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1.
《African Journal of Marine Science》2013,35(1):385-396
Following independence of Namibia in 1990, abundance of that country's hake stocks was monitored by trawl surveys conducted by the Norwegian F.R.V. Dr Fridtjof Nansen using a systematic survey design. Precision from such designs is considered to be better than with a random design, but it cannot be quantified through standard analysis of variance. In 1998 and 1999, the trawl surveys were duplicated in full using a commercial trawler that operated in parallel with the Dr Fridtjof Nansen. Both vessels had the same fishing gear and rigging. In both years, biomass and distribution patterns estimated by the vessels were similar. The paired datasets collected from the surveys were used to analyse variability in the point samples. Absolute differences between pairs of catches were, in general, proportional to the catch, but they varied randomly following a normal distribution around the catch level. Local variability was analysed as random noise, modelled and later reapplied on single vessel data series to evaluate the effect of sample size and replicates on the survey mean. In a survey with 200 stations, local sample noise accounted for about 4% of the variability in the survey mean. Alternatively, running series of simulated surveys by bootstrapping on pairs of catch data gave similar results, when a small systematic vessel effect was adjusted for. The main statistical techniques applied were less susceptible to outlier catches than straightforward correlations or regressions and could therefore, perhaps with some advantage, also be used to estimate the vessel factor when intercalibrating trawl survey vessels. 相似文献
2.
Understanding fishermen's perspectives and responses relating to climate variability is important for sustainable fisheries management. To this end, a survey of captains of commercial passenger fishing vessels (CPFVs) was conducted in San Diego. The survey demonstrates that fishermen have observed and adapted to changes in the environment and fish populations associated with climate variability. However, only 12.9% of respondents agreed that global climate change is a possibility. In order to explain fishermen's divergent beliefs on climate change, a semiparametric discrete choice model is used to identify the potential determinants. The empirical results highlight the importance of the following factors: fishermen's experience, observations of the phenomena that are associated with climate variability, and an interaction of fishermen's experience and their observations. 相似文献
3.
Imran M. Momin Neeraj Agarwal Rashmi Sharma Neetu Sujit Basu Abhijit Sarkar 《Marine Geodesy》2013,36(1):66-81
Ocean General Circulation Model (OGCM) simulations from 1970–2007 are used to study the upper ocean heat content variability in the Tropical Indian Ocean (TIO). Model computed heat contents up to 50 m (denoted by HC50 m hereafter) representing upper ocean heat content and 300 m (HC300 m) representing heat content up to thermocline depth are first compared with heat contents computed from observations of two buoys in the TIO. It is found that there is good agreement between the model and observations. Fourier analysis of heat content is carried out in different regions of TIO. The amplitudes of semi-annual variability for HC50 m and HC300 m are observed to be greater than those for the annual variability in the Bay of Bengal, while in the Arabian Sea there is a mixed result. Heat content tendency is known to be governed by net surface heat flux and horizontal as well as vertical heat transports. For understanding the relative importance of these processes, a detailed analysis of these terms in the tendency equation is carried out. Rossby wave is observed in the annual mode of heat transport while equatorial jet and Kelvin waves are observed in the semi-annual mode of heart transport. Finally, the correlation between heat content and sea surface temperature (SST) and sea level anomaly (SLA), taken one at a time, is computed. It is found that the correlation improves significantly when both these quantities are together taken into account. 相似文献
4.
The paper reports computed data on the seasonal variability of the Atlantic Ocean currents which were obtained through numerical integration (using conservative difference schemes) of non-linear equations of hydrothermodynamics taking into account an upper quasi-homogeneous layer and the bottom topography. The seasonal variability of the meridional heat transfer is discussed. The results were obtained using an adaptation approach.Translated by Vladimir A. Puchkin. 相似文献
5.
The mixed layer depths over the Arabian Sea were computed for the three successive years 2004-2006 using ARGO floats data. The large availability of ARGO floats for the above period resulted in better estimation of mixed layer depth (MLD) over the Arabian Sea. The results were compared with World Ocean Atlas 1994 MLD Climatology. Marked variability in MLD on a monthly time scale is observed and it was in accordance with the wind stress and/or net heat gain variability, which are the principal factors influencing mixed layer over Arabian Sea. With the availability of large number of ARGO profile data, an attempt is made to study the monthly variability of Mixed Layer. 相似文献
6.
《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(8):1402-1420
Fourteen temperature sections collected between July 2002 and May 2006 are analyzed to obtain estimates of the meridional heat transport variability of the South Atlantic Ocean. The methodology proposed in Part I is used to calculate the heat transport from temperature data obtained from high-density XBT profiles taken along transects from Cape Town, South Africa to Buenos Aires, Argentina. Salinity is estimated from Argo profiles and CTD casts for each XBT temperature observation using statistical relationships between temperature, latitude, longitude, and salinity computed along constant-depth surfaces. Full-depth temperature/salinity profiles are obtained by extending the profiles to the bottom of the ocean using deep climatological data. The meridional transport is then determined by using the standard geostrophic method, applying NCEP-derived Ekman transports, and requiring that salt flux through the Bering Straits be conserved. The results from the analysis indicate a mean meridional heat transport of 0.54 PW (PW=1015 W) with a standard deviation of 0.11 PW. The geostrophic component of the heat flux has a marked annual cycle following the variability of the Brazil Malvinas Confluence Front, and the geostrophic annual cycle is 180° out of phase with the annual cycle observed in the Ekman fluxes. As a result, the total heat flux shows significant interannual variability with only a small annual cycle. Uncertainties due to different wind products and locations of the sections are independent of the methodology used. 相似文献
7.
Sean Pascoe Wendy Proctor Chris Wilcox James Innes Wayne Rochester Natalie Dowling 《Marine Policy》2009,33(5):750-758
Fisheries management is increasingly involving a wide range of stakeholders in the decision making process. However, in most fisheries, the set of management objectives are poorly defined, and the implicit importance placed on these objectives may vary considerably both between and within different stakeholder groups. This may lead to conflicts within management advisory groups where members from different stakeholder groups view potential management outcomes substantially differently, and inconsistencies in decision making when changes in stakeholder representation take place. In this paper, the institutional structure of fisheries management in Australia and the roles the different organisations play in shaping fisheries management plans are detailed. An explicit hierarchy of management objectives is developed in collaboration with key managers and policy makers. A large survey of stakeholders involved in Australian Commonwealth fisheries management was undertaken to determine stakeholder preferences relating to these objectives. The results highlight the differences in perspectives regarding the relative importance of the multiple objectives of fisheries management. While on average stakeholder preferences generally correspond with their expected preference set, the results also indicate that there is generally low coherence within stakeholder groups. 相似文献
8.
In the context of a deep geological repository of high-level radioactive wastes, the French National Radioactive Waste Management Agency (Andra) has conducted an extensive characterization of the Callovo-Oxfordian argillaceous rock and surrounding formations in the Eastern Paris Basin. As part of this project, an accurate 3D seismic derived geological model is needed. The paper shows the procedure used for building the 3D seismic constrained geological model in depth by combining time-to-depth conversion of seismic horizons, consistent seismic velocity model and elastic impedance in time. It also shows how the 3D model is used for mechanical and hydrogeological studies. The 3D seismic field data example illustrates the potential of the proposed depth conversion procedure for estimating density and velocity distributions, which are consistent with the depth conversion of seismic horizons using the Bayesian Kriging method. The geological model shows good agreement with well log data obtained from a reference well, located closest to the 3D seismic survey area.Modeling of the mechanical parameters such as shear modulus, Young modulus, bulk modulus indicates low variability of parameters confirming the homogeneity of the target formation (Callovo-Oxfordian claystone). 3D modeling of a permeability index (Ik-Seis) computed from seismic attributes (instantaneous frequency, envelope, elastic impedance) and validated at the reference well shows promising potential for supporting hydrogeological simulation and decision making related to safety issues. 相似文献
9.
《African Journal of Marine Science》2013,35(1):937-951
Alternative harvesting schemes for the South African anchovy resource are considered. For this preliminary study, strategies in which quotas are simply related to the pre-catch survey estimates of spawning biomass and recruitment are investigated, using a Monte Carlo simulation approach. The schemes evaluated are the strategies of a constant catch, a constant proportion of the recruitment estimate, and a variant on constant escapement. The relationship between modal recruitment and spawning biomass is assumed known, and the values of parameters such as natural mortality and mass-at-age are initially taken to be exact. True recruitment is assumed log-normally distributed about its modal value. The annual survey estimates of recruitment and spawning biomass are generated with typical measurement errors included. The results show the cost (expressed as a loss of potential annual yield) of imperfect survey information, natural recruitment variability, and constraints on year-to-year catch variability. The analysis is extended to integrate the outcome of specific harvesting strategies over the current estimates of the probability distributions for the model parameters, assuming that these are not updated as harvesting is continued. The final results suggest that the mean annual yield of the South African anchovy resource could be increased by about 40 per cent through use of a more flexible harvesting strategy than is the current practice, without at the same time increasing the risk of collapse. 相似文献
10.
X-ray computed tomography analysis of sediment cores from Eckernförde Bay (western Baltic Sea) indicates that the primary macrostructures and sources of physical property variability are feeding pockets and laminae. Burrowing produces easily discernible macrostructures, yet has a nominal effect overall on sediment property variability. Grain-size distribution is a dominant parameter determining the sediment macrostructure—physical property relationship: the largest variation in sediment properties was associated with sandy sediment and the smallest with muds. However, equally significant is the sorting or spatial distribution of grains within a particular sediment horizon, i.e., whether spatially uniform or patchy. 相似文献
11.
Assessment and integration of conventional,RTK-GPS and image-derived beach survey methods for daily to decadal coastal monitoring 总被引：1，自引：0，他引：1
Coastal monitoring across a broad range of time-scales was recognized in the latest report by the Intergovernmental Panel on Climate Change as key to better understanding the likely impacts of climate change at the coast. A unique and historic coastal monitoring program undertaken at the Collaroy–Narrabeen embayment in south-eastern Australia comprises: 1) 30 years of monthly conventional (Emery method) surveys of five cross-shore profile lines; 2) three years of monthly three-dimensional surveys of the entire embayment using RTK-GPS mounted to an all-terrain vehicle (ATV); and 3) four years of hourly shoreline measurements using coastal imaging technology (ARGUS). This study evaluates the strengths and limitations of conventional, RTK-GPS and image-derived surveys for coastal monitoring at daily to decadal coastal time-scales. High-accuracy RTK-GPS was used to first assess the accuracy of the conventional and image-derived survey methods. The magnitude of daily to decadal coastal variability was then characterized by calculating the temporal semivariogram of the integrated survey dataset. With both measurement errors and the degree of beach variability quantified, the corresponding signal-to-noise ratios (SNR) of each survey method at different time-scales were determined. The value of the simple and cost-effective Emery method was verified by this analysis, with measurement error significantly smaller than the degree of overall beach variability (SNR = 8.4). The accuracy, speed and efficiency of ATV-mounted RTK-GPS meanwhile make it suitable for three-dimensional beach surveys. Image-derived surveys were found to be an effective means of remotely measuring the considerable degree of beach variability identified at time-scales of less than one month. These measurements however become indistinguishable from survey noise (i.e. SNR ≤ 1) when considering typical weekly (or smaller) variations at large distances from the cameras. 相似文献
12.
The most common parameters and functions used to characterize wave groups in linear seas are reviewed and interrelated in a unified manner. A three-axes representation of run lengths is used to characterize wave groups using exponential and Markov chain approximations. A relationship between four parameters (Qp, Qe, κ2, and ρ2) and the correlation coefficient between consecutive wave heights [rHH(1)] is demonstrated. The wave-height function method is reviewed in some detail in order to relate the run length theory with envelope theories. The theoretical estimates used to demonstrate the relationships between the various parameters must be considered as only first-order trends to parameter estimates computed from real wave data due to the statistical variability in these estimates when computed from real wave data. 相似文献
13.
14.
Shin’ichiro Kako Atsuhiko Isobe Satoquo Seino Azusa Kojima 《Journal of Oceanography》2010,66(2):291-297
The present study attempts to establish a scientifically reliable method capable of computing the drifting-object sources
and their outflows. First, the temporal variability of the drifting-object amount is investigated every two months on a beach
west of Japan, where various source regions are anticipated because of spatiotemporally variable northeastward ocean currents
over the East China Sea. Next, in order to specify drifting-object sources, two-way particle tracking model (PTM) experiments
are carried out using simulated ocean currents and leeway drift estimated from QuikSCAT/Seawinds wind data. Finally, an inverse
method with a Lagrange multiplier is applied to estimate drifting-object outflows at each source on the basis of the two-way
PTM results and beach surveys. Accuracy of object-source identification using the two-way PTM is validated by comparing disposable-lighter
sources suggested by phone numbers printed on the lighter surface with those computed by the model. In order to examine the
reliability of the inverse estimation, the number of plastic-bottle caps found in actual beach surveys is compared with that
computed using a forward in-time PTM during the same period of actual beach surveys, over which the outflows obtained using
the inverse method are given at each source in the model. 相似文献
15.
Sarah T. Gille 《Marine Geodesy》2004,27(1):47-57
The Kolmogorov-Smirnov (K-S) test is used to compare probability density functions (PDFs) of geostrophic velocities measured by the TOPEX, Poseidon, and Jason altimeters. Velocity PDFs are computed in 2.5° by 2.5° boxes for regions equatorward of 60° latitude. Although velocities measured by the TOPEX and Jason altimeters can differ, on the basis of the K-S test the velocities are statistically equivalent during the ∼200 day period when the satellites followed the same orbit. Full records from TOPEX, Poseidon, and Jason show less agreement, which can be attributed to temporal variability in ocean surface velocities and differing levels of measurement noise. 相似文献
16.
SARAH T. GILLE 《Marine Geodesy》2013,36(1-2):47-57
The Kolmogorov-Smirnov (K-S) test is used to compare probability density functions (PDFs) of geostrophic velocities measured by the TOPEX, Poseidon, and Jason altimeters. Velocity PDFs are computed in 2.5° by 2.5° boxes for regions equatorward of 60° latitude. Although velocities measured by the TOPEX and Jason altimeters can differ, on the basis of the K-S test the velocities are statistically equivalent during the ～200 day period when the satellites followed the same orbit. Full records from TOPEX, Poseidon, and Jason show less agreement, which can be attributed to temporal variability in ocean surface velocities and differing levels of measurement noise. 相似文献
17.
Validation of a decadal OGCM simulation for the tropical Pacific 总被引：2，自引：0，他引：2
An ocean general circulation model is forced with NCEP reanalysis over the 1948–1999 period. The simulated dynamic height and sea level are compared respectively to the dynamic height computed from hydrological data and to the sea level measured by tide gauges in the tropical Pacific. The model is shown to capture important features of the temporal structure of variability in the tide gauge data over the last several decades. However, the comparison reveals a largely artificial trend in the simulation, which consists of a decreasing dynamic height and sea level in the southwest and northwest of the tropical Pacific. Model sensitivity experiments show this trend is controlled by the NCEP surface wind stresses and more precisely by a weakening in the trade winds and a trend in the off-equatorial wind curl, with this trend existing mainly before the mid 1970s. For studies of decadal variability, the simple removal of a linear trend is an inadequate way to solve the problem, due to the inhomogeneities in the data used in reanalysis products and the non-linearity of models. 相似文献
18.
Variability of sea surface temperature and warm pool area in the South China Sea and its relationship to the western Pacific warm pool 总被引：1，自引：0，他引：1
Sea surface temperature (SST) data derived from satellite and in situ measurements are used to study the thermal variability
in the South China Sea (SCS). Time–frequency–energy distributions, periods of variability, and trends are computed by the
Hilbert–Huang transform method. The SST trend from 1982 to 2005 is 0.276°C per decade in the SCS which is higher than 0.144°C
per decade in the western Pacific warm pool (WPWP). The warm pool (SST ≥ 28°C) area in the SCS has increased by 0.20 × 106 km2 per decade. The SST and area of the warm pool in the SCS are strongly correlated, respectively, with the SST and area of
the WPWP with a time lag of 1 month, suggestive of a strong connection between these two warm pools. Once the annual cycle
is eliminated, decadal oscillations dominate the variability of SST and warm pool area in the SCS. 相似文献
19.
Diel patterns in survey trawl catches for the Cape hakes Merluccius capensis and M. paradoxus off Namibia were studied in order to examine the effect of diel bias on catchability, and its implication for survey abundance estimation and the consistency of the survey time-series. Catch rates (numbers per haul) by species and length from summer demersal biomass surveys conducted during the period 2002–2013 were used, together with a computation of the corresponding light-level data from which the solar zenith angles were obtained. Generalised additive models were fitted to assess the relationship between the catches and a number of explanatory variables. Significant covariates were zenith angle, depth and geographical position. The final models explained 78% and 59% of the variability in catch rates of M. capensis and M. paradoxus, respectively. For M. capensis, the response to zenith angle increased sharply for values above 100°, which represents the time between sunset and sunrise. For M. paradoxus there was a moderate increase in the response to zenith angle during the night. In cases where some fishing took place at night in shallow water, the survey results for M. capensis were more greatly affected than was the case for M. paradoxus, which is related to the different depth preference of the two species. Fishing in depths shallower than 400?m outside daylight hours should therefore be avoided in order to reduce bias and ensure consistency in abundance estimates from surveys. 相似文献
20.
The variability of the sound speed vertical distribution in high-salinity and freshened tropical waters has been computed using the intense convection model. It is shown that the most complicated transformation of theC(z) profile is induced by haline convection in freshened oceanic waters. Computation results are collated with observed data.Translated by Mikhail M. Trufanov. 相似文献