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Autor |
Wang, Y. G.; Thomas, M. R. |
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Titel |
Accounting for individual variability in the von Bertalanffy growth model |
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Jahr |
1995 |
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Can. J. Fish. Aquat. Sci. J. Can. Sci. Halieut. Aquat |
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52 |
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7 |
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1368-1375 |
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Schlüsselwörter |
Fisch, Statistik, Methode, Vergleich, Wachstum, Bertalanffy, Faben |
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Zusammenfassung  |
Estimation of von Bertalanffy growth parameters has received considerable attention in fisheries research. Since Sainsbury much of this research effort has centered on accounting for individual variability in the growth parameters. In this paper we demonstrate that, in analysis of tagging data, Sainsbury's method and its derivatives do not, in general, satisfactorily account for individual variability in growth, leading to inconsistent parameter estimates (the bias does not tend to zero as sample size increases to infinity). The bias arises because these methods do not use appropriate conditional expectations as a basis for estimation. |
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CSIRO IPP&P Biometrics Unit, CSIRO Div. Fish., Box 120, Cleveland, Queensland 4163, Australia |
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Rufnummer |
524 |
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2323 |
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Brunke, M.; Schwörbel, J.; Wendling, K. |
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Titel |
Die Auswirkungen eines Flußtunnels auf die Fliessgewässerbiozoenose: Makrozoobenthon und Fischfauna |
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1995 |
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Limnologica |
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24 |
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4 |
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297-322 |
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Wasserbau, Ökologie, Gewässerverbau, Fisch |
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Zusammenfassung |
Im Stadtgebiet von Idar-Oberstein wurde die Nahe auf einer Laenge von 1880 m durch Ueberbauung und massiven Ausbau der Sohle hermetisch vom Umland abgeschlossen. Zusaetzlich wurde der natuerliche Geschiebebetrieb durch ein Wehr oberhalb des Tunnels unterbrochen. Die Makroinvertebraten- und Fischfauna ist im Tunnel hinsichtlich der Artenzusammensetzung und der Individuendichte verarmt, eine photoautotrophe Besiedlung fehlt. Die Driftdichte ist im Tunnel verringert, die Driftrate erhoeht, der Sauerstofftagesgang stark veraendert. Einfluesse auf die nahen Bereiche ober- und unterhalb des Tunnels liessen sich in dieser Untersuchung nicht feststellen. Hinweise auf oekologische Aspekte bei der Konstruktion aehnlicher Anlagen werden gegeben. |
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269 |
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Chen, Y.; Jackson, D. A. |
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Titel |
Robust estimation of mean and variance in fisheries |
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1995 |
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Trans. Am. Fish. Soc |
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124 |
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3 |
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401-412 |
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fishery-statistics; population-characteristics; statistical-analysis |
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Many fisheries data are commonly summarized by two statistics: mean and variance (or standard deviation). Because observed values are subject to various errors, which often are large and heterogeneous in fisheries studies, outliers commonly exist in the data. The existence of outliers biases estimation of the mean and variance if traditional estimation methods are used. Instead of assuming that errors in fisheries data follow a normal distribution with a constant variance, we propose that errors associated with observations for a variable may encompass a mixture of different levels of normally distributed errors. Based on concepts from a robust regression method, least median of squares, that is not sensitive to atypical observations in data, we develop a simple algorithm to estimate mean and standard deviation. We compare the proposed robust estimation approach with traditional methods and Tukey's biweight robust approach using simulated and field data. Based on simulations, we found little difference in estimated means and variances between the proposed and traditional methods when there were no outliers defined in simulated data. However, when outliers were defined in simulated data, the errors in estimation of the mean and its standard deviation were much smaller with the proposed method than were those estimated with traditional methods. Means and standard deviations estimated with the proposed method changed little, regardless of whether or not the simulated data were contaminated by atypical values. The proposed approach tended to have smaller estimation errors than did the robust biweight method. We demonstrate how the significance and interpretation of fisheries and ecological relationships may be adversely affected when outliers are present. We suggest using our proposed robust method to identify and down-weight outliers in estimating a mean and its standard deviation. One should justify deletion of the identified outliers using the knowledge about fish biology and environmental conditions independent of the variable assessed. |
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308 |
