THE most comprehensive review for 13 years of the ecology of Loch Ness

-- and its monster -- is to be published shortly in the scientific

journal, The Scottish Naturalist.

The 13 research papers do not address the question of the monster

directly, but their findings on the life of the loch shed new light on

what can, and cannot, exist there.

Mr Adrian Shine, the naturalist who heads the Loch Ness Project at

Drumnadrochit, believes much of the evidence points to a sturgeon, but

hopes he is wrong.

''I suppose there could still be something unexplained there, and some

of the unexplained sightings have been by local people of manifest

sincerity unconnected with the tourist trade.''

Naturalists calculate the total fish population of the loch weighs

about 30 tonnes in total.

By a rule-of-thumb, any resident predators feeding on those fish would

weigh no more than a tenth of that, or three tonnes in total. A viable

population would require maybe 10 predators -- making 300kg the likely

maximum size for each.

Forget the left-over dinosaur theory. Mr Shine says the last

plesiosaur was fossilised 65 million years ago, and 10,000 years ago

Loch Ness would have been a giant ice cube.

The loch could never support dinosaurs anyway -- dinosaurs were

reptiles, and Loch Ness is too cold.

Nor could the monster be an amphibian. Studies have shown that none of

the fish in the loch -- like Arctic char, salmon, trout, and eels -- are

exclusively fresh-water.

Nessie is not likely to be a mammal either, although mammals could

account for some of the sightings.

Whales or porpoises would surface enough to be correctly identified

and seals which venture into the loch have been identified.

But deer swim in the loch more than non-experts might think. As Mr

Shine says, few who spot a baffling object moving on the water will

think: ''Aha, Loch Ness, that must be a deer swimming in the water.''

The first locally recorded sighting of a monster appears in the

Inverness Courier newspaper in 1868.

This spoke of a huge fish, and local legend -- long before the modern

image of a long-necked humped creature -- had always spoken of a

fish-like animal.

Mr Shine says the Baltic sturgeon fits all the loch's newly discovered

scientific parameters.

It is a big, sea-going fish which enters freshwater to breed and

spawn, with a reptile-like appearance, and dorsal fin set way back

towards its tail.

Its long snout could conceivably give the appearance of the

characteristic Nessie neck.

It lives in cold northern waters like the Baltic and the North Sea,

but rarely ventures into British fresh rivers.

It can be three metres long or more, weigh 200kg, and it spawns in

early summer. A lost sturgeon could blunder up the seven-mile river Ness

in search of a mate.