首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 156 毫秒
1.
Abstract. The fishery of Parakrama Samudra, an ancient man-made lake of 2662 ha in Sri Lanka (8°-10°N; 80°-82°E), as in most other man-made reservoirs in the island, is dominated by the exotic cichlid Sarotherodon mossambicus (Peters), introduced in 1952. The fluctuations in catch per unit/fisherman over the period 1960 to 1982 are shown to be dependent on the yearly fluctuations in the water-level, the changes in the water-level effects being manifested in the fishery after a period of 3 years. The above results were arrived at by auto-correlation analysis of yearly catch per unit effort against the fluctuation of the water level at the main sluice. The changes in yield in a particular year are correlated to the changes in the water level and are described by the equation;
where Y = yield in kg fisherman-1 month-1 in year t and X = fluctuations in the water-level in year t - 3. The available growth rates in natural and semi-natural impoundments also indicate that the size at which S. mossambicus enter the fishery in Parakrama Samudra corresponds to their size in the third year of life (age 2+). The significance of the above observations is discussed on the basis of available knowledge on the reproductive cycle and the nesting requirements of S. mossambicus which are achieved when significant fluctuations in the reservoir level take place by making available optimal water depths in areas with a suitable substratum. The possible use of the above criteria as a management measure is also briefly discussed in the light of possible irrigational and fisheries conflicts in the utilization of the reservoir resources.  相似文献   

2.
Abstract. The status of the fishery of Pimburctlewa wewu, a man-made lake in Sri Lanka, was studied from January 1985 to January 1986. The annual fish yield in the reservoir is 441 kg/ha, one of the highest in the south-east Asian region. Oreochromis mossambicus (Peters) is the dominant species in the fishery and accounted for about 90% by weight of the total catch. Although there were monthly variations in catch per unit effort, the daily catch per fisherman was not adversely affected. A possibility of having a more productive fishery is suggested In reducing The minimum permissible mesh size in the gillnet fishery during the peak recruitment season in May–June. The possible effects of reducing the mush size are discussed. Using the length-frequency data of O. mossambicus , the asymptotic length and the growth constant were estimated to be 39.3cm and 0.34 respectively. The estimates of total mortality (2.42). natural mortality (0–82) and mean selection length (24.6 cm) were based on these growth parameters Yield-per-recruit analysis indicated that the O. mossambictus fishery in the reservoir was optimally exploited.  相似文献   

3.
Abstract– Stock dynamics of the introduced tilapia Oreochromis mossambicus and co-occurring indigenous cyprinids were studied in a typical lowland reservoir in Sri Lanka. All species exhibited peaks in reproductive activity during the rainy seasons in November and May. O. mossambicus was estimated to grow to 14 cm in its first year and to 21 cm in its second. A high natural mortality ( M was found, both for the cyprinids ( M =1.3 yr−1 to 4.7 yr−1 over a range of species) and for O. mossambicus ( M = 1.9 yr−l and 1.7 yr−1 for females and males). The fishing mortality ( F ) of O. mossumbicus , estimated for the length range from 15.0 to 18.5 cm, was 5.5 yr−1 for females and 4.7 yr−1 for males. The total fish biomass was estimated at 1 829 kg/ha, with 128 kg/ha O. mossambicus and 1 098 kg/ha small pelagic cyprinids, mainly Amblypharyngodon melettinus . The total biological fish production was around 5 400 kg/ha/yr, with O. mossambicus and the small pelagic cyprinids accounting for 400 kg/ha/yr and 3 600 kg/ha/yr respectively. The commercial fishery yielded 242 kg/ha/yr (including 70% or 169 kg/ha/yr O. mossambicus ), indicating an incomplete utilization of the total biological fish production. It was concluded that there is scope for an approximately 100% increase of the total yield. Reimplementation of a 76 mm minimum mesh size, to prevent overfishing of O. mossambicus , is recommended as a management measure. Additional options are direct exploitation of the untapped resource of small pelagic cyprinids, or indirect exploitation by means of a culture-based fishery on Lates calcarifer , a controllable predator.  相似文献   

