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1.
Land-use patterns in the catchment areas of Sri Lankan reservoirs, which were quantified using Geographical Information Systems (GIS), were used to develop quantitative models for yield prediction. The validity of these models was evaluated through the application to five reservoirs that were not used in the development of the models, and by comparing with the actual fish yield data of these reservoirs collected by an independent body. The robustness of the predictive models developed was tested by principal component analysis (PCA) on limnological characteristics, land-use patterns of the catchments and fish yields. The predicted fish yields in five Sri Lankan reservoirs, using the empirical models based on the ratios of forest cover and/or shrub cover to reservoir capacity or reservoir area were in close agreement with the observed fish yields. The scores of PCA ordination of productivity-related limnological parameters and those of land-use patterns were linearly related to fish yields. The relationship between the PCA scores of limnological characteristics and land-use types had the appropriate algebraic form, which substantiates the influence of the limnological factors and land-use types on reservoir fish yields. It is suggested that the relatively high predictive power of the models developed on the basis of GIS methodologies can be used for more accurate assessment of reservoir fisheries. The study supports the importance and the need for an integrated management strategy for the whole watershed to enhance fish yields.  相似文献   

2.
Abstract  Culture-based fish yield in non-perennial reservoirs of Sri Lanka was related to reservoir morphometry and stocking density. The reservoirs were stocked mainly with fingerlings of one Chinese and three Indian major carp species, common carp, Cyprinus carpio L., and the genetically improved farmed tilapia strain of Nile tilapia, Oreochromis niloticus (L.), at four pre-determined species combinations and a range of stocking densities [ SD (fingerlings ha−1)]. Twenty-three reservoirs were harvested successfully at the end of the culture period of 2002–2003. Basic limnological and morphometric parameters, including shoreline development ( D L ) and shoreline area ratio ( R LA ), were estimated for each of the 23 reservoirs. Bray–Curtis similarity and non-metric multidimensional scaling using mean values of limnological data revealed that reservoirs could be ordinated into two major clusters, one with intact sample distribution due to similar trophic characteristics and the other with scattered sample distribution. Reservoirs in the cluster with similar trophic characteristics showed significant correlation ( P  < 0.05) between R LA and total fish yield ( Y ). A multiple regression equation, Y  = −693 + 4810  R LA  + 0.484 SD , was generated to estimate fish harvest in relation to SD .  相似文献   

3.
The recreational catfish harvest was classified in 349 reservoirs larger than 200 ha distributed over 40 states of the contiguous USA. Harvesting occurred in 282 reservoirs, averaged 2.8 kg ha−1 year−1 and represented 15.6% of the total fish yield. The genus Ictalurus contributed most to catfish fisheries (mean = 2.0 kg ha−1), followed by Ameiurus (1.1 kg ha−1) and Pylodictis (0.4 kg ha−1). Five distinct clusters of reservoirs were identified, differing relative to geographical distribution, catfish harvests, angler favouritism towards catfish and physicochemical characteristics. Reservoir clusters across the northern USA had low harvests and essentially featured reservoirs in the upper periphery of the native range of catfish. Harvesting in reservoirs in the south-west of the country, where catfish have been introduced, was higher than in the north, yet yield remained low. Within their native range, three overlapping clusters included one with medium and another with high harvests, both types dominated by Ictalurus, and a cluster with very high harvest dominated by Ameiurus . Variability in harvests was attributed to zoogeography, reservoir physicochemical characteristics and fishing effort. Management of catfish fisheries of the three less-productive clusters may focus on enhancement through habitat manipulation and stocking; the two more productive clusters offer the greatest flexibility for management through regulation of harvest.  相似文献   

4.
The spawning ground of the Japanese sardine, Sardinops melanostictus (Schlegel), was distributed over the oceanic waters as well as the coastal waters along the Pacific coasts of western and eastern Japan during 1978–1992. The area of the spawning ground in the coastal waters on the continental shelf has ranged from 95 000 km2 in 1992 to 143 000 km2 in 1988, constituting 44–77% of the total area of the spawning ground. The area of the coastal spawning ground was relatively constant in spite of the large fluctuations in egg abundance, i.e. size of the spawning population, from 88 trillion (1987) to 668 trillion (1989) in the waters. Spawning adults seemed to extend over the coastal waters irrespective of the size of the spawning population. In contrast to the coastal waters, the spawning area in the oceanic waters offshore of the continental shelf increased from 31 000 km2 in 1978 to 183 000 km2 in 1988 and then shrank to 83 000 km2 in 1992, as a function of the spawning population size. The egg distribution density in the coastal waters stayed less than 6000 m−2 mo−1, but it reached as high as 27 400 m−2 mo−1 in the expanded spawning ground in the oceanic waters. The oceanic waters seemed to function as a reserve spawning ground for the sardine in years of extremely high spawning population.  相似文献   

5.
Water consumption from Russia's southern rivers has increased substantially in recent years as a consequence of intensified economic activity. The volume of irreversible river-flow withdrawal from the Azov Sea basin varies between 11 and 13 km3 year1. The majority of the abstracted water is used for irrigation. By 1990, the decrease in discharge into the Caspian Sea was 41 km3 year1. Withdrawals of water from the Kura, Terek, Ural and other rivers have so far exceeded the ecologically admissible limits and become critical. The paper discusses methodological approaches for the elaboration of standards for water withdrawal and ecologically safe discharges into the southern seas. New data are presented on the dynamics of fish abundance as a function of the hydrological characteristics of rivers and water salinity. The results of the system analysis and regressive modelling formed the basis of a programme to develop policies for water management for fisheries in the lower Don. The principles and criteria for water withdrawal under variable hydrological regimes for the rivers entering the Azov and the Caspian Seas should be tested for their applicability for other water bodies (e.g. rivers, water reservoirs and lakes).  相似文献   

6.
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   

7.
We use trivariate kernel density estimation to define spawning habitat of northern anchovy ( Engraulis mordax ) and Pacific sardine ( Sardinops sagax ) in the California Current using satellite data and in situ egg samples from the Continuous Underway Fish Egg Sampler (CUFES) deployed during surveys in April by the California Cooperative Oceanic Fisheries Investigations (CalCOFI). Observed egg distributions were compared with monthly composite satellite sea surface temperature (SST) and surface chlorophyll a (chl a ) data. Based on the preferred spawning habitat, as defined in SST and chl a space, the satellite data were used to predict potential spawning habitat along two areas of the west coast of North America. Data from the southern area (21.5 to 39°N) were compared to observations from the CUFES data for the period 1998–2005. Northern anchovy and Pacific sardine exhibited distinctly different spawning habitat distributions. A significant relationship was found between satellite-based spawning area and that measured during surveys for sardine. CUFES area estimated for sardine was similar in magnitude to that estimated from satellite data (∼60 000 km2). In contrast, spawning habitat of anchovy averaged between 1000 and 200 000 km2 for the period 1998–2005, for CUFES and satellite estimates, respectively. Interannual variability in the area (km2) and duration (months) of estimates of suitable habitat varied between species and between the northern (39 to 50.5°N) and southern portions of the California Current. Long-term monitoring of habitat variability using remote sensing data is possible in the southern portion of the California Current, and could be improved upon in the northern area with the addition of surveys better timed to describe relationships between observed and estimated spawning habitats.  相似文献   

8.
An analysis of covariance relating basin area ( A , km2) to river length ( L , km) and discharge rate ( D , m3 s–1) was performed for two continents and showed that the two covariates ( L and D ) were highly significant and that the strength of the relationship changed between continents. For comparison, D was excluded but the result remained the same. Although geomorphological models are useful for establishing global levels of production, these regressions should be applied with caution. Historically, simple statistical models were developed to predict fish catches in rivers. These, based upon regression of catches on channel length or basin area for Africa and Central Amazonia, are contrasted in this paper because of their generally similar approach.  相似文献   

9.
Abstract– Data from the Swedish Electrofishing Register were used to study the effects of lakes on the growth of yearling (0+) brown trout in outlet streams. It was found that growth increased close to lakes. On average, the length of the longest yearlings was 10% greater 0-100 m downstream from lakes as compared with more than 1 km downstream. Growth enhancement was most pronounced downstream from large lakes. This was exemplified with maximum yearling lengths in September in inlet streams (maximum yearlings 50-100 mm) and outlet streams (65-130 mm) of Lake Stora Le (area 200 km2), and inlet streams (50-75 mm) and outlet streams (65-95 mm) of Lake Anten (area 18 km2). It is suggested that this is a combined effect of both increased water temperature and outflow of lake seston. The growth pattern found was not correlated to population abundance or to the abundance of competitors or predators.  相似文献   

