The importance of Loch Lomond National Nature Reserve for Fish

Loch Lomond NNR with 19 fish species is ranked top in fish conservation value of 235 NNRs in Great Britain due to species diversity, presence of rare species and unusual forms and combinations.     

A comparative assessment of temporal variation in diet of powan, Coregonus lavaretus (L.), from Loch Lomond and Loch Eck, Scotland, U.K.

Stomach contents of powan caught throughout the year from Loch Lomond and Loch Eck were examined. Adult powan in Loch Lomond fed mainly on planktonic Cladocera, switching to benthic food during December-April. Bosmina coregoni was the principal planktonic food with Daphnia hyalina an important late summer and autumn prey. Loch Eck powan fed throughout the year on chironomid larvae and Pisidium spp. from the benthos and ingested large amounts of non-food material. Mean dry weights of food in stomachs were correlated with water temperature in Loch Lomond but not in Loch Eck and were higher in powan from Loch Eck over most of the year.     

Ferox Trout (Salmo trutta) as `Russian dolls': complementary gut content and stable isotope analyses of the Loch Ness foodweb

1. Conventional collection methods for pelagic fish species (netting, trawling) are impractical or prohibited in Loch Ness, U.K. To investigate trophic relationships at the top of the Loch Ness food web, an alternative strategy, angling, provided samples of the top predator, the purely piscivorous ferox trout ( Salmo trutta ).
2. The gut contents of these fish provided further samples of prey-fish, and subsequent examination of prey-fish guts revealed their dietary intake, analogous to the famous nested `Russian dolls'. Each trophic level separated by gut content analysis provided further complementary samples for stable isotope analysis and thus information on the longer term, assimilated diet.
3. Ferox trout exhibited considerable cannibalism to supplement a diet of Arctic charr ( Salvelinus alpinus ). However, conspecifics stemmed from a lower isotopic baseline in relation to charr, so ferox trout exhibited a lower trophic level than predicted (4.3) by using the δ¹⁵N values. Charr displayed dietary specialisation with increasing length, and isotopic values supported by the gut data placed the charr at a trophic level of 3.5. The isotope data also indicated that charr carbon was primarily autochthonous in origin.     

A seasonal and ecological study of the phytoplankton of Loch Lomond

The seasonal succession of phytoplankton in Loch Lomond has been studied both quantitatively and from observations on net plankton. From a qualitative investigation of net phytoplankton Loch Lomond may be described as diatom-desmid in nature although from the quantitative studies the general domination of the population by diatoms becomes clear. During the vernal phytoplankton increase diatoms contributed more than 90% of the population throughout the loch. The bulk of the phytoplankton production occurred in the southern region, where the standing crop was considerably greater throughout the year than in other regions of the loch.Patterns of seasonal succession are described for all species which make an important contribution to the productivity of the loch and the observed successions related to measured physical and chemical changes in the water. Explanations are put forward to account for the absence of a second (autumnal) pulse ofMelosira in Loch Lomond. The appearance ofAnabaena circinalis is a possible indication of the changing trophic status of the southern region of the loch.     

The genetics of sympatric Arctic charr [Salvelinus alpinus (L.)] populations from Loch Rannoch, Scotland

Two morphologically and ecologically distinct forms of Arctic charr, Salvelinus alpinus , are found in Loch Rannoch, Scotland. The differences in morphology are adaptations to different modes of life, one being pelagic, the other benthic. Both forms have been the subjects of extensive genetic studies including cytogenetics, nuclear and mitochondrial DNA analysis, and protein electrophoresis. Significant differences between the two forms are revealed by some techniques but not others and provide evidence for the reproductive isolation of these two morphs. The findings are discussed in relation to the derivation of sympatry and the phylogenetics of Arctic charr.     

Climate-induced changes in high elevation stream nitrate dynamics

Mountain terrestrial and aquatic ecosystems are responsive to external drivers of change, especially climate change and atmospheric deposition of nitrogen (N). We explored the consequences of a temperature-warming trend on stream nitrate in an alpine and subalpine watershed in the Colorado Front Range that has long been the recipient of elevated atmospheric N deposition. Mean annual stream nitrate concentrations since 2000 are higher by 50% than an earlier monitoring period of 1991–1999. Mean annual N export increased by 28% from 2.03 kg N ha⁻¹ yr⁻¹ before 2000 to 2.84 kg N ha⁻¹ yr⁻¹ in Loch Vale watershed since 2000. The substantial increase in N export comes as a surprise, since mean wet atmospheric N deposition from 1991 to 2006 (3.06 kg N ha⁻¹ yr⁻¹) did not increase. There has been a period of below average precipitation from 2000 to 2006 and a steady increase in summer and fall temperatures of 0.12 °C yr⁻¹ in both seasons since 1991. Nitrate concentrations, as well as the weathering products calcium and sulfate, were higher for the period 2000–2006 in rock glacier meltwater at the top of the watershed above the influence of alpine and subalpine vegetation and soils. We conclude the observed recent N increases in Loch Vale are the result of warmer summer and fall mean temperatures that are melting ice in glaciers and rock glaciers. This, in turn, has exposed sediments from which N produced by nitrification can be flushed. We suggest a water quality threshold may have been crossed around 2000. The phenomenon observed in Loch Vale may be indicative of N release from ice features such as rock glaciers worldwide as mountain glaciers retreat.     

The fish community of Loch Lomond,Scotland: its history and rapidly changing status

The fish community of Loch Lomond is of national importance. Its diversity of species and rare populations of powan (Coregonus lavaretus) and freshwater feeding river lampreys (Lampetra fluviatilis) warrant high conservation status. It is also of value for its sport fisheries for sea-trout (Salmo trutta), salmon (Salmo salar) and pike (Esox lucius). Historical records demonstrate that the species composition of the fish community has remained stable over a very long period until recently when a series of introductions of fish species new to the catchment has resulted in successful colonisation by a number of species. These have resulted in fundamental changes in the ecosystem. Here using historical records the long-term stability of the fish community is examined, recent rapid changes in the fish community are documented and some of the resultant effects of changes in the fish community are demonstrated.     

Assessment of eutrophication in Loch Lomond by desk analysis

Phosphorus and chlorophyll a levels were predicted for Loch Lomond from desk-derived P loss coefficients and flushing rates related according to existing eutrophication models. These were in close keeping with measured values.