9
The Loch and its Surrounds

‘Loch Lomond…the white pebbled shores on which
its gentle billows murmur, like a miniature ocean,
its rocky promontories rising from the deep water,
rich in wild flowers and ferns.’

The Highlands and Western Islands of Scotland
John MacCulloch (1824)

Loch Lomond has been under continuous study longer than any other large body of fresh water in Scotland. In 1938 the University of Glasgow initiated a course in freshwater biology, opening its first lochside field station at Rossdhu eight years later, and moving to the present site near Rowardennan in 1964. One of the fruits of this long-term investigation was the unravelling of the loch’s pyramid of energy, which has at its broad base countless millions of microscopic water plants or phytoplankton, progressing upwards by successive stages to comparatively small numbers of fish-eating birds and even fewer mammals. Much of the University Field Station’s research on Loch Lomond, the River Endrick and some of the smaller water bodies in the area is beyond the scope of the present work, but a number of relevant publications are included in the bibliography for further reading.

The underwater environment

The dual nature of Highland and Lowland Loch Lomond is shown clearly in the two portions’ differing response to heat and light from solar radiation. In the fjord-like northern basin (Fig. 9.1) the effect of heat radiation from the sun during the summer months brings about the seasonal phenomenon of thermal stratification. As the slowly warming surface water (the epilimnion) becomes less dense than the cold water below (the hypolimnion), from late spring to late autumn the two layers are effectively separated by an intermediate zone of rapidly lowering temperature known as the thermocline. This invisible barrier severely inhibits any exchange between the wind-circulating surface water above and the still, deep water below. First forming at about 15 m below the surface, where there is sufficient depth of water the thermocline slowly descends to about 30 m, reaching its maximum development by the end of the summer. With the onset of falling surface temperatures and frequent strong winds in late autumn, the stratification breaks down, with remixing of the upper and lower water layers. The separation of warm and cold water in the expansive southern basin during the summer tends to be very transitory. With minimum wind shelter from the much lower surrounding hills, together with the buildup of wave strength over greater distances, any layering that does develop in the relatively shallow water of the southern basin is unstable and readily overturned.

Fig. 9.1 The over-steepened sides to the northern half of the loch plunge to a depth greater than the North Sea.

Light from the sun dictates the potential depth of the euphotic zone; that is from the loch surface to the lowest level where daytime photosynthetic activity in the drifting phytoplankton is sufficient to sustain life during the hours of night-time darkness. Light penetration of the loch’s water depends not only on the intensity and duration of sunlight reaching its surface according to season and cloud cover – the latter having the greatest effect in the high rainfall mountainous region – but also on the amount of light absorbed by dissolved and suspended particle matter within the water itself. Light absorption by peat particles in the loch’s waters is at its highest in the northern basin, especially following a rapid runoff of surface water from the surrounding upland catchment area after a period of heavy rain. Overall, the lower limit of the euphotic zone in Loch Lomond varies between 6 and 9 m below the water surface. Within the euphotic zone lies the upper phytal zone, which is where sufficient light reaches the loch bed to permit the growth of rooted aquatic plants. Throughout Loch Lomond this zone rarely exceeds 4 m below the water surface. At mean loch level, water depth from zero to 4 m makes up only about 10 per cent of the total surface area of Loch Lomond, by far the largest proportion of these shallows in the southern and central basins. However, with the unstabilising effect of wave movement on the loch bed (Fig. 9.2), it is only in areas sheltered from the prevailing westerly winds that these well-lit waters in the phytal zone reach anything like their full potential for plant and animal life. Below the euphotic zone and the maximum depth of light penetration lies the profundal zone, where no plant growth is possible and only a few specialised deep water animals can exist.

Both plant and animal productivity also depend on the total amounts of mineral and organic nutrients fed into the loch by inflowing rivers and streams. Compared with the soft sedimentary rocks and fertile soils that make up the loch’s southern catchment, the hard and often peat-covered metamorphic rocks around the loch’s northern basin yield very little in the way of soluble minerals. This means that the waters in the Highland part of the loch are oligotrophic (poor in nutrients), whereas those in the Lowland portion are for the most part mesotrophic (moderately enriched with nutrients). Disparity between the upper and lower loch, originating from their differing geology and soil types, is further enhanced by mineral fertilizers used in agriculture and organic matter (silage effluent, treated sewage, etc.) discharging into the southern basin by natural drainage and waste-water drains from the more intensively farmed and densely populated Lowland region. Some watercourses entering along the loch’s southern margin carry sufficient mineral and organic material to create locally eutrophic conditions (rich in nutrients). This unusually wide range of nutrient loading and productivity in the same water body goes some way to explaining Loch Lomond’s exceptional diversity of plant and animal life.

Fig. 9.2 The unstabilising effect of wave movement on exposed shores prevents the establishment of many plants and animals.

Aquatic life of the loch and lochside edge

Beyond the limit of solar penetration, the profundal zone is a world of darkness and cold but stable temperatures. At these depths the accumulated fine silts and clays that make up the bed of the loch support a very limited fauna, comprising mainly of tube worms (Tubificidae), tiny pea-shell cockles (Lamellibranchiata) and the larvae of dancing (non-biting) midges (Chironomidae), all of which are dependent for food on organic debris ‘raining’ down from the euphotic zone above. The number of different profundal species is small, but amongst them are two which deserve individual mention. Arcteonais lomondi is a mud-burrowing worm that was new to science when first described from the northern basin of the loch; even now it is known elsewhere only in the deep waters of Loch Morar. The other is the bivalve mollusc Pisidium conventus, a surviving arctic relict from a considerably colder period in Britain’s past, which occurs right down to the deepest parts of the Loch Lomond trench.

In the euphotic zone above, by far the largest contribution to the aquatic food chain comes from the phytoplankton, the microscopic plant life that drifts suspended in the upper waters of the loch. None of the more abundant species of phytoplankton are restricted to any one part of the loch, although population densities vary considerably between the north and south basins. As would be expected in a situation where there are significant differences in nutrient concentrations, the total biomass of these plants is far greater in the mesotrophic and locally eutrophic waters of the southern basin than in the oligotrophic waters further north. During the warm and lengthening daylight hours of spring and early summer, there may be up to 65,000 individuals to every litre of water before, in the northern basin at least, the barrier of thermal stratification deprives them of stored nutrients stirred up from the deeper waters below. Under favourable conditions of prolonged sunshine and warmth the phytoplankton in the southern basin multiply rapidly to well in excess of the above figures, creating an algal ‘bloom’ visible to the eye. The filamentous green alga Oedogonium in the eutrophic waters around the mouth of the River Endrick can accumulate to such an extent that it has a detrimental smothering effect on the rich community of ephemeral mud plants concentrated in the more sheltered parts of this corner of the loch. In algal bloom years, another readily noticed is the blue-green alga Coelosphaerium, in particular where it collects by wind drift along the shore, coating the surface of the water with what resembles green paint. These algal blooms, together with the recent appearance and rapid spread in the loch of the naturalised Canadian pondweed (Elodea canadensis), which in turn is steadily being replaced by another North American species, Nuttall’s pondweed (E. nuttallii), points to increased nutrient loading of the southern basin, despite Loch Lomond’s resilience to water pollution through its large size. An expansion of the breeding population of mute swans (Cygnus olor) in the southern half of the loch, which has built up from a fairly static three to five nesting pairs in the early 1980s to 16 nesting pairs by 1996, is undoubtedly a response to the additional food resource now available from the two foreign pondweeds.

The next tier in the food chain is made up of the zooplankton, the smallest of aquatic animal life, including microscopic rotifers (Rotifera) and small crustaceans such as waterfleas (Daphnia) which are just visible to the naked eye. These feed on the phytoplankton, or in some cases, on other zooplankton. Occurring in much lower numbers than the phytoplankton, the populations of both herbivorous and carnivorous zooplankton fluctuate as the loch’s seasonal phytoplankton crop waxes and wanes.

Included within the euphotic zone is the littoral zone, a term used here in a topographical sense to describe the loch bed from the water’s edge to the lowest limit of light penetration. Although well represented in the southern half of the loch, the littoral zone is restricted to a very narrow band in the steep-sided northern portion. At a casual glance there appears to be little in the way of plant growth at the water’s edge around Loch Lomond’s predominantly stony fringe, a hostile environment subject to scouring waves at high water followed by desiccation when the loch level is low. Closer examination reveals a patchy growth of mosses and liverworts, amongst them Cinclidotus fontinaloides, Grimmia retracta, Rhacomitrium aquaticum and Marsupella emarginata var. aquatica, all typical of periodically inundated lakeside rocks. Even less obvious to the unpractised eye is an assemblage of lacustrine lichens that appear as a dark band on the exposed rocks when the water level drops in summer (Fig. 9.3). Several uncommon or rare species – Dermatocarpon meiophyllizum, Placynthium flabellosum, P. pannariellum, Porocyphus kenmorensis and Verrucaria praetermissa – are known to be represented. With its varied underlying geology, Loch Lomond could well prove nationally important for this little-studied community of specialised lichens, their water-line habitat evolved over millennia having been lost in a number of other large lochs in Scotland through substantial rises in water levels for the generation of hydro-electric power.

Fig. 9.3 As the loch level falls, a dark band of lacustrine lichens is exposed on Torrinch.

Throughout the greater part of the loch, the underwater macrophyte flora is fairly constant in its succession as the littoral zone falls away from the water’s edge. Most characteristic of wave-cut terraces of cobbles of loose stones intermixed with coarse sand is a patchy lawn of shoreweed (Littorella uniflora) dotted, except in the enriched waters of the southern basin, with the rosettes of water lobelia (Lobelia dortmanna). This part of the loch bed above the low water mark can be exposed for many weeks at a time during the driest summers. As the water deepens, the loch bed slowly changes to ever finer particled sands, silts and muds. With depth the shoreweed is replaced by common quillwort, often associated with a sparse growth of alternate-flowered water-milfoil (Myriophyllum alterniflorum) and a stonewort, Nitella flexilis, one of a group of large green algae that superficially resemble higher flowering plants. At the deepest point of light penetration only the quillwort persists. Because of its submerged mode of life, the presence of this aquatic relative of the terrestrial ferns is only obvious through its naturally shed ‘quills’ amongst the gathered wrack along the shore. Away from the mainland and island shores, much the same community of littoral zone plants can be found on some of the loch’s reefs and shoals. The cobbled bed of Rossdhu Bank, to the southwest of Inchmoan, exhibits at low water a fine mosaic of quillwort and the aquatic moss Fontinalis antipyretica growing between the tightly packed stones. At a deeper level, the McDougal Bank between Inchmurrin and the west mainland shore has sufficient accumulated silty mud and organic matter to support a lush tangle of alternate-flowered water-milfoil and perfoliate pondweed (Potamogeton perfoliatus), both growing exceptionally tall as they reach upwards towards the light.

Even with the enrichment of the waters around the southeast corner of Loch Lomond, the diversity of littoral plants present on the gently shelving Endrick Bank does not substantially increase because of the churning action by frequent wind-driven waves on this very exposed site. Where the sandy substrate is sufficiently compact, however, shoreweed and needle spike-rush (Eleocharis acicularis) carpet the loch bed between the high and low water marks (Fig. 9.4). Shielded from the force of the waves by the sand bar encircling the river mouth, the composition of the loch’s aquatic flora undergoes a noticeable change. Weak growing mud plants, which barely have a toehold on the exposed western side of the bar, greatly increase in number; and given further protection behind Crom Mhin Point, emergent and floating-leaved species appear for the first time. Within the shelter of Crom Mhin Bay, a mixed bed of amphibious bistort (Persicaria amphibia) and yellow water-lily (Nuphar lutea) covers a large area of the water surface, with uncommon species such as lesser water-plantain (Baldellia ranunculoides), small water-pepper (Persicaria minor) and awlwort (Subularia aquatica) found sparingly around the cattle-trampled muddy edge. It is only as the water level falls that a rich assemblage of small ephemeral plants is revealed, including water-purslane (Lythrum portula), and the nationally scarce six-stamened waterwort (Elatine hexandra) and eight-stamened waterwort (E. hydropiper), exposure stimulating them into flowering.

Fig. 9.4 Shoreweed carpets the exposed sandy bed of the loch along the edge of the Ring Point.

To see the best selection of aquatic plants around the loch’s shoreline requires a visit to the Balmaha Marshes (Plate 1), once a lochside meadow worked for marsh hay by the cotters (sub-tenants) of nearby Auchengyle. Since broken up by storm-force waves into a patchwork of small islands and pools, the former meadow exhibits a colourful profusion of aquatic and marsh plants, including purple loosestrife (Lythrum salicaria), yellow loosestrife (Lysimachia vulgaris), tufted loosestrife (L. thyrsiflora) (see p. 130) and bogbean (Menyanthes trifoliata). Unfortunately, some of this diversity seems destined to be lost, as a vigorous growth of bulrush (Schoenoplectus lacustris) expands year by year, possibly in response to the water enrichment now experienced in the southeast corner of the loch. The occurrence in the Balmaha Marshes of the nationally rare Loch Lomond dock (Rumex aquaticus) (see p. 129) is of particular note, for as its English name suggests, in Britain this northern water docken is found only on Loch Lomondside. Despite attracting attention to itself by occasionally growing up to 2 m in height, the Loch Lomond dock was not added to the British flora until 1935, when it was first found by Glasgow botanist R. MacKechnie. Also present is the slender rush (Juncus filiformis), here at one of its few stations outwith the English Lake District, growing sparingly in alluvial grassland just above the water’s edge. With the raising of the loch level for the Loch Lomond Water Scheme, however, this uncommon species is in danger of being lost through accelerated shore erosion. Just north of this productive spot lies Balmaha Bay, its water surface once described as ‘powdered white’ with the flowers of water crowfoot (Ranunculus aquatilis). The propeller blades of countless recreational boats have long since taken their toll on this idyllic scene, but in summer the botanist should still have little trouble identifying up to three dozen other aquatic and marsh species around the bay and boatyard grounds.

The water’s edge vegetation of stony shores also benefits when sheltered from wave action, this no more evident than on Clairinsh, which is partially shielded by the bulk of neighbouring Inchcailloch. Periodically inundated and enriched with silt, Clairinsh’s northwestern shore (Fig. 9.5) supports a well-developed tall herb community, made up of common bistort (Persicaria bistorta), hemlock water-dropwort (Oenanthe crocata), angelica (Angelica sylvestris) and a fine show of globeflower (Trollius europaeus). Other flowering plants found around the southern loch that appear dependent on nutrient replenishment of the shore-zone by flood or spray-carried silt include wood goldilocks (Ranunculus auricomus), columbine (Aquilegia vulgaris), lesser skullcap (Scutellaria minor) and dog violet (Viola canina), all four rather scarce in the west of Scotland. As an occasional inhabitant of the Loch Lomond shore-zone, the royal fern (Osmunda regalis) (Plate 2) still occurs in a few places, despite rapacious fern dealers and collectors having brought this fine species to the verge of extinction. With the over-steepened gradient to the northern half of the loch, the periodically inundated pebble and boulder shore forms only a narrow, nutrient-poor strip between the open water and the woodland edge. Given some protection from the erosive waves, however, a tussocky flora of bog-myrtle (Myrica gale), purple moor-grass (Molinia caerulea) and common sedge (Carex nigra) may be found. Where the stones on the lochside shore are well compacted is the most likely spot to come across the very localised small-fruited yellow sedge (Carex serotina). The extremely rare creeping spearwort (Ranunculus reptans) may have once occurred on Loch Lomond’s shores, the presence of the hybrid ((R. x levenensis)) between it and the closely related but widespread lesser spearwort (R. flammula) having recently been confirmed.