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Magnusson, K. G. |
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Titel |
An overview of the multispecies VPA -- theory and applications |
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Jahr |
1995 |
Publikation |
Rev. Fish Biol. Fish |
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5 |
Ausgabe |
2 |
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195-212 |
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Schlüsselwörter |
vpa, statistik, modell, vergleich, fischerei |
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Zusammenfassung |
Multispecies virtual population analysis is an attempt to take species interactions into account when assessing the status of fish stocks. It was introduced primarily with the aim of lowering the uncertainty in the natural mortality rate as used in single species VPA and to take account of variability between years and ages by calculating inside the model the part of the mortality rate caused by predation. The output of the MSVPA is therefore – in addition to stock sizes and fishing mortality rates as in single species VPA and intraspecific – and possible species replacement are not considered and neither is predation on larvae and prerecruits. The potential relevance of multispecies models lies in long-term forecasts since short-term forecasts from multi- and single species models differ only slightly. In making long-term forecasts, predicting recruitment is of fundamental importance and the value of MSVPA in throwing light on the processes governing recruitment is limited. MSVPA is concerned primarily with calculating postrecruitment mortalities, and although in principle there is nothing to prevent prerecruitment predation mortalities being calculated, such estimates are not likely to be reliable or useful. Predation on the larval stages can be of major importance in determining recruitment but is not addressed in the MSVPA. Thus, it is quite possible that processes which are not dealt with in the MSVPA are much more important in determining the future of the fisheries. In view of all this uncertainty, it is inevitable that it will be questioned whether multispecies management advice is superior to single species advice. |
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498 |
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2298 |
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Walters, C. |
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Titel |
Estimation of historical stock sizes and recruitment anomalies from relative abundance time series |
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Zeitschrift, Artikel |
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Jahr |
1995 |
Publikation |
Can. J. Fish. Aquat. Sci. J. Can. Sci. Halieut. Aquat |
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52 |
Ausgabe |
7 |
Seiten |
1523-1534 |
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Schlüsselwörter |
stock-assessment; approximation-; anomalies-; recruitment-; abundance-; growth-; survival-; algorithms-; fishery-management; marine-fisheries |
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Zusammenfassung |
Often only simple relative abundance time series and basic growth and (or) survival estimates are available for assessing impacts of fishing and environmental factors. Assessment then involves fitting production models to the series, while forcing the model with observed catch or effort series. A key uncertainty in this approach is how to deal with recruitment variations due to factors other than stock size. A dynamic programming algorithm can be used to compute maximum likelihood estimates of the recruitment anomaly sequence, given prior knowledge of growth parameters, the natural survival rate, and proportion of the variation in the relative abundance index that is due to abundance measurement errors. |
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1779 |
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Quartly, G. D. |
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Titel |
Altimeter repeat-track analysis -- a comparison of various algorithms for producing the mean profile |
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Zeitschrift, Artikel |
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Jahr |
1995 |
Publikation |
J. Atmos. Ocean. Technol |
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12 |
Ausgabe |
3 |
Seiten |
674-686 |
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dynamical-oceanography; remote-sensing; satellite-altimetry; sea-level-measurement; geoid-; geostrophic-transport; statistical-analysis; errors- |
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Sea surface height may be measured by a satellite-borne altimeter and its along-track slope used to infer geostrophic currents. A major difficulty is that, in general, the local geoid and satellite orbit are not known to the accuracy desired. Thus, comparison is often made between repeat flights of an altimeter along fixed ground tracks in order to infer the changes in the currents. In practice, it is convenient to calculate a mean height profile from many repeat passes and use this as a reference, so that individual altimetric profiles yield variations about this mean. It is thus important to derive a high-quality reliable estimate of the altimetric mean in order to minimize the errors in the inferred flows for the individual repeats. This work examines various methods for deriving the mean profile. |
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1302 |
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Autor |
Porch, C. E. |
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Titel |
Trajectory-based approaches to estimating velocity and diffusion from tagging data |
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Zeitschrift, Artikel |
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Jahr |
1995 |
Publikation |
Fish. Bull |
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93 |
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4 |
Seiten |
694-709 |
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Schlüsselwörter |
dispersion-; migrations-; tagging-; Pisces-; swimming-; models-; dispersal-; migration- |
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Several new models are developed to estimate the velocity and diffusion of a population from tagging data. The new estimators apply the inverse principle to the individual trajectories of recovered tags rather than to their local abundance. These models require fewer assumptions and less information than do published abundance-based methods. Techniques are presented for a variety of circumstances, and both discrete and continuous parameterizations of the velocity field are included. The sensitivity of the estimators to violations of the assumptions was examined numerically by using stochastic simulations. The results suggest that the estimators are fairly robust but may fail under certain conditions. Extensions to accommodate these situations are discussed. |
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1295 |
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Fotland, A.; Mehl, S.; Sunnanaa, K. |
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Methods of index calculation and presentation of fish abundance data using standard computer programs |
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1995 |
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fishery-management; fishery-statistics; stock-assessment |
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Standard 0-group indices and distribution maps are now produced based on hand-drawn maps using AutoCad with some additional procedures. This paper briefly describes the method. The paper further describes ways of importing coastlines and survey data directly into standard computer programs such as AutoCad and SAS. Standard methods are used for gridding data, producing isolines and further calculation of abundance indices and presentation of distributions. Interactive editing of distribution maps are made, which makes corresponding automatic updating of indices possible. |
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435 |
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Angermeier, P. L.; Smogor, R. A. |
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Titel |
Estimating number of species and relative abundances in stream-fish communities: Effects of sampling effort and discontinuous spatial distributions |
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Zeitschrift, Artikel |
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Jahr |
1995 |
Publikation |
Can. J. Fish. Aquat. Sci. J. Can. Sci. Halieut. Aquat |
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52 |
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5 |
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936-949 |
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Fisch, Fließgewässer, Habitat, Verbreitung |
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The authors sampled fishes and measured microhabitat in series of contiguous habitat units (riffles, runs, pools) in three Virginia streams. Monte Carlo simulations were used to construct hypothetical series of habitat units, then examined how number of species, similarity in relative abundances, and number of microhabitats accumulated with increasing number of habitat units (i.e., sampling effort). The curves indicated that 90% of the species present were usually found by sampling 5 to 14 habitat units (stream length of 22-67 stream widths). Estimates of species relative abundances required less sampling effort for a given accuracy than estimates of number of species. Rates of species accumulation (with effort) varied among streams and reflected discontinuity in species distributions among habitat units. Most discontinuity seemed to be due to low population density rather than to habitat selectivity. Results from an Illinois stream corroborated our findings from Virginia, and suggested that greater sampling effort is needed to characterize fish community structure in more homogeneous stream reaches. |
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Natl. Biol. Serv., Virginia Coop. Fish Wildl. Res. Unit, Virginia Polytech. Inst., Blacksburg, VA 24061-0321, USA |
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nein |
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Rufnummer |
620 |
Signatur |
2414 |
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Borregon, J. L.; Paredes, C.; Elorza, F. J. |
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New algorithms for the statistical modelling of geological heterogeneous media: Comparative results |
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1995 |
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algorithms-; statistical-analysis; heterogeneity-; radioactive-waste-disposal; geology-; simulation-; aquifers-; geochemistry-; groundwater-pollution; pollution-control; waste-disposal-sites; environmental-protection |
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The characterization of an heterogeneous geological media can be approached by means of an statistical treatment of the field data. This lets us know its spatial variability behaviour, in probability terms. The algorithms presented in this work belongs to the scope of simulation of geological heterogeneous random fields. The aim of that characterization is related with the reseach studies of nuclear waste repositories in deep geological structures. Several stochastic generation algorithms are presented, based in the geostatistical regionalized variable, fractal geometry, and spectral Fourier theories. Some of them are deeply exposed here to their understanding. As a result of the paper, some comparative schemes are showed with numerical, geostatistical and spectral analysis of the implicit autorregresive generation methods. |
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241 |
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