ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03227.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

There are two fundamental types of research problems facing the management of Atlantic salmon in Atlantic Canada. First, there are problems associated with assessment of individual and mixed stocks: these can be divided into estimating optimal spawning requirements, estimating current spawning escapements, and forecasting available harvests at least one year in advance. Second, there are problems related to the large number of Atlantic salmon stocks, at least 350, and the small number of biological staff. One solution to many of these problems is to focus research efforts on small index rivers where upstream and downstream fish migrations are counted and randomly sampled. These rivers can be used to estimate optimal yield and to forecast harvest in distinct geographical areas. They also provide base‐line data to examine phenomena such as fluctuations in ocean survival, density‐dependent growth and mortality, or even large‐scale environmental perturba

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03228.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Tropical fish were collected by trawling in Yemeni waters. Age determinations were made on sections of vertebrae which were cross checked with scales. The values for the von Bertalanffy growth constantsKwere in the range 0.08–0.31. Total mortalities (Z) calculated from age compositions were in the range 0.31 to 0.67 for 11 species. The mean of 0.46 agreed closely with that derived from the formula of Pauly (1980a) of 0.45. Since the former included fishing mortality (F) in addition to natural mortality (M) it was suggested that a lower value be used in the Gulland (1968) yield formula:Y =0.5M Bo. Recruitment to the fishery for most species occurred by 3 years of age. The demersal fish stocks in Yemeni waters may not exceed 109×103tonnes at the present time. Using a value forMof 0.3, the annual sustainable yield may be in the region of 16×103ton

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04005.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The geographical distributions of inherited biochemical markers were used to measure the amount of genetic isolation between stocks of Namibian and South African anchovy,Engraulis capensis. A contingency‐table analysis of allele frequencies for 10 polymorphic protein‐coding loci revealed no significant frequency differences between spawning areas. The average Nei genetic distance between samples was 0.0003 and there were no geographic trends in the amount of genetic distance between populations. Average population heterozygosity for 31 loci was 0.115 and this accounted for 99.26% of the total genetic variation. The remaining 0.24% was due to all temporal and spatial differences combined. The observed amount of genetic divergence between populations was used to estimate the amount of migration between spawning areas, using the stepping‐stone model of migration. As few as 13 migrants may account for the observed genetic divergence between spawning areas. The validity of using the genetic stock concept in the management of marine fishes is disc

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04006.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Data are presented to show how the number and growth of juvenile salmon in streams in the Scottish Highlands are influenced by various physical (temperature, water chemistry, depth and velocity, type of substratum) and biotic (food resources, competition, recruitment) factors.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03229.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Bullhead catfish,Ictalurus nebulosus, and rainbow trout,Salmo gairdneri, were subjected to two coal‐derived substances to evaluate each material for potential carcinogenic activity. Substances tested included a solvent‐refined coal heavy distillate and a sediment extract from an industrially polluted river in Ohio. Two subfractions, one containing the polycyclic aromatic hydrocarbons and the other containing the nitrogen heterocycles of each material were also tested. Following a 16‐h exposure period, the gill and liver tissues were removed and examined by standard light and electron microscopy techniques. Hyperplasia of the gill tissue and some engorgement with blood of the secondary lamellae were observed with the light microscope. At the electron microscope level, hepatocyte mitochondria were swollen with a loss of cristae, and rough endoplasmic reticulum fragmented. Results suggest that most of the treatments studied induced pathological responses in fish. Of the two fish tested, the rainbow trout was the most sensitive indicator of environmental poll

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04007.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

A short review summarises the chief conclusions of an 18‐year investigation of the population dynamics of migratory trout,Salmo truttaL., in a Lake District stream. The chief factors affecting growth, survival and production have been identified and their effects summarized in a series of mathematical models. The implications of this work are discussed in relation to long‐term investigations, data analysis and modelling, and the scientific management of trout populations. It is shown that mathematical models, based on long‐term investigations, can be used to assess the effects on a fish population of changes due to natural causes (e.g., droughts and spates) or human activities. One of the main objectives of future work should be the development and improvement of models that can be used as tools for the conservation and management of fish s

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03230.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The precise nature of the stock and recruitment relationship in natural populations is of vital importance to any attempt at stock enhancement by removing or by‐passing a limiting factor, or at management by manipulation of spawning stock. In this paper the evidence for and against a dome‐shaped stock and recruitment curve is reviewed, and consideration given to several factors which complicate the conventional, simplistic interpretation of density‐dependent mortality. These include environmentally mediated changes in ‘carrying capacity’, distribution of spawning, and the need to consider whole river systems. The implications of these factors for fisheries management and stock enhancement are

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03231.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The seasonal fluctuations in the ascorbic acid (AsA) and ascorbic acid 2‐sulphate (AsA 2‐sulphate) content of mullet,Mugil cephalus, tissues were examined. Ascorbic acid concentrations in brain, gill and hepatic tissues showed seasonal changes, but the pattern of AsA fluctuations in each tissue differed. The AsA content of mullet brains decreased during the summer, whereas hepatic AsA concentrations increased during this period and were maximal by the end of June. Hepatic AsA reserves declined after environmental water temperatures dropped below 18°C and reached a minimum (20 μg g−1) by the end of January. Greatest fluctuations in AsA content occurred in gill tissues, which had a four‐fold range of tissue concentrations. There were also seasonal changes in the AsA 2‐sulphate content of brain and hepatic tissues. These differences among mullet tissues in the seasonal patterns of AsA content may be due to diverse effects of environmental variables on tissue AsA reserves. The ability of hepatic and renal tissues of mullet and several other teleost species to synthesize AsA was also investigated. L‐gulonolactone oxidase activity was detected in all the species examined, but in all cases the biosynthetic capacity was less than a seventh that in goldfish,Carassius auratus, livers. Mullet appear to have only a limited capacity to s

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb04008.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Fingerlings of brown trout (Salmo trulta m. farioL.) were introduced to sections of different types of streams situated in natural catchments and those modified by Man's activity. At stations where environmental conditions were modified by such forms of impact as pollution, flow variability and impoundment, trout did not survive 5 months. In the natural river sections mortality rates increased downstream along the river continuum and were associated with increased predation. Growth rates in the upper reaches were primarily restricted by abiotic factors—temperature and trophic status: however, they were to a large extent modified by density‐dependent regulation and intraspecific competition. The influence of the abiotic/biotic regulatory process, expressed as fish metabolic performance, is discussed as a framework for the determination of the carrying capacity of the riverine ecosys

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1985.tb03232.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY