Llyn Tegid Research Articles

The delivery of multiple benefits on the Llyn Tegid reservoir safety improvements project

When Wales’ largest natural lake, Llyn Tegid, required significant reservoir safety works, the execution of sympathetic yet well-engineering solutions ensured that the scheme could stand the test of time and achieve multiple benefits for future generations. Placing sustainability at its heart, the scheme, delivered in Spring 2023, totalling £7 million, has involved strengthening works to 3 km of embankments to protect the popular tourist town of Bala from extreme weather. Boosting the wellbeing of residents and visitors within the picturesque Snowdonia landscape, works on the high-risk reservoir did not come without unique challenges. From designing for overflowing events and significant mature tree removal, to protecting internationally important habitats and working within the live reservoir basin, to name just a few. The scheme's success has been a testament to building the right team, implementing the right contractual and management controls, and establishing the right culture for compliant and high-quality solutions. Opportunities for carbon reduction and maximising value for money have been taken alongside new works to facilitate possible future expansion of Bala Lake Railway. Involving the community at every stage of this award-winning scheme, the delivery of benefits has been many, and the experiences are ones to live on for all.

Dee regulation reservoirs

The management of water resources on the River Dee represents a major example of advanced river basin management. It combines the supply of water, flood alleviation, fishery management, recreation and hydro-power generation. Three reservoirs, Llyn Tegid, Llyn Celyn and Llyn Brenig assist in managing flows in the River Dee. A fourth, Alwen Reservoir, supplies water directly by pipeline. The history, reservoir development and operation of the Dee Regulation scheme are discussed.

The influence of sluice gate operation on the migratory behaviour of Atlantic salmon Salmo salar (L.) smolts

ABSTRACTNumerous studies have examined the effects of high-head dams on salmonid smolt migration, but few have examined smolt behaviour at sluices managed to regulate water levels. We quantified passage success and time to passage of wild and hatchery origin juvenile (smolt) Atlantic salmon (Salmo salar L.) migration in relation to sluice operation (for water level and flood risk management) at Bala sluices on the upper River Dee, North Wales, including the occurrence of flow-reversal conditions from the Dee to Llyn Tegid (Lake Bala) immediately upstream. Ninety four smolts (67 wild, 27 hatchery origin) were caught, acoustic tagged, released at the capture site and tracked with a fixed receiver array in April to May 2015. Of the tagged fish, 91.5% successfully reached and passed the sluice gates. Of the tracked smolts that reached the sluices, 6.6% failed to successfully migrate downstream through the sluices and 3.2% took over 4 days to pass. There was no significant difference in travel speed, nor the proportion successfully passing, between wild and hatchery reared fish. Smolts migrated quicker at higher flows. Smolts travelled at lower speeds through the sluices than the preceding section from which they originated, suggesting that migration may have been delayed by the sluice gates. Smolts passed through the sluice reach more quickly with higher discharge. Specifically, smolts moved quicker through the sluice reach when the aperture of the gate nearest the outside bend and thalweg increased, but the heights of the other gates did not significantly affect smolt speed past the structure. Flow reversal episodes occurred only by day, whereas more smolt activity occurred by night (66.5% between dusk and dawn); under these conditions we found little evidence for loss of fish to the lake (three fish [3.2%] visited the lake and did not pass the sluices, but were last detected above the sluices), or contribution to delayed passage, as a result of flow reversal. It is concluded that at sites operating undershot sluices, where smolts migrate, upper water column orientated migration routes should be maximized where the thalweg hits the structure as this is likely to be the main route of transit adopted by smolts.

Assessment and conservation of whitefish (Coregonus lavaretus (L.)) in the U.K.

The whitefish (Coregonus lavaretus (L.)) is of high biodiversity value in the U.K., where it exists as a total of only seven native populations in England (Brotherswater, Haweswater, Red Tarn and Ullswater), Scotland (Loch Eck and Loch Lomond) and Wales (Llyn Tegid also known as Bala Lake), and is protected by national conservation legislation. However, an absence of fisheries means that information on its populations is scarce and must be obtained by dedicated surveys and associated activities. A standardised national assessment protocol using hydroacoustics and survey gill netting is described and results are presented from its use on the three whitefish populations of Scotland and Wales. For the remaining four English populations where the assessment protocol has not yet been specifically applied, comparable data are available from similar surveys, augmented by long-term fish entrapment records at one lake. These surveys revealed that the whitefish populations of Loch Eck, Red Tarn and Ullswater were in favourable condition. However, the condition of whitefish in Brotherswater, Haweswater, Llyn Tegid and Loch Lomond was considered to be unfavourable. Conservation measures specific to the whitefish populations of greatest concern in Haweswater, Llyn Tegid and Loch Lomond are described, including the management of water levels, local control of nesting cormorants (Phalacrocorax carbo (L.)) and establishment of refuge populations.

