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Loch Ness

The Scottish Naturalist

Founded 1871

A Journal of Scottish Natural History

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J.A. Gibson
John Hamilton
John C. Smyth
A. Rodger Waterston
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The Scottish Naturalist, now published by the Scottish Natural History Library, is an independent journal primarily devoted to the study of Scottish natural history. It was founded in 1871 by Dr. F. Buchanan White, of Perthshire, and in 1988 completed one hundred years of publication. For a summary of the record of publication, see the inside back cover.

Although the journal's main interests have always centred on the history and distribution of Scottish fauna and flora, it is prepared to publish contributions on the many aspects of Scottish natural science embraced by its title, including Zoology, Botany, Geology, History, Geography, Archaeology, and the Environment.

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ounded 1871

A Journal of Scottish Natural History
With which is incorporated The Annals of Scottish Natural History
and The Western Naturalist

Record of Publication

The Scottish Naturalist and Journal of the Perthshire
Society of Natural Science 1871

The Scottish Naturalist 1872-1891

The Annals of Scottish Natural History 1892-1911

The Scottish Naturalist 191-1939, 1948-1957, 1961-1964

The Western Naturalist 1972-1982

The Scottish Naturalist 1983-date

Published by The Scottish Natural History Library





Loch Ness and Morar Project

International Society of Cryptozoology

Society for the History of Natural History

Symposium on

The Loch Ness Monster

Royal Museum of Scotland, Chambers Street, Edinburgh

25th July 1987

Reprinted from The Scottish Naturalist

1988, pages 111-199






Loch Ness and Morar Project


1. Morphometry.  
Basin Form 112
History and Sediments 115

2. Thermal Structure.
Stratification 118
Physical Studies 118
Factors affecting Sonar 119
The Record 121
Possible Errors 123
Shear 126
Conclusion 128


Phytoplankton 137
Zooplankton 137
Littoral and Sub-littoral Benthos 140
Profundal Fauna 144


Littoral Zone


Profundal Zone


Pelagic Zone


1. The Controversy  
Introduction 160

Biological Considerations
Habitats 161
The Candidates 162

Physical Factors and
Inanimate Explanations
Optical Effects 163
Submerged Logs 167
Gothic Revision 167
Floating Logs 170

2. The Sonar Contribution
Previous Records 171

Deep Water Contacts

Strength 177
Depth 178
Movement 181
Fish Shoals 182
Boat Wakes 182
Thermal Effects 182
Side Echoes 182
Tethered Debris 185

Operation Deepscan Supplement




Underwater Photography 192
Echo-sounders 193
Scanning Sonars 193
Temperature probes 194
Vessels 194
Additional Equipment 194

Summary 194
Acknowledgements 195
References 196




Basin Form

Loch, Ness is the greatest body of fresh water in the British Isles, having a volume (74.52m3 x 108) in excess of all the lakes and reservoirs of England and Wales combined (Smith and Lyle, 1979). It is a glaciated tectonic lake extending for 35km within the north eastern section of the Great Glen. The remarkably regular basin has a mean width of about 1.5km, with steep sides sloping to a flat bed, interrupted only by a rise opposite the Foyers River, which divides the two deep basins of 220m depth. The maximum depth of 230m is considerably deeper than the seas around our shores, and places Loch Ness second only to Loch Morar (310m) among British lakes. Fault line origins, however, give Loch Ness the greatest mean depth, of 132m. The catchment area is 1,775km2, mostly of hard rock yielding few nutrients.The loch is drained by the River Ness to the north. Figure 1a (8K) maps the main river inputs.

The above depths were determined by Sir John Murray's Bathymetrical Survey of the Scottish Fresh‑Water Lochs (Murray and Pullar, 1903-08, 1908a and 1910) using a wire sounding machine, but they were disputed by a sonar depth of 297m recorded by Vickers in 1969 (Eastaugh, 1970). During the 1980s, careful searches of the reported area, a quarter mile south of Urquhart Castle, were made by the Loch Ness and Morar Project using a Kelvin Hughes M.S.48 hydrographic echo‑sounder, calibrated on site in accordance with survey practice, but no depths much in excess of 220m were found.

Figure 1b (18K) shows a characteristic echo profile of the loch and contrasts its trench-like profile with that of Loch Morar. Time advances left to right on the record and it is important to note the compression of vertical scale induced by boat speed. The profile illustrated in Figure 2a (19K) results from a faster speed and also serves to illustrate 'side echoes', which in the past have been interpreted as extensions of the side walls continuing down beneath loose sediment for hundreds of metres. As the conical sonar beam profiles 'down' a steep slope it registers not vertical depth but the range of the nearest portion of slope, which is to the side and therefore shallower than true depth. As the loch bed begins to register and the boat draws clear of the wall, the beam's outer edges and side lobes still return echoes from the side, which now appear at a greater depth, thus giving rise to the above impression. A sonar frequency of about 10kHz or less is required for true sediment penetration. Underwater television pictures in Figure 2b (15K) of the steep rocky walls, contrast with the flat silt of the abyssal plain.

There is no foundation for speculations concerning ancient constructions, since there is no evidence that the loch level was ever much lower than it is today; nor of submerged caverns, subterranean connections and the like, since there is no limestone in the area.

Great advances have been made in hydrographic sonars. In September 1987 Simrad U.K. Ltd extended a collaboration while their demonstration vessel R/Y Simson Echo was in the loch. The vessel mounted a multibeam or 'swath' sounder (E.M. 100). Data is recorded continuously from 32 beams, which form a fan athwartships. This greatly reduces the number of survey lines necessary and hence the time required.

On 7th September 1987 a survey was made of Urquhart Bay. A graphic, constructed in Figure 3 (13K), serves to show the bay contours sloping away from the river mouths and then dropping steeply to the main basin floor. The peaks and spikes would be removed by software processing in a full survey and result from second time around returns, side echoes from steep slopes, and from an area of boat moorings. The plot contains over 200,000 data points.

History and Sediments

The three hundred million-year-old fault was glaciated by successive ice ages until approximately 12,000 years ago, when the lake we know today was formed. Meltwater raised the sea level until the land, relieved of the ice burden, rose to bring the loch to its present altitude of 16m. The Loch Ness and Morar Project has extracted sediment cores from Ness and Morar in an attempt to shed light upon the post‑glacial history.

Much of the material remains to be worked but so far, no evidence of a marine transgression has been found at Loch Ness. A core from Loch Morar (9m above sea level) was found by Dr. H.J.B. Birks (pers. comm.) to contain abundant cysts of marine algae, which suggests that the sea could have entered, although the spores could conceivably have been wind borne.

The deep basin floor of Loch Ness is covered by black lake sediment, of which a 4m core only just penetrated to clay, thus suggesting that the organic sediment is of at least that depth. This core has yet to be dated, but a 2m core from the basin floor of Loch Morar has been estimated by Dr. Birks (pers. comm.), on the basis of pollen content, to have penetrated between 5,500 and 6,500 years of post-glacial sediment. This sheds some light upon rates of deposition and, incidentally, upon the likely depth of sediment in Loch Ness. At the seaward end of Loch Ness the sediment consists of clays, an interesting feature of which is that a firm yellow‑brown layer approximately one metre thick overlies a blue‑grey material which is very fluid.

The organic content of the loch sediments has been established to increase with depth (Lee and Collet, 1908). From an analysis of our own profundal substrate samples (J.D. Hamilton, pers. comm.), the percentage composition of the organic matter ranges from 18.3% to 34%, similar to the Bathymetrical Survey results. Like this earlier study, it would also appear that the Urquhart Basin has less organic matter than the Invermoriston Basin, which may be due to the Foyers barrier retaining the organic material within the southern basin.

1988 The Scottish Naturalist p118



In a lake, the onset of stratification in summer consists of the separation of the upper less dense warm water, known as the epilimnion, from the deeper cold water, or hypolimnion, by a region of sharper temperature change, termed the thermocline. Photosynthesis is limited to the epilimnion, where depletion of nutrients cannot be replaced from the hypolimnion until mixing occurs in winter (Figure 4a, 7K).

In eutrophic (richer) lakes, the decay of organic matter descending to the hypolimnion deoxygenates it, to the detriment of deepwater life. In deep oligotrophic (poorer) lakes, such as Loch Ness, these profound effects do not follow, since nutrients are already low in the epilimnion and there is no deoxygenation of the vast hypolimnion, which remains over 80% oxygen saturated. The oligotrophic nature of Loch Ness therefore, offers the compensation of stability in exchange for low productivity. It is spared the seasonal booms and crashes of more productive waters, and a variety of life extends to its deepest regions.

The great body of water does not fall below a uniform 5C in winter, and consequently there is no inverse stratification and no freezing. Indeed the influence of the loch's stability extends to the area around the shoreline, where the release of heat ensures that snow seldom lies for long. On 10th January 1987, for example, the air temperature was 4.4C after a very cold spell of overnight temperatures down to -14C. The water temperature was 6.4C to a depth of at least 50m. Of course the loch is still relatively cold from a biological point of view and many of its inhabitants are relicts from glacial times.

Physical Studies

The biology of Loch Ness may have been neglected until recently, but physical studies have been particularly rewarding. The steepness of the 'walls', length, and regularity of the basin, together with the loch's orientation N.E-S.W. in line with the prevailing winds, all tend to simplify and amplify thermal effects. The absence of salinity complications has also facilitated observations in support of hypotheses afterwards extended to oceanography.

It was during early investigations at Loch Ness that the first internal temperature seiches were discovered (Watson, 1904; Wedderburn, 1907). These arise when wind, blowing warm surface water to the leeward end, tilts the isotherms lengthwise in this direction. The cessation of wind stress permits recovery of the isotherms but, because of momentum, they overshoot and oscillate for some days (Figures 4a, 4b, 17K and 6a, 6b. 6c, 6d, approx 12K each)). L.H. Mortimer (1955) of the Freshwater Biological Association showed the effect of the earth's rotation on the currents accompanying seiches, which leads to a deflection to the right and hence a cross-loch tilting of the isotherms (Figure 8 , 15K). Mortimer's observations of asymmetry in the seiche led Dr. S.A. Thorpe of the National Institute of Oceanography to establish the presence of a 'surge' wave front characteristic (Thorpe, Hall and Crofts, 1972). Thorpe (1977) has since conducted other work, including the mechanisms of mixing and turbulence.

Factors affecting Sonar

The Project considers it important to understand the nature of thermal characteristics likely to affect sonar work. For example, sonar beams propagating horizontally are refracted by temperature gradients and it is also important to recognize direct echoes caused by them. Conversely, we wish to discover the extent to which thermoclines can themselves be monitored by sonar, and their relationship to 'scattering layers'. Lastly, we are seeking to establish the role played by physical factors in the distribution of biomass. The thermocline movements may affect the range of vertical migrations, and internal seiches can cause horizontal transport.

Observations will first be made on the build‑up of stratification, and then the role of sonar discussed. From 19th June to 7th October 1983 temperature measurements were made from a mooring to the north of the deep basin (220m) off our station just south of Achnahannet (see map in Figure 1a). The readings were too infrequent and irregular to give a valid continuous record, and were complicated by our position near the node of the main longitudinal seiche, which doubles the frequency, and towards the northern side of the basin, where we were subject to the transverse seiche. An example of daily records (Figure 5a, 7K) reveals large changes in the depth and degree of stratification. Nevertheless, the averages of readings per week (Figure 5b, 6K) serve to show progressive deepening and convergence of the isotherms towards autumn.

Further background is provided by the record from the fixed station (see map in Figure 1a) employed in 1984. This was moored towards the south end of the loch, in the centre of the deep basin, about 4.5km north of Fort Augustus, thus simplifying interpretation, and readings were taken at least four times per day. The result is shown in Figures 6a, 6b, 6c, 6d. Winds were measured with a simple hand-held device (Ventimeter) and currents, where recorded, are merely observations of drag on the temperature probe wire. A detailed discussion of the record will not be attempted in this review but the following comments may be helpful.

The Record

The record begins on 22nd July (Figure 6a, 12K), as N.E. winds mix and deepen the 17C epilimnion, until 26th July when the wind changes to S.W. As the water is transported to the N.E., successive isotherms break surface, exposing colder layers which will mix into the warm water to leeward (Mortimer, 1952). The epilimnion begins to recover as the winds moderate on 28th July and with calmer weather, the upper isotherms generally deepen, although possibly checked by S.W. winds from 31st July to lst August, until they are forced down by strong N.E. winds (Figure 6b, 14K) from lst to 3rd August. As a result of mixing, the epilimnion is now cooler (14C) and deeper. Stratification becomes marked.

The disturbances generate a seiche in the lower isotherms with a period of approximately 54 hours characterized by a rise in temperature of 18 hours and a fall of 36 hours. The wind cycle appears to have various amplifying and dampening effects on the seiche until 13th August (Figure 6c, 11K) when calmer weather accompanies a loss of regularity and amplitude. From 15th August a consistent 15C isotherm re‑enters the record and an epilimnion is ultimately deepened by N.E. winds, from 23rd to 24th August, to bring about a situation similar to that at the beginning (Figure 6d, 10K).

The process continues throughout the summer as calms produce transitory shallow epilimnia which are soon mixed in by winds. Mass transports caused by seiches spread the heat deeper by turbulence. The most effective mixing is accomplished by the autumnal equinoctial gales, which since the loch is no longer gaining heat, are able to produce an epilimnion of near uniform temperature. It is from this simple situation that our description of the sonar contribution begins.

Figure 7 (19K) shows one of the 252 sonar profiles made with Simrad EY-M (narrow beam 11 degrees) and Skipper 603 (wide beam 33 degrees) echo-sounders off the Achnahannet station in 1983. The record for 29th September has an epilimnion at an almost uniform 11.3C with the thermocline at 40m. Two temperature graphs serve to show the depth and degree of stratification to be related to the echo trace. A striking illustration of transverse tilt is provided by Figure 8, (15K), where the isotherms conform to the tilt registered on the trace, although it would appear that three layers are involved.

An example of mixing occurs during a short period of high winds from 2nd to 4th August (Figure 9a, 59K). It is not clear whether a seiche was in progress (although the trace shows tilts suggestive of currents), but the temperature graphs before and after the episode show a cooling and deepening of the epilimnion. Prior to the autumn situation the gradients are complex, and another example (Figure 9b, 67K) shows the destruction, or at least removal, of a secondary thermocline at about 10m by S.W. winds from 28th to 30th August.

During the fixed station experiment of 1984, a Lowrance Eagle Mach 2 was run every hour for at least five minutes from 31st July to 24th August and in addition, almost always when temperature probes were being taken. In Figures 6e (28K) and 6f (31K) examples of the records are attached beneath their relevant positions and often show the thermocline. From the foregoing it might seem that sonar is quite reliable in resolving thermal structures but a considerable degree of caution is required in use and interpretation.

Possible Errors

Monitoring of open water 'scattering' layers as early as 1982 had highlighted the problems of 'second time around' returns, which can confuse or obscure the record. With range set to less than water depth, echoes will return from the lake bed and be received during the 'listening' phase of subsequent pulses. If the set range is sufficient to include the lake bed, second time around echoes can still be received, having been inter‑reflected between the bed and water surface. They appear on the chart as diffuse layers, and are accentuated by the high gain settings necessary for thermocline detection. These returns are indicated on some of the charts, and in practice limit the choices of effective range settings. Such returns can be identified since they change range with alterations in pulse repetition frequency, i.e. range settings.

Another cause for confusion lies in the frequent association of biological 'scatterers', such as fish and plankton (Schroder, 1962), with the thermocline, at least by day. Detritus has also been suggested, but we have never found detectable traces in samples.

In Figure 10 (31K), a comparison of simultaneous runs with wide and narrow beam sounders clearly shows the contribution of fish to the wider beamed sounder's return. In Figures 6e and 6f, during the fixed station work, many of the daytime returns from depths of around 30m are strengthened by the layer of fish. For further discussion see sections on plankton and fish.

1988 The Scottish Naturalist p126

The records sometimes show inconsistencies between the degree of stratification and the strength of echo trace. It is particularly noticeable that, on the narrow‑beam Simrad EY‑M, thermal gradient traces often appear patchy. An examination of Figure 8, (15K) for the southern profile shows discontinuities and traces to be reasonably consistent, but to the north, strong traces register from lesser gradients. This may be partly accounted for due to the thermocline being divided into 'layers' of weak gradient, several metres thick, divided by much thinner 'sheets' with steep gradients (Woods, 1968; Simpson, 1970). Our one‑metre temperature sampling interval would not resolve microstructure adequately. We believe, however, that the explanation lies in turbulence, to which echo‑sounders are particularly sensitive, as shown by traces throughout the paper recording the raising and lowering of samplers and illustrated vividly in Figures 9a and 9b showing mixing. In the above example the transverse tilts, by definition, imply strong currents moving in opposite directions. Echoes are often pronounced near the side walls where greater turbulence is to be expected.


Shear is actually associated with most thermoclines and waves within them sporadically produce inversions known as Kelvin-Helmholtz billows (Woods, 1968; Thorpe, 1974). We believe this turbulence to be the main factor in regulating the strength of echo returns, possibly by creating multiple interfaces of small size but high gradient. In support of this, attention is drawn to the 1984 fixed station record in Figure 6f (31K) for the period 3rd to 7th August, which includes the sharpest thermocline observed. The records for the night of 3rd August show the gradient strongly after the fish have left it and while the isotherms are rising. However, by the time of the temperature profile at 10.00 hrs the interface echo was weak or undetectable despite the intensity of stratification. It is at this point that the isotherms are at rest and the currents therefore at their slackest. A conclusive thermocline trace does not re‑enter the record until 5th August at 22.00 hrs, when the isotherms are once again in significant motion.

The foregoing conclusions seem particularly relevant to our observation in October 1985 of a surge front wave of the type described by Thorpe. These waves (Figure 11a, 12K) lead the seiche and have a length of approximately one kilometre and a speed, depending on amplitude, of approximately 1.5 km/hr. Figures 11b, 11c, 11d, 11e, 11f, show a continuous echo trace from 18.55 hrs on 11th October to 14.44hrs on 12th October, superimposed with some relevant temperature graphs and current observations, all taken from a moored position close to that of the 1984 fixed station. S.W. winds on the previous night had reached hurricane strength over parts of Scotland but had calmed to a gentle breeze by the time we took station. The record commences (Figure 11b, 115K) with a shallow 12-15 metre epilimnion of a uniform 10C. At 23.15 hrs (Figure 11c, 76K) the thermocline dipped sharply and a spectacular wave train of decreasing regularity was observed. Temperature probes (Figure 11d, 93K) show a rapid lowering of the isotherms with discontinuities corresponding to the echo trace, and at 01.15 hrs an increasing subsurface current to the S.W. set against the surface drift. By 02.28 hrs the surface water was also moving against the wind and by 08.00 hrs (Figure 11e, 75K) was rapid enough to cause difficulty with temperature probes and plankton sampling, because the wires assumed unacceptable angles. At 13.07 hrs (Figure 11f, 86K) the current was easing, and at 14.30 hrs was slack. By this time the S.W. wind had freshened and the surface drift had reverted to N.E.

Obviously the entire event was attended by a high degree of shear as the epilimnion slid beneath our station and it will be noted that the surge front wave crest registers particularly strongly. We speculate that the crest comprises turbulence similar to that observed by Woods (1968) on thermocline sheet waves, although of a greater amplitude. The two initial waves are of 23m and 45m amplitude. The trace from 06.30 hrs to 08.15 hrs (Figure 11e), when the strongest currents were observed, is interpreted as consisting of Kelvin-Helmholtz billows (Thorpe, 1988). The cause of the near surface turbulent effects seen from about 08.15 hrs is less obvious but coincides with the influx of slightly warmer surface water and is probably also associated with shear.

The plankton hauls (Figure 11g, 10K) show a mass influx at 02.08 hrs, and it is evident that fish are also being transported, sometimes in very localized concentrations (see sections on zooplankton and fish).


In conclusion, it may be said that echo‑sounders have considerable value in the detection of general thermal conditions, but do so by registering degrees of turbulence rather than gradient, even though the two are often associated. Future experiments will include induced artificial turbulence, which may then propagate across potentially unstable structures, thus revealing their positions (see Figure 12, 12K).


A measure of the neglect shown towards Loch Ness may be judged from the fact that the first basic observations to be made there since the Bathymetrical Survey in the early years of this century were made over fifty years later, by teams investigating the 'Monster' controversy. Student expeditions from Birmingham and Cambridge Universities made plankton hauls, while Mackal and Love (1970) of the Loch Ness Investigation Bureau took water samples (Figure 13a).

The situation changed, however, when from 1977 to 1980 a comparative study of five major lochs, including Ness and Morar, was undertaken by the Institute of Terrestrial Ecology. Wide‑ranging papers were edited by Maitland (1981) in the book The Ecology of Scotland's Largest Lochs. The Project's general biological objectives have therefore concentrated upon areas not covered by the comparative study, such as plankton and fish migrations. A special study has been made of the abyssal fauna.


Primary productivity is low. The high latitude and frequent cloud reduce sunlight to a short growing season. Photosynthesis is further limited, by suspended peat, to a shallow photic zone. Rooted plants are restricted to a depth of about 6m around the shoreline. The hard rocks of a steep catchment yield few nutrients to fast flowing rivers and streams entering the loch. Acidity will tend to slow bacterial decay of organic particles and hence the release of their nutrients (Figure 13a, 12K).

Thus the phytoplankton crop is low, and was found by the Cambridge expedition to have a diatom population of 200/1 as compared to 5,000/1 for Lake Windermere (Baker, 1962). Bailey-Watts and Duncan (1981) found the plankton in Loch Ness to be dominated by chrysoflagellates, with a total cell count of 568/1 at the time of the chlorophyll 'a' peak in August. Some of the species are shown in Figure 13b (19K).


The cladoceran grazers of the phytoplankton consist of Diaphanosoma brachyurum, Holopedium gibberum, Daphnia hyalina and Bosmina coregoni. The larger predators are Polyphemus pediculus, Bythotrephes longimanus and Leptodora kindti. Copepods are represented by Diaptomus gracilis, the most numerous species, and Cyclops strenuus abyssorum. See Figure 13c (16K).

Zooplankton of most open waters appear adapted to avoid predation by transparency, and at Lochs Ness and Morar are also adapted to low productivity, by remaining relatively small and by producing fewer but larger eggs than their counterparts in more productive waters. Food seems to be stored in some copepod specimens as oil globules. Peak numbers have been found in October (Maitland, 1981: 144). Project work was conducted in collaboration with Dr. A. Duncan of Royal Holloway College in September 1983, with the aim of determining vertical and horizontal distribution. A Clarke‑Bumpus collector was used to take horizontal hauls, which have yet to be worked, and a 31‑litre Patalas sampler was used for the vertical work.

The vertical hauls are shown in Figures 14a (49K) and 14b (40K) with a summary in 14c (16K). From 12.00 hrs on 12th September 1983 to 05.00 hrs the following morning, five hauls were made, in conjunction with temperature profiles and echo‑soundings, from the mooring off the Achnahannet station. The results show a clear concentration of plankton at the thermocline at 13.00 hrs which involved most species. Thereafter, a migration takes place towards the surface, particularly in the case of Cyclops and Diaptomus. Total numbers increase towards midnight, possibly due to horizontal transport in response to the rising of the isotherms. Some of the peak densities are noted and have no convincing connection to the echo traces, which, although complicated by second time around returns and reflections from the mooring, appear to bear more relationship to the temperature profile.

There has been considerable research on acoustic scattering by marine zooplankton. Theoretically even a 200kHz echo‑sounder of high sensitivity could detect layers of organisms as small as one millimetre, and euphausiids of 15‑22 mm have been assessed by multifrequency methods (Greenlaw, 1979). In fresh water, where plankton sizes are generally much smaller, convincing records have been made at 200kHz of Chaoborus larvae in the absence of thermoclines (Northcote, 1964). However, these insect members of the zooplankton have a length of 9mm-12mm together with paired air sacs at either end, contributing to much higher scattering strength than from the more typical cladocera and copepods. Chaoborus is absent from Loch Ness, and the largest of the more abundant herbivores measure up to 2mm.

Schroder (1962) reported the detection of one millimetre freshwater plankton at densities of as little as 2/litre, although the sonar frequency was not stated. Examination of the traces suggests that plankton horizons presented cannot be distinguished from the thermocline records. Indeed, the prime conclusion of the paper is that the "zooplankton in Lake Constance is mostly found by the echo‑sounder in layers with sharp gradients (thermoclines) where it is also to be found during vertical migration". At our frequency of 50kHz (33 degree beam) no correlations were evident at concentrations of 10/litre.The frequent concentration of zooplankton in thermoclines must also inevitably associate them with the temporal and localized shear to which echo-sounders are so sensitive. It would seem difficult to design thresholds for echo integration of zooplankton volume scattering where thermal gradients exist.

An example of horizontal transport appears to occur in the strong currents noted during the surge shown in Figure 11d (93K). Four sets of net samples were made, all but the first to a depth of 36m in 6m stages. A closing net of 28cm diameter was used. The results indicate a mass influx of plankton as the currents strengthened.

To conclude, we have observed zooplankton in Loch Ness concentrated at the thermocline by day and exhibiting a vertical migration at night. It may be of interest that this migration has not been observed in Loch Morar, where the water is much clearer but where there are far fewer midwater fish (Figure 14c, 16K); here the plankton remain in the top 15m of water by day. In Loch Ness considerable horizontal transport of plankton occurs, particularly during a seiche. We are not convinced that, at the concentrations observed, our echo‑sounders have yet made a contribution to recording zooplankton (50kHz‑200kHz) and draw attention to possible confusion owing to the presence of turbulence. Layers of small fish may also give misleading (diffuse) returns, particularly at depth and on wide‑beamed sounders. Diagnosis is possible if a vertical migration takes place (see Figure 20a, 13K).

Littoral and Sublittoral Benthos

The steep and stony shores of Loch Ness provide a restricted habitat with considerable exposure to wave action (Figure15a, (7K). The fauna is therefore similar in some respects to that of fast‑flowing streams, in that the organisms must retain their positions among stones (Figure 15b, 11K), rather than on the silts, muds and plant life of more lentic waters.

A comprehensive survey of the animals dwelling within the first 50cm of water, conducted by the Institute of Terrestrial Ecology (Maitland, 1981) confirms that the community is dominated by insect nymphs. Stonefly (Plecoptera) make up 30% and mayfly (Ephemeroptera) 18% of the fauna, some of which are adapted to retain position by the possession of grasping claws or present a low profile to the water by a dorso‑ventral flattening of their bodies. A common mayfly, Ameletus inopinatus, is generally confined to streams above 300m or to lochs much further north, so its presence here suggests a preference for the lower temperatures found in deep, windy lakes, even at the surface, owing to regulating effects of mixing.

Other benthos include triclads, various nematode and oligochaete worms, the gastropod Lymnaea peregra, the crustaceans Asellus spp. (found in more sheltered areas) and ostracods, water mites, and caddis (Trichoptera) and chironomid larvae (Figure 15c, 25k). Typical Project hauls at Achnahannet and the Horseshoe Scree ‑ additional to Maitland's list ‑ are included in Figure 15d (10K).

The steeply sloping walls of Loch Ness provide a narrow and ill‑defined sublittoral zone, but hauls from 20m‑30m depths at Urquhart Bay as well as Borlum Bay, in sandy sediments, have revealed the organisms listed in Figure 15e (10K). These littoral and sublittoral communities, together with terrestrial insects falling into the water, provide the food for the inshore fish populations.

Profundal Fauna

In contrast to the turbulence and variety of physical conditions among the stones of the shoreline, the fine and relatively rich silts of the abyssal regions offer remarkable stability. In an environment of great hydrostatic pressure, constant darkness, and a scarcely changing low temperature of 5.6C, high oxygen levels (over 80% saturation), permit surprising variety in the profundal community of the 200m deep basin floors.

The first samples were taken during the Bathymetrical Survey (Murray, 1904: 442). It would appear however, that no further collections have been made until the present work. For a description of the sediments and a literature review of the benthos see Maitland (1981: 205). The Project has made a particular study of the profundal fauna at both Ness and Morar and a few comments are appropriate here.

A variety of qualitative and quantitative collection techniques have been used, including dredges, grabs and a static 'colonization experiment'. At Loch Ness, over thirty species have been recorded, some of which are doubtless casual occurrences, with an average density of 295 individuals per sq m. Recognized characteristic profundal fauna is present, such as oligochaete worms, chironomid larvae (non‑biting midges) and Pisidium spp. (pea mussels) but, numerically, ostracods predominate, comprising 62.6% of the community. The dominant bivalve mollusc, Pisidium conventus, is more normally found in arctic streams, but at our latitudes is confined to the cold water of deep lakes or to high altitudes. It is considered to be an ice-age relict species in Loch Lomond (Hunter and Slack, 1958). The dominant chironomid, Sergentia coracina has been similarly described in southern Sweden (Brundin, 1949). The community also has its predators, such as chironomids of Procladius spp. and the large copepod Acanthocyclops viridis, which are more cosmopolitan in distribution although apparently absent from the littoral zone of Loch Ness.

Some interesting occasional records include caseless caddis and the flatworm Phagocata woodworthi, which has been recently discovered in the littoral near a sewage outfall (Reynoldson, Smith and Maitland, 1981). This North American triclad is speculated to have been introduced on equipment imported in the search for the Loch Ness Monster. Another native of North America, the amphipod Crangonyx pseudogracilis, has been spreading northwards since its discovery in the London area (Crawford, 1937), and its occurrence during the present work is the first record for a Scottish loch. It could well have been responsible for small fast moving images first seen on underwater television in 1981. It may be significant that Crangonyx was captured only in the passive colonization substrate. Fish, again first noted during the television work of 1981, have now been netted and identified as Charr Salvelinus alpinus. Figure 16a (24K) shows some of the members of the abyssal fauna.

The role of the echo‑sounder during this work was limited but aside from enabling the quick location of the depths to be sampled, sonar can often aid the control of sampling equipment. In particular, it was noted that the Ekman grab penetrated too deeply to enclose the vital top 5cm of sediment. With the echo‑sounder, sampling was quicker and more effective since the sampler could be allowed to free fall to within a few metres of the bed and then be gently lowered. Figure 16b (10K), shows a grab being deployed, and also a method for the recovery of long term experiments, in this case our colonization substrate sampler, by the location and grappling of a buoyant rope laid horizontally and with the end weighted.

In general, it seems that the depths offer a refuge, not only for ice‑age relicts but also for a variety of widely occurring 'pond life' unsuited to the turbulence and predation pressures of the shoreline. It will now be necessary to examine the rocky side walls to define the limits of the two communities and to see if there is also a third.


As the ice retreated, the loch was colonized from the sea by coldwater salmonids, which entered fresh water only to spawn. Thus the Salmon Salmo salar still migrates via the River Ness, as does the Sea Trout Salmo trutta. However, with the passage of time and increasing sea temperatures another variety of Salmo trutta, the Brown Trout, and the Charr Salvelinus alpinus now spend their whole life cycles in the loch. It seems possible that new populations of Charr may have entered during the period of the Loch Lomond re-advance (Greer, pers. comm.).

Other species gaining access by sea migrations are the Three‑spined Stickleback Gasterosteus aculeatus, the Brook Lamprey Lampetra planeri and the Eel Anguilla anguilla, which has an opposite life cycle to the salmonids in that it matures in the loch after having been spawned in the Sargasso Sea.

The exclusively freshwater 'coarse fish', which have been spreading northwards since the ice age (Maitland, 1977), are represented only by the Pike Esox lucius and the Minnow Phoxinus phoxinus. The Minnow was not recorded by Maitland (1981); it was first observed by the Project in 1985 at Bona Narrows just downstream of the loch proper, but in June 1987 it was also recorded in sheltered water at Fort Augustus.

