摘要:

Abstract–Habitat use and population dynamics in brown troutSalmo truttaand Arctic charrSalvelinus alpinuswere studied in an oligotrophic lake over a period of 10 years. Previous studies showed that the species segregated by habitat during summer. While brown trout occupied the surface water down to a depth of 10 m, Arctic charr were found deeper with a maximum occurrence at depth 10–15 m. Following the removal of a large number of intermediate sized fish in 1988–89, habitat segregation between the species broke down and Arctic charr were found in upper waters, while brown trout descended to deeper waters. The following year, both species were most frequently found in surface waters at depths of 0–5 m. During the last four years, the species reestablished their original habitat segregation despite another removal experiment of intermediate‐sized fish in 1992–1994. The removal of fish resulted in an increased proportion of large (≥ 25 cm) fish in both species. Furthermore, the charr stock responded by reduced abundance and increased size‐at‐age. The results revealed plasticity and strong resistance to harvest populations of brown trout and Arctic charr. This is probably due to internal mechanisms of intraspecific competition within each population, which result in differential mortality a

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00036.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract–Reproductive activities of individually identified fluvial Dolly Varden (Salvelinus malma) were observed during a breeding season in a small stream. Males and females both established dominance hierarchies based on body size. Females spawned from late October to late November, with no apparent peak, and larger females spawned earlier than small ones. Males competed for access to females by adopting two types of mating tactics: pairing and sneaking. The tactic used depended on the male's position in the dominance hierarchy of the breeding group. Seasonal reproductive activity and mating success of males were positively correlated with body size, with only the largest male monopolizing most of the mating opportunities, and the small males were rarely successful in mating. Smaller males, however, lost as much weight as large males during the breeding season. Females preferred the largest male in the breeding group as a mate, while males courted females of any size. It is suggested that the polygynous mating pattern is a consequence of size‐related differences in competitive ability among males, and the degree of monopolization is affected by both the temporal distribution and the spawning tactics of the fema

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00037.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract–Experimental comparisons were made between release as unfed fry and release as six weeks fed parr, upon the growth and final population density of young salmon and trout over a ten week period. Salmon and trout released into experimental channels as unfed fry at densities of about 19 fish. m‐2showed rapid reduction in numbers, chiefly by downstream dispersal, accompanied by negligible growth. After substantial reduction in numbers, there was a reduced rate of dispersal and rapid growth. Salmon and trout retained in a hatchery at high density (80 to 200 fish. m‐2) and fed for six weeks on proprietary food showed slow, but measurable, growth. After release into the channels these fish adjusted their numbers, mainly by downstream dispersal, and showed an increased growth rate. At the end of a ten week period, salmon introduced as fed parr had approximately twice the population density of salmon introduced as unfed fry. No similar difference in population density could be shown for trout. For both species, the fish introduced as fed parr had a lower mean weight after ten weeks than had the fish introduced as unfe

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00038.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract–Four quantitative (area‐standardized electrofishing, trap nets, small‐mesh [1.3 and 2‐cm bar mesh] gill nets, large‐mesh [2.5 and 5‐cm bar mesh]gill nets) and two qualitative (non‐standardized electrofishing, dip netting) sampling techniques were concurrently used to capture larval to adult fish in forested wetland habitats on seasonally inundated floodplains of two Alabama (USA) streams. Standardized area electrofishing appeared to be the best sampling technique for collecting and quantifying species because of high catch rate, broad species and size coverage, and rapid sampling. Electrofishing accounted for most fish (47 and 57% of pooled catch), almost all taxa, and a broad range of fish sizes. Large‐mesh gill nets captured few fish (2% and 8%), a distinct subset of the species present, and the largest fish. Light traps were the most efficient and taxa‐comprehensive sampling technique for larval fish. Light traps captured the vast majority of the pooled larval fish catch, including 6 of 7 families recorded at the sites. Larval fish dip netting captured larval fish of most families known to be present but in low numbers. For surveys of species composition and rapid bioassessments, nonstandardized electrofishing and larval fish dip netting appear adequate. For intensive research studies, the combination of area electrofishing, large‐mesh (and in some cases small‐mesh) gill nets, and light traps provide thorough and comprehensive data on wet

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00039.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract–Ageing and calculation of growth rate of eels has always been controversial, and remarkably little validation has been reported. This article describes the growth of yellow eels from three lakes in the Burrishoole system, Ireland, as determined by back‐calculation from otoliths prepared by burning and cracking. Eels captured by fyke net ranged in length from 25.0 cm to 98.5 cm and the ages ranged from 6 to 49 years. Back‐calculated growth was slow, with mean annual increments of 2.08 cm, 1.40 cm and 1.97 cm for the three lakes. Yellow eels captured in the Burrishoole system in 1987 and 1988 were marked by Pan Jet inoculated alcian blue dye and released back into the three lakes. Recaptures made over the following three years yielded considerable growth data. Mean annual growth rates recorded were 2.30 cm, 1.07 cm and 0.97 cm. These data compare favorably with the calculated growth rates, thereby validating the otolith analysis for the eels in the Burrishoole s

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00040.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY