The results of the analysis of the contents of 274 brown trout stomachs taken over a period of one year from Llyn Alaw, in Anglesey, North Wales, are described. The annual composition and seasonal changes of the diet were determined using number, volume and occurrence methods. The bottom fauna is classified according to accessibility to the trout as food and the utilization and apparent selection of the fauna by the trout is discussed. Food in relation to trout size is considered in detail.
The littoral fauna of Llyn Tegid, North Wales, in 1968/9 is compared with the results of similar faunal investigations made by Rothwell(n6eDunn) in 195112 (Dunn, 1953) and Hynes in 1957and 1959(Hynes, 1961. Theresultsshow thelongtermeffectsupon thelittoralfauna 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. Thc reduced water level fluctuations in recent years has resulted in a re-establishment of some of the fauna. I. INTRODUCTIONThe conversion of natural lakes into reserviors for water supply and flood and drought control schemes results in changes in the level of the water. Changes in the mean level and increased fluctuations about the new mean, inevitably affect the littoral fauna. The effects are 2-fold. The fauna may be affected directly when organisms are left stranded by the receding flood water and the animals die of dessication. The ability of a species to follow changes in water level will determine its survival. Secondly, the change in mean level and increased fluctuations will not only alter the physical nature of the bottom, but result in loss of macrovegetation. Many species are deprived of a habitat and may be replaced either by new species or by increased numbers of existing species which are favoured by the new conditions. The changes that occur in the littoral zone will in turn affect the feeding and growth of fish.Llyn Tegid is a mesotrophic lake lying in the hilly county of Merionethshire, North Wales, at an altitude of 164 m. Before 1955 the outlet from the lake was controlled by sluices constructed by Thomas Telford in the early years of the 19th century so that the water level fluctuated over a range of 2 m. A further control outflow scheme came into operation in 1955 which enabled the lake to be controlled over a range of 4.3 m (14 ft) by reducing the minimum lake level. This provided short term detention capacity to control floods in the river downstream and water for release into the river to maintain flow during periods when it would naturally fall below this flow. Llyn Tegid storage water was kept as low as possible in the winter for flood prevention and about
Scales from 7071 barbel from the River Severn were used for age and growth determinations. The scales showed clear annual checks which were laid in May when most fish spawned. Scale structure and length frequency distributions showed an almost total absence of 1968 year class barbel. Growth was significantly faster in some sections of the sampling area than in others. Back-calculated growth analysis showed a systematic decrease in length for each age for females and males in the 1961 to 1967 year classes. Females grew significantly faster than males after four years of age and reached greater ultimate size. There was a preponderance of males between the ages of I11 and VII and a dominance of females in older age groups. The overall sex ratio of males to females was 2.41 : 1. A distinct seasonal growth pattern was shown.
Five hundred and thirty one of a total of 3122 tagged Barbus barbus (L.) in the middle Severn were recaptured using electric fishing and angling. Ninety two barbel were recaught downstream of the site of tagging, 152 upstream and 287 did not move. Electric fishing was selective for home recaptures. The barbel population was divisible into mobile and static components; 86% remained within 5 km, the remainder wandering more widely up to a maximum of 34 km from their site of tagging. Movement seemed to be dependent on size of the fish.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.