摘要:

SUMMARY.1. Brown trout were once given a variety of latin and common names, but are now regarded as belonging to only one polymorphic species,Salmo truttaL. A review of their geographical distribution shows that this species was originally native to Europe but has been successfully introduced in at least twenty‐four countries outside Europe.2. Brown trout provide valuable commercial and sports fisheries, e.g. commercial and rod catches of sea‐trout in England and Wales averaged 110,547 fish per year from 1983 to 1986 and the minimum value of these fisheries is estimated to be £55M.3. It is concluded from this brief review that the major objectives of scientific research on wild brown trout should be: (a) an assessment of the current status of stocks; (b) the maintenance of existing populations; (c) the development and improvement of mathematical models that can be used as tools for the conservation and management of this important national and international reso

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01343.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. This short review summarizes a long‐term investigation of brown trout in two populations that probably represent opposite extremes of life histories in this polymorphic species; Bhick Brows Beck serves as a nursery for the progeny of migratory trout (mixture of sea and estuarine trout) and Wilfin Beck is populated by resident trout.2. Population density in Black Brows Beck was always much higher than that in Wilfin Beck, and was regulated by density‐dependent survival in the early stages of the life cycle. There was no evidence for similar density‐dependent regulation in Wilfin Beck; simple proportionate survival occurred with fairly constant loss‐rates. Survival was reduced in both populations by summer droughts and also by spates in Wilfin Beck.3. Black Brows trout were always larger than Wilfin Beck trout of similar age; fry size at the start of the growth period was chiefly responsible for these differences. Variations in water temperature were chiefly responsible for differences in growth rates between year‐classes within each population. Food intake was not a limiting factor, except in the first winter of the life cycle and for adults over 3 years old in Wilfin Beck. Variation in individual size was inversely density‐dependent in Black Brows Beck and decreased with age in Wilfin Beck, these changes being due to natural (stabilizing) selection.4. There is strong evidence for genotypic differences between the populations. The implications of this are discussed, especially the need to conserve different populations that may contain unique genetic material, and the importance of restocking with fish reared from the indigenous population that should always contain the optimum genotypes for a particular habitat. Restocking with juveniles should be done with caution because it could lead to a decrease in both numbers and size variation when the population is regulated by density‐dependent mechanisms.5. One major objective of future work should be the development and improvement of mathematical models that can be used to predict the optimum density for trout in different populations, the maximum attainable growth rate in different habitats, and the effects on trout populations of environmental changes due to natural causes (e.g. droughts and spates) or hum

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01344.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. The life cycle of salmonid fishes is described.2. The performance and environmental requirements of the various life stages of the trout (Salmo truttaL.) are reviewed, (a) The literature gives predictive relationships between water temperature and rate of embryonic development, food requirements and growth rate, (b) Water temperature, intragravel oxygen supply rate, water pH, the occurrence of mechanical shock, disturbance of spawning gravels, sedimentation and water chemistry can all influence the survival of the intragravel stages, (c) The survival and/or well‐being of the free‐swimming stages and the success of spawning are influenced by such factors as dissolved oxygen concentration, pH, water depth, water velocity and water chemistry.3. Human activities such as impoundment, river transfer, drainage works, land improvement, afforestation and deforestation can all influence trout populations via changes in flow regime (and related effects such as sedimentation), temperature regime and water chemistry.4. Man can also influence trout populations directly by cropping for food and/or sport and by artificial stocking.5. Examples of practical application of present knowledge are given and some future research needs are lis

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01345.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Review of published studies on genetic variation, as shown by electrophoretic studies of protein variation, in natural brown trout (Salmo truttaL.) populations from Britain and Ireland, Finland, France, Greece, Iceland, Norway, Sweden, U.S.A. and U.S.S.R., revealed abundant geographical variation in gene frequency with individual populations containing only a limited part of the gene diversity of the species.2. Thirty‐eight (54%) of the seventy gene loci examined have been found to be polymorphic in the species with an average population showing polymorphism at 16% of its loci (range 0‐34.8%).3. The brown trout is naturally subdivided into a large number of reproductively isolated and genetically distinct populations within, as well as among, drainages.4. Two independent post‐glacial colonizations, by genetically distinct races, followed by independent evolution in separate drainages over the past 13,000 years is seen as responsible for the genetic diversity of brown trout in north‐western Europe.5. Many genetically unique populations have been lost in the past 100 years and there is an urgent need to identify and conserve the remaining genetic diversity. Genetically unique populations are an irreplaceable resource for rational management in relation to angling and future aquaculture po

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01346.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. The hypothalamic‐pituitary‐interrenal axis of the brown trout,Salmo trutta, is activated in response to most forms of environmental stress. This results in an elevation of blood cortisol levels.2. Experimental elevation of blood cortisol levels in otherwise unstressed brown trout caused a dose‐dependent increase in mortality rate due to disease. In our studies.,Saprolegnia‐infection, furunculosis and bacterial fin‐rot were the principal diseases.3. Chronic cortisol elevation also suppressed several of the endocrine processes controlling sexual maturation, resulting in a significant reduction in the size of the gonad in both male and female fish.4. It is argued that many of the deleterious effects of sublethal pollution (including acidification) on natural trout populations can be attributed to chronically‐elevated blood cortisol levels and that a knowledge of such physiological changes would allow an assessment of the impact of pollution events and act as an early warning of potential disease and recruitme

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01347.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY..1. Chalkstream trout are fast‐growing, short‐lived with a stable age structure that is a consequence of the lack of extremes in the abiotic environment, especially of water temperature and flow.2. Levels of secondary (invertebrate) production arc high and there is no evidence that interspecific or intraspecific competition for food resources limits growth.3. Dietary studies show a broad similarity between trout and other species, but indicate differences that reflect variations in the micro‐habitat distributions between fish species.4. Trout numbers appear to be limited initially by the availability of gravel spawning areas, and then by areas suitable for newly‐emerged fry. Reduction in stream discharge in the spring, either naturally or by man, can lower the number of 0+ trout that survive.5. Eels are not important predators on trout eggs or fry. but a reduction in pike numbers can lead to a decrease in the mean weight of pike. Small pike do not pose a serious threat to stocked yearlin

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01348.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Brown trout (Salmo trutta)life history and habitat use were studied in two Norwegian rivers: the Vosso river system, western Norway, and the Søre Osa, eastern Norway.2. Age‐groups were partly segregated in feeding habitats, the youngest fish living mainly in running water and in the littoral zone of lakes, the older fish also exploiting pelagic waters and deeper epibenthic habitats. In a population with free access to and from the sea, some individuals smoltified and became sea‐run migrants, performing yearly migrations to the coastal sea, whereas others stayed as freshwater residents throughout their entire life span.3. Within local populations, females were larger and less variable in size than males. This was partly because females matured at an older age than males, partly because the sexes tended to exploit feeding habitats with different food and growth Conditions. Within age‐groups, females were more pelagic and migrated more than males, whereas males were more confined to running water and epibenthic areas than females. In the pelagic zone, males were more abundant in near‐surface water, and females more abundant in deeper areas. When exploiting the same feeding areas, the two sexes grew at the same rate. There therefore appears to be a connection between feeding habitat and the reproductive ecology of bro

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01349.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. Intensive research into the life history of brown trout started In 1948 when the Brown Trout Laboratory was opened in Pitlochry. Over the next 15 years significant contributions were made to the brown trout literature upon which the Laboratory based advice to landowners and anglers wanting to develop their fisheries.2. Increasing pressure from the government for more work on Atlantic salmon tended to divert research funds and time away from brown trout investigations. The International Biological Programme's major study at Loch Leven from 1966 to 1972 ensured a continuing interest in trout in standing waters. Over this period little attention had been paid to trout in rivers. This changed when a number of investigations were started on the River Tweed by Edinburgh University.3. A major constraint to brown trout conservation and management has been illegal fishing and lack of records on stocking activities and catches. The granting of Protection Orders under the Freshwater and Salmon Fisheries (Scotland) Act, 1976, has been a major incentive to increased interest in the improvement of trout fisheries.4. Brown trout stocks have been reduced in certain areas due to the effects of afforestation, acidification, land drainage and farm wastes. Various remedial measures have been proposed and implemented.5. To meet the increasing demands for trout fishing, many loch and reservoir fisheries are now stocked with rainbow trout in preference to brown trout. Attention should be paid to the interaction of these two species in both standing and in running waters., where fish farm escapees and inadvisable releases go unrecorded.7. Research into the genetic effects on wild stocks from the liberation of large numbers of hatchery‐reared brown trout has been lacking and probably many ‘pure’ indigenous stocks have been lost. More work in this field is essential.8. Proposals are outlined for future brown trout research and recommendations are made for better management. Suggestions are also put forward for changes in the legislation to further protect Scottish brown trout s

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01350.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY..1. Ireland's fauna and flora are, compared with those of Britain and Continental Europe, relatively impoverished as a consequence of our glacial history. Salmonids are, however, well represented here and, because cyprinids are not. they make up a large proportion of the freshwater fish biomass.2. It may be more accurate to regard our trout fauna as a mosaic of subspecies and races rather than a single species. Two principal immigrations are thought to have contributed to the extant strains one of which includes the valuable long‐lived sea trout and freshwaterferox.Their fidelity to specific spawning areas isolates and maintains the purity of trout strains but certain aspects of spawning behaviour may leave some of them susceptible to cross fertilization with others.3. Strains of trout may take distinguishable external forms or they may not be easily recognized by eye. In spite of their great interest in the conservation and management of trout, anglers are largely unaware of their genetic status.4. Artificial restocking of salmonids has been carried out in Ireland since the nineteenth century; most effort has been expended on Atlantic salmon but, in the last 25 years, the restoration of trout populations depleted by pollution and arterial drainage has been the object of these exercises. There is concern for the consequences of wild trout strains being diluted by these efforts although, to date, evidence to support that happening is sparse.5. Problems associated with deterioration in water quality have multiplied over the past 20 years and trout is the species most affected by fish kills. These tend to be seasonal, exacerbated by low water and dry weather. The smallest streams, which may be as narrow as 30 cm, which are the stronghold of trout in many catchments, are at greatest risk.6. Ireland's cyprinid fauna results from introductions but it is rapidly developing ‐ as is coarse angling. Roach is the species spreading fastest. Studies show that roach will share the diet of trout and. possibly more significant, will compete with them for the angler's

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01351.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARY.1. The diversity, value and status of the trout resource within the Welsh Water Authority area is described.2. Reported angling catches of sea trout have increased in recent years but there is an apparent decline in brown trout stocks. Factors affecting the distribution, status and diversity of the trout resource are identified and discussed.3. Investigations are being carried out to evaluate the apparent problems and to provide information required to formulate management solutions. A management strategy is proposed which allows for the maintenance and development of the resource, whilst ensuring the preservation of strains of trout which have conservation value in their own right.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1989.tb01352.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY