摘要:

AbstractSmall amounts of radioactivity in liquid effluent are discharged under authorization into Lake Trawsfynydd in north Wales. MAFF inspectors from the Directorate of Fisheries Research (DFR) advise the Welsh Office on the terms of authorization and on the power station operators' compliance with them. DFR also has the responsibility for environmental monitoring, including fish caught for consumption. Trout angling is particularly popular in Lake Trawsfynydd, and because of angling pressure, additional brown trout,Salmo truttaL., and rainbow trout,Oncorhynchus mykiss(Walbaum), need to be introduced. An important factor in determining the concentration of radionuclides in these fish is the length of time that they spend at liberty. During the fishing season, samples of these stocked trout were tagged and released to assess the average residence time. This was found to be 6 days for rainbow trout and 10 days for brown trout. Less than 7% of the recaptured stocked trout of either species had a residence time of more than 20 days. Radiocaesium concentrations in recaptured trout were very low. Trout which avoided recapture and overwintered in the lake were found to have radiocaesium concentrations similar to those of indigenous trout sampled at the same time.

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00092.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe survival of small‐sized (<50.8 cm) chinook salmon,Oncorhynchus tshawytscha(Walbaum), and coho salmon,Oncorhynchus kitsutch(Walbaum), caught by sport fishing was determined to assess the potential for increasing the size limit for these fish. Fishermen were recently catching smaller salmon than in the 1970s, but salmon growth rates had not changed. To be an effective management option, the survival rate of hooked and returned fish must be high. The overall survival rates were high: 76% for chinook salmon and 70% for coho salmon. There was no significant difference in survival of the coho salmon with size of hook used (P= 0.31). Any mortality among fish was generally acute; fish hooked deep in the mouth or gills generally bled and died shortly after capture. Fish hooked in the gills had a significantly greater mortality (P= 0.0002). The overall high survival rate for these species was the result of a small proportion of fish being hooked in the gills or deep in the mouth. Since the survival rate of the salmon was high, the size limit could be increased to allow smaller fish to grow to sizes preferred by sport fisherme

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00093.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effects of perch,Perca fluviatilisL., and bronze bream,Abramis brama(L.), predation on the production of insects emerging at the water surface and the autumn biomass of benthic macro‐invertebrates were assessed in a series of experimental ponds. The study attempted to discover whether fish affect food availability for diving and dabbling ducks in freshwater habitats. Ten ponds (bisected by fine netting) were used for the study: one was left totally fish‐free, whilst one half of each of three groups of three ponds was stocked with either perch, bream or perch plus bream. The relative abundance of emerging insects (mainly Chironomidae) was significantly reduced in two perch ponds, two perch + bream ponds and two bream ponds. The autumn standing crops of benthic macroinvertebrates were significantly reduced in one perch pond, three bream ponds and one perch plus bream pond. These results support findings of a contemporaneous large bio‐manipulation experiment carried out in two adjacent lakes. During the biomanipulation studies, aquatic invertebrate standing stocks greatly increased after the removal of fish and decreased following resto

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00094.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAt the River Bush salmon station in Northern Ireland, a genetically marked strain of Atlantic salmon,Salmo salarL., was established, with a low frequency (0.194) of a glucose‐6‐phosphate isomerase genotype (GPI‐3* 100/93). As part of a salmon enhancement programme, 43500 of these fish were stocked as swim‐up fry into a tributary of the nearby Margy River in Spring 1990, following a baseline genetic survey which indicated an absence of the GPI–3*93 allele in the wild population. This survey also indicated a significant frequency difference of a malate dehydrogenase allele (MDH‐B1,2*85) present both in the stocked and wild fish. A post‐stocking electrofishing survey in summer 1990 indicated higher summerling densities in stocked sections compared with unstocked (control) sections, with an estimated survival of stocked fry to summerling ranging from 24% to 29%. Genetic analysis based on GPI‐3*100/93 and MDH‐B1,2*100/85 genotypes provided similar estimates of the overall contribution of stocked fish at 59.8% to 61.9%, respectively, although there was a disparity between markers in estimated contributions to stocked and control sections. A further genetic survey in 1991 estimated that 32.2% (MDH) to 69.1% (GPI) of the 1 + parr population consisted of stocked fish, the MDH‐based estimate having declined greatly between summerling and 1 + parr stages. Possible reasons for the disparity of marker results are outlined, and the implications for use of low‐frequency gene