In collaboration with members of the Ness Fisheries Board, together with Dr. A. Duncan and Mr. R. Greer, various netting experiments have been carried out. Underwater television (UW/TV) has so far made contributions in the littoral and abyssal zones, while sonar has been most extensively used in the pelagic. Much work remains to be done on the ageing and electrophoresis of the specimens.

Littoral Zone

The littoral is dominated by brown trout to a depth of about 20m, below which charr prevail. The really shallow and sheltered water harbours minnows, three‑spined sticklebacks and salmonid parr. Eels live on the loch bed and range widely along the shoreline, being most concentrated off river mouths. Work on the growth rate of the Loch Ness eels has been conducted by Mackal and Frake (Mackal 1976: 319‑330).

Benthos is doubtless an important food source and many of the brown trout seem particularly specialized, e.g. a 21.7cm fish contained 143 snails (Lymnaea peregra). In summer, however, a substantial proportion of the trout diet consists of a terrestrial input of adult insects. Figure 17a (27K) presents some relevant information on the fish of the littoral. Figure 17b (16K) shows underwater television pictures of trout and eels in Urquhart Bay, concentrated in the rich organic leaf deposits at 30m off the mouth of the River Coiltie in early June 1987. As summer progresses. a considerable amount of gas generates in this material and also in other parts of the bay, possibly because of higher water temperatures. In October 1987 only an occasional Eel was observed here. Gas has not been detected in the fine deepwater sediments.

It is along the shoreline that the migrating salmon pass before spawning in rivers, and attention is drawn to the fact that salmon, as the largest fish present, owe very little to the loch's rather poor food chain. After only a few years as small parr they will then mature at sea, and return at weights up to 20kg. There is no fish counter on the River Ness, but two counters installed on the Rivers Garry and Moriston showed less than 900 fish in a peak year of 1975 (Maitland, 1981: 243). Although this does not include the rivers in Urquhart Bay, a comparison may be made with a maximum count of just over 3,000 fish entering Loch Morar in 1966. The picture is rather sad when one recalls the comments of Captain Burt at Inverness in 1758, that the price of salmon was a penny a pound and that "the merest servants who are not at board wages will not make a meal upon salmon if they can get anything else to eat" (Mills, 1980).

Profundal Zone

We have yet to observe fish by underwater television on the loch 'walls' beneath about 150m. The fish of the profundal are not amenable to detection by sonar because of attenuation and widening beam angle, so the information presented results from UW/TV (Figure 18a, 7K) and netting experiments at 180m-220m depth on the deep basin floors(Figure 18b, 7K). Future experiments will include lowering deep‑towed narrow‑angle transducers to assess this region.

The presence of deepwater fish was confirmed in 1981 through UW/TV, and in 1982 the first three specimens of charr were netted from 220m. It is always something of a problem to be certain that fish are really caught at depth and not during the long setting and retrieval process, but of the twelve charr caught at this depth, seven contained profundal fauna including Pisidium conventus. Some fish believed to have been caught at 200m had surface zooplankton in the lower gut, thus suggesting that a relatively fast descent takes place (Figure 18c, 15K). Versatility is thought to enable Charr to inhabit relatively sterile lakes and to avoid direct competition with the less adaptable brown trout.

On the other hand, it has been shown that there are two distinct races of charr, a pelagic and benthic form, in Loch Rannoch (Walker, Greer and Gardner, 1988). Electrophoresis has shown genetic differences between the stocks and initial results with our Loch Ness specimens also appear to show two varieties, although the visible differences, larger eyes for example, do not appear obvious at this stage.

Pelagic Zone

The offshore waters to 30m are dominated by charr, which feed upon the larger zooplankton such as Daphnia, Leptodora and Bythotrephes. As part of the fixed station work of 1984, depth‑marked nets of various meshes were suspended beneath the raft to a depth of over 30m, aligned N.E.-S.W. The results in Figure 19a (17K), show a poor catching frequency between 8th and 21st August with charr taken at approximately 10m by night, when it is also evident that trout extend over the surface. In addition to zooplankton, the trout contained a proportion of winged insects (Figure 19b, 26K). The only fish caught by day were two trout at approximately 30m; one of the trout contained two charr and may have been a "ferox".

Although in general the catches tend to support the presence of vertical migration, it should be borne in mind that echo‑sounding shows individual fish within the net depth by day, and it seems likely that avoidance was significant. No monofilament net was used. The catch depths could well be a result of the depths at which the net was visible to given species, or of their periods of maximum activity. Nevertheless it seems from this result and from much longer nets set on the surface that charr, at least specimens of over 20cm, rarely come within three metres of the surface even at night.

Echo‑sounding with a variety of instruments reveals the basic pattern of summer activity. Figure 20a (13K), shows that by day, a scattered population of individual fish range down to the thermocline. Rough calibration suggests these fish to be over 20cm in length. In the region of the thermocline a well defined layer of fish at greater density requires a narrow‑beam sounder to resolve individuals (Figure 20b, 16K), which may otherwise blur into the thermocline traces. The calibration suggests that this layer includes fish which are very much smaller than the scattered population and which would not have been caught by our net meshes. These are mainly charr, including the 0+ age group (confirmed by trawling during 1988), but we have also made some interesting incidental catches of trout and salmon parr in open water. At dusk, this layer makes a distinct vertical migration and by midnight it is within six metres of the surface. It seems that little dispersion takes place and at dawn the layer sinks. Again, as by day, a scattered population of individuals is detected at depths to 30m unrelated to the layer.

Figure 20d (42K) details the limits of the vertical migration as observed from the 1984 fixed station between 31st July and 24th August. Unfortunately the above netting programme obscures parts of the record. Throughout the period the layer descended to a maximum of 35m, usually sufficing to bring it within a temperature of 10‑11oC and always to under 12oC. It descended to at least 30m, however, even though it may have reached the 12C isotherm at a lesser depth. Some degree of temperature preference would seem to be shown by the deeper (35m) daytime depth on 3rd August when the isotherms are depressed. The fish do not necessarily seek out or remain in thermoclines (see 4th August) but there is more chance of any preferred temperatures being 'compressed' into this area. In the generally cooler epilimnion temperatures (and overcast conditions) during the summer of 1988, the layer's daytime depth could be as little as 18m (at a temperature of 12.5C), well above the thermocline.

Much work remains to be done at other times of year. In the meantime, isolated observations suggest that the migrating layer becomes established in late May, although its daytime depth is only 24m. An interesting question to determine is whether this is due to lesser light levels or to cooler epilimnion temperatures. The migrating layer seems to disperse around October, when scattered fish may be detected to depths of 50m or more. The winter mid‑water fish population is reduced.

Regarding the horizontal transport of fish (Figure 20c, 27K), attention is also drawn to the surge record in Figure 11c (76k). Since the soundings are from a moored position, the speeds at which a fish at a given depth crosses the beam will shorten or lengthen its characteristic arched signature. Fish at greater depths will obviously spend longer in the beam because of its width.

It is noticeable that the influx of fish exhibits compressed arches, particularly when the strong currents were noted, in contrast to the generally long arches shown beforehand. This is suggestive that the movement is a passive one due to the currents, rather than active swimming. Harden‑Jones (1969: 16) suggests that in the absence of visual cues, fish are unable to detect laminar flow, but this could change in the presence of a discontinuity in the current, such as shear

A further point is that even a simple echo‑sounder can resolve horizontal movement in one plane, without affecting vertical accuracy, by giving a small tilt to the transducer. Thus, fish traces will show asymmetrical uprange and downrange components, depending upon their direction of movement along the beam axis. Even a vertical transducer is likely to have some bias to the beam. This is very noticeable in the surge tracings where fish show a distinct downrange trend. On this occasion the bias of the transducer was not known, but it seems likely that the traces show a movement in conformity with the current. It will also be observed that fish are concentrated behind internal wave crests. Fixed station records in Figure 20c (27K) also show a bias but with periodic changes of direction in parallel with seiche-induced currents.

During Operation Deepscan in 1987 an attempt was made to map fish distribution after the break up of the scattering layer. At 12.00 noon on 7th October, seventeen craft (equipped with Lowrance X-16 sounders) made simultaneous profiles, sectioning the length of the loch. Each then made a run in mid-loch to the next station, thus yielding a continuous 17.5km record within a 15minute time span. It had been hoped to chart the thermocline at the same time but despite maximum sensitivity being applied, this was not detected. We surmise that this was due to the calm weather reducing the movement of the isotherms and resulting shear. Temperature probes over the period; show an epilimnion of a uniform 11.5C to 30m.

Figure 21 (12K) shows the results of visual fish counts and although no replicates were made, it appears that some interesting variations in density were present. There are more midwater fish well offshore and numbers increase towards the S.W. end of the loch. Further research seems worthwhile on the role played by physical factors in fish distribution. At the same time, it would be valuable to discover the periods of peak activity of the fish forming the layers, possibly by lowering transducers from fixed stations to keep range and angle constant.

It would be desirable to adopt more sophisticated acoustic estimation techniques but our observations highlight some possible problems (Figure 22, 33K). With scattered fish, it is customary to adopt an echo-counting system, which becomes less useful as density increases, as in the scattering layer, because of overlapping signals. The method used for higher densities, echo-integration, is liable to suffer inaccuracy because of these fish being found in the region of the thermocline with its associated echoes. By night, fish which have risen close to the surface, could be scattered by the approach of the survey vessel.

In August 1988 the scattering layer lay at 18-20ms, well above the thermocline and echo-counting with relatively few (30%) overlaps was possible. A Simrad Hydro Acoustic Data Acquisition System (HADAS) was interfaced to the output of an EY200 (49kHz) Scientific Sounder. The subsequent software analysis has measured area densities of up to 1,000 fish/hectare within the layer.




The work of the Loch Ness and Morar Project during the 1980s reflects evolution not only of method but also of attitude to the Loch Ness controversy. The history of organized searches during the 1960s and 1970s has been described by Fitter (1988); see also Dinsdale (1961), Mackal (1976) and Rines et al. (1976). Although successive investigators remained impressed by a portion of eyewitness testimony, it must be understood that, by the end of that period, most experimental evidence had been subject to review and to a degree of rejection. Some of these alternative interpretations were ultimately to become available in book form (Binns, 1983; Campbell, 1986; see also Razdan and Kielar, 1984).

The evolution of method itself bears tacit witness to a revision of expectations. By the end of the sixties, intensive surface surveillance gave way to underwater work, after having failed to reproduce any of the highly varied 'classic monster' photographs (Mackal, 1976: 122). In turn, for all their early promise, underwater camera vigils at Lochs Ness and Morar had been discontinued by the late seventies. The realization that passive underwater cameras were not going to provide an easy positive, let along negative, answer could only prelude a more active approach and a long period of verification for the single category of experimental evidence, which seemed repeatable and for which no satisfactory explanations had been put forward.

Sonar, although a long range tool, lacks definition, and its prime role lies in demonstrating the presence of something of interest in the first place. In turning to sonar and examination of its previous contributions, the Project acknowledged that such a demonstration was after all necessary. The motives for experiment have also changed. Fairness to the eyewitnesses may justify research, but other evidence hardly merited a position of advocacy. At Loch Morar, Project work had already diversified to contain a major component of general limnology, which in a revisionist climate, did much to justify continued organized expeditions. Effort shifted in 1980 from underwater cameras in the clear waters of Loch Morar to sonar in the uniform basin of Loch Ness. The objective was seen in terms of exploring a neglected habitat, the presence of which gave grounds for controversy but in which that controversy played only a part. Thus the problem is being tackled through active examination of the environment, rather than by all or nothing ambuscade.

Work in the 1980s is not a quest for the dragon of popular expectation. The media‑christened 'Monster', by definition imaginary and by connotation prehistoric, has an existence in the realms of entertainment copy, quite independent of research findings (Meredith, 1977: 156). Admittedly some 'Gothic revivalist' expectations emerged during the seventies, as described in a perceptive apologia by Bauer (1986). The concept, however, had received little fuel from previous fieldwork, such as Baker's (1962) dismissal of the huge multi‑humped stereotype as boat wake effects, or from Mackal's (1976) analysis of possible candidates in the light of ten years of research by the Loch Ness Investigation Bureau. Examination of the controversy through the environment reveals some paradoxes between ecology, evidence, and the choice of operational method.

Biological Considerations


Despite low productivities it is clear that Loch Ness could support resident or migratory fish predators. The months which returning Salmon spend in fresh water before spawning represent a bonus to the food chain which would once have been very substantial, and even now provides sufficient incentive for seals to enter (Williamson, 1987). In documenting a Common Seal Phoca vitulina present from 16th November 1984 to 11th June 1985, Dr. Williamson points out, incidentally, that it was readily identified by about thirty people and that no increase in Monster sightings was noted. If migratory fish are considered as a food source, one might expect predator activity in the littoral zone. Mackal's analysis (1976: 85 and 346) concludes that 52.7% of sightings occurred in bays around river mouths but recognizes that these may result from human activity being greater at such places. See also sections on Submerged and Floating Logs.

It was nevertheless on sound biological principles that the littoral was chosen for the underwater vigils during the 1970s, at Loch Ness by time lapse photography (Rines et al, 1976) and at Loch Morar by silhouette underwater television (Shine, 1976). Results at Loch Morar were negative and at Loch Ness were to prove controversial. No such work has been continued.

The charr of the open waters also represent a large biomass, since they enter the food chain at a lower level than other fish of their size, feeding directly upon zooplankton without the intermediate link provided by the 'foragers'. They are already subject to predation by the ferox trout. If larger predators were to utilize this source, they should be sonar detectable. By day (in summer) a depth of 30m may be expected, with a possible upward migration at night.

The paradox of the loch's oligotrophy actually extending the range of usable habitat has been discussed. The community of the profundal zone has provided unexpected variety and sufficient concentration to support its own fish population. This region is very large, because of the mean depth, and although it would be premature to propose the basin floors as habitats for anything unexpectedly large, perhaps they should not be overlooked either. Benthic creatures would be difficult to detect by sonar unless excursions into the water column occur. It may be worth pointing out that benthic fish are likely to exhibit peculiar form and behaviour if they do occasionally surface.

At present, the least hospitable regions would appear to be the side walls, although these are difficult to assess by sonar, and the vast water column between the profundal and pelagic zones. Yet it was here that the Loch Ness Investigation Bureau were to achieve their sonar results

Theoretical relationships between biomass and potential Monster production have been explored by Sheldon and Kerr (1972), calculated from Ryder's (1964, 1965) Morphoedaphic Index (total dissolved solids/mean depth); also by Scheider and Wallis (1973) using a size‑density relationship, and the method of least squares, to fit a power function to data from a marine area of low productivity theoretically similar to Loch Ness.

Both authors estimated a similar biomass, for the terminal predator feeding on fish, as 15,675kg and 15,725kg respectively. The true figure, however, is likely to be below that of Sheldon and Kerr's, because they used data from the slightly richer Loch Lomond, but neither figure takes into account migratory fish, which allows greater biomass. Terrestrial inputs, e.g. allochthonous leaf material and winged insects, should not be underestimated either.

The Candidates

There is considerable speculation concerning the identity of the Loch Ness Monster; put another way, this means seeking an explanation, perhaps many explanations, of the sightings record. Assuming for a moment that there may be an unusual single animate explanation, and confining discussion to vertebrates, environmental factors are as follows.

Low water temperatures are evidenced by the presence of cold stenothermic and holarctic species. As shown in Figure 5b, epilimnion temperatures above 12C are present for only four months of the year. Although the winter temperature of about 5.6C is actually higher than in shallower lakes further south, reptiles would seem to be eliminated. Mammals (e.g. pinnipeds) would presumably have already drawn attention to themselves by their more frequent need to breathe.

Freshwater invertebrates spread rapidly to favourable habitats, but it has been emphasized that the connection to the sea has been virtually the only avenue for colonization by fish. Salmon, Sea Trout, Lampreys and Eels still migrate via the River Ness. Ten thousand years after the final passing of the ice, the European coarse fish have yet to arrive; indeed the varieties available in the British Isles are limited through the inundations of the present North Sea and English Channel about 7,500 years ago.

The amphibian hypothesis would require a uniquely large and exclusively aquatic species to spread rapidly north in the wake of the ice and to suffer equally rapid extinction elsewhere. If, as seems reasonable, we look to the sea for unusual residents or visitors (the amphibia have no marine representatives) then the fish would seem to offer the most likely candidates.

Known fish are quite capable of answering the criteria of size (median length 4.57m: Mackal, 1976: 344), the obviously uncharacteristic nature of surface appearances, the problems of access or reproduction, and just about everything else. Were the eyewitnesses to find vindication in the discovery (say) of Sturgeon Acipenser sturio, or indeed any vindication, most would doubtless be content. Science might be delighted with the presentation of an outsized eel (the original local interpretation incidentally), but perhaps to 'Monster hunters' ten years ago, this would be "not quite Nessie".

This does not mean that other explanations are impossible but at least an acknowledgement of the most plausible candidate from an environmental point of view, has done something to bridge the divide between science and 'fringe', which opened in the 1970's as described so well by Bauer (1986). The original newspaper report (Northern Chronicle, 27th August 1930) described a "fish .... or whatever it was". If we look for a fish 'on principle' , we are unlikely to miss anything else, because we are going to have to look everywhere. Examination of Loch Ness has proved rewarding in itself.

Physical Factors and Inanimate Explanations

Optical Effects

Before looking for unusual animate causes for the sighting record, our observations allow comments upon :some suggested alternatives. Logs, boats and boat wakes, windrows, otters, swimming deer, and ducks are all documented as producing Monster sightings (Binns, 1983: 165-200). These phenomena are more noticeable in calm weather, when even ducks can generate wakes apparently out of all proportion to their size. On a vast sheet of featureless water no accurate assessment can be made of size or speed for an unfamiliar object, since there is no visual clue to range. Mackal's (1976) analysis rejects all but 258 out of 3,000 sightings.

Physical effects can further distort perceptions. The temperature regime is fundamental to mirage effects (Figure 23a, photo 9K) noted by the Bathymetrical Survey (Murray and Pullar, 1908a and 1908b), and the relevance of this to lake monsters is discussed by Lehn (1979). It was the recognition of a mirage illusion, which led witness Alex Campbell to the original withdrawal of the archetypal plesiosaur sighting (Gould, 1934: 100-113). This sighting has been more influential than any other in supporting the Jurassic hypothesis of monster lore.

Professor Lehn described optical distortions affecting observations of familiar objects, such as branches, through direct non‑uniform thermal gradients in the air overlying cold lakes. The most usual effect is to extend the image vertically, but it may also be compressed, appear to move sinuously and may finally disappear without a ripple. Optical distortions occur in the calm weather associated with Monster sightings, since lake temperatures can then more readily influence air temperature in the lower strata. The most pronounced distortions occur when the observer is close to the water level. It is suggested that Loch Ness water temperatures will be significantly lower than the air temperatures for the first half of the year, thus guaranteeing strong gradients. This is actually an oversimplification.

For the first quarter of the year (until March-April), water temperatures are actually above the mean air temperature, and the Bathymetrical Survey describes mirages as a winter and spring phenomenon, attributable to warming of the lower layer of air (Murray and Pullar, 1908b). The consequent temperature inversion, although formed by an opposite process, still has the effect of distorting images vertically.

Fixed station records from 1984 (Figure 23b, 13K) show the moderating influence of the loch upon air temperatures, when compared to the maximum, minimum and 09.00 hrs readings from St. Benedict's Abbey weather station, situated on the loch shore 8.6m above the water level. It will be seen that, even in summer, the air temperature falls below water temperature at night. By dawn an inversion will result, giving rise to 'desert' type mirage effects. By mid‑morning a direct gradient will become established and intensify during the afternoon.

This can cause distant objects to appear  elongated vertically. During the transition between the two conditions, optical effects will be particularly complex. In general, therefore, gradients are likely to be less pronounced than those described by Professor Lehn for frozen lakes, but more complex, giving rise to opposite conditions for distortions in the course of a single day.

Mackal was clearly already dissatisfied with sightings of very long necks, and his analysis refers to the "tail, head‑neck". It would seem, however, that the majority of observers have not been influenced to overstate height. The median height for the 258 observations considered was 0.6m (Mackal, 1976: 344)

Submerged Logs

Craig (1982) has proposed that pine logs lying on the loch bed may generate sufficient gas not only to bring them to the surface, but also to propel them before they sink again. Similarly there have been suggestions of mats of decaying vegetation (Burton, 1961).

It can be stated immediately that hours of television observation of the loch floor in deepwater have revealed no more than occasional twigs projecting from the fine silt. If logs are present here, they are a rarity. Intact leaves find their way into the sediment, but at a temperature of 5‑6 oC decomposition is slow. No sign of gas bubbles can be provoked by probing the sediment in front of the camera and no gas has been observed in cores or other mud samples brought rapidly to the surface. Loch Ness should not be visualized as a stagnant pond.

