73), then an amateur naturalist and would-be adventurer, was lured from England to Loch Morar in Lochaber, by a tale of a small boat being attacked by Morag the monster reputed to live in its waters.
At 1017 ft, it is the deepest body of fresh water in the British Isles and since 1887 there have been multiple "monster" sightings.
Mr Shine decided his route to fame and possible fortune was to find this beast and he spent hours rowing in the loch at night with his flashbulb camera at the ready offering himself as bait.
He even built an underwater hide in the very clear water, but Morag never showed up.
Undaunted, he switched his attention to Loch Ness and soon was involved in the setting up of the Loch Ness and Morar Project.
He is still part of the story, most recently taking part in the transformation of the Loch Ness Centre in the former Drumnadrochit Hotel.
He said: "I am stepping back a bit but still have a room in the new set up, which is more interesting and accessible.
"I think it is very apt that the old Drumnadrochit Hotel is the centre, as it is where Aldie Mackay worked back then when she made the sighting.
"We have had good times and done a lot of work on the loch over the years and we have Mrs Mackay to thank for it. There is a certain continuity that her hotel is still actively involved in the story."
Mr Shine, who spoke to Mrs Mackay about her sighting, said: "She was very reticent about her experience and it would appear it only came out after her husband met with the local water bailiff Alex Campbell in the Drumnadrochit Hotel to discuss the coming salmon fishing season and it was Mr Mackay who dropped his wife in it by telling Mr Campbell about the sighting.
"He was a stringer for the Inverness Courier and a story eventually appeared (on May 2) that was followed up by other papers.
"I remember talking with her in the 80s and one of the things she objected to was the use of the word 'monster' which she felt was nonsense."
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Mr Shine has published over a dozen scientific papers and articles on Loch Ness and has initiated collaborations with researchers and students from over 20 universities, developing innovative new sampling equipment and techniques and supplying samples.
"I was a grammar school boy with no degree but I have had many a mentor over my 50 years," he said.
He admitted to becoming more sceptical over the years about a "monster", but believed the vast majority of witnesses to something strange in the loch were sincere and did see something.
"Cynics might say they are lying, drunk or publicity bandits, but I don't believe that to be the case," he said.
Mr Shine has been involved in numerous efforts to prove or disprove the "monster" theory including Operation Deepscan in 1987 when sonar sweeps were made along the loch using an armada of 24 small boats in line abreast. Three sonar contacts were made near Urquhart Castle showing something big, but it could have been a seal or group of salmon.
And when Vladivar vodka came to Loch Ness to try and lure the creature from the water with their beverage, Mr Shine helped construct the giant cage of lobster pot for the stunt.
"It had to be capable of being flown, floatable and able to stand on land," he said.
The drinks company left with great publicity but no trace of a monster.
Mr Shine still hopes to find out what is behind the mystery, but says the beauty of the monster is that no one can disprove it, short of draining the loch.
He remains fascinated by the environment of the loch itself rather than the notion of a mysterious creature which has not been proved to exist.
Some theories that hold some credibility is that the "monster" is a sturgeon or catfish that can grow to an immense size, or seals that make their way up the River Ness from the sea in pursuit of salmon.
The sturgeon would have had to make a serious navigational blunder to reach Loch Ness in search of a mate, fail to find one and go away again, said Mr Shine.
In Victorian times and lakes were stocked with catfish and it is possible some escaped.
However in 2018 The Loch Ness Project assisted a team from Otago University, New Zealand led by Prof Neil Gemmell that analysed the DNA found throughout the massive loch.
Mr Shine said: "We helped gather the water samples for DNA analysis of what was living in the loch. No sturgeon or catfish DNA was detected, but lots of eels' DNA."
But he points out that the DNA survey does not necessarily discount a random and short visit by a sturgeon, and it certainly does not rule out a very large eel being the source of sightings.
And there is always the possibility that some of the sightings were caused by "displacement water wakes" from vessels sailing in the loch.