Fig. 9.5 Globeflower and other wetland plants thrive in the periodically inundated stony shore-zone of Clairinsh.

Completing the range of mainland and island lochside habitats are the headlands or points, which by their very existence are almost certain to be the hardest rocks in the vicinity. At the end of July some of these rocky headlands can be exceptionally colourful, with goldenrod (Solidago virgaurea), common knapweed (Centaurea nigra), devil’s bit scabious (Succisa pratensis), harebell (Campanula rotundifolia) and several leafy-stemmed hawkweeds (Hieracium spp.) amongst the most frequent species encountered.

Compared to most other large lochs in Scotland, Lomond with its relatively shallow and enriched waters in the southern basin has an abundant and diverse benthic (bottom-dwelling) invertebrate fauna. The succession of stony, sandy and muddy substrates of the littoral zone supports the larval or nymph stages of a large number of flying insects – may-fly (Ephemeroptera), stone-fly (Plecoptera), caddis-fly (Trichoptera), crane-fly (Tipulidae) and dancing midges. Many other small animals such as the freshwater shrimp (Gammarus pulex) and the water slater (Asellus aquaticus) find food and shelter amongst the vegetation and stones. Of the truly limnic freshwater species of snails and limpets (Gastropoda) which occur, only half are to be found in the northern half of the loch, indicative of the low calcium content in the Highland waters. This north–south distribution of univalves is paralleled amongst the bivalve molluscs present. New species of mollusc are recorded in Loch Lomond from time to time. Little more than 40 years ago, the presence of Jenkin’s spire snail (Potamopyrgus jenkinsi) was confined to the saline muds of the tidal reaches of the River Leven. Then in 1959 it was found for the first time in a stony stretch of the River Endrick, and in the following year along the southeastern corner of the loch itself. The species’ discontinuous distribution at this early stage of the colonisation of Loch Lomond and its feeder rivers suggests dispersal by chance, possibly through the movement of water birds. A more recent and quite unexpected appearance in the southern basin of the loch was of an allied species, Bithynia leachii, which has few known localities in the northern half of Britain. It is suspected that this small water snail was inadvertently introduced alongside several translocated southern coarse fish species (see below).

Overall, the littoral zone in the southern loch sustains mean densities of 6,000 benthic animals per m², rising to 11,000 where protected from unstabilising waves. With the rich feeding of the Endrick Bank acting as a magnet to wading birds on spring and autumn migration, this corner of Loch Lomond is a favourite haunt of the rarity-seeking birdwatcher. The tally of different waders alone which have been recorded at the water’s edge on one or more occasions stands at 35, including several North American species. Happily, these long-distance vagrants are no longer greeted with a hail of gunshot, as was the case in the Victorian collecting era.

Matching the abundance of planktonic and invertebrate life in Loch Lomond is the widest variety of indigenous and introduced fish found in any freshwater body in Scotland. The 15 native species are: sea lamprey (Petromyzon marinus) – Loch Lomond is the only site in Britain where the adult sea lamprey is known to feed in fresh water – river lamprey (see p. 130), brook lamprey (Lampetra planeri), Atlantic salmon, sea/brown trout, powan (Fig. 9.6, see also p. 130), pike, minnow (Phoxinus phoxinus), roach, stone loach (Noemacheilus barbatulus), European eel, three-spined stickleback (Gasterosteus aculeatus), nine/ten-spined stickleback (Pungitius pungitius), perch and flounder (Platichthys flesus), with the occasional appearance of thick-lipped mullet (Chelon labrosus) which can enter the loch from the Clyde Estuary via the River Leven on a high spring tide. The absence of Arctic charr (Salvelinus alpinus) has engendered much discussion, especially as it is known from Highland lochs to the north, east and west of Loch Lomond, with the nearest charr water only just outwith the catchment. A published account of one claimed to have been caught in 1891 was discounted as a North American brook charr (S. fontinalis). Possible confusion with this allied species, then only recently introduced into Scotland, cannot explain away the inclusion of Arctic charr in a list of Loch Lomond fishes prepared at the end of the eighteenth century by a local minister, the Reverend John Stuart. Not only was Stuart an exceptionally observant naturalist, he had spent the best part of 30 years living beside the charr-inhabited Loch Tay and would undoubtedly have been familiar with the species at first hand. It has been further suggested that the name of a small island off Rowardennan – Eilean nan Deargannan – is derived from the Gaelic name for Arctic charr (tarrdheargan), meaning little red-bellied fish. Whether or not a small population of this relict species existed in Loch Lomond to within comparatively modern times is a question that may never be answered.

Fig. 9.6 A relict species, the powan is found in very few British fresh waters (Peter Maitland).

The North American brook charr was not the only introduction of a non-indigenous sporting fish to Loch Lomond, although no game species has ever become naturalised. A few rainbow trout (Oncorhynchus mykiss) are taken from the loch most angling seasons, but this is not unexpected considering the number of smaller waters in the catchment that are regularly stocked with this popular North American fish. Translocation of coarse fish from southern Britain – principally through the discarding of surplus live bait – has led to several viable populations becoming established. Of these, the gudgeon (Gobio gobio) is confined to the shallow waters around the Endrick Mouth, but dace (Leuciscus leuciscus) have spread throughout the southern half of the loch. The most prolific of all the introductions has been the ruffe (Gymnocephalus cernua), which from the first few recorded in 1982 may now have caught up with the native powan as the most abundant fish in the loch. This has had a significant effect on the ecological balance between predator and prey in the loch’s food chain through altering the diets of most fish-eaters. Unconfirmed rumours of other new releases circulate from time to time, so the list of permanent additions to the loch’s coarse fish community is probably not yet closed.

Otters regularly frequent the loch and island shores, and examination of their food remains confirms that they have increasingly turned to ruffe as part of their diet. Sharing the upper position in the food chain are a number of water birds: cormorant (Phalacrocorax carbo), great crested grebe (Podiceps cristatus), grey heron, osprey (see p. 132) and several species of fish-eating wildfowl. During the summer months Loch Lomond supports small but regionally important numbers of both fish-eating and bottom-feeding duck, such as red-breasted merganser, goosander, shelduck (Tadorna tadorna), tufted duck (Aythya fuligula) and, until only a few years ago, common scoter (Melanitta nigra) (see p. 131). Apart from the goosander, the loch’s populations of all other species of duck have fallen sharply in recent years. The decline is attributable to the ever-increasing numbers of recreational power craft utilising the breeding birds’ feeding and nursery areas, coupled with the appearance on the loch of North American mink (Mustela vison) (Fig. 9.7). Mink were first farmed for their pelts in Scotland in the late 1930s, but it was to be the postwar years before the industry really expanded. Two mink fur farms were established in the Loch Lomond area, one of them at Fintry beside the River Endrick. By the mid-1960s it had become clear that a feral population originating from escaped animals was well entrenched in the middle reaches of the river. Spreading yet further downstream, mink went on to colonise the loch. Importantly, prior to the mink’s invasion of Loch Lomond, the islands on which many waterfowl nested had virtually no mammalian predators, so the mink’s impact on the resident breeding birds was all the greater. There can be little doubt that this unwelcome addition to the Loch Lomondside fauna is here to stay, local control measures effecting little more than a temporary reduction to numbers.