Two locations, however, have been noted where logs are to be observed in quantity: off Dores (Figure 24a, photos 7K), where they are presumably driven by the prevailing wind, and in Urquhart Bay (Figure 24b, photos 12K) where in addition they have been brought down by rivers (Figure 24c, map 7K). These logs are to be found particularly in the shallower water to 10m, and therefore above the summer thermocline, but no sign of gas within them has been detected by diving. By contrast, the leaf litter off the River Coiltie and to a lesser extent in other parts of the bay, does emit gas in considerable quantity during the summer (Figure 24d, 9K). Off Fort Augustus, gas has been detected rising over a wide area. One localised source lay as deep as 100m. We have yet to observe vegetation mats on the surface. Submerged logs, however, even without gas propulsion, may have something to answer for during underwater photography in the seventies.

Gothic Revision

During Operation Deepscan, Osprey low light level underwater television (UW/TV) cameras were mounted aboard one of the cruisers to examine objects of interest on the loch bed. Nine objects were located by the sweeps and fixed by Decca. Anchoring the UW/TV cruiser above loch bed contacts 200m deep, did not prove possible in the time available and these await inspection by remote operated submersible.

The vessel therefore operated in shallow water to examine objects known to be present, including the wreck of a late‑nineteenth century sailing vessel in Urquhart Bay. This was the area in which controversial underwater photographs were obtained by the Academy of Applied Science in 1975 (Rines et al., 1976). Six photographs were produced, interspersed with pictures of the underside of the boat from which the 1.2 minute time lapse camera was suspended. The camera was believed to be 40ft (12.19m) beneath the boat, moored in 80ft (24.38m) of water.

Initial reaction to these photographs was that they showed the loch bed and inanimate objects (Meredith, 1977: 6-11). More sophisticated interpretations followed on the basis that the camera was too far from the loch bed to have photographed objects lying there. Furthermore, two calibration shots of fine sediment differed from the objects photographed. Upward pictures of the boat, were interpreted as evidence of agitation of the camera by possible contact with the subject on six occasions, spread over a period of 19 hours five minutes.

Subsequently, observations made by expedition participants (Dinsdale, pers. comm.; and R. Raynor, pers. comm.) have suggested that the mooring was such as to allow the boat to swing inshore sufficiently for the camera to touch the loch bed.

Figure 25a (33K) constructs the implications of the above observations and shows the probability of the camera grounding inshore. Echo charts (Figure 25b 10K) show the degree of variation in depths recorded from our vessel moored in this position and indicate objects on the bottom. Diving inspection by Mr. R. Raynor using an Osprey T.V.P. (underwater television camera capable of taking still photographs through the lens) was to reveal a number of logs in the area, some of which are shown (Figure 25c, 8K). One in particular, allowing for twelve years of decay, bears considerable resemblance to the 'gargoyle head' photograph of 1975. Silt is also present in coarser particles than deeper down (where the original calibration pictures appear to have been taken) and there is evidence of silt particles in the 1975 pictures.

Finally, the upward pictures of the boat can be explained by the camera frame rolling or resting on the loch bed. After the 'gargoyle head' picture, at least three consecutive frames showed the surface; a total of 3.6 minutes, far better accounted for by the camera lying on the bottom than by physical assault: a pendulum motion is precluded in water.

Peaty water, combined with narrow camera angle and small (16mm) format, were bound to render interpretations difficult. Recognizing these ambiguities, the naming of the Loch Ness Monster as Nessiteras rhombopteryx (Scott and Rines, 1975) was based upon wider evidence and prompted by concern for conservation.

Floating Logs

Holiday (1968: 39) described a sighting (in August 1963) which might have come into this category had the object not proceeded against the wind. It is recorded that on the evening preceding the sighting, a strong S.W. wind was blowing. Next morning the loch was calm, after which the wind reverted to S.W. Such conditions could have generated a seiche. Figure 6b, showing currents and in particular the record of physical events following a surge (Figure 11d), makes it clear that water currents may sometimes be in opposition to the wind during the summer stratification. This will be most pronounced in late summer as gradients reach a maximum and autumn gales generate the most powerful seiches. It is also the time when logs and branches are washed down by rivers. After storms, lines of logs may be observed, drawn into the confluences of Langmuir circulations (linear streaks of foam). Indeed in Figure 8, showing tilting of the isotherms by Coriolis forces, with currents in opposite motion, it can be seen that colder water can break surface to the left of the advancing surface layer and move in an opposite direction. Most students of the subject will be aware of Adomnan's account of St. Columba's encounter with a water beast in the River Ness. Thorpe (1988) has pointed to another story of the saint sailing against the wind and suggests the above effects as an explanation.

No particular correlation with sighting reports will be attempted here, but it would be as well to place on record that in Loch Ness, where physical effects are particularly significant, logs are washed in at a time when they may well be seen to move upwind. In strong winds they will be disposed in straight lines associated with foam. They may even be capable of changing direction.

In considering alternative explanations for the sightings record, it is noticeable that they actually point to accuracy of observation and vindication of quite bizarre experiences. It would seem difficult on this basis, to dismiss close‑range observations by local people, who simply describe something powerful in the loch.


Previous Records

Eye‑witnesses may see things they do not understand. However, many unfamiliar observations can be made at Loch Ness, and here of all places it is likely that controversial interpretations will be placed upon them. The same is true of other forms of observation, including sonar. The difference is that some experimental analysis can be applied to sonar evidence, since it seems repeatable (Mackal, 1976: 123). Furthermore, as in surface sighting reports, it is now possible to recognize different categories of sonar contact. It is important to recognize however, that a connection has yet to be demonstrated between underwater data and what may be seen on the surface.

Figure 26 (30K) summarizes sonar contacts of interest gained in the sixties and seventies. It will be seen that all results come from sonars capable of being directed horizontally, thus greatly increasing searching power in mobile modes and range of coverage when used on fixed stations.

With regard to contacts of apparently very great dimensional extent, attention is drawn to some difficulties arising in the interpretation of results from fixed station work, particularly in Urquhart Bay. The Birmingham team, after conducting further work, were to emphasize the refractive effects (exactly similar to mirages) of changing thermal gradients upon ray paths at ranges beyond 200m (Tucker and Creasey, 1970). In this connection, Mortimer (1973) proposed an examination of the reflective properties of internal waves. Our observations have shown the extent of these reflections (Figure 11a). Whether or not the actual wave fronts caused reflections in this case, thermal effects in Urquhart Bay will be particularly complex owing to seiche fronts progressively bending into the bay as they pass. This could be sufficient to cause horizontal refractions in addition to vertical ones, resulting in portions of the loch bed giving apparently mobile returns from midwater. One such echo, which remains stationary however, is thought to originate from a side lobe.

Thermal and turbulent effects will be further complicated by river outflow. In summer the river water can be warmer than the loch, but by autumn the opposite is the case (Figure 27a, graph 9K and 27b, echo chart 12K). The situation is worsened by irregular loch bed contours, existing and partially sunken moorings, considerable boat traffic and to some extent by rising gas. It cannot be overemphasized, however, that Urquhart Bay is not typical of Loch Ness as a whole.

A particular echo characteristic (again in Urquhart Bay) reported by the Academy of Applied Science in 1972 and 1976 consisted of sinuous multitraces (Klein and Finkelstein, 1976). On the later occasion, it was noted that contacts with this signature resulted from rowing boat turbulence (Meredith, 1977: 128‑130). During the latter part of the 1972 trace (accompanying the well known 'flipper' pictures) a rowing boat was present ferrying between the vessels engaged.

Examination of the trace shows the close‑in returns (probably side lobe echoes) fluctuating in range and strength, implying that the transducer was swinging in midwater rather than resting on the loch bed as illustrations suggest. Some of the echoes could therefore result from elements of topography. Lastly, the sonar was theoretically aimed at another moored vessel, beneath which the camera was sited. This vessel is known to have been moored by chain and should this have entered the beam, it would have registered extremely strongly. Perhaps therefore, parts of the trace consist of this chain. The Academy recorded other traces however, without 'turbulent' signatures, both on fixed stations and during mobile tows. Figure 31 (16K) shows some effects of boat wakes on a side scan sonar record.

This leads to consideration of discrete sonar contacts reported deep in the main water column, as recorded by Love (1970). The biological questions raised by contacts in this area are recognized since, if animate, they would lie deeper than expected for predation on scattering layer fish and shallower than might be expected for excursions by benthic creatures. Perplexing observations establish however, that some of the loch's profundal insect larvae, Sergentia sp., occasionally migrate into the water column in a pre‑pupal stage and are caught within the top 30m of water.

The Project has addressed this question since 1981, initially using the methods of R. Love and the 'criteria for anomaly' in terms of strength, depth and movement, proposed by Baker and Westwood (1960).

Deep Water Contacts

In 1982, from the beginning of May to the end of August, two scanning sonars were operated for over 1,500 hours in day and night patrols, mainly in the deep northern basin. The working method is shown in Figure 28a (10K). Twelve contacts of interest were secured by the Furuno 106A (Figure 28b, traces 33K and Figure 28c, table 12K) and a further twenty‑eight by the Simrad SY (Figure 28d charts 64K and Figure 28e, table 22K). They appeared to be discrete single target echoes and no other type of contact was detected which could not be dismissed as side echoes. Accurate navigational positioning was not possible but the contacts appeared widely spread. On some days none would be detected and then two or three would result from the next patrol. Although more contacts were gained at night with the Simrad SY, this could be biased in that surface conditions were then more favourable. Most contacts occurred below the scattering layer but sometimes strong ones appeared within it. The search depth was limited to 160m by side lobe echoes from the loch bed.


Clearly, contacts were being sought with a strength greater than that of the known fish, although perhaps in the expectations of the 1980s, not very much stronger. The sonars are designed to detect large fish shoals but performed quite well on single targets, although only through a small proportion of the stated beam angle to the half power point. The sensitivity of the Furuno 106A was reduced to eliminate practically all fish above the thermocline, which as we have shown, are present in some abundance over the whole loch surface. A vertical calibration using a 20.36 cm diameter air-filled spherical float was conducted and recorded for comparisons. The target strength of a solid sphere is given by:

T.S. = 10 log D2/16
(where D is the diameter of the sphere in metres).

The calibration sphere would therefore have a strength of -6dB. However, since the sphere was not solid, resonance could produce considerable inaccuracies, in general leading to a greater strength. The actual target strength of the sphere, when subsequently (1988) measured in situ, with a freshwater calibrated Simrad ES400 (38kHz) split-beam system, was -23dB. A fairly conservative comparison can therefore be made between the target strength of the sphere and that of fish, using the formula derived by Love (1971):

T.S. = 19.1 log L -0.9 log F-62
(where L is fish length in cm and F is the frequency).

For the 150kHz sonar a -26dB target would be roughly equivalent to a fish one metre in length. This is towards the upper limit for salmon expected in Loch Ness.