Assessment and conservation of gwyniad (Coregonus lavaretus (L.)) in Llyn Tegid, U.K.: persistence in the face of eutrophication, water level fluctuations and ruffe (Gymnocephalus cernuus (L.)) introduction

The whitefish (Coregonus lavaretus (L.)) exists as only one native population in Wales, U.K., where it occurs in Llyn Tegid and is known as the gwyniad. This population is of national conservation importance but faces a number of environmental threats. Although eutrophication has not directly impacted on gwyniad habitat availability, associated low oxygen levels in the hypolimnion periodically approach its tolerance limit of 2 mg L-1. Anthropogenic water level fluctuations and a 1980 introduction of ruffe (Gymnocephalus cernuus (L.)), a predator of gwyniad eggs, also pose potential threats. Despite these concerns, gill-netting surveys in the 1960s, 1991, 2003 and 2008 have shown no marked changes in gwyniad population biology in terms of length, weight and condition factor. Furthermore, hydroacoustic surveys from 2003 to 2009 have shown an increasing trend in total fish abundance. On the basis of gill-netting data, this increase is shared by gwyniad which in July 2009 reached a population density of 2,302.2 fish ha-1 (lower and upper 95% confidence limits of 1,795.8 and 2,951.4 fish ha-1, respectively). Nevertheless, a precautionary approach has been adopted to the conservation of this unique population and from 2005 to 2007 a translocation programme transferred 81,300 eggs from 366 male and 50 female gwyniad to the nearby water body of Llyn Arenig Fawr. Monitored hatching rates were generally high and in 2009 a hydroacoustic and gill-netting survey revealed that although the fish community of this site was sparse (1.7 fish ha-1, with lower and upper 95% confidence limits of 0.8 and 3.8 fish ha-1), it now included adult gwyniad. Although it does not yet confirm successful translocation, this observation does demonstrate that the gwyniad is able to reach sexual maturity in the recipient site.

Sediment fingerprinting as an environmental forensics tool explaining cyanobacteria blooms in lakes

Cyanobacteria (blue-green algae) blooms in water bodies present serious public health issues with attendant economic and ecological impacts. Llyn Tegid (Lake Bala) is an important conservation and amenity asset within Snowdonia National Park, Wales which since the mid-1990s has experienced multiple toxic cyanobacteria blooms threatening the ecology and tourism-dependent local economy. Multiple working hypotheses explain the emergence of this problem, including climate change, land management linked to increased nutrient flux, hydromorphological alterations or changing trophic structure - any of which may operate individually or cumulatively to impair lake function. This paper reports the findings of a sediment fingerprinting study using dated lake cores to explore the linkages between catchment and lake management practices and the emergence of the algal blooms problem. Since 1900 AD lake bed sedimentation rates have varied from 0.06 to 1.07 g cm −2 yr −1, with a pronounced acceleration since the early 1980s. Geochemical analysis revealed increases in the concentrations of total phosphorus (TP), calcium and heavy metals such as zinc and lead consistent with eutrophication and a rising pollution burden, particularly since the late 1970s. An uncertainty-inclusive sediment fingerprinting approach was used to apportion the relative fluxes from the major catchment land cover types of improved pasture, rough grazing, forestry and channel banks. This showed improved pasture and channel banks are the dominant diffuse sources of sediment in the catchment, though forestry sources were important historically. Conversion of rough grazing to improved grassland, coupled with intensified land management and year-round livestock grazing, is concluded to provide the principal source of rising TP levels. Lake Habitat Survey and particle size analysis of lake cores demonstrate the hydromorphological impact of the River Dee Regulation Scheme, which controls water level and periodically diverts flow into Llyn Tegid from the adjacent Afon Tryweryn catchment. This hydromorphological impact has also been most pronounced since the late 1970s. It is concluded that an integrated approach combining land management to reduce agricultural runoff allied to improved water level regulation enabling recovery of littoral macrophytes offers the greatest chance halting the on-going cyanobacteria issue in Llyn Tegid.

Invasive fish species in the largest lakes of Scotland, Northern Ireland, Wales and England: the collective UK experience

An invasive species is defined as an alien (or introduced or non-native) species whose establishment and spread threaten ecosystems, habitats or species with harm. Such threats to UK lake fish communities have long been appreciated and this review assembles case histories, including new data, from the largest lakes of Scotland, Northern Ireland, Wales and England to examine the hypothesis that at least some of these introductions have become invasive. Loch Lomond in Scotland has experienced six introductions [chub (Leuciscus cephalus), common bream (Abramis brama), crucian carp (Carassius carassius), dace (Leuciscus leuciscus), gudgeon (Gobio gobio) and ruffe (Gymnocephalus cernuus)], of which the most significant has been that of the percid ruffe, which has been implicated in a recent decline of the native coregonid whitefish (Coregonus lavaretus). In Northern Ireland, the introduction of the cyprinid roach (Rutilus rutilus) to Lough Neagh has apparently had a negative impact on some overwintering waterfowl, although the native coregonid pollan (Coregonus autumnalis) remains abundant. Llyn Tegid in Wales has received three introductions [rudd (Scardinius erythrophthalmus), ruffe and silver bream (Blicca bjoerkna)], although no impacts on the native whitefish or other fish populations have been observed. In England, individuals of at least 12 native and non-native fish species have been brought to Windermere for the purpose of live-baiting, although only those of the cyprinids roach and common bream have established abundant populations. At the same time, the native salmonid Arctic charr (Salvelinus alpinus) has declined markedly while the native esocid pike (Esox lucius) has shown changes in abundance, distribution and individual condition, although these developments have not been shown to be causally linked. None of these introductions were sanctioned by appropriate fisheries or other regulatory bodies and almost all of them probably arose from the release or escape of live-bait used by pike anglers. Of the 10 species introductions documented here, four (common bream, gudgeon, roach and ruffe) have established abundant populations and two of these (roach and ruffe) have apparently caused or currently threaten harm, supporting the hypothesis that at least some of these introductions have become invasive.

Genetics of whitefish and vendace in England and Wales

Proportion of loci polymorphic (P) and mean heterozygosity per locus (Hexp) were P= 0.130 and Hexp= 0.096 for C. albula from the English Lake District and P= 0.217 and Hexp= 0.046 for C. lavaretus from the English Lake District and Llyn Tegid, Wales in 1991–2. Significant deviation from the Hardy‐Weinberg model was observed at the superoxide dismutase (sSOD*) locus in C. albula from Bassenthwaite Lake. This could have been due to chance, to the Wahlund effect or to selection. Genetic distances between the two species were consistent with their taxonomy and genetic differentiation was much greater for the C. lavaretus populations than for the two geographically close C. albula stocks. Llyn Tegid C. lavaretus showed unique alleles at two loci and conservation of fish in this lake is therefore of great importance. Red Tarn C. lavaretus differed most from other Lake District populations probably due to founder effects from early stocking events and/or from selection due to the high altitude of this lake.

Three decades of post-impoundment data on the littoral fauna of Llyn Tegid, North Wales

Faune collectee avant la construction du barrage (1951-52) et apres (1978-79). Nombreuses especes eliminees au debut mais a mesure que le niveau d'eau a change de moins en moins frequemment ces especes ont reapparu dans la zone littorale. Cependant, quelques taxa semblent avoir disparu alors que d'autres ont pris plus d'importance. Peu de changement dans la densite des animaux

The distribution of perch, Perca fluviatilis L. throughout their first year of life in Llyn Tegid, North Wales

The distribution of 0+ perch, Perca fluviatilis L., in a lacustrine environment is described. Since the perch occupied many different habitats within the ecosystem throughout their first year of life a number of sampling techniques were required to sample the population. The early larvae and post larvae were planktonic and their distribution could be related to the effect of the winds. As soon as the young perch developed fins an inshore migration began. Virtually all the fish had completed this migration by the time they reached a total length of 19 mm but the majority of the population reached the shoreline before attaining this size. During June and August the 0+ perch formed large shoals around the shoreline especially in sheltered areas in water less than 3 m deep. At the end of August probably in response to falling lake temperatures the perch fry migrated into deeper water.

Observations on the development of Bunodera luciopercae (Müller, 1776) (Trematoda: Allocreadiidae) under field and laboratory conditions

Abstract. The intramolluscan development of Bunodera luciopercae was studied in laboratory infected pisidia maintained at three thermal regimes and compared with the seasonal development within a population of naturally infected first intermediate hosts at Llyn Tegid, Wales. At 4–8°C B. luciopercae did not develop beyond the sporocyst stage, although the development at 16–21°C We s similar to that reported by previous workers. The early stages of the intramolluscan development of B. luciopercae at Llyn Tegid were similar to the observed development at 16–21°C. However, the results suggest that falling autumn‐winter temperatures may initiate the production of immature cercariae within first generation rediae. Cercariae matured and were shed at Llyn Tegid during a short period between March and May. Live, juvenile B. luciopercae were artificially transferred from recently killed perch Perca fluviatilis, gill netted from Llyn Tegid, into live uninfected, laboratory maintained perch. The effect of temperature on the development of B. luciopercae in its definitive host was investigated at four thermal regimes. At 16–20°C development did not proceed normally and the infection had disappeared after 130 days. At 4–8°C and at natural environmental temperatures, gravid flukes were produced after 158–168 days. An increase in temperature on infected fish maintained at 4–8°C for 43 days did not stimulate parasite maturation. It is suggested that B. luciopercae may require an extended period of vernalization to elicit maturation in its definitive host and that temperature has a major influence on the life history of this parasite.

Host specificity of the parasite fauna of perch Perca fluviatilis L. from the British Isles, with special reference to a study at Llyn Tegid (Wales)

Five‐hundred and fifty‐nine perch (Perca fluviatilis L.) were examined from Llyn Tegid between January 1975‐July 1976 for protozoan and metazoan parasites. Sixteen species of parasites were recorded, and these results were compared to previous studies at Llyn Tegid, and elsewhere in the British Isles. It was concluded that the parasite fauna of perch is influenced by the diversity and abundance of the local aquatic invertebrate fauna, the local ichthyofauna, the local piscivorous avian fauna and the history and geographic isolation of the environment. The importance of a large series of observations on a variety of habitats was stressed.

A technique for determining the distribution of pelagic fish larvae

A technique is described for studying small scale distributional patterns of fish larvae in the pelagic region. A plankton net is mounted beneath the bows of a small boat, the contents of the net are emptied continually by a suction pump. This system has advantages over previous techniques as it allows a large number of small discrete samples to be taken over a wide area in a short space of time. Preliminary results showed the population of perch larvae in Llyn Tegid is extremely clumped and the overall abundance of the larvae decreases as samples are taken progressively further away from the south‐west end of the lake.

Studies on grayling, Thymallus thymallus L., in Llyn Tegid and the upper River Dee, North Wales.

Scale and length/weight data from 2071 Llyn Tegid grayling and 1803 River Dee grayling were used for age and growth determinations. The time of scale annulus formation varied from autumn in some years to spring in other years. Seasonal changes in length, weight and the condition factor were described. The main growth period was from spring to autumn with very little growth occurring during the winter. Annual growth in length was back‐calculated from scale measurements, and von Bertalanffy's model was fitted to the resulting length for age data. Comparisons were made between the specific growth rates and ultimate lengths (Lx) of Llyn Tegid and River Dee grayling, and between the growth of male and female grayling. Males grew faster than females after the onset of sexual maturity. Calculated lengths were converted to weights using a combined length/weight relationship for Llyn Tegid and River Dec grayling. Changes were evident in this relationship throughout the life of the fish.

Film and television in fishery research at Llyn Tegid (Bala Lake), Wales

A 35 mm Robot Royal camera and an electronic flash unit were used at 20–40 m depth in an attempt to identify fish shown on echo‐sounder traces. No photographs were obtained. An 8 mm Eumig automatic electric‐drive cine camera system was used with daylight at 2–8 m depth to test if the equipment served as a deterrent to the fish. Fish were filmed and their behaviour was unaffected by the presence of the equipment. A simple closed‐circuit television system was used with daylight at 0–3 m depth. Low contrast, inherent in the particular equipment, prevented its use at greater depths. Meaningful observations of perch were possible. The use of television camera tubes sensitive to extremely low levels of daylight, and of infra‐red sensitive tubes with an infra‐red light source is briefly discussed. It is concluded that such systems might help to identify problems of netting technique and assist with observations of fish behaviour.

A further note on the seasonal formation and movement of the thermocline in lakes

Measurements of air temperature, wind speed and the temperature depth profile at Llyn Tegid, North Wales, from April to November 1969, are used to establish equations which are then used for the observed meteorological data to predict the temperature profile of the lake during this period and in particular the conditions under which the thermocline rises or sinks. A fair measure of agreement is found between observed and predicted profiles.

The profundal fauna of Llyn Tegid, North Wales

Benthic fauna samples were quantitatively collected each month from the 6 to 40 m depth zone of Llyn Tegid for a period of one year. The seasonal distribution, abundance and life cycles of the invertebrate species are discussed in addition to a general description of the physical and chemical environment in which they live. The abundance and composition of the profundal fauna is compared with that of a similar survey carried out by D. R. Dunn in 1951/2 and shows a fourfold increase in total numbers of animals. The contribution to the increased profundal fauna of all animals recorded in 1951/2 and of those that have colonized this zone since that time are discussed.

The effect of water level fluctuations on a littoral fauna

The littoral fauna of Llyn Tegid, North Wales, in 1968/9 is compared with the results of similar faunal investigations made by Rothwell(née Dunn) in 1951/2 (Dunn, 1953) and Hynes in 1957 and 1959 (Hynes, 1961). The results show the long term effects upon the littoral fauna of the change in mean water level and the increased water level fluctuations produced for a time by the controlled outflow scheme, which came into operation in 1955. In 1961 Hynes recorded big reductions in numbers and variety of invertebrates living in the littoral zone. The reduced water level fluctuations in recent years has resulted in a re‐establishment of some of the fauna.

Some observations on the food of the gwyniad Coregonus clupeoides pennantii Valenciennes of Llyn Tegid (Lake Bala), North Wales

The seasonal variations in the diet of adult gwyniad Coregonus clupeoides pennantii=C. lavaretus from Llyn Tegid, North Wales were studied. Stomachs were examined to determine fullness, volume and identity of contents.A clear seasonal cycle in food intake was found. Feeding rates were low from January to April but increased during the summer (May‐June) and remained at a high level until December. The period of low feeding intensity coincided with the time of spawning and the time of annulus formation of both scales and otoliths. The diet showed seasonal changes and two main periods were distinguished : December to July, when the fish fed mainly on bottom fauna, and August to November, when the diet included both bottom fauna and midwater and surface foods.The gwyniad were shown to be opportunistic in feeding, the composition of the diet reflecting availability of food items rather than selective feeding on the part of the fish.

The parasite fauna of the fish of the Shropshire Union Canal, Cheshire

A survey was made of the parasites of 603 roach Rutilus rutilus (L.), 15 bream Abramis brama (L.), 201 perch Perca fluviatilis L., 30 pike Esox lucius L. and four eels Anguilla anguilla (L.) caught in the Shropshire Union Canal at Backford, Cheshire from December 1964 to August 1966. Twenty‐seven species of parasites were found, 17 in roach, seven in bream, ten in perch, ten in pike and two in the eel. Two species of Protozoa, seven species of Monogenea, five species of Digenea, six species of Cestoda, two species of Nematoda, one species of Acanthocephala, two species of Hirudinea, one species of Crustacea and mollusc glochidia were recorded. The following parasites are believed to be new records for the British Isles: Henneguya oviperda (Cohn, 1895), Dactylogyrus suecicus Nybelin, 1936, D. wunderi Bykhovskii, 1931, Asymphylodora kubanicum (Isaichikov, 1923), and Philometra rischta Skryabin, 1917.One table shows the species of parasites found, together with data on the site of occurrence in the host, and the percentage and intensity of infection of the fish. A second table compares the occurrence of the parasites in four other localities in the British Isles, Loch Lomond Scotland, Llyn Tegid (Bala Lake), Merionethshire, Rostherne Mere, Cheshire and the River Lugg, Herefordshire. A further column gives the normal hosts in the U.S.S.R.A limited comparison is made of the numerical occurrence of six species of parasites in the canal, Llyn Tegid and Druzno Lake, Poland. It is concluded that unless relatively large samples of fish of all length groups are collected on a regular basis throughout the year such comparisons will have little meaning.The concept of the characterization of parasite faunas is briefly noted. It is suggested that the high degree of host specificity shown by many of the species of parasites is evidence in support of the concept.