摘要:

AbstractSeasonal habitat use by over‐yearling and under‐yearling brook trout,Salvelinus fontinalis(Mitchill), was examined in a second‐order stream in north‐central Pennsylvania, USA. The habitat occupied by brook trout and available habitat were determined in a 0.5‐km stream reach during the spring, summer and autumn of 1989 and the spring and summer of 1990. Cover, depth, substrate and velocity were quantified from over 2000 observations of individual brook trout. Habitat used by under‐yearling brook trout was more uniform between seasons and years than that used by over‐yearling brook trout. Over‐yearling brook trout occupied areas with more cover and greater depth than did under‐yearling brook trout, suggesting ontogenetic shifts in these variables. Differences for velocity and substrate were not as great as those for cover and depth. The selection of areas with low water velocities governed trout habitat use in spring, whereas cover and depth were the most important habitat variables in summer and autumn. Principal component analysis showed that available habitat and trout habitat centroids diverged most in spring, indicating that habitat selection by brook trout may be grea

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1996.tb00125.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractQuantitative electric fishing and multiple mesh‐size gillnetting of fish communities in the Hawkesbury‐Nepean River system, near Sydney, were carried out upstream of, within and well below each of three major points of treated sewage effluent discharge. Approximately half of the fish sampled were caught by electric fishing, comprising 515 individuals in 3 h of electric fishing (172 fish per hour). The remaining 439 fish were caught in 72 h of gillnetting (six fish per hour). In total, 16 fish species were collected by electric fishing and only seven species by the gill nets. Differences were found in the total abundances and numbers of species collected by each method in relation to points of treated sewage effluent discharge, but neither community variable showed consistent differences between the areas above, within and well below points of treated sewage effluent discharge in all three river regions. However, classification and ordination of electric fishing catch data produced distinct fish community groups in relation to sewage discharge, while similar analyses of the gillnetting data failed to reveal such differences in community structure. It was suggested that the increased sampling efficiency of electric fishing, both in terms of the number of fish sampled per unit effort and number of species collected, allowed for significant increases in the power of univariate and multivariate analysis methods in detecting such environmental disturbances in large riv

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1996.tb00126.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe space and depth distribution of the bottom‐line fisheries on the continental shelf of south‐east Brazil were analysed, and an attempt was made to identify the areas and depths where fishing effort is concentrated to delimit the main fishing grounds. Four main fishing grounds were identified based on the effort and catches between 1975 and 1985. These were, in decreasing order of importance: north of Espírito Santo state, near the Abrolhos archipelago; adjacent to Rio de Janeiro state, under the influence of Cabo Frio upwelling; north of São Paulo state, encircling Alcatrazes archipelago; and the outer edge of the Rio de Janeiro and São Paulo state continental shelves, between the Guanabara and Sepetiba bays. The concentration of the fisheries, the greater catches and the best productivity indices were found in outer and deeper areas along the edge of the continental shelf. There was a concentration of fishing effort and higher catches in deeper grounds, from the north to the south of the regional fishing area. The bathymetric distribution of the fisheries showed that they intensified from 30 m depth to the outer edge of the continental shelf. The fishery productivity indices increased towards a depth of 50 m, but fell thereafter. Fishing activities were lowest during the winter season for the whole region, but intensified during the summer‐autumn or spring‐summ

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1996.tb00127.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractArtificial reconditioning of Atlantic salmon in fresh water over two successive years produced kelt survival rates of 28% and 55% in years one and two, respectively. Eye damage and failure to identify non‐feeders were important factors contributing to high mortalities. Average fecundities of kelts reconditioned for the first (1220 ova kg‐1) and second (1093 ova kg‐1) year were lower than obtained for virgin control fish (1590 and 1728 ova kg‐1respectively). Average survival to swim‐up for progeny of first‐year (64.5%) and second‐year (71.4%) reconditioned fish were similar to survival of virgin control fish progeny (72.3% and 68.9% respectively).Ranched kelts showed better growth parameters than for freshwater reconditioning but had lower average fecundities (1310 ova kg‐1compared with 1820 ova kg‐1) and lower average progeny survival to swim‐up (60.8% compared with 88.6%) than

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1996.tb00128.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractMore than 100 fish species are associated with southern African estuaries, many of which are caught by recreational anglers and/or commercial fishermen. Mismanagement of either a catchment or an estuary invariably leads to an impoverished system which is of little value to fishes or people. By taking this cause‐and‐effect scenario to its logical conclusion, it should be possible to assess the ‘state’ of an estuary by monitoring the biological ‘health’ of the aquatic community. Fishes are a dominant and highly visible component of the estuarine fauna and, by virtue of their key positions in the aquatic food web, can reflect either natural or anthropogenic alterations to the environment. In addition, their mobility enables them to respond rapidly to both deteriorating and improving estuarine conditions. Such attributes may assist scientists and managers in being better able both to assess the magnitude of detrimental impacts, and to monitor the ecosystem response to ameliorative actions. This paper attempts to show that an understanding of the biology and ecology of fishes associated with estuaries can lead to the identification of threats to the environment and result in improved management of these systems. The use of fish communities as an indicator of estuarine health is also examined, and ways of incorporating biological and ecological data into decision‐support systems are discussed. The adoption of a set of environmental quality objectives for South African estuaries, together with a system of appropriate environmental quality standards, i

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1996.tb00129.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractGlobal warming is expected to result in considerable changes in northern European freshwater fish populations, fisheries and aquaculture. Shifts towards cyprinid and percid dominance in fish assemblages are expected, together with a decrease and collapse of salmonid and other coldwater fish populations. Most of the evident changes will occur in shallow lakes, where no thermal stratification occurs. The potential ranges of some fish species will shift northwards but pronounced changes will occur in the relative abundance of individual fish species. Total fish production will increase but because of changed composition of fish communities the commercial and recreational value of catches will decrease. Salmonid aquaculture productivity will increase provided that fish farmers adapt to new circumstances and cold, oxygenated water is available in larger quantities during summer.

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1996.tb00130.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractSince 1975, with partial recoveries in 1979 and 1984–1986, the numbers of finnock and adult sea trout,Salmo truttaL., in the Burrishoole system, western Ireland, have declined. The population decreased sharply from 1987, and collapsed in 1989 and 1990. Finnock were virtually absent in 1989 and one‐year maidens equally so in 1990. Sea trout smolt recruitments from 1992 to 1994 were the lowest recorded since 1970. The modal fork length of finnock decreased from 28 cm in 1987 to 26 cm in 1990. Up until 1989, the percentage return of smolts, as finnock, ranged from 11.4 to 32.4%. In 1989 a minimum was reached at 1.5%, with values of 10.0, 3.7, 7.4 and 9.9% from 1990 to 1994. Marine survival of smolts, to total first return to fresh water, historically ranged from 19 to 66%. Survival dropped to 1.8% in 1989. Observed changes in the structure of the sea trout population and the collapse in marine survival suggest that the current west of Ireland sea trout problem is based in the marine habi

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1996.tb00131.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1996.tb00132.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1996.tb00133.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Book reviewed in this article:Coasts and Seas of the United Kingdom: The JNCC Coastal Directories Project. Peterborough:JNCC.Marine Protected Areas: Principles and Techniques for Management. By Susan Gubbay.Recent Advances in Aquaculture IV. Edited by J F Muir and R J Roberts.

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1996.tb00134.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY