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.

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.

Divergence of brown trout (Salmo trutta) within glacial refugia

2000 ◽  
Vol 57 (11) ◽  
pp. 2201-2210 ◽  
Author(s):  
Núria Sanz ◽  
José-Luis García-Marín ◽  
Carles Pla
Keyword(s):  
Population Structure ◽  
Brown Trout ◽  
Salmo Trutta ◽  
Allelic Variation ◽  
Glacial Refugia ◽  
Species Differentiation ◽  
Gene Pools ◽  
Genetic Population ◽  
Geographical Patterns ◽  
Brown Trout Salmo Trutta

The Pleistocene glaciations produced a range of changes that affected the genetic population structure of fish species. Usually, studies focused on the population structure of species in postglacial recolonized areas and less attention was devoted to species differentiation within refuge areas. Allelic frequencies for 21 polymorphic protein-coding loci were compared among 25 collections within a northwestern Iberian glacial refuge of brown trout (Salmo trutta) using adjusted frequencies for nine populations to account for introgressions with exogenous hatchery fish. The high divergence observed (FST = 0.645) and geographical patterns of allelic variation are interpreted to reflect the existence of strong population structuring among native populations of this refuge. Four major geographic groups were defined within the region: (i) in the Tajo River, (ii) in the Duero River, (iii) in the Sil River, and (iv) among Cantabrian Sea flowing rivers including present anadromous populations. These gene pools have diverged genetically and ecologically in response to climatic oscillations. Anthropogenic effects on habitat and fish populations seriously compromise their future.

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.

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.

scholarly journals Influence of discharge, hydraulics, water temperature, and dispersal on density synchrony in brown trout populations (Salmo trutta)

2016 ◽  
Vol 73 (3) ◽  
pp. 319-329 ◽  
Author(s):  
Victor Bret ◽  
Benjamin Bergerot ◽  
Hervé Capra ◽  
Véronique Gouraud ◽  
Nicolas Lamouroux
Keyword(s):  
Water Temperature ◽  
Brown Trout ◽  
Salmo Trutta ◽  
Age Groups ◽  
Negative Influence ◽  
Spawning Period ◽  
Emergence Period ◽  
Discharge Water ◽  
Brown Trout Salmo Trutta ◽  
Influence Of Substrate

Environmental factors may cause synchronous density variations between populations. A better understanding of the processes underlying synchrony is fundamental to predicting resilience loss in metapopulations subject to environmental change. The present study investigated the determinants of synchrony in density time series of three age groups of resident brown trout (Salmo trutta) (0+, 1+, and adults) in 36 stream reaches. A series of Mantel tests were implemented to disentangle the relative effects on trout synchrony of geographical proximity, environmental synchrony in key environmental variables affecting trout dynamics (discharge, water temperature, hydraulics, and spawning substrate mobility), and density-dependent dispersal. Results indicated that environmental synchrony strongly explained trout synchrony over distances less than 75 km. This effect was partly due to a negative influence on 0+ trout of strong discharges during the emergence period and a more complex influence of substrate mobility during the spawning period. Dispersal between reaches had a weak influence on results. Juvenile and adult densities were strongly driven by survival processes and were not influenced by environmental synchrony. The results suggest that the environment can have general effects on population dynamics that may influence the resilience of metapopulations.

Winter Habitat Utilization by Stream Resident Brook Trout (Salvelinus fontinalis) and Brown Trout (Salmo trutta)

1986 ◽  
Vol 43 (10) ◽  
pp. 1970-1981 ◽  
Author(s):  
Richard A. Cunjak ◽  
Geoffrey Power
Keyword(s):  
Brown Trout ◽  
Brook Trout ◽  
Salmo Trutta ◽  
Salvelinus Fontinalis ◽  
Focal Point ◽  
Age Groups ◽  
Habitat Utilization ◽  
Point Sources ◽  
Energetic Cost ◽  
Brown Trout Salmo Trutta

Habitat utilization by brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) is described from three winters of underwater observations in a southern Ontario river. Older trout (>age 1) generally occupied positions in deeper and faster water than age 0+ trout. In winter, at sites of sympatry, brown trout occupied greater focal point water depths than brook trout; both species had similar focal point water velocities. At all sites, and for both age groups and species, there was a strong preference for positions beneath cover. Relative to summer, trout positions in winter were characterized by slower water velocities and greater overhead cover, In winter, most trout were in aggregations, usually in pools beneath cover and close to point sources of groundwater discharge. Gregarious behaviour appeared to increase as water temperatures decreased; no such relationship was evident in the summer. Specific strategies for overwintering varied between sites and age groups but generally conformed to the theory of energetic cost minimization for position choice. These variable patterns appear to be adaptive.

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