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1.
We studied whether incorporation of terms for environmental factors (temperature, herring and 0-group cod) into the stock recruitment functions for the Barents Sea capelin ( Mallotus villosus ) would increase the ability to predict recruitment. We also investigated the effects of alternative estimates of the capelin spawning stock (SSB) and juvenile herring on model predictability. By using nonlinear regression, the modified Beverton–Holt and Ricker stock recruitment models were fitted to time series of capelin spawning stock, capelin recruitment, juvenile herring, 0-group cod and temperature from 1973 to 2000. The modified Beverton–Holt model with a term for juvenile herring fit capelin recruitment data well. Inclusion of terms for temperature and 0-group cod abundance did not significantly improve the model fit. The best model predicts an almost proportional relationship between the spawning stock and the capelin recruitment when the abundance of juvenile herring is high.  相似文献   

2.
In 1984, kittiwakes at Hopen laid eggs ca. 14 days later than previously found in North Norway and on the Kola Peninsula. The mean clutch size, egg volume, and hatching success were otherwise very similar to those documented on the mainland. Although feeding trips were very long, a rapid chick growth and high rate of chick survival suggested that food availability was not a limiting factor in 1984. In contrast to other sites at Svalbard where polar cod Boreogadus saida and crustaceans dominate kittiwake diets, the diets of chicks at Hopen consisted mainly of capelin Mallotus villosus which the adults probably collected at or beyond the polar front southeast of the island.  相似文献   

3.
本文作者于1987～1988年由国家南极考察委员会派遣随JARE29赴日本南极昭和站、瑞穗站和阿斯加等站进行考察,根据日本同行提供的1984～1988年昭和站大气中二氧化碳浓度连续变化资料以及相应年份该站年平均气温资料进行研究,结果表明:从1984年到1988年该站大气中二氧化碳浓度变化趋势与该站年平均气温变化趋势是相当一致的,二者呈明显正相关。此外,还给出该地区从1984年到1988年大气中二氧化碳浓度变化的年增长率,其值分别为1.21ppmV/年(1984～1985年)、1.35ppmV/年(1985～1986年)、1.68ppmV/年(1986～1987年)和1.99ppmV/年(1987～1988年)。  相似文献   

4.
本文分析了中国石油生产近20年变化的原因,对一些学者认为80年代中国会成为超级产油大国,后又悲观断定80年代中国可能变成石油净进口国作了评述。同时对90年代中国石油生产前景作了初步展望。  相似文献   

5.
Results of analyses of stomach and intestinal contents from hooded ( Cystophora cristata ) and harp ( Phoca groenlandica ) seals captured in the pack ice belt of the Greenland Sea in summer (July-August) in 2000 and winter (February-March) in 2001 revealed that the diet of both species were comprised of relatively few prey taxa. Pelagic amphipods of the genus Parathemisto , the squid Gonatus fabricii , polar cod ( Boreogadus saida ) and capelin ( Mallotus villosus ) constituted 63-99% of the observed diet biomass in both seal species, irrespective of sampling period, but their relative contribution to the diet varied both with species and sampling period/area. For hooded seals, G. fabricii and capelin were the dominant food items in winter 2001, but the summer 2000 diet comprised a mixture of this squid and polar cod. Parathemisto was most important for the harp seals during summer 2000; in winter 2001 the contribution from krill and capelin were comparable to that of Parathemisto . Multivariate analyses revealed differences in the intestinal contents of hooded and harp seals in areas where the two species' occurrence spatially overlapped. Different foraging depths of the two species may have contributed to the observed differences in diets.  相似文献   

6.
In June 1986- 42 young Arctic cod were caught in ice-covered waters of the Barents sea with dip-nets by scuba divers. From August to June 1987 the fish were kept at -PC and fed on frozen shrimp ( Pandalus borealis ). Length and weight were measured monthly. A fast weight increment of about 0.7% per day was observed in the autumn (Sept.-Nov.). In the winter (Jan.-Feb), the growth rate declined to 0.05% per day. However, daily food intake only decreased by 50% during these winter months. Since the fish were exposed to constant illumination in the aquarium, this growth experiment indicates that something else than light has a significant influence on growth in Arctic cod.  相似文献   

7.
The distribution of capelin was mapped in the area east of Hopen. Zooplankton was sampled with Juday net and 1 m2 MOCNESS sampler, and analysed with respect to hydrography and capelin abundance. The capelin "front" coincided more or less with the physical Polar Front, and this complicated the interpretation of the results. Strong indications for a grazing impact by capelin on zooplankton were nevertheless obtained. The zooplankton biomass was significantly lower in the area with high abundance of capelin than in the area with no capelin. This effect was due to a lower biomass of relatively large zooplankton (> 1 mm size fraction) and seen most clearly in data obtained with the MOCNESS. The biomass of zooplankton in the upper 100 m was very low where capelin was present, suggesting rapid depletion of the major prey items. The biomass (m −2) of capelin in the capelin front area was about three times higher than the biomass of zooplankton in areas without capelin. The capelin front would therefore have the potential to graze down the available prey in 3-4 days. Light seems to be an important factor for the predation impact by capelin, resulting in strong interactions between capelin predation and zooplankton vertical distribution.  相似文献   

8.
Quinghai Hu is a large, high-altitude, saline lake in north-western China, and supports a fishery based on an endemic species of naked carp (snow trout). The fish take seven years to attain maturity and a marketable weight of 300 g, and have a lifespan of 14–21 years under the present fishery regime. They seasonally migrate from the lake to spawn over the gravel beds of inflowing rivers, but these areas have been reduced by weirs and irrigation diversions and recruitment may have declined. The population may have been affected also by a 1.85-m fall in the lake level over the past 30 years, and by associated changes in salinity. The fishery was opened to large-scale exploitation in 1958. Yields declined sharply (max. 28,523 tonnes, 1960) as the larger, older fish were removed, and then more slowly (min. 2523 tonnes, 1983). Since 1987 the fish factory has been limited to an annual quota of 1200 tonnes, taken by a fleet of four pair trawlers. Another 800 tonnes are taken by licensed fishermen, mainly using gill nets, and perhaps 1000 tonnes are taken illegally. The estimated total catch in 1992 was 3000 tonnes. New trawlers introduced in 1989–90 substantially increased the factory's catch per unit effort, and in 1990 the quota was virtually filled in one month in a zone within 20 km of the factory. Although this could suggest that the stocks will be conserved if the quota is retained, at least half of the catch in 1989–92 consisted of immature individuals. Trawling operations recently were suspended following a further decline in the catch after 1992. While the new trawlers are capable of a major increase in effort, neither the changing environment, the fish stocks or the present markets favour intensified pressure. Gillnets may provide better control over the minimum size limit and may cause less damage than trawling. Other options to improve the viability and profitability of the fishery include improvements in handling, processing and marketing. Failure to develop the fishery may encourage attempts to introduce exotic fish, at some risk to survival of the local species.  相似文献   

9.
Correlations between guillemots (including Common Guillemots Uria aalge and Brünnich's Guillemots U. lomvia) and their prey (divided into five prey categories, capelin Mallotus villosus , herring Clupea harengus , polar cod Boreogadus saida , plankton, and a mixture of other prey species) at two depths (10-100 m and 100-200m) were estimated along an extended transect of 3,060 nautical miles (5,667 km) in the Barents Sea in April/May 1986. Spatial concordance was highest during daylight hours when the largest number of birds were seen on water (presumably feeding birds). Capelin was the single prey category which was most often associated with birds but no single prey category could alone explain the distribution of birds. Although only a small fraction of guillemots could be identified to species, there was some evidence that capelin were of greater importance to Common than to Brünnich's Guillemots. Overall correlation between birds and total prey density was statistically significant at the smallest scale of 5 nautical miles (n.m.). The removal of herring from the calculations increased the strength of the correlation. The depth at which prey was located had little effect on the distribution of birds. The correlation between birds and prey was scale dependent, and reached a maximum at 90 n.m., although there seemed to be some upper threshold in the coefficient at c. 40 n.m. Numerical concordance (including only 5 n.m. periods where both prey and birds were present) was significant at the 5 n.m. scale but was higher for high density than for low density prey patches. The results are discussed in relation to the few similar studies in other oceans and in relation to the severe reduction of important prey species in the Barents Sea.  相似文献   

10.
广东省碳减排总量目标的地区分解及其盈亏格局   总被引：1，自引：0，他引：1  
林文声  胡新艳 《热带地理》2014,34(5):618-626
合理界定初始排放权并进行排放权交易是实现减排目标和减排资源最优配置的关键。对低碳试点省广东进行减排目标地区分解,既能明确减排责任,又能使碳交易变得更加明确而具有可操作性。设定广东碳减排目标的假设情景,以碳排放核算方法和最优经济增长模型为基础,引入兼顾人均平等和历史责任的“碳预算”思路,对广东省减排目标进行地区分解,计算各市排放权配额并测算未来时期排放权的盈亏格局,初步模拟广东省各市之间“碳交易”基础。结果表明：1）1985―2020年全省累积碳排放配额区间为524 659.185 5~542 518.565 2万t,人均碳排放配额区间为57.065 5~59.008 0 t/人。人均碳排放配额、人口数量和实际碳排放量是影响各市排放权配额的重要因素。2）预计到2020年7个城市将出现“碳预算”赤字,主要分布于珠三角;14个城市拥有“碳预算”盈余,集中分布在粤北山区和东西两翼。  相似文献   

11.
The grain embargo, introduced by the United States on the USSR after the invasion of Afghanistan, reduced Russian grain supplies by about six million tonnes in 1979/80. This resulted in some reduction in meat output, but the effects were not as great as had been anticipated as the Russians were able to find alternative sources of supply for much of the embargoed grain. The embargo resulted in the United States' grain prices falling, although this was partly prevented by the United States government purchasing grain destined for the Russian market. Costs to the United States government and taxpayer were kept down by the government reselling this grain for export during the summer of 1980. Despite some shuffling of markets between suppliers, the grain market has more or less returned to normal, helped by strong world demand for grain.  相似文献   

12.
The occurrence of macromolecular antifreeze agents (so-called Thermal Hysteresis Factors) in blood plasma of fishes from Spitsbergen waters was investigated in August 1983, October 1984, and January 1986.
Thermal hysteresis was found in the plasma of three species of Spitsbergen fishes: shorthorn sculpin (Myoxocephalus scorpius) , polar cod (Boreogadus saida) , and sea snail (Liparis liparis) . This is the first time thermal hysteresis is reported from the sea snail. Seasonal changes in the amount of thermal hysteresis were observed in blood plasma of the shorthorn sculpin and the sea snail.
With the exception of the polar cod, blood plasma of deep water fishes displays no thermal hysteresis. The reason for this is probably that the polar cod also occurs in shallow ice laden sea water, where an'antifreeze'would be needed to protect against inoculative freezing.
No thermal hysteresis was observed in blood plasma of the saithe (Pollachius virens) , despite the fact that the saithe was observed swimming in ice laden sea water at a temperature of -1 to – 1.5°C under natural conditions, and was rapidly killed when it came into contact with ice in the laboratory. It is not known how the saithe survives in ice laden water under natural conditions.  相似文献   

13.
In 2013, demand for coal in the UK was 60 million tonnes. Of this, 12.7 million tonnes (21%) came from indigenous sources; the majority of which was from surface mining (8.6 million tonnes). Many planning applications for surface mining of coal and the coal extraction that follows, are often a source of conflict with the communities who live within shallow coalfield areas. Policies which enforce a gap, or ‘separation zone’, between communities and surface coal mining operations exist in Wales and Scotland, but do not exist in England. This paper examines the effect of applying separation zones on the availability of shallow coal resources within two study areas; one within the South Wales Coalfield, the other within the Midlands Coalfield (comprising the Yorkshire, Nottinghamshire and North Derbyshire Coalfield areas). Density profiles and a shape-index algorithm are used to compare and contrast settlement morphology (i.e. shape or footprint) and distribution to determine whether they have a bearing on the areal extent of any potential separation zone applied. The implications on the availability of shallow coal resources of applying different separation zone distances around settlements within these two areas are explored. Results reveal that although the settlement morphology is important in determining the area of the separation zone, and has greatest influence in the South Wales Coalfield, the area of coal resource sterilised by the application of separation zones is greatest in the Midlands Coalfield due to it having a higher proportion of urban development situated on the surface extent of the shallow coal resource.  相似文献   

14.
The continuously decreasing average coal rank (heating value), inadequate investment, and ever stricter air-emission controls have caused the average efficiency of electricity generation from coal in the U.S. to plummet to a mere 32% by the year 2008. The U.S. gas-fired powerplants are 30% more efficient than the coal-fired ones, with average efficiency of 43% in 2008. Replacing each 1,000 MW e generated by an average coal-fired powerplant with an average gas-fired powerplant would avoid today 7 million tonnes of CO2 emissions, 1.2 million tonnes of toxic ash, and significant issues with water contamination. The parallel upgrades to the more efficient supercritical steam turbines would decrease current emissions by up to 50% (from the current average plant efficiency of 32% to over 45%). The CO2 captured in the new combined-cycle powerplants might be used to enhance oil recovery in local fields, where feasible. The CO2 enhanced oil recovery (EOR) can never become the main sink for the gigantic CO2 volume generated each year by electric powerplants. Currently, EOR could absorb only 1% of that volume.  相似文献   

15.
Herein, we undertake a geomorphological analysis in which spatial and temporal trends of bed and bank erosion along an 18-km length of Hotophia Creek, Mississippi, are estimated for the period between 1961 and 2050. The evaluation was undertaken for two scenarios of channel response to channelization during 1961–1963. One scenario represents the ‘actual’ response of the channel and includes the effects of installing a series of grade-control structures (GCS) between 1980 and 1996, while the other represents a hypothetical scenario in which the channel is left to adjust naturally. This allows the effectiveness of GCS in reducing in-channel erosion to be assessed. The analysis relies on the availability of channel survey data to develop empirical bed and bank response models for each adjustment scenario, supplemented by bank stability modelling to predict future rates of bank erosion. Results indicate that channel erosion rates decline nonlinearly with respect to time since 1961, for both adjustment scenarios. However, by the year 2050, the “with” GCS adjustment scenario results in the cumulative removal of some 663,000 (9%) extra tonnes of sediment relative to the “without” GCS scenario. Most (63%) of this excess is derived from enhanced bed erosion during 1976–1985 and 1985–1992, with the remainder derived from increased bank erosion during 1985–1992. Detailed analysis of the patterns of erosion and deposition, and their association with the GCS, provides evidence to support the view that GCS installed along Hotophia Creek have, for the most part, been ineffective in reducing channel erosion rates. This is because the GCS were installed too late to prevent bed degradation, caused by the 1961–1963 channelization, migrating upstream. In addition, some structures have disrupted the downstream transmission of bed material from eroded reaches upstream, exacerbating bed degradation and bank erosion in incised reaches downstream.  相似文献   

16.
人口迁移是一个时空路径依赖过程,同时受迁移存量和周边迁移状况影响。当前人口迁移预测大多建立在时间序列模型之上,重点考虑迁移流在时间维度上的联系,忽视了其中的时空关联。该文将特征向量时空滤波方法与普通泊松模型相结合,考虑迁移流中可能存在的时空滞后和同期两种结构,对1985-2015年不同时段的中国省际人口迁移流数据进行建模和估计,并利用拟合程度较优的模型预测2015-2025年省际人口迁移的发展趋势。结果表明:1)特征向量时空滞后和同期滤波泊松模型均能较好地模拟研究时段省际人口迁移过程,自1985年以来我国省际人口迁移流不仅受迁出地和迁入地经济、社会等因素影响,也与过去迁移存量及周边迁移流密切相关;2)区域人口规模和GDP对迁移流的“推—拉”作用符合预期,地区人口规模较高和经济发展水平较低会促进人口外迁,反之则有利于吸引外来人口;3)与特征向量时空滞后滤波泊松模型相比,时空同期模型更便于捕捉省际人口迁移过程中的时空路径依赖特性,意味着当前人口迁移流的发展更易受到同时期周边迁移流的影响,表现出明显的羊群效应;4)预计2015-2025年我国省际迁移总量持续增加,呈现更集聚的空间模式,高迁入与高迁出区域在空间上相连,形成一条南北贯通的“高密度迁移地带”。将特征向量时空滤波模型拓展到人口迁移这一空间相互作用领域,可为当前构建更加完善的要素市场化配置体制机制等提供科学参考。  相似文献   

17.
The historic data on the fisheries on Norwegian spring spawning herring and Barents Sea capelin show that the migration pattern and time of spawning have changed for these species. Furthermore, modern techniques like tagging, hydroacoustic abundance estimation and virtual population analysis have shown that the abundance, both of the adult and the immature parts of the population, fluctuates widely. Predators (other fish, seabirds, sea mammals) of pelagic fish must have experienced corresponding fluctuations in food availablilty.  相似文献   

18.
北京地区风沙活动的监测   总被引：8，自引：4，他引：4  
贺大良 《中国沙漠》1992,12(2):27-33
1990-1991年北京风沙整治研究试验站又对北京市东南部沙质土壤地区做了风沙活动的监测,以判断近五年来沙荒地改造利用的效果。监测结果表明:1、北京地区风沙日数继续下降,由1981-1985年的平均每年19.8次下降为1986-1990年的12.4次。扬沙天气日数有所增加,由1951-1985年平均占71.6%,增加为1986-1990年的77.4%。今后防治的重点仍应以防治本地沙源为主,风沙日数下降与当地植被覆盖增加相关。2、风沙天气日数/大风天气日数的比值由前35年的1.40下降为近5年的0.82,说明近五年的防治风沙是有成绩的,风沙日数的减少不单纯是因为大风日数减少所致。3、对典型地段起沙量的观测表明:同样风速下的起沙量大幅度降低,原因是植被保护增加和耕作面形成土壤结壳。4、对沙壤质农田的降尘进行了连续观测,1990年4月-1991年3月年降尘总量267.9 吨/平方公里.年,月平均降尘22.31 吨/平方公里.月,此值略大于北京全市平均值。对今后风沙的防治也提出了原则意见。  相似文献   

19.
This paper evaluates recent changes in narwhal ( Monodon monoceros ) catches in Siorapaluk, the northernmost community in Greenland, in consideration of the effects of changing climate and uncertainty of stock delineation. The catch statistics show a significant increase in narwhal catches by hunters in Siorapaluk after 2002, which does not appear to be a result of increased effort. Hunters attribute the increase to changed sea-ice conditions providing access by boat to Smith Sound as early as June and July. This indicates that climate change is likely to have a considerable impact on narwhal hunting in northern Greenland. Traditional ecological knowledge and scientific surveys suggest that narwhal in Smith Sound constitute an independent stock. The absence of scientific recommendations for this stock has been seen as an opportunity to increase quotas in West Greenland. Scientific management recommendations are urgently needed to allow the authorities to assign sustainable quotas for this stock. The development of collaborative management agreements and locally based monitoring are recommended to ensure local acceptance of regulations, and to allow rapid responses to climate change.  相似文献   

20.
Food samples from six high-arctic seabird species were collected during spring and summer seasons between 1982 and 1990 in the Svalbard region. The material came from coastal localities on the island of Spitsbergen and the marginal ice zone in eastern Svalbard waters. Polar cod Boreogadus saida was the most frequently occurring prey in the ice-covered areas. Analysis of otoliths showed that most polar cod were one-or two-year olds. These year classes are known to associate with sea ice. Other ice-associated (sympagic) organisms, such as gammarid amphipods, were not found to be of high importance as prey for seabirds in the study area. However, the sea ice occurring in the area was mainly one year old. Such ice contains a less developed sympagic fauna than multi-year ice. The pelagic amphipod Parathemisto libellula , which is not sympagic but occurs in the water column, was also found to be an important prey in the marginal ice zone, especially for the Briinnich's guillemot Uria lomuia . The smallest of the seabird species studied, the little auk Alle alle , differed from the other five species in its diet, preying mainly upon smaller items such as copepods and young stages of amphipods, euphausiids and decapods. The diet of the various seabird species was in general more diverse in the coastal areas than in the marginal ice zone.  相似文献   

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