Fig. 9.7 North American mink are well established throughout Loch Lomondside (Don MacCaskill).

Considering some of the summering wildfowl in a little more detail, the shelduck was first confirmed breeding on Loch Lomond in 1877, when inland nesting of this estuarine species was still a rare event. Regular monitoring of the shelduck population in the shallow waters around the southeast corner of the loch during the 1970s showed the breeding population to be stable at around 18 pairs producing good numbers of young. Up to 70 non-territorial immature birds were also regularly present. Within just a few years of the mink’s arrival the number of breeding shelduck was reduced by two-thirds, the immature flock having dwindled away completely through lack of recruitment. Numbers of red-breasted mergansers also fell significantly. The one-time assembled creches of almost 100 young mergansers are no longer seen. The goosander was first recorded nesting near the head of Loch Lomond in 1922, but was very slow to colonise right down to the southern basin. Probably because most pairs spend the early stages of their breeding cycle on running water away from the disturbance problems of the loch, they now appear to have overtaken the merganser as the most numerous diving duck. The last few years has seen late spring gatherings of 100 or more goosanders prior to their summer moult. Immature and post-breeding females undergo moult on the loch itself, but the males take themselves off to moult elsewhere, possibly as far north as the Norwegian fjords. Although the evidence is only circumstantial at present, it seems likely that the compelling attraction of Loch Lomond to goosanders is the presence of massive shoals of ruffe. The advent of the invasive ruffe has also significantly changed the diets of the loch’s cormorants and grey herons, food analysis studies confirming that both species are taking full advantage of the seasonal abundance of this easily caught fish. Counts of cormorants indicate that the usual population on the loch is between 40 and 50 non-breeding birds, although double that number is on record. Local recoveries of cormorants that had been ringed as young birds in the nest suggest that most originate from an inland freshwater colony at Mochrum and Castle Lochs in southern Scotland. Long-term monitoring of grey herons around Loch Lomond has demonstrated that the breeding population is subject to periodic fluctuations in its numbers. The highest count was achieved in 1975, with 60 nesting pairs in residence; the lowest count of only six breeding pairs in 1963 resulted from heavy mortality during the preceding very severe winter. The largest individual colony to date – up to 40 pairs in the 1970s – is situated beside the rich feeding grounds of the Endrick Marshes. Their choice of deciduous trees for nesting is not often seen in Scotland, where most grey herons show preference for conifers.

Hinterland wetland habitats

At times of prolonged heavy rainfall the loch’s incoming rivers can become very swollen, causing them to back up and overtop their banks. The water spreads rapidly, the flood plain of the River Endrick, for example, sometimes forming a continuous sheet of water with the loch itself. Looking down at the Endrick’s lower reaches from a high vantage point near Drymen, a seventeenth-century traveller described the area as ‘besieged with bogs’. Several hundred years of agricultural drainage later, such hinterland wetlands are no longer in a pristine state, but neglected and half-forgotten spots that are rich in plant and animal life are still to be found.

Turning initially to the head of the loch, a popular locus for visiting botanists in the mid-nineteenth century was a series of low-level valley bogs running alongside the lower reaches of the River Falloch. The rarer species that they came specifically to see – pale butterwort (Pinguicula lusitanica), bog orchid (Hammarbya paludosa) and marsh clubmoss (Lycopodiella inundata) – have all apparently disappeared from this particular locality, victims of a combination of over-collecting and land drainage. A last remnant of these valley bogs can be found bordering the northern end of the Geal Loch near the Falloch Mouth. Consisting mainly of purple moor-grass/bog myrtle mire, the system does receive some mineral flushing along its eastern edge from base-rich schists on the hill slopes above. Characteristic plants still retaining a presence in this valley bog are the great sundew (Drosera longifolia) – one of a small group of insectivorous plants – cranberry (Vaccinium oxycoccos), white-beaked sedge (Rhynchospora alba) and few-flowered sedge (Carex pauciflora). A walk across the bog on a damp but warm summer’s evening will quickly confirm that this type of habitat is a breeding ground par excellence for the scourge of Scotland, the biting midge, especially the ferocious Highland midge (Culicoides impunctatus).

Unlike the almost vanished valley bogs, comparison with old photographs shows that the Geal Loch (Fig. 9.8) has changed little with time. Aquatic plants fringing its clear oligotrophic water include bogbean, bottle sedge (Carex rostrata), slender sedge (C. lasiocarpa) and common reed (Phragmites australis), with water lobelia, bog pondweed (Potamogeton polygonifolius) and patches of white water-lily (Nymphaea alba) appearing as the loch progressively deepens. Just to the south of the Geal Loch, the edges of an overgrown pool that partially dries out in summer has mats of floating club-rush (Eleogiton fluitans). Most interesting of all is the elusive and nationally scarce pillwort (Pilularia globulifera), a mud-growing fern-ally susceptible to drainage schemes and declining throughout much of its range in Britain.

Fig. 9.8 The Geal Loch and a remnant of valley bog in lower Glen Falloch.

Wards Low Ground or Ponds lies just inland from the southeastern corner of Loch Lomond. Underlain by drainage-impeding clay, this eutrophic water body is noted for its beds of sedges (Fig. 9.9), principally bladder sedge (Carex vesicaria) and northern water sedge (C. aquatilis). A conspicuous stand of the uncommon hybrid C. x hibernica (C. aquatilis x nigra) attracts the sedge specialist’s attention, while the presence of the horned pondweed (Zannichellia palustris) confirms the enriched nature of the ponds’ shallow waters. Kept free of sedge growth only by the trampling of cattle, which are grazed there in late summer, the exposed margins to the drying-out ponds have a similar but less diverse community of small ephemeral plants as already described for the lochside edge around the Endrick Mouth. Water levels would appear to have to be just right, for two of the pond’s specialities – the mudwort (Limosella aquatica) and the moss Physcomitrium sphaericum – are not seen every year. Mud samples collected in July from just above and below the water line produced an average density of over 4,000 invertebrates per m², providing an alternative feeding ground for summer resident and autumn migrant waders when higher than usual loch levels submerge the entire Endrick Bank. One noteworthy aquatic invertebrate recorded is the very local water beetle Helophorus strigifrons, which is found amongst the sedge litter around the seasonal pools. Duck mussels (Anodonta anatina) living in the rich mud of Wards Ponds have, because of their exceptional growth, been mistaken in the past for the closely related but larger swan mussel (A. cygnea). Water rails (Rallus aquaticus) are well established in the sedge beds, but along with migrant spotted crakes (Porzana porzana) which turn up with some regularity in spring, their distinctive calls are more likely to be heard than birds actually observed out in the open. Because of the spotted crake’s skulking behaviour, positive proof that they actually breed in the Endrick Marshes has yet to be obtained. At the end of the season almost all of the site is flooded as a sanctuary for wintering wildfowl. Such is the all-the-year-round wildlife interest of Wards Low Ground, it is hard to imagine that this was once cultivated land growing crops of turnips and potatoes.