4.
The inland fisheries of Sri Lanka are essentially artisanal on most of the reservoirs in the country. The annual inland fish production declined dramatically after 1990, when state patronage for the development of the inland fisheries was discontinued for 4 years. This decline was shown to be a result of growth overfishing of the two dominant cichlid species which accounted for over 90% of landings. This was a result of using small mesh ( < 6.9 cm) gillnets in the absence of the State-sponsored monitoring procedure in the fishery after 1990. This indicates that it is necessary to monitor inland fisheries management in Sri Lanka through a centralized authority in the current situation. However, in some Sri Lankan reservoirs, fishing communities can be categorized as 'organized' because they collectively make decisions to define procedures for the rational exploitation of the fishery resources. In reservoirs with 'organized' fishing, the communities themselves have developed mechanisms to regulate the landing sizes of dominant cichlid fish species through community-based fisheries management strategies. In such reservoirs, over-exploitation of fish stocks was not evident, even after 1990, when state-sponsored monitoring procedures were suspended. Based on these observations, an alternative approach is recommended for the management of Sri Lankan reservoir capture fisheries in which the Government and resource-users have equal responsibilities in the management of the resources.  相似文献   

5.
Abstract  The artisanal, stake net fishery for shrimp in the Negombo lagoon, Sri Lanka, was studied over 2 years. There are around 22 sites, at which 57–63 stake nets can be fixed, at sites close to the sea mouth of the Negombo lagoon. The estimated mean catch rates of the fishery were 23.21 and 26.19 kg per operation in 1998 and 1999, respectively. The estimated annual fish productivity from the fishery reduced from 240 t in 1998 to 215 t in 1999. Subadults of penaeid shrimps formed 82% of the stake net catch. The net monthly income per fishermen varied from Rs. 5000 to 33 200 (mean = 13 667). In the Negombo lagoon stake net fishery, a mechanism for equity sharing was formulated by the fishing community.  相似文献   

6.
Tropical reservoirs are primarily constructed for irrigation, generation of hydroelectricity and water supply schemes. Development of inland fisheries is a secondary use of most reservoirs. In Sri Lanka, most reservoirs are scattered in the rural areas of the country so that investigation of the fisheries of individual reservoirs with a view to developing management plans is prohibitive. The present study was instigated to explore the possibilities of developing suitable yield predictive models, which can be used in developing management strategies for the Sri Lankan reservoirs. The study was carried out in 11 perennial reservoirs of Sri Lanka. Basic limnological parameters (conductivity, dissolved phosphorus, total phosphorus, chlorophyll a [chl a] content and alkalinity) were determined in each of these reservoirs. Daily data on fish catch and fishing effort were collected in each reservoir. Data on catchment areas (CA), reservoir area (RA) and reservoir capacity (RC) were obtained from the irrigation and survey departments. It is evident that chl a is positively influenced by nutrients (dissolved phosphorus and total phosphorus), morphoedaphic indices derived as alkalinity to mean depth (MEIa) and conductivity to mean depth (MEIc) ratios and CA/RC ratios. MEIa and MEIc are also positively influenced by CA/RC ratios. All these morphological and edaphic parameters were found to positively influence fish yield in reservoirs. As fishing intensity (FI) is also a major determinant of fish yields, fish yield was better accounted by multiple regression models in which FI and individual morphological and edaphic parameters were used as independent variables. Of these multiple regression relationships, the best predictive power for fish yield (Y in kg ha?1 yr?1) was found by Y=18.9+6.78 FI+0.0073 CA/RC where FI is expressed as boat‐days ha?1 yr?1 and CA and RC are in km2 and km3, respectively. In this relationship, FI and CA/RC account for about 68% of the variation in fish yield.  相似文献   

7.
Abstract. The occurrence and abundance of eels were investigated in five lowland reservoirs in south-eastern Sri Lanka. Paired fyke nets and longlines were used for sampling eels. Two tropical species of eel. Anguilla bicolor McClelland and Anguilla nebulosa McClelland, were caught. In two of the five reservoirs investigated only A. bicolor was found and in another two reservoirs both species were caught. Eels seemed to be absent from one reservoir. The CPUE in reservoirs with eel was between 0·13 and 2·60 eels of both species per fyke net and night, and the total weight was between 81 and 814g. A small capture-recapture experiment in Badagiriya, where eels seemed to be most plenliful, gave a population estimate of only six eels or 1·2 kg per ha (eels longer than 40cm). Such a low abundance was regarded as unrealistic. Stocks of eel could presumably, at least in some reservoirs, withstand commercial exploitation but more information is needed on recruitment, growth and migration before any advice can be given on the management of stocks.  相似文献   