10.
Abstract This study was conducted to evaluate the effects of stocking density and monosex culture on growth, survival, yield and feed conversion ratio of freshwater prawn Macrobrachium rosenbergii in concrete tanks. Juvenile prawns with an average weight of 1.8 g were stocked into triplicate tanks at densities of 5, 10, 15 and 20 prawns/m2, grown for 168 d and fed a 34% tilapia diet. Stocking density had significant effect on prawns. Final mean body weight decreased with the increasing density, being highest at 5 prawns/m2 (29.6 9). and lowest at 20 prawns/m2 (17.4 g). Total yield increased from 135 g/m2 (1,350 kg/ha) at a density of 5 prawns/m2 to 261 g/m2 (2,610 kg/ha) at density 15/mz to 245 g/m2 (2,450 kg/ha) at 20/mz. Feed conversion ratios were high and ranged from 3.7 (5 prawns/m2) to 5.6 (20 prawns/m2).
In monosex culture of freshwater prawns stocked in triplicate tanks at a density of 5 prawns/m2 for 112 d, the all-male population had the best growth performance and feed conversion ratio, followed by the mixed-sex and all-female populations. The all-male population had 99% marketable prawns (>20 g) with an average yield of 159 g/m2 (1,590 kg/ha); the mixed-sex population had 90% marketable prawns and the yield was 135 g/mz (1,350 kg/ha); and the all-female population had 75% marketable prawns with an average yield of 108 g/m2 (1,080 kgha).  相似文献   

11.
ABSTRACT:   Common silver biddy Gerres oyena were collected monthly between November 2002 and November 2005 in Okinawa Island of southern Japan. The seasonal reproductive cycle of this species was investigated using the gonadosomatic index (GSI) and through histological observation of gonads. Temporal variation in the GSI reflected gonadal development from histological observations; ovary development occurred from March to September and testes development occurred between March and August. Maximal development was observed in April and May in both sexes. While mean values for hepatosomatic and lipidosomatic indices decreased markedly in females relative to males during gonadal development, mean condition factors decreased with gonadal recrudescence in both sexes. The minimum standard length (SL) at sexual maturity was 89.7 mm for females and 81.4 mm for males and the size at which 50% of individuals were sexually mature was 104 and 92 mm SL in females and males, respectively. The power relationships of batch fecundity (BF) versus standard length (SL, mm) and body weight (BW, g) of females can be expressed as BF  = 46.7 × e1.64 SL and BF  = 19 697 × e0.49 BW , respectively.  相似文献   

12.
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   

13.
ABSTRACT:   Photosynthetic activities of hermatypic corals (28 genera, c . 68 species and c. 92 specimen) were measured in November 2000 at Sekisei lagoon, Okinawa, Japan, using an underwater pulse amplitude modulated fluorometer. Maximum quantum yield (Fv/Fm) ranged from 0.61 to 0.70 and had an average value of 0.664 (standard deviation [SD], 0.0289). Following the measurement of Fv/Fm, quantum yield (Fm'-F)/Fm' at eight-leveled actinic-light intensities were obtained from all specimens. Values of electronic transport rates (ETR) were nearly the same under low photosynthetic active radiation (PAR; µmol quanta/m2 per s) condition and varied with increasing PAR. The value of ETR at 100 µmol quanta/m2 per s ranged from 21.3 to 30.0 and had an average of 27.8 (SD, 2.09). In August 2001, a coral bleaching event was observed in Sekisei Lagoon. During the event, photosynthetic activities of 21 specimens of eight species (seven genera) were measured. By applying two indicators, Fv/Fm and ETR at 100 µmol quanta/m2 per s obtained in August 2000, 18 of 21 specimens were suggested under the bleaching process. In case of Porites lutea , seven colonies were visually evaluated for their condition of bleaching and were found to have two 'normal', three 'slightly bleached' and two 'heavily bleached'. From the density of zooxanthellae, colonies evaluated 'normal' or 'slightly bleached' did not show an apparent difference. However, they were clearly identified by Fm/Fv and ETR at 100 µmol quanta/m2 per s.  相似文献   

14.
The present study investigates the success of stocking fingerlings of Indian major carps ‐Gibelion catla (Hamilton), Labeo rohita Hamilton and Cirrhinus mrigala Hamilton – to enhance fish yield in 58 small reservoirs in Odisha State, India. Fish stocking and yield data were collected from State Fisheries Department, Odisha. The relationships between area, stocking density and fish yield of different size groups of reservoirs were assessed using the Pearson correlation coefficient (r). Fish yield increased significantly (p < 0.05, t‐test) from 204 kg/ha/year in 2012–13 to 323 kg/ha/year in 2013–14 due to adoption of CBF. The corresponding per capita fish production increased from 398 kg fisher?1 year?1 to 702 kg fisher?1 year?1 benefitting more than 8,000 fisher households. Reservoirs in the size group 100–500 ha showed the highest response of fish yield with respect to stocking of fingerlings. The size of fingerlings at stocking and area of the reservoir had greater impact on enhancing fish yield. Stocking had a profound positive impact on fish yield. This study forms a baseline evaluation of the impact of stocking on small tropical reservoirs in India. It also recommends management measures and discusses issues, and the way forward for sustainable fisheries enhancement in small tropical reservoirs in eastern India.  相似文献   