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00095.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractStudies were conducted to determine the composition and relative abundance of commercially desirable and less desirable fish populations of Rawal Dam reservoir. Fifteen fish species belonging to 11 genera were identified. The less desirable species were abundant, constituting 62.3%, 84.8% and 78% of the total number of fish sampled on three occasions. Carnivores were represented by two species with very low percentage composition by number or weight. The ratio of total weight of forage fish to that of carnivorous fish indicated an unbalanced population in the lake. The proportion of the fish population at harvestable size suggests a balanced population, but this index may have been overestimated because of a minimum harvestable size.

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00096.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe major food items of adult largemouth bass,Micropterus salmoides(Lacepède), in Lake Naivasha, Kenya are not markedly different from those in its native range. Although insects and their larvae are major components of the diet for both temperate and equatorial populations of juvenile bass, the equatorial population also eatsProcambarus clarkii(Girard), juvenile fish and aquatic weeds. In temperate populations they also eat crustaceans, rotifers and oligochaetes. The frequency of occurrence of the major prey organisms in the stomachs ofM. salmoidesvaries seasonally with population peaks in these organisms. Similar to North American populations, the Naivasha population feeds during the day between dawn and dusk. In contrast to temperate populations, the population ofM. salmoidesin this equatorial lake feeds throughout the year, with feeding intensity correlated with water temperature

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00097.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe ability of consumers and fishermen to distinguish‐between wild striped bass,Morone saxatilis(Walbaum), and its hybrids may be important to marketing farm‐raised fish and managing wild stocks. The ability of randomly selected persons to distinguish between wild and hybrid specimens was examined and it was found that a significant improvement in recognition occurred with only minimal training. Average correct response of 70% without training rose to nearly 90% after training. Moreover, the respondents' sex and age were important factors in determining successful identificat

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00098.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe population dynamics of culture‐based fisheries are studied by means of a mathematical model, which incorporates explicit sub‐models for density‐dependent individual growth and size‐dependent mortality. The model applies to populations of carps, i.e. common carp, Chinese carps, and Indian major carps, and coregonids.The effects on production of stocking density and size of seed fish, fishing mortality, and size at harvesting are studied in a model population of carp. Management implications of the modelling results are emphasized. An adaptive approach to management, involving judicious experimentation with stocking and harvesting regimes, is proposed to gain information on the dynamics of actual fisheries, and to optimize their pro

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00099.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractTwenty‐seven years of daily salmon,Salmo salarL., rod catch and flow data from the River Derwent were analysed. Daily catch was standardized for each month between June and October and the mean value determined for each 2‐cumec flow band. In June and July the mean standardized catch remained relatively low and stable for flows up to approximately 9 cumecs. Thereafter it increased steadily with increasing flow, reaching a peak at 21 cumecs and 41 cumecs for each month respectively. A linear model accounted for the greatest proportion of the variability in August and September with mean standardized catch increasing steadily up to a maximum value of 43 and 39 cumecs respectively. However, in October, a quadratic model was more appropriate, with mean standardized catch decreasing as flow increased up to 9 cumecs and thereafter increasing steadily with flow, reaching a maximum value at 21 cumecs. The pattern of the relationship at higher flows was not clear because of the paucity of data. These findings are discussed in relation to the management of the water resource for the maintenance of the fish

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00100.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Book reviewed in this article:Freshwater Fisheries Management. Edited by Robin G. Templeton.The New Rivers and Wildlife Handbook. Edited by Diana Ward.

ISSN:0969-997X    

DOI:10.1111/j.1365-2400.1995.tb00101.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY