Responses of the fishing sector to transitional constraints: From reactive to proactive change,Yucatan fisheries in Mexico     

Carmen Pedroza  Silvia Salas 《Marine Policy》2011

Most fisheries management studies have concentrated on understanding resource dynamics and have paid less attention to understanding the dynamics of those who use the resources. This situation limits the knowledge about the fisheries system as a whole and specifically about the viability of management schemes. It is vital to understand how the actors within the fishing sector (fishing firm owners/managers, fishers, fisheries managers, and traders) may respond to changes in fishing resources trends, market dynamics, and fisheries policies before they are implemented. These issues are explored in this paper by applying a longitudinal analysis of the Yucatan Mexico's fishing industry. The analysis is presented within the framework of the theory of change and coping strategies. The study primarily involved interviews during 2008 with the main owners of companies in the fishing industry and with fisheries managers and other stakeholders. Time-series catch data on the main fishing resources are also reviewed to evaluate changes across three historical periods and describe how the actors have perceived and responded to those changes. Given conditions of uncertainty in resource availability, changes in market demand and changes in institutional arrangements, the viability of traditional business and resource management practices are discussed. The analysis presents different kind of triggers that have modified the conditions of the fishing sector and had had impacts on the socio-economic–ecological system in which fisheries are embedded. The need for adaptive strategies in the whole chain of the fisheries business and resource management is stressed, given the current changes and conditions of fisheries. The discussion states a series of actions that could improve the relationships between business practices and fisheries management.  相似文献   

Spatial pattern of coastal fish assemblages in different habitats in North‐western Mediterranean     

Gabriele La Mesa  Andrea Molinari  Silvia Gambaccini  Leonardo Tunesi 《Marine Ecology》2011,32(1):104-114

Variability of fish assemblages across habitat structures can depend on spatial scales. A hierarchical sampling design was used to assess the spatial variability of temperate fish assemblages in different habitats and at multiple scales. Underwater visual censuses were carried out along the coasts of Elba Island (NW Mediterranean) on Posidonia oceanica beds, rocky algal reefs and sandy habitat at three spatial scales, namely tens of metres (individual replicates), hundreds of metres (sites) and tens of kilometres (locations). At the assemblage level, there was a clear relationship between fish and habitat type and the observed habitat‐related differences were largely dependent on species identity. Fish assemblages on P. oceanica beds and rocky reefs shared a high number of species, whereas overlap with sandy assemblages was negligible. Multivariate analyses revealed significant differences in fish assemblages among habitats, although there was also a significant habitat × site interaction. These differences relied mainly upon assemblage composition and species richness. Assemblages on rocky reefs and P. oceanica meadows usually harboured a higher number of species and individuals compared with sandy assemblages. Nevertheless, the patterns of habitat‐related differences in species richness and, especially, in the total number of fish, changed significantly from site to site. Eight species showed significant differences over habitats, but they were not consistent due to the interaction of habitat with site. Predictability of fish at both assemblage and population levels decreased with the scale of observation, and the spatial pattern of fish observed at the smallest scale was likely dependent on factors other than habitat type.  相似文献   

Recent observations of the WR central star of the planetary nebula LMC-N66     

Miriam Peña  Manuel Peimbert  Silvia Torres-Peimbert  Maria Teresa Ruiz  Jose Maza 《Astrophysics and Space Science》1996,238(1):55-58

The recent evolution of the central star of the planetary nebula LMC-N66 is presented. Before 1987, it showed a weak continuum with aT _eff120 000 K andL _bol25 000L and in a few years it developed strong WR features (P Cygni line profiles in N v at 124.0 nm and C IV at 155.0 nm, wide Heii emission, etc.) typical of a WN 4.5. Additionally the stellar continuum increased by a large factor and the absolute visual magnitude of the star changed from + 1.24 in 1987 to–2.57 in January, 1995. The WR features and enhanced continuum, evidencing a powerful mass-loss event remained with small variations for more than 5 years. Recent ultraviolet and optical data shows that the mass-loss seems to have diminished abruptly in the last three months.  相似文献   

Analysis of gravity source moment inversion. Part II: Usinga priori information about the source     

Walter E. Medeiros  João B. C. Silva 《Pure and Applied Geophysics》1995,144(1):95-116

The method of moment inversion, based on the approximation of the gravity anomaly by thetruncated series obtained from its multipole expansion, uses, implicitly,a priori information about the anomalous body. The series truncation imposes a regularizing condition on the equipotential surfaces (produced by the anomalous body), allowing the unique determination of some moments and linear combinations of moments that are the coefficients of the basis functions in the multipole expansion series. These moments define a class of equivalent distributions of mass. The equivalence criterion is based on the misfit between the observations and the field produced by the series truncated at a prefixed maximum order for the moments. The estimates of the moments of the equivalent distribution are shown to compose the stationary solution of a system of first-order linear differential equations for which uniqueness and asymptotic stability are guaranteed. Specifically for the series retaining moments up to second order, the implicita priori information introduced requires that the source have finite volume, be sufficiently distant from the measurement plane and that its spatial distribution of mass present three orthogonal planes of symmetry intersecting at the center of mass. Subject to these hypotheses, it is possible to estimate uniquely and simultaneously the total excess of mass, the position of the center of mass and the directions of the three principal axes of the anomalous body.  相似文献   

A Geoelectrical Investigation for Ground Water in Crystalline Terrains of Central Bahia, Brazil   总被引：1，自引：0，他引：1  