15.
Environmental heterogeneity can create boundary conditions for the co-occurrence of marine predators and their prey. If one or both are spatially constrained by their tolerance to environmental variables, then spatial differences in the availability of possible habitats define the volume of distributional overlap. Cod ( Gadus morhua L.) and its prey, herring ( Clupea harengus L.), in the vertically stratified Bornholm Basin of the Baltic Sea are presented as an example. A non-linear model was used to estimate oxygen avoidance thresholds for both species. Herring avoided oxygen saturation levels below 50%, while cod tolerated oxygen saturation down to 16%. The threshold of 50% oxygen saturation, below which cod could not encounter its prey, herring, was applied to a time series of vertical oxygen profiles from the centre of the Bornholm Basin to estimate the size of the overlap volume during the winter period from 1958 to 1999. Dependent on the oxygenation of the deep-water, the overlap volume varied between 57 km3 and 250 km3.  相似文献   

16.
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   

17.
The relationships between surface area, stocking density and fish yield in 40 small reservoirs in India between 1994 and 1999 were examined. A significant positive correlation (r = 0.6) was found between stocking density and fish yield. Area was negatively correlated with stocking density (r = ?0.57) and fish yield (r = ?0.62), but its correlation with efficiency of stocking was not significant for all the size groups of small reservoirs.  相似文献   

18.
Abstract  The distribution and overall biomass of an underfished vendace, Coregonus albula L., population in the mesotrophic Henne Reservoir (Germany) was studied using hydroacoustics and gill nets. Additionally, midwater trawling was carried out. Overall fish biomass, based on five hydroacoustic surveys (June to September 2002), ranged from 188 kg ha−1 in early August to 302 kg ha−1 in September 2002. The overall mean fish biomass was 256 kg ha−1 (±48 kg ha−1 SD). Biomass of fish smaller than 25 cm total length (mostly vendace) varied from 56 kg ha−1 in August to 99 kg ha−1 in September, with an overall mean fish biomass of 74 kg ha−1 (±17 kg ha−1 SD). The echograms showed temporal variation in fish distribution in Henne Reservoir. In June, fish were fairly evenly distributed over the whole reservoir but in September a dense aggregation of fish (mostly vendace) was found in the deeper water layers near the dam. The distribution of vendace stock, its impact on water quality and fisheries management, biomanipulation and effort for mass removal are discussed.  相似文献   

19.
A 34-day study was conducted to estimate the effect of stocking density on growth, biomass, and yield of harvestable animals in red swamp crawfish, Procambarus clarkii (Girard). Juvenile crawfish were stocked at l, 2, 4, 8, and 16 crawfish per m2 into plastic-lined metal pools planted with rice ( Oryza sativa ) with three replicate pools at each density. Crawfish averaged 35 ± 1.5 mm (SE) total length at the time of stocking.
Growth in total length and weight was significantly affected by density ( P < 0.01), ranging from 91.5 mm and 20.7 g for crawfish stocked at 1 per m2 to 62.5 mm and 6.3 g for crawfish stocked at 16 per m2. The total crawfish biomass ranged from 20.7 g per m2 for crawfish stocked at 1 per m2 to 88.7 g per m2 at 16 per m2. The portion of that biomass made up of harvestable sized animals (>75 mm total length) ranged from 100% at 1 per m2 to 0.7% at 16 per m2. Gross revenues per ha were projected for crawfish yields at each stocking density with and without a graded product.  相似文献   

20.
Abstract –  We used radio telemetry to measure the habitat use and movements of 20 tagged pikeperch (44–59 cm) in the hydropeaking Pyhäkoski Reservoir, Finland, during June 1999–2000. The hydrological conditions in the 8-km-long reservoir were measured and then modeled over eight discharge rates between 30 and 700 m3 · s−1. Pikeperch preferred relatively low water velocities and deep water depths especially during the winter. During the summer, pikeperch moved actively in different parts of the reservoir. No relationship was found between hydroelectric plant operations and distances moved by pikeperch during the summer. Movements peaked in autumn but decreased during the winter to a restricted area. After 1 year of monitoring, 4 out of 20 tagged pikeperch remained in the Pyhäkoski Reservoir, three had died when descending from hydroelectric dams, 10 had descended downstream to other reservoirs or sea, two were captured by local fishermen, and one fish's signal was lost for unknown reasons.  相似文献   

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