The largest salmon reported to have been caught in Scotland (by netting), and for which records are available, was taken in 1891 (Mills, 1980: 4). The length was 1.35m and the weight 31.75 kg. The Loch Ness record is believed to be 23.58 kg (Witchell, 1974: 10). Figure 28c (12K) shows several contacts to be 3dB-9dB in excess of the -26dB calibration. Much depends upon whether a fish possesses a swim bladder, since this accounts for over 50% of the echo strength and also upon aspect to the beam.

With the Simrad SY, the paper recorder could not record strength and at acceptable sensitivities, the calibration sphere showed little reduction in strength. Our policy was not to reduce sensitivity beyond the point where side echoes were readily identifiable, in case a proportion of one should 'break through' the threshold and give a misleading impression. We also wished to examine weaker contacts, which could still be of interest. Accordingly the 'calibration' was carried out with a 30cm trout, which registered weakly to 50m. The traces (Figure 28d, 64K), therefore include a weaker range of strengths, some of which could be from salmon or ferox trout. We would emphasize that salmon would not normally be expected to be present in midwater and are usually fished for in the littoral zone. During the 1988 acoustic stock assessment, the maximum fish target strengths obtained were -36dB at 49kHz, suggesting that fish of over 30cm are uncommon.

Some of the Simrad targets do appear strong and obviously all represent infrequent occurrences, but they also serve to demonstrate a 'grey area' between the larger known fish and anything larger still.

A last reservation concerns the nature of time-varied gain function and scanning sonar signal processing, which may tend to emphasize targets at the expense of background noise. Further work must include more precise methods of recording target strength. The current proposal is to use the Simrad ES400, which uses a split‑beam principle and accurate T.V.G. to determine target strength.


Echo‑sounding establishes that the fish of the open water are generally confined to the first 30m of water. Contacts beneath this depth (about 50m range allowing for standard tilt) were tracked for as long as possible. Figure 29a (27K) shows the majority of strong contacts in excess of 50m.

We consider this to be the most interesting feature of the results. Ecologically, there seems to be no reason why creatures in the open water of Loch Ness should not be large, but if that is what the contacts represent, the depth is sometimes surprising.

Bearing in mind the difficulties associated with horizontal beams, it was hoped that the echo‑sounder profiles of 1983 (see map in Figure 1a, 8K), despite their low search potential, might record the characteristic deepwater contacts. At least the observation of fish might establish a context. Although strength determination is difficult, it would appear that no contacts of the greater strengths were acquired in 252 standard profiles, totalling 403.2 km. The rarity of moderate strength contacts deeper than 40m in summer, is shown in Figure 29b (16K). Situations when fish may be observed deeper than usual are  shown in Figure 29c (21K). For example, in May 1987 the loch showed a temperature variation of only 6.3 C -6.8C to a depth of 60m, and fish were detected to at least 50m. In October 1986 contacts were made between 80m and 120m at the southern end of the loch. Although no temperature profile is available, previous records suggest that this could be in response to a lowering of the thermocline by seiche movements. There is some evidence of a thermocline at 60‑70m. Similar observations have been made in previous years. It seems difficult to shed light upon the nature of deepwater contacts during the intervening period, when our observations suggest more predictable and shallower distributions. An exceptional sequence of deepwater contacts is shown in Figure 29d (33K). Occasional fish were noted at depth during the fixed station work of 1984, but the range was limited to 60 metres. It has been suggested that kelts swim deep (Baker and Westwood, 1960), and this may be relevant to spring observations.

Another possibility occurring to us, is that autumn contacts could be caused by logs and branches brought in by the rivers, although the sunken concentrations at the leeward end of the loch suggest that they generally float long enough to reach there. We have seen very little evidence of branches on the deep sediments. However, if sinking slowly, logs could be carried considerable distances by seiche currents.


It is known that fish do not in general make rapid changes of depth and this has been considered significant in assessments of previous results (Braithwaite, 1968). We were not equipped in 1982 to record boat movements accurately and any assessments made in Figures 28c (12K) and 28e (22K) are restricted to vertical estimates of target depth when gained and lost. Margins of error are impossible to quantify, since the effective beam width will vary with the strength of the target and the short tracking times achieved render estimates tentative.

Although echo‑sounding shows very ordered vertical movements of the fish population, it must be understood that the trout, charr and eels all possess 'open swimbladders' and that rapid movements are not impossible. Occasional records from the fixed station suggest quite considerable vertical movements from time to time (Figure 20d, chart 42K).

In recognition of the difficulties of judging speed from a moving platform, a raft was four‑point moored over 190m of water towards the southern end of the loch in 1984 (see map in Figure 1a, 8K). From 1st July to 24th August the Furuno 106A was operated continuously or every 20mins, to search the midwater around the raft to a range of 240m and a depth of 160m. The fixed position permitted accurate tracking and the elimination of possible side echoes. Many moderate strength contacts (106) were recorded to depths of approximately 40m but not of the strengths noted in 1982. It must be said however, that considerable equipment problems were experienced, particularly with the recording unit and some interesting reports have had to be disregarded. Anchor warps obscured and confused parts of the sweeps. Moderate strength contacts, could now be considered with confidence to be real single objects and indeed to be moving. In future work it would be important to judge movement in relation to water currents but it should be noted that just as sinking inanimate objects, such as logs, may be transported by seiche currents, so may animate ones such as fish (Figures 11a and 20c, 27K). Having considered the contacts in relation to strength, depth and movement, some specific alternative possibilities should be explored.

Fish Shoals

In shallow water, Trout have been observed to shoal on the approach of a diver or television camera. Fish concentrate inshore, within the scattering layer and in autumn loose shoals are to be found at the near surface (Figure 30, 22K). None has been observed in deep water. Shoals often exhibit 'tails' on echo‑sounder records, due to inter‑reflections between the fish returning over an extended period. Only one of our contacts showed any vertical extent on the record.

Boat Wakes

One of our traces, gained on shallow tilt, exhibited disproportionate strength and had multitrace characteristics. Inspection of the log book showed that the contact lay in the direction of a boat passing close by. The trace was therefore dismissed (Figure 31, 16K).

Thermal Effects

The discrete nature of the contacts would suggest that they are not direct reflections from shear instabilities. Refractions however, are quite likely to occur as the summer progresses, although minimized by the relatively short ranges used. Downward refractions would cause contacts to appear progressively shallower with increasing range. Measurements of temperature, show the loch to be almost isothermal from winter until May. Thereafter, variations in depth and degree of stratification with time and place make predictions of long ray paths impossible.

Side Echoes

These are the most difficult class of echoes to assess, because of the constant proximity of the steep rocky walls. Echoes acquired by echo‑sounder side lobesare shown in Figure 32a (18K). With scanning sonar it is inevitable that the horizontal beams and side lobes must sooner or later be reflected, to return as 'wrap around' echoes. These are a constant and generally recognizable feature of the traces and appear as long vertical stripes. The short 'single target' echoes appear distinct from these. It is conceivable however, that localized highly reflective rock faces at particular angles could give rise to this form of echo.

It will be noticed that some of the trace paths, parallel the line of obvious side echoes as the vessel moves towards the shoreline. Other examples however, show range changes opposite to the vessel's motion relative to the side walls (Figure 32b, 13K). An experiment was mounted in 1983 whereby the range was doubled during a contact, thus halving the pulse repetition frequency. This, in the case of a wrap around echo, should result in an apparent range change. No such changes occurred. The scanning sonar beams depressed beyond 60 degrees recorded a 'normal' second time around echo from the loch bed but this should be easily recognized.

Tethered Debris

A possibility which could not be dismissed, was that some echoes resulted from debris in some way tethered to the loch bed. Fishing gear jettisoned from trawlers on passage through the Caledonian canal was a possibility, or even lost equipment from previous expeditions. This possibility was explored during the 'Operation Deepscan' experiments, described in the following supplement.


Events turned full circle with the Operation Deepscan series of 1986 and 1987 (Figure 33a, photo 10K), which were larger scale repetitions of Dr. Baker's (1962) Cambridge Expedition. They consisted of 'sonar curtain' sweeps, conducted over the deep basins by formations of echo‑sounder equipped vessels. The objectives of Operation Deepscan were:

1) To search the deepwater basins for contacts of strength; to fix their positions and to revisit the sites in order to establish whether such contacts were tethered debris.

2) To chart objects of more general interest lying on the loch bed. If feasible, these would be investigated by underwater television or subsequently examined by remote-operated submersible.

3) To continue the general scientific programme with work in the profundal zone and observation of the autumn fish distribution with regard to thermal structure.

In the interests of continuity, results from 2 and 3 above have already been incorporated into the relevant sections of this paper.

Operation Deepscan set out to overcome an impasse which had arisen, in that contacts of strength could be obtained by using the search and tracking power of scanning sonars during mobile patrols but the results were subject to the problems of horizontal sound propagation. Fixed station work lacked searching power, as to a great extent did repeated echo‑sounding profiles, since beam coverage is limited to the area beneath the vessel.

Echo‑sounders however, yield the least ambiguous results, since beams can be kept reasonably clear of the side walls and penetrate thermal gradients perpendicularly, thus minimizing refractions. Echo-sounders also fix positions simply and any lack of individual searching power could be compensated by the use of so many.

With the support of Lowrance Electronics Inc., vessels of the Caley Cruiser hire fleet were equipped with X-16 sounders working on the 50kHz frequency option with 30 degree transducers (Figure 33b, 8K). Tests carried out in October 1986 were designed to suppress mutual interference generated by the sounders. The X-16 includes a discrimination feature, which awaits verification from a succession of pulses before printing a given echo. In order to aid this facility, the ranges around which pulse repetition frequency changes, were staggered in sequence along the line of vessels. Considerable success was achieved, although at the expense of sensitivity. Transmission interference can either be suppressed or is easily recognizable. What is interpreted as 'returning echo' interference (returns from pulses initiated by other sounders), cannot be so readily suppressed, because of the longer length. Figure 33c (17K), shows the effects of operating sounders in proximity. No contacts of interest were obtained during the 1986 tests and operations were limited by high winds.

A fully developed experiment took place between 4th and 14th October 1987 (Figure 33d, photo 7K). From 4th to 8th October, sweeps were conducted in the northern basin for training purposes and to optimise equipment settings. No contacts of interest resulted from these.

Figure 33e (3K) shows the deployment of a fleet used in two full sweeps of the deep basins on 9th and 10th October. Nineteen vessels, operating X-16 sounders as described above, formed a line abreast at approximately 45m spacings. Contacts gained below 30m or on the loch bed were notified by radio to a flagship and a surface marker dropped. Follow‑up elements, with sonar engineers aboard, then moved in to attempt to hold contact pending the arrival of New Atlantis. This vessel was equipped with a Simrad EQ100 to determine strength, a Simrad SY scanning sonar for possible tracking, and a MK53 Decca Navigator and Racal Decca C.V.P. 3500 plotting system to record positions.