Walter E. Medeiros  Olivar A. L. de  Lima 《Ground water》1990,28(4):518-523

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Small-Scale Horizontal Variability of Mean and Turbulent Quantities in the Nocturnal Boundary Layer     

Viviane S. Guerra  Otávio C. Acevedo  Luiz E. Medeiros  Pablo E. S. Oliveira  Daniel M. Santos 《Boundary-Layer Meteorology》2018,166(3):395-422

The study of the boundary layer can be most difficult when it is in transition and forced by a complex surface, such as an urban area. Here, a novel combination of ground-based remote sensing and in situ instrumentation in central London, UK, is deployed, aiming to capture the full evolution of the urban boundary layer (UBL) from night-time until the fully-developed convective phase. In contrast with the night-time stable boundary layer observed over rural areas, the night-time UBL is weakly convective. Therefore, a new approach for the detection of the morning-transition and rapid-growth phases is introduced, based on the sharp, quasi-linear increase of the mixing height. The urban morning-transition phase varied in duration between 0.5 and 4 h and the growth rate of the mixing layer during the rapid-growth phase had a strong positive relationship with the convective velocity scale, and a weaker, negative relationship with wind speed. Wind shear was found to be higher during the night-time and morning-transition phases than the rapid-growth phase and the shear production of turbulent kinetic energy near the mixing-layer top was around six times larger than surface shear production in summer, and around 1.5 times larger in winter. In summer under low winds, low-level jets dominated the UBL, and shear production was greater than buoyant production during the night-time and the morning-transition phase near the mixing-layer top. Within the rapid-growth phase, buoyant production dominated at the surface, but shear production dominated in the upper half of the UBL. These results imply that regional flows such as low-level jets play an important role alongside surface forcing in determining UBL structure and growth.  相似文献   

The influence of the environmental status of Casa Caiada and Rio Doce beaches (NE-Brazil) on beaches users     

Luci Cajueiro Carneiro Pereira  Jos A. Jimnez  Carmen Medeiros  Rauquírio Marinho da Costa 《Ocean & Coastal Management》2003,46(11-12):1011-1030

This paper describes the environmental status and the social perception of Casa Caiada (bay 1) and Rio Doce (bay 2 and bay 3) as a consequence of the several impacts that these beaches have been suffering. The methodology adopted in this work was based on interviews with beach users and direct observations of the physical, biological and human aspects. The obtained result denotes that in Casa Caiada the better beach quality is a consequence of the better water quality, infrastructure and services permitting a higher investment in housing development, recreation, commercialization, fishing, tourism, amongst others. In contrast, northward of Rio Doce (bay 3), the beach has been considered of bad quality for the beach users. In Casa Caiada the users were the most demanding when describing the status of the beach and the necessary changes to mitigate the actual situation. On the other hand, in the most degradated area (bay 3) the users were less demanding when proposing possible changes to improve the beach/water and life quality.  相似文献   

Traffic-related immissions and their impact on historic buildings: implications from a pilot study at two German cities   总被引：1，自引：1，他引：0  

Michael Auras  Silvia Beer  Petra Bundschuh  Joachim Eichhorn  Martin Mach  Dirk Scheuvens  Michael Schorling  Jonas von Schumann  Rolf Snethlage  Stephan Weinbruch 《Environmental Earth Sciences》2013,69(4):1135-1147

Besides the enormous improvement of air quality in Germany due to the reduction of sulphur dioxide emissions in the last decades, high immissions of nitrogen oxides and fine particulate matter are frequently observed at traffic-rich urban sites. The changed chemical composition of air pollution requires a new investigation of its impact on historic buildings constructed of natural stone. In a pilot study a multi-disciplinary approach was chosen to obtain information on the actual pollution situation of historic buildings and monuments at traffic hotspots in Germany. The study concentrated on the two German cities of Munich and Mainz of different size, traffic volume and stone inventory. Dose–response functions were calculated to demonstrate the change of impact of different pollutants over the last three decades, and for comparison of traffic hotspots and housing areas of both cities. Numeric modelling on a city-scale was used to identify the historic buildings and monuments affected by elevated traffic immissions. Because a relevant part of these pollutants is dominated by short-range transport, the differences of wind speed and deposition rates were calculated using a street-scale 3D flow and dispersion model regarding traffic volume, wind regime and adjacent buildings. Finally, particulate matter was sampled at different positions of two buildings heavily exposed to traffic emissions. Individual particles were investigated by environmental scanning electron microscopy. After classification of the particles into different chemical groups, the fraction of traffic-induced particulate matter was quantified. Summarizing the results, it must be stated that soiling by traffic-related particulate matter, deposition of nitrates deriving from exhaust emission and other diffusely emitted components bear a severe damage potential for natural building stone at least locally at traffic-rich urban sites.  相似文献   

Long term spectral variability in the soft gamma-ray repeater SGR 1900+14     

Andrea Tiengo  Paolo Esposito  Sandro Mereghetti  Lara Sidoli  Diego Götz  Marco Feroci  Roberto Turolla  Silvia Zane  Gian Luca Israel  Luigi Stella  Peter Woods 《Astrophysics and Space Science》2007,308(1-4):33-37

We present a systematic analysis of all the BeppoSAX data of SGR1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ～20 days after the August 1998 giant flare and during the 10⁵?s long X-ray afterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term spectral evolution only with a change of the temperature of the blackbody component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR1900+14 persistent emission was significantly harder and detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was at least a factor 1.2 below the historical level, suggesting that the source was entering a quiescent period.  相似文献   

H ₂ excitation in turbulent interstellar clouds     

Cesare Cecchi-Pestellini  Silvia Casu  Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2005,364(4):1309-1314

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