Factors influencing the yield of brown trout, Salmo trutta m. lacustris L., in northern Finnish lakes     

T. VEHANEN 《Fisheries Management and Ecology》1995,2(2):121-134

Abstract Lake-to-lake variation in brown trout, Salmo trutta m. lacustris L., yield from stocking was examined in 34 lakes in northern Finland. The trout were mainly stocked as 2–3-year-old fish. Catch statistics were compiled with information on water quality, water level fluctuations, fishing effort and lake geomorphology. Absolute brown trout yields (kgha^-1) increased with increasing stocking rate, but there was an indication of non-linearity at higher stocking densities. Relative yields (kg per thousand trout released) were highest at low stocking rates. Stepwise multiple regression analysis was used to determine the best predictive model for lake-to-lake variability in brown trout yields. Seventeen measured regressands were used initially, and then replaced with scores obtained in a principal component analysis of highly correlated water quality variables and species-specific fish yields. Three major determinants of brown trout yields in these lakes were found in both analyses: fish community, stocking rate and fishing effort. Brown trout yields from stocking were higher in lakes with proportionally high yields of vendace or vendace and whitefish and proportionally low yields of pike.  相似文献   

Long-term trends in the competitive shore fishery along the KwaZulu-Natal coast,South Africa     

《African Zoology》2013,48(2):216-236

Twenty-four years (1977–2000) of competitive shore angling catch and effort data from the KwaZulu-Natal Coastal Anglers Union for the province of KwaZulu-Natal were analysed. Of a minimum of 117 species recorded, the most commonly caught species were dusky shark (Carcharhinus obscurus) (26%), milk shark (Rhizoprionodon acutus) (18%) and shad (Pomatomus saltatrix) (10%). By weight, the top species were dusky shark (34%) and diamond ray (Gymnura natalensis) (19%). All the above species showed considerable inter-annual variation in their respective contributions to annual catch. Probably as a result of changes in fishing patterns, dusky shark and milk shark showed a general decline in percentage contribution to catch over the period, while contributions of lesser guitarfish (Rhinobatos annulatus), giant guitarfish (Rhynchobatus djiddensis), diamond ray (Gymnura natalensis) and brown ray (Himantura gerrardi) increased. Mean overall annual cpue by number and weight showed a non-significant increase over the period, while each of the investigated species showed a constant trend in mean annual weight. There were high proportions of juveniles in the catches of dusky shark (100%), dusky kob (92%) and giant guitarfish (78%). Improvements made to the structure of shore angling competitions and the overall contribution of competition angling to resource management in South Africa is discussed.  相似文献   

Incidental phosphorus losses – are they significant and can they be predicted?     

Paul J. A. Withers  Barbro Uln  Christian Stamm  Marianne Bechmann 《植物养料与土壤学杂志》2003,166(4):459-468

Fresh applications of phosphorus (P) may cause ‘incidental’ losses of dissolved and particulate P forms in land runoff when rainfall interacts directly with fertilizers and manures which are spread, or excreted, onto the soil surface. Research indicates that when incidental P losses (IPL) occur, they often make the dominant (50–98 %) contribution to measured P loads in surface and sub‐surface runoff from field plots, with increased risk of eutrophication where P‐enriched runoff is routed directly to the watercourse. Rates of P loss are temporally and spatially very variable (< 1 to 25 % of total P applied) depending on the amount of P applied; the P release properties of the materials applied (% P extractable in water), the timing of storm events after application and the amounts of runoff generated. Large P applications left on the surface of wet, frozen, compacted, and intensively underdrained soils in high rainfall areas are particularly vulnerable to IPL. Concentrations of P in runoff are often greatest during the first storm event following P application, but can remain high for several weeks, or even months after application. Catchment scale impacts are more difficult to quantify due to the effects of dilution with runoff from fields without IPL, and the contributions of P from other sources. Approaches to predicting IPL are discussed and need to be improved in order to assess the contribution of IPL to catchment P loads in river basin management planning. Strategies to control IPL should focus on adoption of more sensitive management practices in fields with a high risk of rapid runoff or preferential flow, and are likely to very effective.  相似文献   

Yield and N uptake as affected by soil tillage and catch crop     

E.Møller Hansen  J. Djurhuus 《Soil & Tillage Research》1997,42(4):241-252

Two field trials with spring barley (Hordeum vulgare L.) were conducted at two locations in Denmark in order to evaluate the effects of tillage and growth of a catch crop on yield parameters under temperate coastal climate conditions. Ploughing in autumn or spring in combination with perennial ryegrass (Lolium perenne L.) as a catch crop was evaluated on a coarse sand (Orthic Haplohumod) from 1987 to 1992 at three rates of N fertiliser application (60, 90 and 120 kg N ha⁻¹ year⁻¹). Rotovating and direct drilling were also included as additional tillage practices. The experiment was conducted on a 19-year-old field trial with continuous production of spring barley. Ploughing in autumn or spring in combination with stubble cultivation and a catch crop, in addition to minimum tillage, was evaluated in a newly established field trial on a sandy loam (Typic Agrudalf) from 1988 to 1992. Yield parameters and N concentrations in grain and straw were determined. On the coarse sand, N uptake in the grain in ploughed plots without a catch crop was significantly greater when spring ploughed as opposed to autumn ploughed, but grain and straw yields did not differ significantly. Grain yield, straw yield and total N uptake did not differ significantly between direct drilled and autumn ploughed plots, but the trend was for grain yield to be lower with direct drilling. After 19 years of catch crop use, yield parameters in ploughed plots were greater than in plots without catch crops. This was most pronounced in the autumn ploughed plots. Rotovating the catch crop in the spring decreased grain yield compared with underploughing the catch crop in autumn or spring. No significant interactions were found between tillage and N rates. On the sandy loam, grain as well as straw yield and total N uptake were not significantly affected by catch crop or time of ploughing. Grain yield was significantly lower with reduced tillage (stubble cultivation in autumn) than in all other treatments.  相似文献   

Long-term changes in the sea-age at maturity and seasonal time of return of salmon, Salmo salar L., to Scottish rivers   总被引：1，自引：0，他引：1  

D.W. SUMMERS 《Fisheries Management and Ecology》1995,2(2):147-156

Abstract Using catch data, changes in salmon, Salmo salar L., sea-age and seasonal return time were compared between several Scottish east coast rivers over the last 150–200 years. Parallel long-term trends were found, suggesting common influences affecting salmon at sea. Long-term associations with marine environmental factors were investigated by literature review and comparisons with an index of Icelandic sea-ice abundance. Apparent associations were shown to exist since about 1900, although the cause was not demonstrated. However, over a longer timescale, the same associations were not apparent. Unique gradual marine changes since 1900 may have resulted in perceptible associations with salmon data which may otherwise be imperceptible when short-term marine environmental variability is greater than long-term variability. Marine factors must affect salmon, but the complexity of the marine environment and controls on age at maturity and time of return mean that a retrospective analysis cannot be expected to identify the causal factors.  相似文献   

Possible increase in catch of Atlantic elver Anguilla anguilla in 1993 and 1994     

C. Moriarty  F.-W. Tesch 《Ecology of Freshwater Fish》1996,5(4):213-215

Data on catches of O+ elvers from nine countries in Europe and of juvenile eels ascending the St. Lawrence River in Canada are presented and compared with previous records. Consideration of a parallel decline in recruitment in Canada supports the theory that oceanic conditions are responsible for the observed fall in catches. A substantial increase in the Loire, to 95 tons in 1994, may indicate an overall improvement in stocks.  相似文献   

小黑麦的特性及应用研究进展   总被引：7，自引：1，他引：6  

许庆方 《草原与草坪》2008,(4):80-86

作为第一个人工培育的谷类作物,小黑麦（×Triticosecale Wittmack）在我国草田轮作或填闲种植中,可以发挥重要的价值。详细论述了小黑麦农艺措施对小黑麦生长情况的影响,小黑麦的种质特性,抗性生理,以及收获利用等的研究进展,提出在小黑麦饲草加工与利用方面,还应深入研究。  相似文献   

新西兰周围海域双柔鱼渔场及其渔获分布     

陈新军 《上海海洋大学学报》1998,(2):93-101

本文对１９９６－１９９７年度新西兰双柔鱼渔场及其渔获量进行了分析,班克斯半岛周围海域为主要的鱿钓鱼场,占总渔一的一半以上,斯图尔特岛的东部、达尼丁的东南、库克海峡东口等３个渔场的产量出发点也占一定的比例,渔获得量的高低与月相有关,以望为中心的渔获较低,以朔为中心的渔获较高。不同渔场其海底的水深不一,水深可作为寻找渔场的参考指标之一,渔场的形成与表温、水温的垂直梯度关系密切,南岛东部海域表温为－３１  相似文献   

用计算机进行绿鳍马面鲀资源评估和产量预报     

陈卫忠  郑元甲  李长松 《上海海洋大学学报》1998,(1)

用实际种群分析(VPA)法,以计算机为工具,对东海绿鳍马面鲀资源量及产量作估算和预报。在10多年的工作中,以计算机技术的发展为基础,对评估方法作了改进,使得评估效率和精度都有所提高,实践表明,评估结果对渔业生产和管理部门有一定的参考价值。  相似文献   

Exploring tropical fisheries through fishers’ perceptions: Fishing down the food web in the Tonlé Sap,Cambodia          下载免费PDF全文

K. B. KC  N. Bond  E. D. G. Fraser  V. Elliott  T. Farrell  K. McCann  N. Rooney  C. Bieg 《Fisheries Management and Ecology》2017,24(6):452-459

Tropical fisheries are among the most productive fisheries in the world, often providing the primary source of protein for the local population. Despite their importance, data on these systems are relatively limited, thus hampering management and policy development. Here, the implications of increasing fishing pressure are explored by critically evaluating the perceptions of the fishers who rely on these ecosystems to survive. A total of 169 fishers in 26 different fish‐dependent communities in the Tonlé Sap Lake, Cambodia, were surveyed to understand their perceptions of the impact that fishing has had on the ecosystem. The Tonlé Sap is one of the largest, yet poorest studied, freshwater fisheries in the world. Consistent with “fishing down the food web” theory of fisheries, survey data revealed that although fishers observed the total size of fish catch remaining consistent over recent years there has been a drastic decline in the size of individual fish, as well as a reduction in the diversity of species caught. These perceptions are examined with reference to food web theories that explore how fishing pressure leads to ecosystem change, including the more recent “indiscriminate fisheries” theory.  相似文献