The Population of a Trout Stream and the Survival of Released Fish

1958 ◽  
Vol 9 (3) ◽  
pp. 319 ◽  
Author(s):  
AG Nicholls
Keyword(s):  
Salmo Trutta ◽  
Age Groups ◽  
River System ◽  
Fish Population ◽  
Curvilinear Relationship ◽  
Growth And Survival ◽  
Younger Age ◽  
Brown Trout Salmo Trutta ◽  
Preceding Season ◽  
The Mean

The fish population of a river system was studied by electro-fishing in 25 places, after which 1000 marked yearling brown trout, Salmo trutta L., were released at each of 10 sites. In a re-examination 8 to 9 months after the release it was estimated that about 10 per cent. of these were surviving; the survival after 18 months was estimated to be below 5 per cent., and the survival to takable size, at about 3 years of age, at 2 per cent. At no site were the younger age groups of the natural population truly represented in either season, but the numbers of older fish in the second season were greater than those of the corresponding year classes in the preceding season, showing that the streams receive recruitment of younger fish from other sources. Some evidence is produced to show that "nursery" streams provide the source of recruitment. The average annual mortality for fish of 2 and 3 years of age is estimated at from 70 to 80 per cent. for the system. It is estimated that there were about 45,000 takable fish in this river system at the beginning of each season. It is shown that the mean lengths of trout decrease with increasing density of population, and that there is a curvilinear relationship between population density and total weight of all fish per acre. The standing crop of trout at different sites ranged from 1 to 182 lb/acre over the two seasons. The condition factor showed a decrease with increasing age of the fish, and the released fish had a lower factor than resident fish of the same age at all sites. In general there was a relationship between the depth of water and the length of the fish, sections over 14 in. deep having greater populations of larger fish. A study of the ability of each section of stream to carry fish, based on the lengths and condition factors of the fish, the number and weight of the population per acre, and the ability of each section to absorb additions to the population, shows that where populations were low, conditions were Iess favourable to the growth and survival of fish.

Distribution, abundance, growth and food of freshwater eels (Anguilla spp.) in the Douglas River, Tasmania

1984 ◽  
Vol 35 (3) ◽  
pp. 325 ◽  
Author(s):  
RD Sloane
Keyword(s):  
Population Structure ◽  
Salmo Trutta ◽  
Sampling Site ◽  
Age Groups ◽  
Fish Population ◽  
Growth Rings ◽  
Growth Increments ◽  
Annual Growth Rings ◽  
Brown Trout Salmo Trutta ◽  
Freshwater Eels

Population structure, growth and diet of the freshwater eels A. reinhardtii Steindachner and A. australis australis Richardson were studied in the Douglas River, eastern Tasmania. Fish population structure was assessed by electrofishing, and efficiency of capture was determined for 'eels' and 'other fish'. The other fishes encountered during quantitative sampling were the native Galaxias maculatus (Jenyns), G. truttaceus Valenciennes, Pseudaphritis urvillii (Cuvier & Valenciennes), Favonigobius tamarensis Johnston, and the introduced brown trout, Salmo trutta L. A. reinhardtii dominated fish biomass in the lower freshwater reaches; an estimate of 115 gm-2, recorded at the lowest sampling site, is the highest eel biomass recorded in a Tasmanian stream. A decline in the number and weight of A. reinhardtii with increased distance from the sea was related to avoidance of low water temperatures in winter and/or a parallel decline in abundance of suitable forage fish. Measurements of marginal growth increments in burnt eel otoliths indicated the formation of annual growth rings in both species. Age groups 0: 1 and 2 of A. reinhardtii were poorly represented; this was attributed to a residence in the estuary or deep pools of the river, rather than to failure in recruitment. Growth rate of A. a. australis was slower than that of A. reinhardtii. The diet of both eel species changed significantly with size. The diet of larger individuals of A. reinhardtii had an increased dependence on fish; fish were not recorded in the diet of A. a. australis. The diet of small (less than 20 cm) eels was similar for both species, a feature that may lead to direct competition during periods of low summer flows.

Variation within and between Rivers in Adult Size and Sea Age at Maturity of Anadromous Brown Trout, Salmo trutta

1991 ◽  
Vol 48 (6) ◽  
pp. 1015-1021 ◽  
Author(s):  
Jan Henning L'Abée-Lund
Keyword(s):  
Brown Trout ◽  
Sexual Maturity ◽  
Salmo Trutta ◽  
Adult Size ◽  
Age At Maturity ◽  
Migration Distance ◽  
Spawning Area ◽  
Brown Trout Salmo Trutta ◽  
Males And Females ◽  
The Mean

I compared adult size and sea age at sexual maturity among nine populations of anadromous brown trout, Salmo trutta, in two Norwegian rivers to determine the extent of inter- and intrariverine variations. Variation in the mean length of spawners and in the mean sea age at sexual maturity were mainly dependent on the variations found within rather than between rivers. Mean lengths and mean age at maturity of males increased significantly with increasing altitude of the spawning area and with migration distance in freshwater. In females, positive significant correlations were found with mean lengths and altitude of the spawning area and with mean sea age at maturity and both spawning site altitude and migration distance. Mean lengths and ages of males and females were not significantly correlated with the rate of water discharge in the streams during spawning. The size of gravel substrate for spawning was of minor importance in explaining interpopulation variation in mean female size. The increase noted in mean length and in mean sea age at maturity of both males and females is probably an adaptation to greater energy expenditure to reach the uppermost natal spawning areas.

Admixture analysis and stocking impact assessment in brown trout (Salmo trutta), estimated with incomplete baseline data

2001 ◽  
Vol 58 (9) ◽  
pp. 1853-1860 ◽  
Author(s):  
Michael M Hansen ◽  
Einar E Nielsen ◽  
Dorte Bekkevold ◽  
Karen-Lise D Mensberg
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Population Level ◽  
Genetic Distances ◽  
Scaling Analysis ◽  
Genetic Contribution ◽  
Multidimensional Scaling Analysis ◽  
Genetic Impact ◽  
Brown Trout Salmo Trutta ◽  
The Mean

Studies of genetic interactions between wild and domesticated fish are often hampered by unavailability of samples from wild populations prior to population admixture. We assessed the utility of a new Bayesian method, which can estimate individual admixture coefficients even with data missing from the populations contributing to admixture. We applied the method to analyse the genetic contribution of domesticated brown trout (Salmo trutta) in samples of anadromous trout from two stocked populations with no genetic data available before stocking. Further, we estimated population level admixture proportions by the mean of individual admixture coefficients. This method proved more informative than a multidimensional scaling analysis of individual-based genetic distances and assignment tests. The results showed almost complete absence of stocked, domesticated trout in samples of trout from the rivers. Consequently, stocking had little effect on improving fisheries. In one population, the genetic contribution by domesticated trout was small, whereas in the other population, some genetic impact was suggested. Admixture in this sample of anadromous trout despite absence of stocked domesticated trout could be because of introgression by domesticated trout adopting a resident life history.

Reduced hatchery rearing density increases social dominance, postrelease growth, and survival in brown trout (Salmo trutta)

2010 ◽  
Vol 67 (2) ◽  
pp. 288-295 ◽  
Author(s):  
Sofia Brockmark ◽  
Jörgen I. Johnsson
Keyword(s):  
Brown Trout ◽  
Social Dominance ◽  
Salmo Trutta ◽  
Adaptive Behaviour ◽  
Dominance Status ◽  
Growth And Survival ◽  
Hatchery Fish ◽  
Brown Trout Salmo Trutta ◽  
Rearing Density ◽  
Natural Density

Hatchery fish reared for conservation or supplementation often have difficulties adapting to natural conditions, resulting in poor performance in the wild. In a standard hatchery, fish are confined at high densities, which creates a social environment different from that experienced after release. Here we investigated how rearing density influences social dominance, postrelease growth, and survival in brown trout ( Salmo trutta ). Fish were reared at three density treatments: conventional hatchery density, half of conventional hatchery density, and natural density. Four months after hatching, dominance status was determined, and 36 fish from each treatment were released into an enclosed stream and recaptured after 36 days. Trout reared at natural density had higher dominance status and grew faster, both in the hatchery and in the natural stream, than trout from higher densities. Moreover, trout reared at natural density were twice as likely to survive in the stream as trout from higher densities. These novel results suggest that more natural rearing densities would facilitate the development of adaptive behaviour in hatchery salmonids and, thereby, their contribution to natural production.

scholarly journals Trends in Self-Poisoning: Admissions to a Central London Hospital, 1991–1994

1997 ◽  
Vol 90 (9) ◽  
pp. 496-498 ◽  
Author(s):  
Christopher J B Mcevedy
Keyword(s):  
Clinical Practice ◽  
Psychiatric Disorder ◽  
Age Groups ◽  
Common Reason ◽  
Completed Suicide ◽  
Younger Age ◽  
Increased Risk ◽  
The Mean ◽  
The Uk ◽  
Reason For Admission

Self-poisoning is a common reason for admission to hospital; and, although most patients admitted do not have a psychiatric disorder, as a group they are at greatly increased risk of completed suicide. Admissions to a hospital in Central London over a four-year period were examined with special attention to patients admitted more than once. From 1991 to 1994 admissions for self-poisoning rose by 108%, with larger increases in the younger age groups of both sexes. 9% of patients were admitted more than once, the mean interval to repetition being three months. A third of the repeaters were readmitted within one month. The increase in admissions for self-poisoning, which has been noted elsewhere in the UK, is unlikely to be due wholly to changes in clinical practice. In view of the relation between parasuicide and suicide, further research and analysis is urgently needed.

The physiological impairment of free-ranging brown trout exposed to metals in the Clark Fork River, Montana

1995 ◽  
Vol 52 (9) ◽  
pp. 2038-2050 ◽  
Author(s):  
Aïda M. Farag ◽  
Mark A. Stansbury ◽  
Harold L. Bergman ◽  
Christer Hogstrand ◽  
Elizabeth MacConnell
Keyword(s):  
United States ◽  
Brown Trout ◽  
Salmo Trutta ◽  
Fish Population ◽  
Western United States ◽  
Reference Sites ◽  
Clark Fork River ◽  
Brown Trout Salmo Trutta ◽  
Upper Clark Fork River ◽  
High Concentrations

Tissue metal accumulation and physiological responses were measured in brown trout (Salmo trutta) collected from two sites on the Clark Fork River, Montana, and two reference sites to determine the health status of the resident fish population. Concentrations of metals in tissues, products of lipid peroxidation, and microscopic Cu inclusions were significantly higher in fish collected from the upper Clark Fork River site than in fish from reference sites. Metallothionein concentrations were higher in the livers of fish from the upper Clark Fork River than in those of fish from reference sites. The health of the fish population in the upper Clark Fork River is probably impaired because of previously reported elevated concentrations of metals including As, Cd, Cu, Pb, and Zn in the surface water and aquatic invertebrates in the upper Clark Fork River. The high concentrations of metals in the surface waters and sediments of the Clark Fork River are typical of rivers in the intermountain western United States where discharges from mining activities have occurred since the late 1800s. Thus, our findings can be used as a guide for researchers throughout the intermountain western United States who may investigate similar field conditions.

scholarly journals Demographic and Clinical Characteristics of Early Travel-Associated COVID-19 Cases

2020 ◽  
Vol 8 ◽  
Author(s):  
Reham M. Marei ◽  
Mohamed M. Emara ◽  
Omar M. Elsaied ◽  
Gheyath K. Nasrallah ◽  
Tawanda Chivese ◽  
...  
Keyword(s):  
Clinical Data ◽  
Clinical Symptoms ◽  
Age Groups ◽  
The Elderly ◽  
World Health ◽  
Female Ratio ◽  
Younger Age ◽  
The Mean ◽  
Health Organization ◽  
Male To Female

