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.     

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 ( L_x ) 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.     

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.     

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.     

Growth and survival of Atlantic salmon (Salmo salar) in Llyn Dwythwch, North Wales

SUMMARY. Atlantic salmon fry have been annually stocked into Llyn Dwythwch, North Wales, since 1969, in an attempt to increase the natural stocks of the area. The growth and survival of 1- and 2-year-old salmon were investigated, and compared with that of other lake-reared populations and also with salmon in the natural stream environment. Lake-reared salmon follow the same patterns of slow and rapid growth as found for river fish, but the growth rate was superior in the former. The variation in length – weight relationship with age and sex was investigated. Survival rates in general compared favourably with the survival in rivers, with high mortality rates of salmon in Llyn Dwythwch resulting from predation at spring stocking by the resident brown trout. This was later avoided by stocking larger fish in the autumn.     

Translocation of marbled African lungfish,Protopterus aethiopicus (Telostei: Protopteridae), and its fishery in Lake Baringo,Kenya

The translocation of the marbled African lungfish Protopterus aethiopicus into Lake Baringo created a new fishery for the local community, who capture them primarily in a bottom-set long line fishery. Its introduction, development and current fishery status in the lake are documented. Annual catch data were obtained from the District Fisheries Office, while catch and effort data of the long line fishery were recorded at one active fish-landing site between February and October 2001. Lungfish comprise a significant component of commercial landings, sometimes exceeding catches of the Baringo tilapia Oreochromis niloticus baringoensis as the most landed species by weight. Daily catch rates and effort varied considerably, ranging from 5.51–15.18kg day^?1 and from 50–590 baited hooks day^?1, respectively. Daily catch per fisher ranged from 0–35.72kg, while the overall mean catch per unit effort (CPUE) was only 0.003kg per hook-hour. This study provides the only baseline CPUE data for a lungfish long line fishery that the authors are aware of, for comparison with future studies in this or other lakes where lungfish are similarly exploited. Recommendations for improved management and the maintenance of a viable lungfish long line fishery in Lake Baringo are presented.     

The life cycles of Leptophlebia vespertina (L.) and L. marginata (L.) (Ephemeroptera) in Llyn Dinas, North Wales

Data is presented on the life cycles of Leptopblehia vespertina (L.) and L. marginata (L.) in Llyn Dinas, an oligotrophic North Wales lake. Both species are univoltine and growth continues throughout the winter although somewhat retarded. Except during July and August there is a clear size separation of the two species, L. marginata being larger and emerging earlier. The egg incubation period was determined directly from laboratory studies. The results are discussed in relation to previous research in the English Lake District.     

Trout in Llyn Alaw, Anglesey, North Wales. I. Population structure and angling returns

An account is given of the survival and contribution to sport fishing of stocked trout and natural river trout in the impounded reservoir, Llyn Alaw, in Anglesey, North Wales. Scales from 2143 trout caught by angling and netting during the first four years after impoundment were used to determine the age and origin of Llyn Alaw fish. The success and future of Llyn Alaw as a trout fishery are discussed.     

The rainbow trout Salmo gairdneri (Rich.) fishery of Lake Titicaca

Rainbow trout were introduced to Lake Titicaca in 1942. A commercial trout canning operation started in 1961 but terminated in 1970. Data for this study were collected in 1966 and 1967, with the object of examining the life history, biology, and commercial fishery of Titicaca rainbow trout. Trout were caught commercially and experimentally by gillnets in different parts of the lake.
Lake Titicaca lies across the border of Peru and Bolivia at 3212 m above sea level. The physico-chemical characteristics of the lake appear ideal for self-sustaining populations of rainbow trout. Growth was constant throughout the year, and was good in relation to growth rates of rainbow trout in other parts of the world. Spawning took place in the tributaries in the winter. Recruitment to the fishery occurs in 7.62 cm stretch mesh gillnets at about 27 cm fork length.
The total annual commercial catch increased to 500 metric tons in 1965 before subsequently decreasing. The simplest explanation for the decline in total catch would be the increase in fishing mortality due to increased fishing effort, although it is possible that the decline in water level has had some effect. It appeared possible that the lake could sustain an annual catch of about 350 tons.     

Genetic impoverishment and cross-incompatibility in remnant genotypes of Ziziphus celata (Rhamnaceae), a rare shrub endemic to the Lake Wales Ridge, Florida

The loss of genetic diversity in fragmented populations ofself-incompatible plant species may result in sexual reproductive failure andlocal extinctions. Florida ziziphus (Ziziphus celata) is aself-incompatible clonal shrub known only from five genetically depauperatepopulations on the Lake Wales Ridge, Florida, USA. Recovery of this speciesrequires identification of cross-compatible genotypes that can be used to createviable (i.e., sexually reproducing) populations. To further development of arecovery program for this highly imperiled species, we investigated its geneticstructure and sexual reproductive viability. We used random amplifiedpolymorphic DNAs (RAPDs) to investigate genetic variability within remnantpopulations and we conducted experimental compatibility trials to determine thecross-compatibility of remnant genotypes. One hundred and ninety-nine uniquestem samples collected from one ex situ and fivein situ populations were assayed for the presence orabsence of a band for 32 RAPD markers. Based on unweighted pair-group meancluster analysis (UPGMA), only 11 multi-locus genotypes (MLGs) were identified.Eight of these MLGs correspond to MLGs identified in an earlier allozyme study.In addition, we identified three new RAPD-based MLGs. Three of the five naturalpopulations consisted of only one MLG, while the largest and most geneticallydiverse population comprised only four MLGs. Coefficients of similarity rangedfrom 96.6% for the most closely related MLGs to 20.7% for the most distantlyrelated. The compatibility trials demonstrated that most MLGs arecross-incompatible. With 69% of all possible one-way crosses tested (38/55), wehave identified only eight compatible crosses via germination trials. Based onthe results of the compatibility trials, we assigned MLGs toself-incompatibility (SI) mating types. On present evidence, the currentbreeding population of Florida ziziphus may comprise as few as two SI matingtypes. These SI mating types will be used to guide future breeding efforts andan experimental introduction.     

Ecology and role of zooplankton in the fishery of Lake Naivasha

Taxonomic composition, distribution, community structure and seasonality of Lake Naivasha zooplankton between 1978 and 1980 are described. The ecological status of the zooplankton in relation to prevailing ecological factors and the lakes fishery are discussed. Species composition of the zooplankton community in Lake Naivasha has been remarkably constant since first observations between 1929 and 1931. The community structure and distribution of the zooplankton in the lake varied little from July 1978 to July 1980, however, there was evidence of species succession among the larger zooplankters, especially the cladocerans. In the littoral area zooplankton contribute significantly to the food and production of juvenile fish. There is an absence of fish zooplanktivores in the limnetic area of the lake. Consequently the limnetic zooplankton is not utilised by higher trophic levels.     

The evolution of the fishery of Oreochromis niloticus (Pisces: Cichlidae) in Lake Victoria

The Lake Victoria ecosystem has experienced changes associated with fishing levels, a rise in lake level in the 1960s, fish introductions, and human activities in the drainage basin. Following the fish introductions of the 1950s and early 1960s, Oreochromis niloticus has become the most abundant and commercially important species among the tilapiines, and the only species which has managed to co-exist with the Nile perch in Lakes Victoria and Kyoga. There is, however, little published information on the biology and ecology of the specie in the new habitats. It has therefore been found necessary to initiate studies on the characteristics of O. niloticus in Lake Victoria.     

The comparative feeding behaviour of brown trout, Salmo trutta L. and Atlantic salmon, Salmo salar L. in Llyn Dwythwch, Wales.

A detailed comparative study of the diets of natural brown trout and stocked Atlantic salmon in Llyn Dwythwch, North Wales, was carried out over a period of 13 months. The annual and seasonal composition of both diets was calculated by number, volume and occurrence methods. Food in relation to fish size was compared by Spearman rank correlation. Interspecific competition was only significant during the summer months when food was abundant. The bottom fauna was classified according to accessibility, and utilization of the fauna and electivity is discussed for each species. The similarity of diet between the salmon stocked into Llyn Dwythwch and those in Welsh rivers implies that the former is the result of inheritance rather than from interactive segregation with the lake trout.     

Recent changes in the fishery of a new tropical man-made lake, Lake Kamburu (Kenya)

Five years after inundation, two varieties of Cyprinus carpio —the common carp and the mirror carp, have appeared in the commercial fishery in Lake Kamburu. Species of Tilapia continue to remain the most abundant fish in the lake and their numbers are on the increase. The second most numerous species is Barbus while Labeo sp. seems to be declining. The numbers of Mormyrus have declined drastically. Species of the genera Tilapia, Barbus and Cyprinus are widely distributed within the lake; Labeo prefers the confluence of the rivers entering into the lake and Mormyrus has moved upriver.     

引水和疏浚工程支配下杭州西湖浮游动物的群落变化

研究了引水和疏浚工程支配下浅水、富营养化杭州西湖浮游动物群落的长期变化,包括浮游动物的优势种类组成、密度及生物量与水环境因子的相关分析.疏浚后的2003年调查中,西湖3个采样站的定量样品中共发现69种浮游动物,其中原生动物26种,轮虫27种,枝角类和桡足类各8种.Ⅰ站浮游动物年平均生物量从1990年的0.186mg/L上升到2003年的0.705mg/L,Ⅱ站和Ⅲ站分别从0.665mg/L和0.740mg/L上升到1.399mg/L和1.195mg/L.浮游动物数量组成中原生动物和轮虫平均占99%,并占78%的生物量.在1980～2003年期间,一些优势种类如砂壳纤毛虫（Tintinnoinea）、针簇多肢轮虫（Polyarthra trigla）和长额象鼻溞（Bosmina longirostris）等显著增加了它们的丰度和优势度;暗小异尾轮虫（Trichocerca pusilla）的优势度在引水后的1990～1995年增加了,但在疏浚后的2003年下降了;而20世纪80年代的一些优势种如毛板壳虫（Coleps hirtus）、螺形龟甲轮虫（Keratella cochelearis）和短尾秀体溞（Diaphanosoma brachyurum）等在3个采样站中失去优势种地位或消失.原生动物和轮虫生物量在营养水平较高的Ⅱ～Ⅲ站明显高于营养水平较低的Ⅰ站;长肢秀体溞（Diaphanosoma leuchtenbergianum）、长额象鼻溞、颈沟基合溞（Bosminopsis deitersi）和汤匙华哲水蚤（Sinocalanus dorrii）在营养水平较低的Ⅰ站具有较大的密度和生物量,而微型裸腹溞（Moina micrura）和粗壮温剑水蚤（Thermocyclops dybowskii）则在营养水平较高的Ⅱ～Ⅲ站具有较大的密度和生物量.西湖各类浮游动物在不同湖区形成不同的分布格局主要由引水水流和水体营养状态差异造成.1990～2003年期间,在采样站变异下,浮游动物中轮虫年平均生物量与水体年平均pH值和叶绿素a含量之间分别有极显著和显著的正相关关系,与水体透明度之间有极显著的负相关关系.引水后的1995年,与轮虫生物量最密切的生态因子是叶绿素a含量,而疏浚后水体碱性环境是影响轮虫生物量最密切的生态因子.     

Feeding habits of the clupeid Limnothrissa miodon (Boulenger), in Lake Kivu

A limnological sampling programme implemented during 1980 in Lake Kivu, Rwanda, confirmed a seasonal increase of the pelagic plankton biomass at the end of the dry season during the windy period of August/September. From plankton samples taken in the littoral and pelagic zones of the Lake it was concluded that a successful introduction of the freshwater clupeid Limnothrissa miodon Boulenger, during 1958–1960, had not obviously influenced the species composition of the Copepoda in the Lake. Examination of stomach contents of different length classes of Limnothrissa proved that the Kivu clupeid is not a strict planktonphagic species. Its diet is adapted to its life cycle and inshore/offshore migration patterns. In pelagic waters of the lake it is an exclusive plankton feeder, while in littoral waters it has more littoral bound feeding habits. Cannibalism was observed among individuals larger than 100 mm, near the margins of the lake. Echosoundings and periodic observations on stomach contents support the hypothesis that Limnothrissa feeds in the late afternoon and digests its food during the night, while a second feeding/digestion cycle starts in the early morning, at sunrise.     

Microsatellite evidence for high clonality and limited genetic diversity in Ziziphus celata (Rhamnaceae), an endangered, self-incompatible shrub endemic to the Lake Wales Ridge, Florida, USA

Genetic data are often crucial for designing management strategies for rare and endangered species. Ziziphus celata is an endangered sandhill shrub endemic to the Lake Wales Ridge of central Florida. This self-incompatible clonal species is known from only 14 wild populations, most of which are small (under 100 plants). Focusing on the five populations discovered in 2007, we evaluate the level of genetic diversity and identify clonal lineages within the wild populations of the species with a set of microsatellite loci. To account for somatic mutations and genotyping errors, we identified clonal lineages using a threshold cutoff for pair-wise genetic distances among samples. The microsatellites had up to 18 alleles/locus, and, consistent with outcrossing, samples were highly heterozygous (average population level H _o  = 0.69). Most populations of Z. celata consist of a single clone, and the most diverse population has only 10 clones. Overall Z. celata comprises 41 multi-locus genotypes, and 30 clonal lineages. With nearly 1,000 recorded plants (595 genotyped) and only 30 clonal lineages, Ziziphus celata is highly clonal: clonal richness, R = 0.049. The pair-wise distance method facilitates identification of clonal lineages, avoiding overestimation of clonal diversity. In most cases, the samples that grouped into a lineage were one to four plants differing from a surrounding genotype by a single microsatellite repeat insertion/deletion mutation, consistent with these having arisen via somatic mutations. Our data will enable managers to incorporate extant diversity from wild populations into ex situ collections. Additionally, our research demonstrates the utility of microsatellites for conservation of imperiled species, identifying genotypes of high priority for preservation.     

Habitat usage of Daubenton's bat (Myotis daubentonii), common pipistrelle (Pipistrellus pipistrellus), and soprano pipistrelle (Pipistrellus pygmaeus) in a North Wales upland river catchment

Distributions of Daubenton's bat (Myotis daubentonii), common pipistrelle, (Pipistrellus pipistrellus), and soprano pipistrelle (Pipistrellus pygmaeus) were investigated along and altitudinal gradient of the Lledr River, Conwy, North Wales, and presence assessed in relation to the water surface condition, presence/absence of bank‐side trees, and elevation. Ultrasound recordings of bats made on timed transects in summer 1999 were used to quantify habitat usage. All species significantly preferred smooth water sections of the river with trees on either one or both banks; P. pygmaeus also preferred smooth water with no trees. Bats avoided rough and cluttered water areas, as rapids may generate high‐frequency echolocation‐interfering noise and cluttered areas present obstacles to flight. In lower river regions, detections of bats reflected the proportion of suitable habitat available. At higher elevations, sufficient habitat was available; however, bats were likely restricted due to other factors such as a less predictable food source. This study emphasizes the importance of riparian habitat, bank‐side trees, and smooth water as foraging habitat for bats in marginal upland areas until a certain elevation, beyond which bats in these areas likely cease to forage. These small‐scale altitudinal differences in habitat selection should be factored in when designing future bat distribution studies and taken into consideration by conservation planners when reviewing habitat requirements of these species in Welsh river valleys, and elsewhere within the United Kingdom.     

Seasonal variations in phytoplankton size structure in Lake Cromwell (Laurentian Shield), Quebec

Seasonal variation in phytoplankton size classes was studied over the period of a year in a small, mesotrophic, brown-water lake. Throughout the sampling period, species from 2–16 μm (GALD) dominated the phytoplankten community. Small phytoplankters (2–8 μm) were predominant in winter and early spring populations while algae of 8–16 μm became important in summer (phytoplankton < 2 μm was not counted). Principal coordinate analysis resulted in a cyclic pattern of dates in the reduced space, winter and early spring samples being well separated from the other dates. In multiple linear regressions between environmental parameters and size classes, temperature was always the most important variable.