Figure 33f (5K) shows the coverage of the sweeps. Sensitivity reduction resulted in some known moderate‑strength targets not being recorded. On the north to south sweep of 9th October, three contacts of interest were reported (Figure 33g, 17K). On no occasion was the follow‑up vessel able to regain contact in order to make strength assessments. Contact 1 (78m) may be considered of moderate strength. Contact 2 (171m) is strong, but returning echo interference cannot be ruled out. Contact 3 is more interesting, in that it is obviously strong and its depth of approximately 174m is exceptional.

Contact 3 was gained by one of the follow‑up vessels just behind the line (the line had failed to record the contact) to the east of the northern basin opposite Urquhart Bay. As the vessel stopped and turned, the contact would appear to have crossed near the centre of the beam. Contact was not regained by New Atlantis but a Decca fix was taken. The following day's sweep gained no contacts and an extra line of five boats deployed onto the above Decca fix also failed to regain contact.

This is of particular interest, since at least two fixed targets were located in the course of the operation (see Figure 33h, 15K). Attention is drawn to the contact of 12th October, which was gained by a small flotilla over the western side wall, in an area not covered by the main sweeps. Although the follow-up was not possible until the evening, the contact was relocated without difficulty and so established to be fixed. Subsequently, in July 1988, fixed contacts recorded in the course of Operation Deepscan were relocated in collaboration with Simrad and investigated by the Sutec R.O.V. Sea Owl. Both jettisoned rope and a piece of instrumentation were in fact found. Tethered debris has now been proved to exist in Loch Ness but none has been found between Foyers and Urquhart Bay where contacts were recorded in 1982.

With regard to the interesting Contact 3, a slowly sinking log cannot be absolutely dismissed but failure to regain contact during the immediate search patterns argues against this. Another reservation must recognize the possibility of returning echo interference. It will be noted however, that the vessel concerned was stationed to the flank, astern of the sweep line and transmission interference has been eliminated from the trace. No similar trace has been found among the other echo charts, from both training and full sweeps, which together represent 3,651km of search.


In searching the water column for previously reported sonar contacts, scanning sonars have operated for 1,500 hours in mobile patrols and for over 1,000 hours on fixed stations. Echo‑sounder records have been obtained over a distance of 400km of standard profiles and over 4,000km (including 1986) in massed sweeps. Contacts of interest have been noted and a process of elimination conducted, similar to that applied to 'unpeeling' the scattering layers. We suggest forms of turbulence as an explanation for previous contacts of apparently great dimensional extent. It is interesting that some recognized causes of eyewitnesses' misidentification are common to sonar, which is sensitive to boat wakes and refractions equivalent to mirages, while even logs are still under consideration.

Shortcomings in the work result from operational difficulties. Mobile patrols with scanning sonar had good searching power, but results could be subject to ambiguities and movement could not be convincingly demonstrated. Mooring the station, in the interests of tracking precision, sacrificed search potential and the warps reduced effectiveness. Vertical echo soundings, so desirable to reduce ambiguities, also lacked coverage. Massed sounders bring their own problems of interference and associated reduction of sensitivity. Clearly, experiments such as Operation Deepscan are limited to a short duration; for example, only one limited night sweep was conducted.

Work has been largely confined to the deep basins and there remain areas where sonar methods are more difficult. It must also be said that if an unusual population contained a small number of particularly large individuals, and further, if they were not normally present in midwater, then we might not detect them. In the case of a single occasional migrant, detection would be virtually impossible.

Nevertheless, contacts of interest, in terms of strength (sometimes considerable), depth and possible movement, do occur. By establishing a background against which anomalies may be judged, it is recognized that overlaps sometimes exist in all three criteria, with the presence and behaviour of the known fish population. On the other hand, superficially pedestrian explanations, such as a record‑class salmon in the main water column, deep swimming fish shoals and midwater logs, can all be seen to represent anomalies in themselves.

Through sonar and underwater television the controversy has been approached indirectly, by examination of the environment. Even the apparently obscure consideration of temperature is seen to dominate not only the distribution and behaviour of the biomass but is also a recurring element in discussion of the controversy. Thermal factors can have extreme effects on observations, both above the waterline, such as mirages and the possibilities of objects moving upwind and also underwater, on sonar records, through turbulence and refraction.

The habitats offered by the loch have been defined and a framework established, bounded by the pelagic, littoral, side wall and profundal zones. The centre of the frame, consisting of the bulk of the water column, contains enigmas, which whether or not they may vindicate sighting reports, are worthy of resolution. In a wider sense, we are moving to fill the data vacuum, so long the battleground of speculation lying between protagonists in the Loch Ness controversy.



Underwater Photography  

Osprey S.I.T. Underwater Television Camera (O.E. 1323)
Resolution 7600 T.V. lines
Sensitivity 5 x 10-4 Lux
Lens 5.5mm f:1.5 (corrected lens port)
Focus Fixed 150mm to infinity
Angle of View 110 degrees diagonal (in water).

Osprey T.V.P. (O.E. 2300/36) Capable of taking still photographs through the same lens.
Electrical Characteristics As above
Lens 24mm f:2.5 (dome port correction)
Focus Variable 127mm to infinity
Angle of View 84 degrees diagonal in water
Photographic Camera 35mm format (250 shot cassette)
Surface Control Cyclops (O.E. 1210-1212)
Lamp 100w variable (O.E. 1130)
Reproduction in this paper by Northscene Video using Sony Videographic Printer U.P.-811

Echo Sounders
Simrad EY-M  
Frequency 70kHz
Beam Width 11 degrees (- 3 dB)
Pulse 0.6 m/sec
PRF 91 per min. at 120m range
TVG 40 log R

Simrad Skipper 603

Also with Kelvin-Hughes Side-scan Sonar
Frequency 50kHz
Beam Width 33 degrees (- 3 dB)
Pulse Variable
TVG Variable

Lowrance Mach 1

192kHz 8 & 20 degree Transducers
Lowrance Mach 2
50kHz 45degree Transducer

Lowrance X-16

Dual Frequency 192kHz & 50kHz - for
Operation Deepscan : 50kHz option, 30 degree

Scanning Sonars

Furuno F.H. 106A
Frequency 150kHz
Beam Width 6 degrees (-3dB)
Linked to F.C.V. colour display for range track and tape recorder.
1982 Fixed Settings  
Range 240m
Tilt Normally 30-40 degrees in direction of travel
Scanning Sector
120 degrees on automatic. Targets tracked manually
Gain 8
T.V.G. Level 3
T.V.G. Time 5

Simrad SY
Frequency 80kHz
Beam Width 10 degrees (-3dB)
Linked to AR 650 paper recorder. Time base 54sec/cm approx.
1982 Fixed Settings  
Range 250m
Tilt As above.
Gain 5 (Set on AR 650 paper recorder)
T.V.G. 3 + filter
Processing AGC

Temperature Probes
Single thermistor pHOX 62T (combined oxygen temperature probe)

Motor Cruisers "New Atlantis" available from Caley Cruisers of Inverness.
Research Vessel "Simson Echo" (Simrad demonstration vessel).
Motor Fishing Vessel "Ocean Bounty".
Remote Operated Vehicle Sutec Sea Owl

Additional Equipment used in Operation Deepscan
MK 53 Decca Navigator
Racal Decca Colour Video Plotter CVP 3500




Throughout the 1980's the Loch Ness and Morar Project, conducted volunteer expeditions to Loch Ness, using a range of relatively simple sonar equipment. Qualitative observations are presented through a general description of the environment. The elements contributing to acoustic 'scattering layers' are analysed and separated. The role of the temperature regime is emphasized and turbulence due to shear instability is suggested as a dominant cause of echoes. Initial observations explore the relationship between physical factors and the distribution of biomass.

1988  Loch Ness: Sonar and Underwater Television p195

The current neutral attitude to the Monster controversy is made clear and discussion is mainly against the accumulated background of physical and biological information. A particular study has been made of strong deepwater sonar contacts, reported by the Loch Ness Investigation Bureau of the 1960s. The presence of occasional contacts, which are exceptional in terms of strength and depth is established, while the extent to which they represent anomalies is discussed. Although these may not meet popular expectations and whatever their relationship to the controversy may be, they would seem to merit further enquiry.


The information presented in this paper resulted from the perseverance and discipline of the many individual volunteers who made up the field membership of the Loch Ness and Morar Project throughout the 1980's. The following organizations also provided contingents: St. Benedict's Abbey Combined Cadet Forces, the Sea Cadet Organization, the Venture Scout Movement, the Fort George Volunteers, the West Yorkshire Fire Services Sailing Club, the Royal Corps of Transport Sailing Club (42 Sqd.), the Drake Fellowship and the Dockland Scout Project.

The following companies were generous with the loan of equipment: Osprey Electronics, Simrad Albatross Ltd., Lowrance Electronics Inc., Tamtech Ltd., Chloride U.K. Ltd., Swiftech Ltd., Sutec U.K. Ltd. and Instrument Rentals U.K. Ltd.

Special thanks are due to Mr. and Mrs J. Hogan and Caley Cruisers Ltd. for the constant support they gave with elements of their hire fleet, particularly the New Atlantis sonar-equipped motor cruiser.

The scientific programme was undertaken in collaboration with the following organizations: the Ness District Salmon Fisheries Board and the Department of Zoology, Royal Holloway College. The British Ecological Society kindly provided financial support for work on pelagic fish.

Valuable support and advice was given by the following individuals: Dr. H.J.B. Birks (cores), Dr. A. Duncan (zooplankton), Dr. J. Evans (phytoplankton), Mr. R. Greer (Charr), Mr. J.D. Hamilton (sediments), Dr. T. Lindem (acoustic fish stock survey), Fr. Andrew McFillop (weather records), Dr. S.A. Thorpe (physical limnology), Mr. P. Wilkinson (fish), and Dr. B. Woodward (acoustics).

We also wish to thank the residents of Drumnadrochit, Fort Augustus, and Dores for all their goodwill and support, especially Mrs M.Gore, the Hon. J. Kirkwood, Mr. A. Menzies, Mr.G. Menzies, Mr. A. Harmsworth and Mr. R.A. Bremner.

1988 The Scottish Naturalist p196

General support was received from the Loch Ness Centre and the Highlands and Islands Development Board. Reproduction of videotape pictures are by North Scene Video. Photomicrographs are by Mr. C.J. Chesney. We are extremely grateful to Mrs Jane C. Shine for all the other illustrations and Deepscan photographs.


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Mr. Adrian J. Shine and Mr. David S. Martin,

Loch Ness and Morar Project, Loch Ness Centre,

DRUMNADROCHIT, Inverness‑shire IV63 6TU.

Copyright: May be used for private research only




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Scottish Naturalist and Loch Ness