Fig. 9.9 Drained for the growing of crops in the nineteenth century, Wards Low Ground has reverted to open water with extensive sedge beds.

Just a short distance from Wards lies the Aber Bogs (Plate 3), the largest remaining tract of flood plain fen on Loch Lomondside. The land-use history of the bogs is fragmentary, but the absence of any underlying peat points to the fen having developed over worked-out diggings for turf. Until the mid-1930s, this 24 ha former sedge-dominated meadow was cropped annually for marsh hay. Neglected apart from winter wildfowling from then on, the unharvested vegetation gradually built up a thick litter layer above the water table, the drying out surface receptive to an invasion of reed canary-grass (Phalaris arundinacea) followed by willow. The quality of water feeding into this low-lying site had deteriorated over the years, a result of domestic and agricultural pollutants finding their way into the old drainage channels. Subsequent management aimed at arresting the decay of the site and further loss of diversity in the fen flora has involved diverting the most polluted water sources, clearing away much of the colonising willow and raising the internal water level within constructed embankments. Initial results have been encouraging, with early signs of a recovery by the former mixed sedge and herb rich vegetation. Cowbane (Cicuta virosa) and tufted loosestrife are to be found in some abundance, the latter species in particular representative of northern fens. In contrast, the presence of the blunt-fruited water-starwort (Callitriche obtusangula) adds a southern element to the flora.

With the wet and cool climate, the Aber Bogs are not generally noted for butterflies, but in the sheltered south-facing sun traps where the herb-rich purple moor-grass fen at the drier northern edge of the bogs merges with woodland, the small pearl-bordered fritillary (Boloria selene), green-veined white (Pieris napi) and orange tip (Anthocharis cardamines) all fly in their appointed seasons. The additional presence of fenland moths such as the valerian pug (Eupithecia valerianata), marsh pug (E. pygmaeata), fen square-spot (Diarsia florida) and bulrush wainscot (Nonagria typhae) add considerably to the Aber Bogs’ entomological status. Of several species of common damselfly and dragonfly recorded, the azure damselfly (Coenagrion puella) is by far the most abundant. Documentation of the other invertebrate life is still at an early stage, but the discovery of the nationally scarce money spider (Maro sublestus), at the time known only from Wicken and Woodwalton Fens in East Anglia, is an indication of what may await further study. Eels and pike have probably always been denizens of the bogs’ man-made watercourses, but how and when the non-native crucian carp (Carassius carassius) first colonised is anybody’s guess.

For birds, the open fen surrounded by a fringe of osiers (Salix viminalis) and other willows forms an ideal habitat for sedge warbler (Acrocephalus schoenobaenus) and reed bunting (Emberiza schoeniclus); and a visit at dusk-fall on a fine evening in mid-May can be a revelation as to the high numbers of grasshopper warblers (Locustella naevia) proclaiming territory occupation with their reeling song. The population of water rails noticeably increased after the internal water level was raised. Spotted crakes and even bitterns (Botaurus stellaris) have been known to occur. The odd marsh harrier (Circus aeruginosus) appears on spring passage most years, but hen harriers regularly hunt over the reed beds outwith the breeding season. One unexpected summer resident of the Aber Bogs is the whooper swan (Cygnus cygnus) (see p. 131), descended from captive Icelandic birds that gained their freedom when a local wildfowl collection was closed down. Roe deer (Capreolus capreolus) are perfectly at home in this rather swampy habitat; and compared to those which live in the less nutrient-rich conifer plantations, show superb antler growth. Although rarely seen, the water shrew (Neomys fodiens) – Britain’s smallest aquatic mammal – is seemingly not uncommon in the bogs, for on several occasions the species’ skeletal remains have been found in regurgitated food pellets of barn owl (Tyto alba) collected from a nearby roost.

Attention has already been drawn to the loch’s southeastern shore as a regionally important stopping-off point for migrant waders, but together with the Endrick’s lower flood plain the area is well known for its breeding species too. At a time when breeding populations of waders of agricultural land elsewhere on Loch Lomondside have been in serious decline, the loch shore and hinterland grazing marshes (Fig. 9.10) still attract the oystercatcher (Haematopus ostralegus), lapwing (Vanellus vanellus), ringed plover (Charadrius hiaticula), curlew (Numenius arquata), redshank (Tringa totanus), common sandpiper (Actitis hypoleucos) and common snipe, albeit in reduced numbers. Almost every spring dunlin (Calidris alpina) can be seen displaying, and not that many years ago up to three pairs stayed on to nest. Other passage waders have shown a promising interest in the area; wood sandpiper (Tringa glareola), black-tailed godwit (Limosa limosa) and jack snipe (Lymnocryptes minimus) have all been observed undergoing courtship display in spring. But even the most optimistic were taken aback when Temminck’s stint (Calidris temminckii) was discovered nesting on the Ring Point in 1979. The grass-lined nest containing four eggs was concealed in low vegetation amongst widely spaced tussocks of soft rush (Juncus effusus), on a ridge of wind-blown sand some 9 m from the water’s edge. Although only a one-off occurrence it was the ornithological event of the decade, the male’s ‘butterfly’ display flight and trilling song transporting the observer for a moment to distant lands in the far north of Europe.

Fig. 9.10 The mouth of the River Endrick and its surrounding marshes.

All the common species of dabbling and diving duck summer in the Endrick Marshes, including several pairs of shoveler (Anas clypeata), a species dependent on shallow enriched water. Amongst the less familiar ducks, pintail (A. acuta) and gadwall (A. strepera) regularly appear in April and May, but to date evidence of their breeding is lacking. Garganey (A. querquedula), on the other hand, have almost certainly nested on one or more occasions. Equally of note was a female scaup (Aythya marila) seen with a brood of ducklings in three successive seasons 1987–89. Wildfowl around the Endrick Mouth really come into their own as winter approaches, when migrants from as far away as the Arctic Circle take up seasonal residence. And when the smaller lochs and reservoirs in the north Clyde area begin to ice over as the temperature drops below zero, Loch Lomond can temporarily draw in hundreds of additional wildfowl to its slow to freeze waters. Regular counts undertaken over 40 years show that at some point during the winter months the combined presence of ducks – mainly wigeon (Anas penelope), mallard (A. platyrhynchos) and teal (A. crecca) – geese and swans in and around the Endrick Marshes can total 2–3,000 birds, rising to 4,000+ if the number of greylag geese (Anser anser) foraging the fields in the Endrick Valley happens to be particularly high. The size of the greylag population is initially dependent on the availability of cereal stubble in the surrounding area, but as winter progresses, the number of geese present increases as they turn their less than welcome attention to the spring flush of sown grass. Large skeins of migratory pink-footed geese (A. brachyrhynchus) pass right through the area in autumn, but some of the birds do temporarily reappear on Loch Lomondside if the winter weather in the east of Scotland is severe. Until 1972, small numbers of the rare bean goose (A. fabilis) wintered in the Endrick Marshes, their place now taken by a flock of Greenland white-fronted geese (A. albifrons) (see p. 131).

Comparatively little attention has been paid to the numbers of gulls that pass over the Endrick Marshes to roost overnight on the open waters of the loch, but counts of 5,000 herring gulls (Larus argentatus), 2,000 common gulls (L. canus) and 500 lesser black-backed gulls (L. fuscus) have been obtained.

