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1.
Abstract. The inland fishery in Sri Lanka (6–10°N; 79–82°E) is essentially a fishery confined to man-made lakes and is dominated by the introduced cichlid Sarotherodon mossambicus (Peters). Catch statistics of 20 such major reservoirs indicate that the yield of this species ranges from 64·0 to 918 kg per ha and accounts for between 56 and 99% of the total yield in individual reservoirs. The yield of S. mossambicus is closely related to the fishing pressure exerted. Catch/effort data from the individual reservoir fisheries when analysed collectively simulate changes in a single large fishery. In the fishery the relationship of yield to effort is described by the equation: Y = 4·OX – 53·8X ( r = 0·92; P < 0·001), where Y = yield in kg per ha per annum and X = number of craft-days per ha per annum, indicating that the reservoirs in Sri Lanka remain underfished. However, very high increases in fishing pressure in two reservoirs, for which data are available over a 5-year period, indicate that the increases have resulted in a significant decline in the catch per unit effort. The reasons for the success of the S. mossambicus fishery in individual reservoirs, and also simulation of features of a single large fishery in reservoirs, with widely different hydrological and limnological regimes, are discussed in qualitative terms. It is hypothesized that the abundance is determined by factors other than food availability. Fresh management strategies to optimize the fishery from the point of view of optimal fishing pressure permissible from the present analysis are suggested.  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.
In the coastal zone of the Sea of Okhotsk off Hokkaido, Japan, the giant ezo scallop ( Patinopecten yessoensis ) is widely cultivated on the sea bed, making its fishery a major industry. However, the area experiences intense cyclones, including typhoons, about once a decade and the scallop resources appear to have received severe damage from the storms. Such an event occurred on 29 October 1988. The storm caused 12-m-high wind waves, which appeared to be fully developed sea waves. The water above the sea bed repeatedly moved back and forth at speeds of 1∼2 m s-1 causing damage to the scallops due to collisions and rubbing with gravel and other scallops. From a comparison of wind data with the annual catch of scallops, intense cyclones seem to play an important role on the year-to-year fluctuations in the scallop fishery.  相似文献   

5.
Nine juvenile loggerhead sea turtles tracked during 1997 and 1998 in the central North Pacific by satellite telemetry all travelled westward, against prevailing currents, along two convergent fronts identified by satellite remotely sensed data on sea surface temperature (SST), chlorophyll and geostrophic currents. These fronts are characterized by gradients in sea surface height that produce an eastward geostrophic current, with gradients in surface chlorophyll and SST. Six of the turtles were associated with a front characterized by 17°C SST, surface chlorophyll of about 0.2 mg m–3, and eastward geostrophic current of about 4 cm s–1, while the other three turtles were associated with a front with 20°C SST, surface chlorophyll of about 0.1 mg m–3, and eastward geostrophic flow of about 7 cm s–1. These results appear to explain why incidental catch rates of loggerheads in the Hawaii longline fishery are highest when gear is set at 17°C and 20°C, SST. Further, from the seasonal distribution of longline effort relative to these fronts, it appears that the surface longline fishing ground lies largely between these two fronts during the first quarter and well to the south of the 17°C front, but including the 20°C front, in the second quarter. These findings suggest seasonal or area closures of the longline fishery that could be tested to reduce incidental catches of loggerheads. Finally, these results illustrate the insights which can be achieved by combining data on movement of pelagic animals with concurrent remotely sensed environmental data.  相似文献   

6.
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   

7.
Abstract The fishery resources and fishing income in three different mangrove areas were evaluated. The mangrove-rich area provided high catches of shellfish and finfish and yielded high fishery income, compared with the mangrove-poor areas. Luxuriant mangrove areas supported a catch of 11 kg shellfish ha−1 day−1 and 4.5 kg finfish ha−1 day−1, corresponding with an economic gain of US$ 14 (Rs 603.7) day−1 for shellfish and US$ 3 (Rs 130.5) day−1 for finfish. The value of maintaining mangroves to ensure better fishery resources and to support coastal economies was identified. Management practices for conserving and enhancing mangroves and associated fishery resources are suggested.  相似文献   

8.
Abstract  Catch per unit effort (CPUE) and species composition in the pair-trawl fishery in commercial Area A of southern Lake Malawi were assessed from 1991 to 2001. CPUE declined from 1.7 t day−1 in 1995 to 0.5 t day−1 in 2001 and the fishery is considered depleted. In 2000/2002, catch composition differed significantly from a 1991 survey, and was dominated by haplochromine cichlids (92% by weight). Of 98 haplochromine cichlid taxa identified in the catch, 18 contributed ≥1% by weight. The artisanal fishery targeted similar species of a similar size. It was recommended that: (1) renewed investment and increased effort in the pair-trawl fishery is not advisable; (2) there was a need for effort limitation in Area A and (3) the pair-trawl fishery should not be managed in isolation of the artisanal fishery.  相似文献   

9.
Abstract— Feed intake, specific growth rate and changes in body composition were studied in age 1+ (140-190 g) brown trout ( Salmo trutta L.) reared at three temperatures (2, 4 and 6°C) under continuous light conditions. Feed in take increased from 35.7 kJ-kg−1.day−1 at 2°C to 95.7 kJ-kg−1-day−1 at 6°C, and the growth rate increased from 0.19%-day−1 to 0.42%-day−1 over the same temperature range. The estimated lower temperature limits for feeding and growth were slightly above 0°C. For all groups of fish, the majority (about 75%) of the weight gain comprised water and protein, but lipid deposition tended to increase with increasing temperature. The deposition of lipid accounted for about 50% of the body energy gain at all temperatures.  相似文献   

10.
The present paper describes the fishery of the Ea Kao reservoir in south Vietnam. Historical data on the total production and total numbers of fish stocked were available from 1983 to 1996, and this information, together with the results of monthly monitoring of the fishery from June 1996 to December 1998, was used in the present study. A number of gears are used in the Ea Kao fishery, the most important being gill, lift and integrated nets, and beach seines. The fishery of Ea Kao is based on the annual stocking of advanced fry/early fingerlings of 0.3–1.0-g bighead carp, Hypophthalmichthys nobilis (Richardson), silver carp, Hypophthalmichthys molitrix (Cuvier & Valenciennes) and rohu, Labeo rohita Hamilton, as well as the self-recruiting indigenous species Toxabramis houdemeri Pellegrin and two exotic species, i.e. Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L. On average, the regularly stocked species contribute to 78% of total production, which has been around 400–450 kg ha−1 in the last few years. The monthly peak catches of stocked species tend to coincide with the rainy season from May to October and the catches of self-recruiting species peak between February and April. A significant relationship ( P < 0.001) exists between the stocking density in year n (SD, n ha−1) and the yield of stocked fish in year n + 1 ( Y , kg ha−1):  相似文献   

11.
Abstract. The reservoir fishery of China is essentially a post-1950 development. China has an estimated reservoir acreage of 2 × 106ha of which about 1.44 × 1O6ha is used for fisheries. The present reservoir fish production averages 214kg/ha/year and accounts for about 8-9% of the total inland fish production, which is around 4.0 × 1O6mt. The total reservoir fish production and production per unit area in China have been steadily increasing since 1980.
The Cwhinese reservoir fishery is essentially a stock and capture fishery. The reservoir management practices and aspects of the present fishery are discussed. Those practices which are not found in the rest of Asia are highlighted.  相似文献   

12.
Abstract – The smolt run of anadromous brown trout ( Sulmo trutta ) in a Norwegian river was studied for three consecutive years. The main run occurred in a period of 7–10 days in the middle or second half of May. Support was found for the hypothesis that high water discharge and temperature triggered the run. Few smolts descended when the discharge was low (<50 m3· s−1) and the water temperature was below 4°C. The maximum number were caught when the discharge was moderate (70–150 m3· s−1) and the water temperature high (68°C). The relative importance of these factors varied from year to year. The first-year discharge explained 38% of the variation in the number of smolts migrating. Discharge and temperature together explained 61% in 1992 and 28% in the second and third year, respectively.  相似文献   

13.
Catch statistics for the king mackerel ( Scomberomorus cavalla ) recreational fishery off west-central Florida were derived from angler interviews conducted during 19 seasonal tournaments held in April–May and October–November of 2004 and 2005. Fishing location, number of fish per line per hour (catch per unit effort), and presence of baitfish from the tournament data were examined in the context of bathymetric gradients and other benthic features (e.g., wrecks or artificial reefs), and the location and persistence of oceanic fronts mapped using satellite imagery of sea surface temperature (AVHRR) and ocean color (MODIS and SeaWiFS). Generalized linear models were applied to identify the relationship between king mackerel catch rates and environmental data. The distance of fishing activity to the nearest front varied substantially, particularly when winds and front position were variable. However, baitfish presence with proximity to water clarity fronts (as defined by water-leaving radiance at 443 nm) significantly influenced successful king mackerel catch. Positive catch rates were significantly influenced by chlorophyll values and period (season and year). Additionally, intermediate water clarity (in the range 0.7–1.0 mW cm−2μm−1 sr−1) led to higher catch rates. Decreased water quality, primarily associated with a large Karenia brevis red tide, led to a lower number of catch and lower catch rates (122 king mackerel, 0.13 catch per unit effort) in fall 2005, compared to spring 2004 (179, 0.14), fall 2004 (360, 0.17) and spring 2005 (296, 0.21), despite a consistent seasonal effort.  相似文献   

14.
Abstract  The bycatch in a tropical Australian banana prawn, Penaeus merguiensis (de Man), fishery is described and contrasted with the closely related tiger prawn, Penaeus semisulcatus De Haan and Penaeus esculentus Haswell, fishery. Most of the similarity between banana prawn fishery catches was accounted for by three teleost species constituting 51.4% of the total bycatch weight. The bycatch assemblage structure of this fishery was significantly different ( P  <   0.05) from the adjoining tiger prawn fishery. The banana prawn fishery had a higher mean bycatch catch rate from shorter duration trawls, but lower estimated total annual bycatch (1502 t yr−1) than the longer duration trawls of the tiger prawn fishery (20 073 t yr−1). This study provides new data for quantifying bycatch and improving the accuracy of quantitative risk assessments currently being used to demonstrate sustainability of bycatch populations. The information will be incorporated into collaborative development of a long-term monitoring programme.  相似文献   

15.
中东大西洋中部海域中上层鱼类资源结构与渔场分布   总被引：1，自引：0，他引：1  
为了解中东大西洋中部海域中上层鱼类资源结构与渔场分布,对2007-2014年入渔FAO34渔区3.11和1.32小区(毛里塔尼亚专属经济区)从事中上层鱼类捕捞的7艘国内渔船的生产数据进行了分析。结果表明,我国入渔船只数量、入渔渔船总产量和作业渔船平均日产量均呈现先增加、后减少的趋势,且在2011年入渔渔船总产量和作业渔船平均日产量到达最大值,2012年入渔船只数量到达最大值。渔获种类主要包括沙丁鱼(Sardina pilchardus)、短体小沙丁鱼(Sardinella maderensis)、金色小沙丁鱼(Sardinella aurita)、日本鲭(Scomber japonicus)和竹筴鱼(Trachurus trachurus),各渔获种类的渔获量年际间波动较为明显。月均产量在17.2~23.6 t/haul,最高值和最低值分别出现在12月和8月;月均总产量在1 279.0~2 414.2 t,最高值和最低值分别出现在1月和8月,12月至次年3月为渔汛旺期。渔场季节变化现象明显,夏秋季向北移动,冬春季向南移动,20.0°~20.8°N、17.4°~18.0°W区域为高产量海域。该海域中上层鱼类洄游现象明显,这可能主要与该海域的不同洋流在不同月份的强弱变化有关,该海域整体渔业资源呈现一定衰退现象。建议渔船入渔该海域从事中上层鱼类捕捞持谨慎态度,加强该海域渔业资源的研究与保护。  相似文献   

16.
Spatial and temporal patterns in catch rates and in allocation of fishing effort were analysed for the coastal fishery in Spermonde Archipelago, Indonesia, to assess whether fishermen can optimise their strategy from catch information, or whether they fish under great uncertainty and merely minimise risks. On average 517 fishing units operated in the 2800 km2 area, catching 21 t fish day−1. Major gear categories were hook and line (59% of total effort and 5% of total catch), and lift nets (16% of total effort and 70% of total catch). The size of individual resource spaces varied with gear type and was smaller in unfavourable weather conditions. Although spatial patterns in catch rates at the scale of the whole archipelago were evident, fishermen could not differentiate between locations, as catch variance within their individual resource spaces was high relative to the contrasts in spatial patterns. The aggregated distribution of fishing effort in Spermonde must be explained by factors such as the small scale of operations, rather than fish abundance.  相似文献   

17.
Abstract. Kurasan and BHT were tested at doses of 100, 200 and 400mg kg-1 incorporated in dry pellets. The administration of these antioxidants did not influence the red blood count of rainbow trout, Salmo gairdneri Richardson, at body weights of 100 to 400g, reared in flow-through tanks at water temperatures of 7 to 13°C and in cage culture at water temperatures of 15 to 2O°C. In laboratory experiments at a water temperature of 14°C, the highest Kurasan dose increased the red blood cell (RBC) count insignificantly by 14% (1.06 vs 0.93 10121-1) after 80 days, haematocrit (PCV) was increased by 27% (0.410 vs 0.32511-1), and haemoglobin (Hb) by 16% (72 vs 62gl-1), This was seen in the cage culture experiment, but not in the experiments in the flow-through tanks. A trend of diminishing haematological parameters of the red blood count and total blood serum protein (TP) of the fish fed with BHT-stabilized diet was recorded only under laboratory conditions at the water temperature 9°C, The decline of RBC count in the experimental group with 0.04% BHT represented 14% (0.90 vs 1.05 10121-1), the decline in PCV amounted to 18% (0.328 vs 0.39811-1), Hb to 17% (57 vs 69g 1-1), and TP to 11% (39 vs 44g 1-1).  相似文献   

18.
The reef fisheries surrounding the south-west coastal cities of Madagascar   总被引：1，自引：0，他引：1  
The artisanal fishery in south-west Madagascar, around the coastal cities of Morondava, Morombe and Tuléar, is particularly active. In the Morombe and Tuléar regions, fishing pressure focuses on coral formations close to landing sites and reef fish constitute the main part of the catch (Lethrinidae, Haemulidae, Siganidae). In Morondava, fishing is practised very close to the shore on sandy substrates, but also on offshore reef shallows. The catches are more diverse and made up of reef fish (Serranidae, Lutjanidae) and non-reef species. Fishing from Morondava targets the highest trophic level of the coral reefs (piscivores/macroinvertebrate feeders: 87% of the catch) whereas in Tuléar and Morombe the higher fishing effort means that lower trophic levels are targeted to maintain catches. Despite the high fishing effort, especially around Morombe and Tuléar (standardizing fishing effort of 5200 hook h km–2 year–1 and of 12 300 hook h km–2 year–1, respectively), the catch per unit effort (CPUE) is still relatively high; it varies from 0.6 to 2 kg h-1 per person over the whole zone and seems to be more linked to the fishing method used and to the degree of professionalism than to variations in the abundance of the resources surrounding the three cities. The relatively high CPUE can probably be explained by a continual immigration and/or recruitment on these fishing grounds. The fish originate from sectors that are far from towns and weakly exploited. A sociological study was carried out concurrently with the fishing survey and focused on present-day transformations within the fishing community.  相似文献   

19.
The present study was carried out to investigate the influence of water temperature on the growth performance and digestive enzyme (pepsin, trypsin and lipase) activities of Chinese longsnout catfish. Triplicate groups of Chinese longsnout catfish (35.6±0.48 g, mean±SE) were reared at different water temperatures (20, 24, 28 and 32 °C). The feeding rate (FR), specific growth rate (SGR) and feed efficiency ratio (FER) were significantly affected by water temperatures and regression relationships between water temperature and FI, SGR as well as FER were expressed as FR=−0.016 T 2+0.91 T −10.88 ( n =12, R 2=0.8752), SGR=−0.026 T 2+1.39 T −17.29 ( n =12, R 2=0.7599) and FER=−0.013 T 2+0.70 T −8.43 ( n =12, R 2=0.7272). Based on these, the optimum temperatures for FR, SGR and FER were 27.66, 26.69 and 26.44 °C respectively. The specific activities of digestive enzymes at 24 or 28 °C were significantly higher than that at 20 or 32 °C. In addition, there was a significant linear regression between FR or SGR and specific activities of pepsin and lipase, which indicated that pepsin and lipase played important roles in regulating growth through nutrient digestion in Chinese longsnout catfish.  相似文献   

20.
The efficacy of clove oil as an anaesthetic and at producing a physiological response (plasma cortisol and glucose) was evaluated in the kelp grouper, Epinephelus bruneus . To acquire complete anaesthesia in less than 3 min and recovery in <10 min, three doses of clove oil were tested at 18, 22 and 26 °C. Although higher anaesthetic doses resulted in shorter induction times and longer recovery times, and a lower temperature resulted in longer anaesthesia induction and slower recovery, we found the optimal dose and administering temperature of clove oil to be 250–300 mg L−1 at water temperature of 18 °C, 150–200 mg L−1 at water temperature of 22 °C and 50–100 mg L−1 at water temperature of 26 °C respectively. Following the administration of 150 mg L−1 of clove oil at 22 °C, the plasma cortisol level was highest (4.24 ± 1.571 μg dL−1) after 12 h and the plasma glucose was highest (92.7 ± 9.61 mg dL−1) after 2 h. These results should be useful to the aquaculture industry, where anaesthesia is necessary for a range of activities.  相似文献   

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