scholarly journals Fish populations in Plynlimon streams

1997 ◽  
Vol 1 (3) ◽  
pp. 541-548 ◽  
Author(s):  
D. T. Crisp ◽  
W. R. C. Beaumont
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Population Densities ◽  
Discharge Data ◽  
Stream Discharge ◽  
Trout Population ◽  
Successful Recruitment ◽  
Species Survival ◽  
Show Evidence ◽  
Brown Trout Salmo Trutta

Abstract. In Plynlimon streams, brown trout (Salmo trutta L.) are widespread in the upper Wye at population densities of 0.03 to 0.32 fish m-2 and show evidence of successful recruitment in most years. In the upper Severn, brown trout are found only in an area of c. 1670 -2 downstream of Blaenhafren Falls at densities of 0.03 to 0.24 fish -2 and the evidence suggests very variable year to year success in recruitment (Crisp & Beaumont, 1996). Analyses of the data show that temperature differences between afforested and unafforested streams may affect the rates of trout incubation and growth but are not likely to influence species survival. Simple analyses of stream discharge data suggest, but do not prove, that good years for recruitment in the Hafren population were years of low stream discharge. This may be linked to groundwater inputs detected in other studies in this stream. More research is needed to explain the survival of the apparently isolated trout population in the Hafren.

Effects of pH on Sodium Uptake in Norwegian Brown Trout (Salmo Trutta) from an Acid River

1980 ◽  
Vol 88 (1) ◽  
pp. 259-268
Author(s):  
PHILIP G. McWILLIAMS
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Population Decline ◽  
Acid Media ◽  
Sodium Uptake ◽  
Trout Population ◽  
Uptake Rates ◽  
Effects Of Ph ◽  
Brown Trout Salmo Trutta ◽  
External Ph

Sodium uptake rates were measured in wild and hatchery reared Norwegian brown trout (Salmo trutta) exposed to media of a range of pH. Sodium uptake was strongly dependent on external acidity, being reduced in media of low pH. Wild fish from the naturally acid R. Tovdal (S. Norway) were more tolerant of acid media than hatchery reared fish. The effects of increasing external sodium concentrations were strongly influenced by low external pH. The results are discussed with respect to brown trout population decline in certain areas of S. Norway.

Repeat Homing of Brown Trout (Salmo trutta) in Lake Eucumbene, New South Wales, Australia

1977 ◽  
Vol 34 (8) ◽  
pp. 1085-1094 ◽  
Author(s):  
R. D. J. Tilzey
Keyword(s):  
Rainbow Trout ◽  
Brown Trout ◽  
Salmo Trutta ◽  
New South ◽  
Tag Loss ◽  
Trout Population ◽  
South Wales ◽  
High Incidence ◽  
Brown Trout Salmo Trutta ◽  
External Form

Spawning runs of lentic-dwelling brown trout (Salmo trutta) and rainbow trout (S. gairdneri) in Swamp Creek, an inlet of Lake Eucumbene, were studied for 4 consecutive yr, and 3517 browns and 415 rainbows were tagged during 1968–70. A further 240 browns and 229 rainbows were marked in other inlets. Recaptures of marked browns in 1969 and 1970 showed a high incidence of repeat homing, up to 25.7 and 10.6% returning after 12 and 24 mo, respectively. Few rainbow trout homed. Tag loss and the mortality and maturation of marked browns were estimated and percentage homing and straying in 1969, 1970 and 1971 was calculated. High percentage homing [Formula: see text] in 1969–70 and the variance in external form in the lentic population suggested some genetic isolation within the brown trout population. Homing ability was not influenced by fish age. Percentage homing fell markedly in 1971 after the removal of nearly all resident brown trout from Swamp Creek and suggested racially distinct stream trout populations to be an important navigational cue to homing brown trout. Key words: repeat homing, Salmo trutta, homing frequency, navigation, racial cue, Australia

The influence of hydrological and biotic processes on brown trout (Salmo trutta) population dynamics

2002 ◽  
Vol 59 (1) ◽  
pp. 12-22 ◽  
Author(s):  
Franck Cattanéo ◽  
Nicolas Lamouroux ◽  
Pascal Breil ◽  
Hervé Capra
Keyword(s):  
Population Dynamics ◽  
Brown Trout ◽  
Salmo Trutta ◽  
Growth Period ◽  
Intraspecific Interactions ◽  
Emergence Period ◽  
Trout Population ◽  
Brown Trout Salmo Trutta ◽  
High Flows ◽  
Survival Mechanisms

Hydrological and biotic forces constrain brown trout (Salmo trutta) population dynamics, but tests of their role across numerous streams are uncommon. In 30 French stream reaches, using 5–8 samples (1 per year) each, we investigated whether the year-to-year seasonal hydrology influenced annual trout densities within reaches, and whether the relationships were shared by all reaches. We also searched for intraspecific interactions between and within cohorts. Trout data were age class (0+, 1+, and adults) densities. For each year, hydrology was described using 13 variables, each computed for a reproduction, emergence, and growth period related to the biological cycle of trout. We used analyses of covariance (ANCOVA) to test how trout densities at year n – 1 and hydrology at year n influenced trout densities at year n. High flows during emergence significantly reduced the 0+ densities, consistently across the 30 reaches. Then, 1+ and adult densities were linked, respectively, to 0+ and 1+ densities from the previous year. Analyses also revealed density-dependent survival mechanisms for the 0+ cohort, suggesting intracohort competition. Therefore, hydrology constrains trout dynamics only during the critical emergence period, after which intracohort interactions regulate the 0+ density. Such mechanisms, validated across 30 environmentally different reaches, seem to be fundamental to trout population dynamics.

scholarly journals Life History Tactics in Cohorts of a Partial Migratory Brown Trout (Salmo trutta L.) Population

ISRN Ecology ◽  
2011 ◽  
Vol 2011 ◽  
pp. 1-7 ◽  
Author(s):  
Ivan C. Olsson ◽  
Larry A. Greenberg
Keyword(s):  
Body Size ◽  
Brown Trout ◽  
Salmo Trutta ◽  
Female Fecundity ◽  
Trout Population ◽  
Delayed Reproduction ◽  
Brown Trout Salmo Trutta ◽  
Downstream Section ◽  
And Migration ◽  
Brown Trout Population

We monitored temporal changes in body size for three cohorts of a partial migratory, lake-migrating brown trout population. We tested if body mass differed between nonmigratory males, migrants, and other members of the cohort (females and immature males). We hypothesized that large-sized individuals would mature as nonmigratory males or migrate at younger ages than small-sized individuals. As previous studies have shown that female fecundity is influenced by body size and that more trout from the downstream section (D) of the stream migrated than from the upstream section (U), we hypothesized that there would be a greater proportion of mature males in D than U. We found that body size of males that reproduced was similar to migrants that migrated the subsequent spring and larger than other cohort members. Reproducing males had a larger body size than equal-aged males that delayed reproduction. Similarly, individuals that migrated had a larger body size than equal-aged individuals that migrated subsequently. The proportion of mature males was greater in D than in U. The fact that body size differentiation occurred late in ontogeny and that age of maturation and migration varied within cohorts suggests that the decision to mature or migrate might be conditionally dependent.

Effect of Experimentally Increased Intraspecific Competition on Sedentary Adult Brown Trout (Salmo trutta) Movement and Stream Habitat Choice

1988 ◽  
Vol 45 (7) ◽  
pp. 1163-1172 ◽  
Author(s):  
Jan Heggenes
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Habitat Choice ◽  
Stream Habitat ◽  
Population Densities ◽  
Habitat Types ◽  
Prior Residence ◽  
Brown Trout Salmo Trutta ◽  
Movement Distance ◽  
Coarse Substrate

Movements and habitat choice of 19 brown trout (Salmo trutta) resident in a stream was monitored during one season, while in the next season the population was increased by introducing 130 wild brown trout captured further downstream. No differences in the movement patterns of resident trout at the two population densities, or of residents compared with nonresidents, were found. Median movement distance was 0 m. Sixty-six percent of the movements were less than ±50 m, 11% were between 50 and 100 m, and 23% were greater than ±100 m. Introduced nonresident trout occupied habitats different from those occupied by residents. Nonresidents were more often observed in shallower areas with less cover and finer substrate, i.e. less preferred habitats. It is hypothesized that this was caused by dominance of resident trout due to their larger size and prior residence. Both resident and introduced trout exhibited preferences for deep stream areas, e.g. water > 50 cm deep, mean water velocities in the range 10–70 cm/s, coarse substrate > 128 mm, and a > 50% overhead cover compared with available habitat. At both low and high population densities, the trout inhabiting pools were significantly larger than trout inhabiting other habitat types. No homing tendency was observed for the displaced trout.

Effect of Population Density on Gillnet Catchability in Four Allopatric Populations of Brown Trout (Salmo trutta)

1992 ◽  
Vol 49 (8) ◽  
pp. 1539-1545 ◽  
Author(s):  
Reidar Borgstrøm
Keyword(s):  
Population Density ◽  
Brown Trout ◽  
Salmo Trutta ◽  
High Mountain ◽  
Catch Per Unit Effort ◽  
Power Functions ◽  
Trout Population ◽  
Brown Trout Salmo Trutta ◽  
Management Implication ◽  
Brown Trout Population

The gillnet catchability of allopatric brown trout (Salmo trutta) populations was studied in four Norwegian high-mountain lakes, with large differences in population densities. The number of fish and the length composition of the populations were estimated by mark–recapture. The catchability coefficient and the catch per unit effort were described by power functions, and the catchability was inversely related to number of fish present. An important fisheries management implication is that brown trout populations with low densities are more vulnerable to gillnets than populations with high densities. Furthermore, the use of gillnet catches as an estimator of brown trout population density will be biased.

Brown Trout (Salmo trutta) Status and Chemistry from the Norwegian Thousand Lake Survey: Statistical Analysis

1993 ◽  
Vol 50 (3) ◽  
pp. 575-585 ◽  
Author(s):  
Arthur J. Bulger ◽  
Leif Lien ◽  
B. J. Cosby ◽  
Arne Henriksen
Keyword(s):  
Water Chemistry ◽  
Brown Trout ◽  
Salmo Trutta ◽  
Aluminum Concentration ◽  
Historical Trends ◽  
Trout Population ◽  
Brown Trout Salmo Trutta ◽  
Discriminant Analyses ◽  
Individual Variables ◽  
Negative Impacts

Substantial negative impacts of acidic precipitation on freshwater fishes have been recorded over the last 50 yr in Norway. We analyzed the present status and historical trends of brown trout (Salmo trutta) populations in relation to water chemistry in 584 Norwegian lakes. Since the 1940s, 39% of the lakes have lost their trout populations, and another 17% of the lakes have declining trout populations; thus, 56% of the populations have been adversely affected. The results of analysis of variance, principal components analysis, and discriminant analyses converge on the variables pH, monomeric inorganic aluminum, and alkalinity as most strongly related to trout status. Lakes whose trout populations are extinct have an average aluminum concentration of 133 μg/L, an alkalinity of −34 μeq/L, and a pH of 4.8 versus 11 μg Al/L, + 27 μeq/L, and 6.0 for lakes with healthy populations. Also, nitrate and sulfate levels are significantly higher in affected versus unaffected lakes. Calcium and sulfate appear to influence trout status moderately as individual variables, but strongly in combination, since they are the major determinants of alkalinity in these lakes. Models based on discriminant analyses showed good success (up to 89%) in predicting trout population status categories from water chemistry.

Numerical changes in stream-resident brown trout (Salmo trutta): uncovering the roles of density-dependent and density-independent factors across space and time

2007 ◽  
Vol 64 (10) ◽  
pp. 1429-1447 ◽  
Author(s):  
Javier Lobón-Cerviá
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Census Data ◽  
Density Dependent ◽  
Stream Discharge ◽  
Space And Time ◽  
Two Factors ◽  
Brown Trout Salmo Trutta ◽  
Northwestern Spain ◽  
Spatial Habitat

The objective was to uncover the roles of environmental, density-independent, and intrinsic, density-dependent factors as drivers of population size in stream-resident brown trout (Salmo trutta) across space and time. The study was based on census data and environmental variables collected every fourth month over 1986–2006 at 12 sites selected along four Rio Esva tributaries (northwestern Spain). Density-dependent hypotheses involving the operation of current and lagged densities on recruitment and subsequent spawner density were analyzed at three increasingly larger geographical scales (site, stream, and river drainage). No evidence supported these hypotheses, suggesting an overall lack of negative feedbacks among year classes. Stream discharge in March when trout emerge and site depth explained substantial amounts of spatiotemporal variation in recruitment. The effects of these two factors on recruitment were sufficiently strong to be detected in year-class mortality and subsequent spawner density. Discharge and site depth determine the amount of spatial habitat suitable for sized individuals during their lifetime and, hence, the maximum number of individuals across space and time. Recruitment dependence, as a delayed density-dependent factor, adjusts the numbers in excess to the numbers established by spatial habitat. These findings differ markedly from the prediction of the most recent theories of population dynamics and are discussed in this context.

Impact of groundwater abstraction on physical habitat of brown trout (Salmo trutta) in a small Danish stream

2009 ◽  
Vol 40 (4) ◽  
pp. 394-405 ◽  
Author(s):  
M. Olsen ◽  
E. Boegh ◽  
S. Pedersen ◽  
M. F. Pedersen
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Reference Conditions ◽  
Habitat Model ◽  
Physical Habitat ◽  
Habitat Conditions ◽  
Groundwater Abstraction ◽  
Stream Discharge ◽  
Brown Trout Salmo Trutta ◽  
The Impact

The purpose of this study was to assess the impact of groundwater abstraction on stream discharge and physical habitat conditions for brown trout (Salmo trutta) in a small Danish stream. Stream discharge was simulated using a lumped hydrological model (NAM) and a scenario was set up for stream discharge reference conditions. Stream physical habitat conditions (WUA) were simulated for four life stages of trout using a hydraulic habitat model (RHYHABSIM). The impact of groundwater abstraction on WUA for trout was assessed by combined simulations from the NAM model and the RHYHABSIM model. The model predicted that groundwater abstraction reduced median annual discharge by 37% and mean annual 90th percentile discharge by 82%. Summer discharge was relatively most affected by groundwater abstraction and WUA was therefore particularly affected by groundwater abstraction during summer. WUA for adult trout was mainly controlled by suitable water depths (>40 cm) even under conditions without abstraction. On an annual basis WUA for fry and juvenile trout was most affected by abstraction. Future modelling should consider improving simulation of low discharges and preferably not use general hydrological models.

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