8.
The Negombo estuary brush park fishery in Sri Lanka was investigated from June 1998 to March 1999. The mean fish yield (all species) in the fishery was 12.46 t ha−1 yr−1. Fin fish species formed about 91% of the yield and the rest was formed by penaeid shrimps and crabs. Fish yield and the twig density in the brush park exhibited a second order polynomial relationship indicating a minimum yield at an intermediate value of twig density in the brush parks. The relationship between fish yield and duration of implantation of brush parks showed an optimal period of 30–40 days for high fish yields. Income levels of fishermen, availability of construction material and suitable sites for implantation of brush parks are some of the factors determining size and number of brush parks per fisherman and duration of installation. Indigenous knowledge within the fishing community about the effect of salinity variations, twig density and mangrove species used on the harvests greatly contribute to effective operation of this fishing practice. Cultivation of mangroves to obtain twigs and branches is a unique feature in this estuary. Indigenous knowledge on mangroves has led to the adoption of sound silvicultural practices. Although cultivating mono-specific mangrove stands may not increase diversity of mangrove forests, it reduces denudation of naturally occurring mangrove forests because of brush park construction, and retains habitats for other organisms. Mangrove management plans in the Negombo estuary should therefore be viewed and treated in an integrated manner that takes into account both resource and social components.  相似文献   

9.
Abstract. Two species of tilapia, Oreochromis mossambicus (Peters) and O. niloticus (L.), from five reservoirs in southern Sri Lanka as well as fish from a fish hatchery and laboratory stock were studied by starch gel electrophoresis at 18 enzyme loci, to determine the degree of mixing of the two species. Two reservoirs showed little or no mixing between O. mossambicus and O. niloticus , while two other reservoirs as well as the hatchery stock showed a high degree of mixing of the two species. The laboratory stock of O. niloticus also showed introgression of O. mossambicus alleles. The similarities of the local stocks to the original African as well as other Asian stocks is discussed.  相似文献   

10.
福建省近海渔业管理目标的比较   总被引：2，自引：1，他引：2       下载免费PDF全文
应用Schaefer和Fox剩余产量模式及其由此衍生的生物经济模式和Gulland最适产量Y0．1模式，分别估算了福建省近海海洋捕捞业的最大持续产量，最大持续捕捞力量，最适产量，最适捕捞力量，最大经济产量，最大经济捕捞力量，最佳经济效益，并对各模式计算的诸项经济指标进行比较，建立了渔业管理3种模式，并根据福建省近海渔业实际情况和渔业发展趋势 ，提出实现3种管理目标的实施步骤。  相似文献   

11.
Abstract Exotic cichlids, introduced to Asia during the second half of the twentieth century, contribute significantly to the reservoir fisheries in the region. The two major cichlid species, Oreochromis mossambicus (Peters) and O. niloticus (L.), tend to interbreed easily. In Sri Lankan reservoirs, introgressive hybridization of these two cichlids takes place. The reproductive biology of O. mossambicus, O. niloticus and their hybrids in three reservoirs in Sri Lanka was evaluated. An imbalance in sex ratio with male dominance was evident. The estimated fecundity for 20-cm fish, using fecundity-total length relationships for various populations, indicated that there was a decline in fecundity in hybrid forms. It is hypothesized that the long-term effect of crosshybridization between the two cichlids might lead to a decline in fish yields in perennial reservoirs of Sri Lanka. The importance of the findings of the present study for the management of the reservoir fisheries in Asia is highlighted.  相似文献   

12.
A glass eel fishery exists downstream of the Arzal estuarine dam in the Vilaine (Brittany, France). Catch statistics were collected between 1996 and 2000, and processed using a subsampling technique which allowed data from a reliable subsample to be extrapolated to the whole fishery. During the same period, glass eel migration into fresh water was monitored using a glass eel trap located on the dam – the upstream limit of the fishery. The analysis of glass eel biology and exploitation shows that the glass eel fishery is very intensive and that there was more or less no escapement during the fishing seasons studied. The proportion of the stock successfully migrating towards fresh water, as compared with the total catch is estimated to range between 0.3 and 3.9%. In such a fishery, the fishing effort affects the abundance. Consequently, the total catch has to be used instead of catch‐per‐unit‐effort to estimate abundance.  相似文献   

13.
Abstract. The eggs and yolk sac fry of the mouth brooding tilapia. Oreochromis mossambicus (Peters), were artificially reared in an experimental hatchery system at different temperatures. The hatchability, embryonic development of eggs and growth of yolk sac fry were studied under controlled conditions. It was shown that the upper lethal temperature for O. mossambicus eggs was above 40°C and the lower lethal temperature between 11°C and 17°C. For yolk sac fry these values lay between 34 and 40°C and 17 and 20°C respectively. Fry survival between 24·3 and 34·0°C was near to 100% while al 20°C it was less than 60%. The somatic growth rates of fry at temperature between 20 and 34·5°C up to 10 days post hatch are presented and were found to differ significantly. At 34·6°C a negative SGR was recorded during the period 6–9 days post hatching, but, during the first 6 days, the SGR at this temperature was more than four times higher than at 20°C. At the elevated temperatures, the utilization of yolk is faster and the loss of weight observed was due to starvation. This should be taken into account when incubating under artificial rearing condition so that initiation of exogenous feeding is timed most appropriately.  相似文献   

14.
Abstract Lake Victoria is one of the African Great Lakes, and an important source of affordable protein food in the form of fish. It provides employment, income, and export earnings to the riparian communities. Despite this importance there are major concerns about the status and exploitation of the fisheries. This study assesses if current extraction rates/yield of Nile perch, Lates niloticus (L.), from Lake Victoria are sustainable for the foreseeable future. The paper reviews trends in catch and effort in the Nile perch fishery and models the expected scenarios using ECOPATH. The fishery exhibits, classic indicators of intensive fishing, erring towards overexploitation, including: (i) decline in total estimated catch of Nile perch in recent years from the peaks in the 1990s. This is coupled with a shift in contribution of catches from higher trophic level species (Nile perch) to lower trophic level (dagaa) species. (ii) Three major trends in the fishing effort are evident: (a) almost doubling of the number of fishers and fishing boats between 1990 and 2000, and the even greater expansion between 2000 and 2002; (b) a large scale increase in the number of gears operational in the lake; and (c) the propensity for use of ‘illegal’ gears. (iii) Catch‐per‐unit‐effort has declined from about 80 to 45 kg per boat day. (iv) Predictive modelling (ECOSIM) of the future of the Nile perch fisheries under a scenario of increased fishing effort suggests that the fisheries are unsustainable and will decline in the long term. It appears that the Nile perch stocks in the three riparian countries are under intense fishing pressure, and unless concerted action is taken, the potential for degradation of the resources is prevalent. In view of the importance of these fisheries, it is recommended that a precautionary approach to further intens‐ification of the fisheries is adopted until such time empirical evidence shows that the fisheries are capable of further expansion and intensification. The main options for management are devolvement of responsibilities for the fisheries to the communities, enforcement of existing regulations, improved monitoring and data collection processes, reducing post‐harvest losses and increasing the value of the products to the export market.  相似文献   

15.
Abstract Postal questionnaires, interviews and accurate reports from anglers were used to study angling activity, yield and catch per effort of grayling, Thymallus thymallus (L.), and brown trout, Salmo trutta L., on three stretches of the regulated river Glomma and two stretches of its tributary, the river Rena in southeastern Norway. Angling activity was expressed as hours angling per kilometre of river and varied from 364 (CL 245–598) to 1337 (CL 912–1991) h km-1. Grayling and brown trout dominated the catches. The catches were estimated between 476 (CL 334–659) and 753 (CL 517–1155) grayling and brown trout per kilometre river stretch. The mean weights were estimated between 216 and 353 g for grayling, and 260 and 395 g for brown trout. The yield of grayling and brown trout was estimated between 8.7 (CL 6.1–12.4) and 46.4 (CL 34.9–62.3) kg ha-1 yr-1. The quotient grayling/brown trout in the catches varied between 0.41 and 5.1, and was found to be significantly negatively correlated with angling effort ( r = - 0.838, P <0.05). Catch per effort was estimated between 132 (CL 82–218) and 382 (CL 287–513) g h-1, and was also negatively correlated to angling effort, according to: Catch per effort (g h-1) = - 0.210 × effort (h km-1) + 405 ( r = and 0.899, P <0.02).
Angling activity in earlier years was determined from number of permits sold where data were available. On stretches where angling activity was moderate, there was a tendency towards increase, whereas on stretches where activity had been high for several years, the activity seemed to have stagnated, indicating that a saturation had been reached.  相似文献   

16.
Culture-based fisheries (CBF) are increasingly accepted as strategies for enhancing inland fisheries, especially in tropical Asia. In Sri Lanka, CBF development in irrigation reservoirs has gained momentum due to concerted efforts of government fisheries authorities for inland fisheries enhancement. In the present study, production trends of five irrigation reservoirs of Sri Lanka before and after the introduction of CBF were investigated and apparently optimal CBF yields were not realised. Hence, the stochastic frontier production function (SFPF) was employed to quantify technical efficiencies (TE) of CBF. For each reservoir, annual averages of input data from 2005 to 2018 (14 years) were used in the TE analysis. Hence, total sample size for estimation of SFPF was 70. Although CBF production gradually increased in all five reservoirs from 2005 to 2018, there were substantial variations of total fish production across the reservoirs. The SFPF indicated that CBF production could be further increased through more efficient management of inputs (i.e. number of fishers, mean number of fishing days per year and stocking density).  相似文献   

