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.

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.

Population density of migratory and resident brown trout (Salmo trutta) in relation to altitude: evidence for a migration cost

2001 ◽  
Vol 70 (1) ◽  
pp. 112-121 ◽  
Author(s):  
T. Bohlin ◽  
J. Pettersson ◽  
E. Degerman
Keyword(s):  
Population Density ◽  
Brown Trout ◽  
Salmo Trutta ◽  
Migration Cost ◽  
Brown Trout Salmo Trutta

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

scholarly journals The viability of the crustacean Eurycercus lamellatus (Branchiopoda, Cladocera) in a high mountain area in southern Norway

2020 ◽  
Vol 40 ◽  
pp. 22-42 ◽  
Author(s):  
Tore Qvenild ◽  
Trygve Hesthagen
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
High Mountain ◽  
Mountain Area ◽  
Growing Seasons ◽  
Western Area ◽  
Brown Trout Salmo Trutta ◽  
High Predation ◽  
Southern Norway ◽  
High Mountain Area

The branchiopod Eurycercus lamellatus is widely distributed in Norwegian lakes, ranging from coastal to alpine areas. On the Hardangervidda mountain plateau in southern Norway, E. lamellatus was searched for in 144 lakes in 11 catchments in the western and 16 catchments in the central and eastern areas. Their occurrence is mainly based on the diet of brown trout Salmo trutta. Eurycercus lamellatus was recorded in 25% and 70% of the lakes in these two areas, respectively. This may be due to striking differences in the environmental conditions, with more dilute water and lower water temperatures in western areas, and hence shorter growing seasons. The occurrence of E. lamellatus in central and eastern catchments increased with lake size, being found in 65% and 85% of lakes with a surface area of <2.0 and ≥2.0 km2, respectively. In the western area, E. lamellatus occurred less frequently in lakes above 1000 m a.s.l. That was not the case for lakes in central and eastern catchments. In this central part of Hardangervidda, the relative abundance of E. lamellatus in the diet of brown trout was obtained from five different lakes, showing that they were preyed upon throughout the growing season (June to October). When the two big crustaceans Gammarus lacustris and Lepidurus arcticus are at low densities in these lakes, E. lamellatus became the staple food item for brown trout, except for larger fish (>400 mm). However, under high predation pressure, E. lamellatus also contributed significantly to the diet of larger fish. The abundance of E. lamellatus seems to vary highly on a yearly basis in one of the lakes (Sandvatn). Even though E. lamellatus is described as a typical littoral species, it was common down to depths of 15 m.

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.

Relationship between Annual Recruitment and Density in a Lacustrine Population of Allopatric Brown Trout (Salmo trutta)

1992 ◽  
Vol 49 (6) ◽  
pp. 1107-1113 ◽  
Author(s):  
Reidar BorgstrØm
Keyword(s):  
Population Density ◽  
Brown Trout ◽  
Salmo Trutta ◽  
Nursery Areas ◽  
Resident Population ◽  
Age Class ◽  
Brown Trout Salmo Trutta

The annual recruitment of brown trout (Salmo trutta) parr from stream nursery areas to an allopatric, lake-resident population was studied during a 5-yr period. The immigration of each cohort to the lake occurred over several years, but the data indicate that the duration of the lotic residence of parr may be regulated by the density of the lake population. At high lake population density, the number of brown trout in age-class 3+ present in the lake by June was low, while at low lake population density the number of 3+ fish increased substantially.

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