A contrast of rivers

The River Endrick, or Anneric (meaning given to spates) as it was once known, is the major inflow into the southern half of Loch Lomond. As the crow flies, the Endrick is little more than 25 km from start to finish, yet because of its wanderings it covers almost twice that distance to complete its journey. A singular feature of the river is that its final stretch suddenly turns north towards the mountains, instead of continuing on a westward bearing towards the sea. Rising at an altitude of 475 m as Mary Glyn’s Burn in the Fintry–Gargunnock Hills, it links up with several other headwater streams before taking the name Endrick below Burnfoot Farm (Fig. 9.11). The Endrick is joined by additional tributaries right up to within 1.6 km from where it discharges into the loch, the most important of these being the River Blane which issues from the southern Campsie Hills. Once clear of the slow to wear down Carboniferous Lavas, the Endrick winds its way through successive bands of much softer Calciferous, Upper and Lower Old Red Sandstones, becoming wider and deeper in stages the further west it flows. The nature of its substrate changes too, as both gradient and current slacken, beginning with a bed of bare rock strewn with large stones and moss-covered boulders, followed in succession by shingle, coarse sand and silt. In an average year the Endrick carries an estimated 13,870 tonnes of fine material in suspension to add to the silt and sand bar fanning out into the loch at the river mouth.

Fig. 9.11 The upper reaches of the River Endrick at Burnfoot.

The old river terraces and oxbow ponds provide a visual record of past shifts in the Endrick’s course. Nowhere can this be seen to better effect than its convoluted progress across the flat flood plain below Drymen bridge. Measurements taken from past Ordnance Survey maps of this stretch of the river show that, until about 1970, the looped meanders were moving position at an average annual rate of just under 0.5 m. Since then the rate of river bank erosion has significantly quickened, the cumulative effect of higher winter rainfall and a more rapid response in peak river flow resulting from an increase in agricultural and forestry drainage schemes throughout the Endrick catchment. In October 1983 a powerful surge of water cut through some 5.5 m of bank at the narrowest point of one of the loops, creating yet another alteration in the course of the river. Further upstream a more spectacular shift in the course of the Endrick will eventually take place where a crook in the river encircles the Haughs of Gartness. The stone-built revetment having broken down, the fast-moving water is slowly but surely eating into the south bank, so that at some point in distant time the Endrick will break through the morainic ridge that impedes its progress to form a new confluence with the River Blane, leaving the present Pot of Gartness section high and dry.

With such instability of the river’s sandy banks, the natural development of water’s edge vegetation along the Endrick is possible only where the current slows down as it approaches the loch. In the lower reaches between Woodend bridge and the river mouth there is a patchy growth of emergent and floating-leaved aquatic plants such as nodding bur-marigold (Bidens cernua), branched bur-reed (Sparganium erectum), amphibious bistort, yellow water-lily and the occasional clump of Loch Lomond dock. Almost all the adjoining fields are hard grazed, so that any water’s edge plants spreading onto the river bank are soon eaten back by farm stock. To see the potential of the Endrick’s riverside flora means a visit to a popular walk downstream from Balfron bridge (Plate 4). Formerly protected by a stock-proof thorn hedge, the river bank within this section was strengthened with stonework in the late eighteenth century to safeguard the Endrickfield printworks and bleach fields against floods. Mixed in with the riverside plants, which include marsh-marigold (Caltha palustris), water avens (Geum rivale), meadowsweet (Filipendula ulmaria) and yellow iris (Iris pseudacorus) is a surprising number of woodland species, remnants perhaps of the Endrick Valley’s long-vanished forest cover. Fortunately, this varied assemblage of plants has not yet been completely overshadowed by a dense leafy cover of butterbur (Petasites hybridus), a fate which has befallen some other stretches of the river bank vegetation in the Endrick’s middle reaches. It does, however, have its fair share of naturalised non-native species, including monkeyflower (Mimulus guttatus), pink purslane (Claytonia sibirica), and both lilac- and white-flowered forms of dame’s-violet (Hesperis matronalis) among other garden escapes. The introduced Pyrenean valerian (Valeriana pyrenaica) appears confined to the river banks at Drumtean and Gartness, but a much more invasive alien – the giant hogweed (Heracleum mantegazzianum) – has become firmly entrenched in a number of places, especially below the golf courses either side of Drymen bridge. On the River Blane just downstream of Duntreath, the giant hogweed is accompanied by the Indian balsam (Impatiens glandulifera).

Following centuries of forest clearance, agricultural improvement and flood protection measures, the last vestiges of low-lying riverside woodlands that are seasonally inundated are one of the most fragmented and precarious wildlife habitats in Britain today. With a history of wood pasture followed by the growing of basket willows, the mixed woodland around the lower Mar Burn in the flood plain of the River Endrick is Loch Lomondside’s best example of its type. Overshadowed by derelict coppice willows, their tangle of branches covered in the commoner epiphytes such as the lichens Bryoria fuscescens and Usnea subfloridana, the ground flora of these almost perpetually wet alluvial soils includes Loch Lomond dock, summer snowflake (Leucojum aestivum) (Fig. 9.12) – which may not be native to Scotland – and elongated sedge (Carex elongata) (see p. 130). A recent colonist here and in some of the lochside flood woodlands is the naturalised skunk cabbage (Lysichiton americanus). Little information is available on the site’s invertebrates, but one species that warrants a mention is the solitary wasp Trypoxylon attenuatum, here found at the northernmost edge of its British range. In these flood woodlands this spider-hunting wasp’s life cycle has been shown to be associated with the Loch Lomond dock, the wasp dividing the plant’s hollow stems into larval/pupal cells by cross-partitions of mud. Of other animals present in the Mar Burn woods, the resident moles (Talpa europaea) have adapted surprisingly well to their watery environment; one huge mound or ‘fortress’ raised above the water table was measured at over 1 m in height. Grey herons begin nesting here as early as February and March, when the trees are still standing in winter flood water and the wood is raked with the last of the winter gales. If strong winds persist, some nests may be built little more than 2–3 m from the ground.

Well oxygenated and rich in invertebrate life, the productive waters of the Endrick are ideal for a wide variety of fish, and all but the upper stretch of the river is well frequented by anglers. The largest number of fish species is to be found only in the slow-flowing lower reaches, two waterfalls acting as barriers to free movement throughout the whole of the river system. Full grown Atlantic salmon and sea trout migrating upstream to their gravelly spawning beds have the ability to leap or swim up the autumn spate water tumbling down into the Pot of Gartness, but they are unable to surmount the much higher Loup of Fintry further upstream. The Loup or ‘Leap’ can be bypassed only by the eel, which, under the cover of darkness, will temporarily take to the land. Stocking the Endrick Valley’s man-made mill dams and other small waters with non-native fish dates back many years, but this activity has been stepped up in recent times. Non-indigenous species present within the river catchment, but not previously mentioned in connection with Loch Lomond – common carp (Cyprinus carpio), rudd (Scardinius erythropthalmus) and tench (Tinca tinca) – have all been introduced either as sporting or ornamental fish. The releasing of unwanted live bait into the lower Endrick almost certainly accounts for the recent establishment of bream (Abramis brama) and chub (Leuciscus cephalus).

Fig. 9.12 Probably an inadvertent introduction, the summer snowflake is very much at home in flood woodlands beside the River Endrick.

Thanks to the vigilance of officers from the Scottish Environment Protection Agency (formerly the Clyde River Purification Board in the Loch Lomond area) and the Angling Association bailiffs, pollution of watercourses within the Endrick catchment has been kept to a minimum, although there have been several individual serious incidents. With generally good water quality throughout, the otter population on the river has continued to thrive at a time when the species was in decline in many parts of lowland Britain. The number of otter territories on the Endrick is less determined by food availability than by the presence or absence of riverside vegetation unaffected by stock grazing or bank erosion. Otters require well-developed river bank cover where they can lie up during the day, safe and undisturbed. Trees at the water’s edge with partially exposed roots are particularly favoured for otters’ breeding dens or holts, studies showing that it is the females that hold the individual territories, the males ranging over two or three. Compared to the satisfactory status of the otter, the water vole (Arvicola amphibius) (Fig. 9.13) has fared badly. The once-thriving population of water voles on the Endrick, which had proved resilient to the colonisation of the river banks by the predacious brown rat (Rattus norvegicus), unwittingly introduced to Loch Lomondside by commercial boat traffic in the nineteenth century, has been unable to absorb the additional losses from mink.

Fig. 9.13 The native water vole faces local extinction since the establishment of North American mink (Norman Tait).

Most visual of all the riverine creatures on the Endrick are the birds. Dipper and grey wagtail (Motacilla cinerea) are found along almost the entire length of the river from Burnfoot to the last stony shallows that were once the Drymen ford. Having a catchment area underlain with fairly base-rich rocks, the river is well buffered from the effects of acid precipitation which could lead to the depletion of these birds’ freshwater invertebrate food. Both dipper and grey wagtail are to be found using bridges and rocky gorges for nesting, safe from rising water levels after heavy rain. Sand martin (Riparia riparia) nest holes in the river banks are all too often washed out by flash floods, leaving those birds that have prudently burrowed into nearby sandy morainic mounds unaffected. The kingfisher (Alcedo atthis) was temporarily lost as a breeding bird on the Endrick after the severe winter of 1962–63, but has since recolonised its former haunts in the ‘pool and riffle’ stretches between Fintry and the confluence with the River Blane. The Endrick Valley has just witnessed a colonisation by shelduck, the parent birds seeking out the still waters of flooded riverside fields when they have small young. Another comparative newcomer to the bird community is the oystercatcher, for in the first half of the twentieth century it was still being described as only an occasional shoreline nesting species on some of the Loch Lomond islands. Today, few of the Endrick’s larger shingle banks are without their demonstrative pair in spring. Most of these shifting shingle banks have a very sparse flora and fauna, one exception being where the course of the river divides for a short distance upstream of Fintry bridge. On this more stable shingle island a willow-dominated shrub cover has developed, which in April and May comes alive with woodland bird song, the willow warbler (Phylloscopus trochilus) just for once living up to its English name.

The major inflow into the northern half of Loch Lomond is the River Falloch, which begins its short life at just over 800 m on Beinn a’ Chroin. Some 17 km long, almost two-thirds of the river is inaccessible to migratory salmonids because of the impassable Falls of Falloch. Although the mountainous catchment area of the Falloch is relatively small, the exceptionally high rainfall draining from hard impervious rock ensures that the flow is often fast and furious, with most of the gravel beds continually on the move. Compared to the Endrick, the water of the Falloch has a low mineral content, which is a further limiting factor on the diversity and density of the invertebrate life of the river bed. Anglers maintain that in the spring and summer months, the fish in the lower stretch of the river are to some extent dependent on the many woodland invertebrates that drop into the water from the overhanging trees. Untypical of the mollusc family as a whole, one species that favours the calcium-poor conditions of the Falloch is the freshwater pearl mussel (Margaritifera margaritifera). Once much sought-after by the makers of top class jewellery, some of the finest freshwater pearls ever found in the country adorn the Scottish crown. In years past, itinerant pearl fishermen have been observed working the River Falloch’s sandy gravel beds, but this now legally protected animal’s continuing presence there requires confirmation.

The River Leven, which carries Loch Lomond’s overflow waters to the Clyde Estuary, shares little in common with the Rivers Endrick and Falloch. Barely 11 km long from source to mouth, the Leven has a natural fall of only 7.5 m from the loch’s outlet to mean sea level, the river becoming tidal below Dalquhurn Point. Since 1971, when the Central Scotland Water Board’s barrage at Dalvait came into operation, the rate of river flow through its gates has been subject to control. There are no other physical obstacles such as waterfalls to impede the movement of migrating fish. Unlike the Endrick Valley, which bears few signs of its former riverside textile works, the banks of the Leven still retain much of their industrial past even after a number of landscaping projects.

Aside from patches of river water-crowfoot (Ranunculus penicillatus) clinging tenaciously to the Leven’s gravelly shoals, there is little to catch the botanist’s eye as the river threads its way through the Vale’s commercial heartland. Once this is left behind, however, the diversity of water’s-edge vegetation downstream considerably improves, only to disappear almost completely again under urban and industrial development once Dumbarton is reached. But upstream of Dumbarton bridge there are several good stands of riverside marsh where there is an increase in siltation at the interface between the outgoing freshwater and the incoming tidal waters. One of the most extensive marshes on the west bank lies below Mains of Cardross (Fig. 9.14). With its head-high beds of greater reedmace (Typha latifolia) and reed canary-grass, dotted here and there with crack willow (Salix fragilis), such a wild spot is all the more unexpected after following the old towpath with its crumbling industrial frontage for any length of time. Readily identified even at a distance by its distinctive colour, the grey club-rush (Schoenoplectus tabernaemontani) in the marsh’s muddy creeks is a clear indication of increasing salinity as river and estuary waters intermix. The characteristic plants of brackish water can also be seen on the Leven’s east bank, where marshy ground was cut off when Dumbarton’s Broadmeadow was embanked in 1859 as a high tide flood prevention measure. As well as the grey club-rush, the sea club-rush (Bolboschoenus maritimus), sea arrowgrass (Triglochin maritima), common scurvy-grass (Cochlearia officinalis) and sea aster (Aster tripolium) are all to be found in these saltings. In 1705 it was at this spot that a Dumbarton minister recorded a bittern ‘booming’ in the reeds, remarking: ‘those that first heard the fowl make this noise were mightily afraid; whereupon they concluded it to be no less than the devil’.

Fig. 9.14 Brackish marshes fringe the River Leven below Mains of Cardross.

As the final tidal stretch of the Leven flows through Dumbarton, one cannot fail to notice in summer the congregation of 150 or more mute swans, such an unusually high number leading to the conclusion that here, as in the southern basin of the loch, their food of subaqueous vegetation is being enhanced by some form of nutrient enrichment. Up to the mid-1950s at least, the town’s quayside area was the district’s last retreat for the black or ship rat (Rattus rattus); the fleas of this animal are now known to have been responsible for outbreaks of bubonic plague or ‘black death’ in the old medieval town. With the merchant ship warehouses and other old buildings swept away under redevelopment, this inadvertently introduced but now rare rodent would appear to be locally extinct.

After passing through the town, the river widens considerably where it discharges in the Clyde Estuary. At low tide in autumn and winter the exposed mud flats can hold up to 500 redshanks, together with smaller numbers of other waders. These gatherings of feeding birds are well worth checking through for the possibility of a rare vagrant, such as the terek sandpiper (Xenus cinereus) which drew ornithologists from far and wide in late September 1996. Going back to the eighteenth century, when salmon were far more numerous in the then unpolluted Clyde, common porpoises (Phocaena phocaena) regularly followed the fish into the Leven as they headed upstream to spawn. Whales too are not completely unknown about the mouth of the Leven. After becoming stranded on a sandbank at ebb tide, a minke whale (Balaenoptera acutorostrata) was killed at the river mouth in June 1905. Ninety years later in February 1995, cetacean watchers had the opportunity of observing a humpback whale (Megaptera novaeangliae) feeding on large shoals of small fish in the main navigation channel below Dumbarton Castle, an unprecedented event in modern times and one which must give satisfaction to those responsible for cleaning the River Clyde of industrial pollution. Cleaner water means that the pleasures of sea angling in the tidal reaches of the River Leven are being rediscovered. Several estuarine species are now caught regularly, in particular the thick-lipped mullet and pollack (Pollachius pollachius), but the days of large shoals of herring (Clupea harengus) making their way upriver as far as Dumbarton quay are long past.

Some notable aquatic and water’s-edge species

The river jelly lichen Collema dichotomum grows only on permanently immersed rocks, unseen except by botanists prepared to risk a soaking. Extremely sensitive to water pollution and in consequence declining throughout most of Europe, the continuing presence of this now rare species in the middle stretch of the Endrick reflects the cleanness of the river.

The Loch Lomond dock (Plate 5) is most frequently found alongside watercourses and in swampy clearings within wet woods, but is capable of successfully colonising even abandoned cultivated land where the drainage system has completely broken down. For such a robust-looking species, the Loch Lomond dock has a surprising number of Achilles heels. It is, as might be expected, very susceptible to any lowering of the water table; one large woodland colony of some 250 plants had virtually disappeared within ten years of a single drainage ditch being excavated through the middle of the site. Foraging cattle, which more often than not ignore the ubiquitous broad-leaved dock (R. obtusifolius), will eat the fresh growth of Loch Lomond dock with apparent relish. Similarly, it appears more prone to defoliation by the dock-leaf beetle (Gastrophysa viridula) than any other species of Rumex found in the area. The most serious threat of all to the Loch Lomond dock’s survival is its readiness to cross with the broad-leaved dock; some pure stands of just a few years ago have been entirely replaced by hybrids.

The tufted loosestrife is at its most abundant in Britain in the Forth–Clyde Valleys, although it is often overlooked on account of its being very shy at flowering. A perennial rhizomatous species, the tufted loosestrife appears to have been unaffected by the annual cutting of the former wet meadows.

Nationally scarce, the elongated sedge was once thought to have been lost to Scotland. In 1967, however, a small but thriving colony was discovered on Loch Lomondside in alder carr fringing the loch shore below Boturich Castle. Subsequent searching revealed two larger populations in wet woodland, one beside the lower reaches of the River Endrick and the other in Rossdhu Park near the loch shore, where shallow lagoons (Plate 6) have formed behind a raised storm beach of sand and gravel. The bright green tussocks appear early in spring, showing preference for sites that are flooded for prolonged periods in winter, and which only partially dry out in summer. A characteristic feature of the elongated sedge’s lifestyle is its habit of occasionally growing in an epiphitic manner on decaying fallen trees, the roots finding sufficient moisture in the thick growth of mosses covering the rotting wood.

A dwarf form of river lamprey which spawns in the River Endrick and its tributaries is the only population in Britain known to mature in a freshwater lake instead of migrating to the open sea. In Loch Lomond the lampreys almost exclusively feed on live powan, attaching themselves to their prey with suckerlike mouths. This dependence of river lampreys on powan is found in few other regions of Europe.

The powan or whitefish was first mentioned as occurring in Loch Lomond by George Buchanan (tutor to the young King James VI) in his History of Scotland published in 1582. A relict cold water species, in Britain the powan is confined to just a few mountain lakes and tarns. Powan feed mainly on zoo-plankton, spawning in Loch Lomond’s gravelly shallows, where it is believed that the introduced ruffe has become a significant predator of their eggs. The powan has long been recognised as an important link in the loch’s food chain. Describing this in 1911, local fisherman/naturalist Henry Lamond wrote: ‘the powan forms the daily food of a vast number of aquatic and semi-aquatic creatures. Black-headed gulls, common gulls and terns pick them up in thousands. Every rocky islet where the gulls have a permanent retreat shows a kitchen midden of mouldering bones. Eels and pike regard it as their staple diet.’ Powan in Loch Lomond show a high incidence of fresh and healed lamprey-inflicted scarring, with up to 25 wounds recorded on a single fish. Another dependent predator of the Loch Lomond powan appears to be the elusive ‘ferox’ or ferocious trout, a deep water form of brown trout which has turned away from its normal invertebrate diet to feed voraciously on other fish, with a resultant large increase in size. Because of the powan’s vulnerability to ‘baldspot’ disease and secondary fungal infection, which is capable of causing mortality on a massive scale – thousands were washed up on the shore in June 1968 – reserve stocks of this now legally protected fish have been successfully introduced to neighbouring Loch Sloy and the Carron Reservoir.

The common scoter is misleadingly named, for the entire Scottish breeding population is probably less than 100 pairs. The few scoter nests found on Loch Lomond have all been on the islands, the eggs concealed beneath ling heather (Calluna vulgaris), bramble (Rubus fruticosus) or dead bracken. Spring counts of territory-holding scoters in the island strewn Luss–Strathcashell basin showed that the population peaked at nine pairs in 1977. Attempts at census-ing females with young after the males had returned to the sea met with only limited success. Numbers of birds fell away from 1978, with only sporadic sightings after 1987. The buildup of powerboat activity in the feeding/nursery areas and the impact of predatory mink on vulnerable incubating females undoubtedly played their parts, but another contributory factor in the scoter’s decline may have been the effect on duckling survival of overwhelming competition for food from large shoals of the introduced ruffe which, like the scoter, feed exclusively on bottom-dwelling invertebrates.

A comparative newcomer to Loch Lomondside is the Greenland white-fronted goose, the first small flocks of this legally protected species wintering regularly in the Endrick Marshes from 1960. After a slow but steady increase, the late winter population has levelled out at a maximum of 350 birds.

Between 1979 and 1995, one or two pairs of whooper swans nested almost annually in the Endrick Marshes (Fig. 9.15). Originally pinioned captives that escaped or were released from a local wildfowl collection, these were gradually replaced by free-flying descendants. For those cygnets that survived the critical first few days of life, predation by marauding foxes (Vulpes vulpes) is believed to be the principal cause of losses at the juvenile stage. Usually the surviving full grown young dispersed from their natal area in the following spring; perhaps coincidentally, but often at the same time as migrating whooper swans were passing through the Endrick Marshes en route to their breeding grounds in the far north.

Fig. 9.15 Whooper swans nested regularly in the Endrick Marshes for a number of years.

Of all the fish-eating birds associated with the Loch Lomond area, the one which most attracts the public’s attention is undoubtedly the osprey. Once lost to Britain as a breeding species through being harried by gamekeepers and collectors, the osprey began recolonising the Scottish Highlands from about 1954. For local ornithologists it took another 36 years of patient waiting before a pair reared young on Loch Lomondside in 1990, the first for certain since 1829 when a pair that nested annually on top of Inchgalbraith Castle was destroyed. After two successful breeding seasons, disaster struck in 1992, when the ospreys were robbed of their eggs, and only the male returned to the site in 1993. Fortunately, a second pair successfully reared three young in a more secluded locality in that year, choosing an old stag-headed oak tree to build their large wind-proof nest instead of the more usual Scots pine. Yet another pair nested for the first time in 1996. Loch Lomond is bountiful enough to support additional pairs of ospreys and, given freedom from disturbance and deliberate persecution, numbers are likely to increase in future as the fledged young that have survived the hazardous period of inexperience reach sexual maturity at around three to four years old. From many observations made on ospreys hunting over the loch and nearby waters, the most frequent prey item is the pike. As the level of the loch falls in late summer, the bottom-living flounder is occasionally taken around the sandy mouth of the River Endrick.