17.
Use of geographical information systems (GIS) in inland fisheries has hitherto been essentially restricted to site evaluation for aquaculture development and assessment of limnological changes in time and space in individual water bodies. The present GIS study was conducted on the land-use pattern of the catchments of nine reservoirs in Sri Lanka, for which detailed fishery data, viz. yield, fishing intensity, landing size of major constituent species, together with selected limnological data such as conductivity and chlorophyll- a , were available. Potential statistical relationships (linear, curvilinear, exponential and second-order polynomial) of fish yield ( FY , in kg ha−1 yr−1) to different land-use patterns, such as forest cover ( FC , in km2) and shrub-land ( SL , in km2), either singly, or in combination, and/or the ratio of each land type to reservoir area ( RA in km2) and reservoir capacity ( RC in km3), were explored. Highly significant relationships were evident between FY to the ratio of SL and/or FC + SL to RA and/or RC . Similarly, the above land-use types to RA and RC ratios were significantly related to limnological features of the reservoirs. The relationships of FY to various parameters obtained in this study were much better correlated than those relationships of FY to limnological and biological parameters used in yield prediction in tropical and temperate lacustrine waters previously.  相似文献   

18.
Abstract. A non-linear programming model was developed to determine the benefits obtainable from the inland capture fisheries of Bangladesh. Functions and parameters of a base model were estimated by deriving non-linear catch-effort and cost functions as well as rice responsive demand functions using both primary and secondary data. Results of LP (linear programming) solution of the base model suggest that the inland fisheries of Bangladesh are capable, under optimal conditions, of generating a total net benefit of Bangladesh Taka (BDT) 1383 million per annum (US$1 = BDT38), most of which (96%) accrues as producer surplus. Under the optimal allocation of total fishing effort the model shows a 13% reduction in overall fish catch with 54% less effort. Sensitivity analysis, through variations of fishing effort, shows that the incorporated variables (e.g. catch, cost, benefit and shadow price) change in line with theoretical expectations. The implication of these results for management is that a reduction in effort would be required in order to generate a greater net economic benefit from the riverine fisheries. Such reduction should be specific to individual fishery and/or fishing grounds.  相似文献   

19.
We describe the seasonal migrations of Argentine chub mackerel ( Scomber japonicus ) into the fishing ground in relation to sea surface temperature conditions and analyse the temperature evolution during the fishing season on the basis of 1955–97 time-series. The upper temperature limit for the presence of schools was around 19°C. At higher values, most schools leave coastal waters (< 50 m) for the shelf. An inverse relationship was observed between catches per unit of effort (CPUE) of the inshore fishery and sea surface temperature. The highest standardized CPUE values corresponded to temperatures lower than 19°C. Above this temperature, the probability of obtaining a standardized CPUE higher than 1 was extremely low, and the standard deviations were minimal. The economic benefit from catches was also analysed through the different months of the fishing season. It was found that the mean benefit corresponding to temperatures lower than 19°C exceeded approximately 15 times that obtained at higher temperatures. A simple fishing strategy was proposed to the commercial fleet in order to improve the economic benefit of the catches. The migratory pattern followed by mackerel during the spawning period was also analysed in relationship to other environmental factors like food availability. Zooplankton composition, size structure and abundance in coastal and shelf waters are described, and their implications for feeding ecology of larvae and adults of the species are discussed.  相似文献   

20.
本文根据近海渔业资源衰退的实际,有针对性地提出渔业和渔业资源管理具体措施和建议,主要是:(1)削减捕捞力量,优化捕捞作业结构;(2)实施TAC制度;(3)渔获量配额管理和提高渔获物附加值;(4)伏季休渔和产卵场保护;(5)种群最小可捕标准和渔具最小尺寸;(6)重点保护生活史k选择的种群;(7)增殖放流明显衰退的经济种类;(8)杜绝毒、炸、电违规捕捞;(9)控制对沿岸海域的污染,保护渔业生态环境;(10)加强资源监测和预测,开展渔情预报;(11)完善渔业统计,建立渔捞记录制度;(12)强化渔业法和水产资源繁殖保护条例的宣传教育力度;(13)开展渔业资源普查工作等等。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号