Background: SARS-CoV-2 continues to claim hundreds of thousands of people's lives. It mostly affects the elderly and those with chronic illness but can also be fatal in younger age groups. This article is the first comprehensive analysis of the epidemiological and clinical outcomes of the travel-associated SARS-CoV-2 cases until April 19, 2020.Methods: Demographic and clinical data of travel-associated SARS-CoV-2 cases were collected for the period between January 16, 2020 and April 19, 2020. More than one hundred and eighty databases were searched, including the World Health Organization (WHO) database, countries' ministries websites, and official media sites. Demographic and clinical data were extracted and analyzed.Results: A total of 1,186 cases from 144 countries meeting the inclusion criteria were reported and included in the analysis. The mean age of the cases was 44 years, with a male to female ratio of 1.6:1. Travel-associated cases originated from more than 40 countries, with China, Italy, and Iran reporting the highest numbers at 208, 225, and 155, respectively. Clinical symptoms varied between patients, with some reporting symptoms during the flights (117 cases; 9.87%). A total of 312 (26.31%) cases were hospitalized, of which 50 cases (4.22%) were fatal.Conclusion: Major gaps exist in the epidemiology and clinical spectrum of the COVID-19 travel-associated cases due to a lack of reporting and sharing data of many counties. The identification and implementation of methodologies for measuring traveler's risk to coronavirus would help in minimizing the spread of the virus, especially in the next waves.

Concentrations of ionic, total, and bound fluoride in plasma.

1979 ◽  
Vol 25 (4) ◽  
pp. 523-525 ◽  
Author(s):  
L Singer ◽  
R H Ophaug
Keyword(s):  
Age Groups ◽  
Fluoride Concentration ◽  
Older Age ◽  
Male And Female ◽  
Ionic Fluoride ◽  
Younger Age ◽  
Significant Difference ◽  
The Mean ◽  
Female Subjects

Abstract We found no significant difference between the means for ionic, bound, and total fluoride concentrations in the plasma of male and female subjects of the same age, living in a community with fluoridated water. When results for the 264 fasting subjects were therefore combined according to age, they indicated that persons over 60 years of age have a significantly higher mean ionic (3.89 mumol/L) and total (6.58 mumol/L) fluoride concentration in plasma than do younger age groups. For younger age groups, means ranged from 2.74 to 3.05 mumol/L for ionic fluoride and from 4.74 to 5.58 mumol/L for total. The bound fluoride concentration was lower in individuals 21 to 30 years of age (1.89 mumol/L) than in older age groups (for whom means ranged from 2.42 to 2.68 mumol/L), but was not significantly different from that of individuals who were younger (2.21 mumol/L). A tendency for the mean ionic fluoride concentration to increase with age was noted, but the concentration was significantly higher than the preceding decade group only in those persons over 60 years of age.

Small-scale dispersal and population structure in stream-living brown trout (Salmo trutta) inferred by mark–recapture, pedigree reconstruction, and population genetics

2012 ◽  
Vol 69 (9) ◽  
pp. 1513-1524 ◽  
Author(s):  
Leif Asbjørn Vøllestad ◽  
Dimitar Serbezov ◽  
Arthur Bass ◽  
Louis Bernatchez ◽  
Esben Moland Olsen ◽  
...  
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Isolation By Distance ◽  
Juvenile Fish ◽  
Age Groups ◽  
Small Scale ◽  
Mark Recapture ◽  
Small Stream ◽  
Brown Trout Salmo Trutta ◽  
Mature Fish

Many animals move among habitats, and even small-scale dispersal of individuals between habitat patches may have strong implications for population dynamics and structure. Here, we use long-term mark–recapture data combined with extensive genotyping and parentage assignment to investigate the importance of small-scale location change of resident brown trout ( Salmo trutta ) in a small stream (1500 m). During the first summer, juvenile fish dispersed downstream (mean displacement 200 m), with smaller juveniles dispersing longer distances. Downstream movement was also predominant during the first winter, but older fish moved little. This limited dispersal resulted in a significant isolation-by-distance structure for ages 1 and 2, but not for older age groups or for the mature fish. Individual pairwise relatedness coefficients decreased with waterway distance for mature fish during the 2002 and 2003 spawning seasons, but only weakly. Overall, between-site genetic differentiation was stronger for the younger age classes, and the signal decayed with age, indicating that the genetic structure observed in the stream is mainly driven by spatial aggregation of close relatives.

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