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Fisheries: Hope or despair? 总被引：1，自引：0，他引：1
Recent work suggesting that fisheries depletions have turned the corner is misplaced because analysis was based largely on fisheries from better-managed developed-world fisheries. Some indicators of status show improvements in the minority of fisheries subjected to formal assessment. Other indicators, such as trophic level and catch time series, have been controversial. Nevertheless, several deeper analyses of the status of the majority of world fisheries confirm the previous dismal picture: serious depletions are the norm world-wide, management quality is poor, catch per effort is still declining. The performance of stock assessment itself may stand challenged by random environmental shifts and by the need to accommodate ecosystem-level effects. The global picture for further fisheries species extinctions, the degradation of ecosystem food webs and seafood security is indeed alarming. Moreover, marine ecosystems and their embedded fisheries are challenged in parallel by climate change, acidification, metabolic disruptors and other pollutants. Attempts to remedy the situation need to be urgent, focused, innovative and global. 相似文献
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Since its introduction by Svensson in 1959, the power law curve y = axb (where x and y are horizontal and vertical direction, respectively) has been widely used in morphological analysis of glacial trough cross-profiles. The numerical constants a and b are obtained by a linear regression analysis of the logarithmic form of the power law curve (ln y = ln a + b ln x). The value b then gives a measure for the form of the cross-section. However, over the years this form of the power law has endured a lot of criticism. This criticism is well founded, since this particular form of the power law is not suitable for curve fitting in morphological analyses. In this paper a general power law is proposed, of the form y − y0 = a|x − x0|b (where x0, y0 are the coordinates of the origin of the cross-profile). A unique and unbiased solution for this equation is obtained with a general least-squares method, thereby minimizing the error between the cross-profile data and the curve, and not between the logarithmic transform of the data and its regression line. This provides a robust way to characterize trough cross-section forms. © 1998 John Wiley & Sons, Ltd. 相似文献
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The Seto Inland Sea--eutrophic or oligotrophic? 总被引：8，自引：0，他引：8
Yamamoto T 《Marine pollution bulletin》2003,47(1-6):37-42
The present water quality conditions in the Seto Inland Sea of Japan are described along with an historical background before and after the measures taken to reduce eutrophication. The directive to reduce phosphorus discharge into this area was very effective, reducing the number of red tides from about 300 cases per year at their peak in 1976 to the recent level of about 100 cases per year, indicating the improvement of seawater quality. However, the hastiness of the measures taken to reduce phosphorous seems to have led to a depletion of dissolved inorganic phosphorus that is an essential nutrient for the growth of phytoplankton. Fishery production has also decreased with the reduction of phosphorus, showing a time lag, and the relationship between them shows a hysteresis-like pattern indicating that the condition of fishery production is currently in a critical stage of collapse. This implies that the phosphorus reduction could have lowered the phytoplankton primary production and also caused a detrimental effect on the fishery production. Noteworthy is the change in the phytoplankton species composition. The dominant species that form red tides have changed from non-harmful diatoms to harmful raphidophytes in the eutrophication process and then finally to harmful/toxic dinoflagellates in the oligotrophication process. This indicates that the measures to reduce phosphorus have caused a change in phytoplankton species composition, thereby altering the food web structure, suggesting that this might be the major cause of the reduction of fishery production. In conclusion, the Seto Inland Sea of Japan is apparently in an oligotrophic condition, and it could be said to be in the state of "cultural oligotrophication" caused by the hasty reduction of phosphorus loading. Dam construction, as another possible cause of the cultural oligotrophication, is also discussed, and evidence relating to the existence of numerous dams in this area is also shown. Stress is placed on the regulation of the level of nutrients and their elemental ratio in the seawater, because these factors are considered to be effective in preventing the generation of harmful algae and in sustaining the fishery production through preservation of the natural environment. A proposal is also described regarding how these factors could be controlled. 相似文献
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Sh. A. Mukhamediev 《Izvestiya Physics of the Solid Earth》2010,46(11):955-965
In the present paper, we consider ideas suggesting various kinds of industrial impact on the close-to-failure block of the
Earth’s crust in order to break a pending strong earthquake (PSE) into a number of smaller quakes or aseismic slips. Among
the published proposals on the prevention of a forthcoming strong earthquake, methods based on water injection and vibro influence
merit greater attention as they are based on field observations and the results of laboratory tests. In spite of this, the
cited proofs are, for various reasons, insufficient to acknowledge the proposed techniques as highly substantiated; in addition,
the physical essence of these methods has still not been fully understood. First, the key concept of the methods, namely,
the release of the accumulated stresses (or excessive elastic energy) in the source region of a forthcoming strong earthquake,
is open to objection. If we treat an earthquake as a phenomenon of a loss in stability, then, the heterogeneities of the physicomechanical
properties and stresses along the existing fault or its future trajectory, rather than the absolute values of stresses, play
the most important role. In the present paper, this statement is illustrated by the classical examples of stable and unstable
fractures and by the examples of the calculated stress fields, which were realized in the source regions of the tsunamigenic
earthquakes of December 26, 2004 near the Sumatra Island and of September 29, 2009 near the Samoa Island. Here, just before
the earthquakes, there were no excessive stresses in the source regions. Quite the opposite, the maximum shear stresses τmax were close to their minimum value, compared to τmax in the adjacent territory. In the present paper, we provide quantitative examples that falsify the theory of the prevention
of PSE in its current form. It is shown that the measures for the prevention of PSE, even when successful for an already existing
fault, can trigger or accelerate a catastrophic earthquake because of dynamic fault propagation in the intact region. Some
additional aspects of prevention of PSE are discussed. We conclude that in the near future, it is too early to consider the
problem of prevention of a forthcoming strong earthquake as a practical task; otherwise, the results can prove to be very
different from the desired ones. Nevertheless, it makes sense to continue studying this problem. The theoretical research
and experimental investigation of the structure and properties of the regions where the prevention of a forthcoming strong
earthquake is planned in the future are of primary importance. 相似文献
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Yu LIU 《中国科学:地球科学(英文版)》2022,65(2):387-390
As an inter-disciplinary area between geography and computer sciences, geographical information science(GIScience) inherits the spatial analysis tradition of the former. Together with other branches of information geography, it seeks the balance between universality and particularity of geographical laws by combining methods from neighboring disciplines(such as big data and artificial intelligence) with the special nature of geographical spaces. Meanwhile, at the core position of the geography discipline, GIScience makes geography stronger from two directions: "strengthening the theoretical foundation" and "improving technology and promoting the practical applications". 相似文献
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Wind in Ireland: long memory or seasonal effect? 总被引：1，自引：1，他引：0
Jean-Christophe Bouette Jean-François Chassagneux David Sibai Rémi Terron Arthur Charpentier 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(3):141-151
Since Haslett and Raftery’s paper Space-Time Modelling with Long-Memory Dependence: Assessing Ireland’s Wind Power Resource (1989), modelling meteorological time series with long memory processes, in particular the ARFIMA model has become very common. Haslett and Raftery fitted an ARFIMA model on Irish daily wind speeds. In this paper, we try to reproduce Haslett and Raftery’s results (focusing on the dynamic
of the wind process, and not on cross-correlation and space dependencies), and show that an ARFIMA model does not properly capture the behaviour of the series (in Modelling daily windspeed in Ireland section). Indeed, the
series show a periodic behaviour, that is not taken into account by the ARFIMA model. Removing this periodic behaviour yields no results either, we therefore try to fit a GARMA model that takes into account both seasonality and long memory (in Seasonality and long memory using GARMA models section). If a GARMA process can be fitted to the data to model Irish daily data, we will show that these models could also be used to model Dutch hourly data.
相似文献
| Arthur CharpentierEmail: |
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Ragone SE 《Ground water》2002,40(5):457-457
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Paul Sava 《Geophysical Prospecting》2016,64(3):581-594
Reverse time migration backscattered events are produced by the cross‐correlation between waves reflected from sharp interfaces (e.g., salt bodies). These events, along with head waves and diving waves, produce the so‐called reverse time migration artefacts, which are visible as low wavenumber energy on migrated images. Commonly, these events are seen as a drawback for the reverse time migration method because they obstruct the image of the geologic structure, which is the real objective for the process. In this paper, we perform numeric and theoretical analysis to understand the reverse time migration backscattering energy in conventional and extended images. We show that the reverse time migration backscattering contains a measure of the synchronization and focusing information between the source and receiver wavefields. We show that this synchronization and focusing information is sensitive to velocity errors; this implies that a correct velocity model produces reverse time migration backscattering with maximum energy. Therefore, before filtering the reverse time migration backscattered energy, we should try to obtain a model that maximizes it. 相似文献
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The cloud amount summer nighttime data obtained from the 1994 to 2007 NASA satellite infrared and visible range measurements taken within the framework of the International Satellite Cloud Climatology Project (ISCCP) were analyzed, and the contribution by lunar signal to the cloud amount was extracted. Although the fact of lunar influence on cloudiness is known, this investigation has made it possible to separate the lunar-phase and lunar-declination effects on cloudiness. The relative cloud amount tends to grow with a change in lunar phase from a quadrature to the New Moon or Full Moon and with an increase in lunar declination by absolute value. Both the effects are statistically significant, the lunar-declination effect is a little stronger. The obtained results do not seem to contradict the theory of lunar tides. 相似文献
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The primary objectives of coral transplantation are to improve reef ‘quality' in terms of live coral cover, biodiversity and topographic complexity. Stated reasons for transplanting corals have been to: (1) accelerate reef recovery after ship groundings, (2) replace corals killed by sewage, thermal effluents or other pollutants, (3) save coral communities or locally rare species threatened by pollution, land reclamation or pier construction, (4) accelerate recovery of reefs after damage by Crown-of-thorns starfish or red tides, (5) aid recovery of reefs following dynamite fishing or coral quarrying, (6) mitigate damage caused by tourists engaged in water-based recreational activities, and (7) enhance the attractiveness of underwater habitat in tourism areas. Whether coral transplantation is likely to be effective from a biological standpoint depends on, among other factors, the water quality, exposure, and degree of substrate consolidation of the receiving area. Whether it is necessary (apart from cases related to reason 3 above), depends primarily on whether the receiving area is failing to recruit naturally.
The potential benefits and dis-benefits of coral transplantation are examined in the light of the results of research on both coral transplantation and recruitment with particular reference to a 4.5 year study in the Maldives. We suggest that in general, unless receiving areas are failing to recruit juvenile corals, natural recovery processes are likely to be sufficient in the medium to long term and that transplantation should be viewed as a tool of last resort. We argue that there has been too much focus on transplanting fast-growing branching corals, which in general naturally recruit well but tend to survive transplantation and re-location relatively poorly, to create short-term increases in live coral cover, at the expense of slow-growing massive corals, which generally survive transplantation well but often recruit slowly. In those cases where transplantation is justified, we advocate that a reversed stance, which focuses on early addition of slowly recruiting massive species to the recovering community, rather than a short-term and sometimes short-lived increase in coral cover, may be more appropriate in many cases. 相似文献