An Ecological Approach to Fisheries Assessment

1987 ◽  
Vol 44 (S2) ◽  
pp. s68-s74 ◽  
Author(s):  
L M. Dickie ◽  
S. R. Kerr ◽  
P. Schwinghamer
Keyword(s):  
Spatial Distribution ◽  
Ecological Approach ◽  
Size Spectrum ◽  
Natural Mortality ◽  
Assessment Methodology ◽  
Ecological Information ◽  
Production Parameters ◽  
Theoretical Considerations ◽  
Data Requirements ◽  
Biomass Size Spectrum

Deductions based on recent ecological information suggest that while current fishery assessment methodology has captured the main features of fishery production, it may not well anticipate the effects of early natural mortality or of major changes in fishing. We propose here a new methodology based on ecological theory related to a characteristic biomass size spectrum. Theoretical considerations coupled with empirical data on population production appear to take into account high natural mortalities at small sizes and the effects of spatial distribution on production parameters throughout the life history. The resulting models offer a somewhat modified view of the relation of fishery yield to effort and the prospect of population assessments with more modest data requirements.

Models on the Slope of, and Biomass Flow up, the Biomass Size Spectrum

1987 ◽  
Vol 44 (S2) ◽  
pp. s136-s140 ◽  
Author(s):  
Uwe Borgmann
Keyword(s):  
Somatic Growth ◽  
Production Data ◽  
Food Chains ◽  
Size Spectrum ◽  
Allometric Relationship ◽  
Complex Models ◽  
Simple Equations ◽  
Growth And Reproduction ◽  
Biomass Size Spectrum ◽  
Number Of Authors

A comparison is made between the different models of the biomass size spectrum proposed by a number of authors. Though superficially dissimilar, the models are all mathematically compatible if the differences in their underlying assumptions are taken into account. The simplest model does not consider the complexities of food webs over food chains, somatic growth, or the continuous nature of the size spectrum. Comparison with the more complex models, however, shows that these omissions do not seriously affect the slope of the size spectrum. For example, one model predicts that the effects of somatic growth and reproduction cancel if cohort biomasses remain relatively constant as the cohorts mature. If growth rate is related to body size in an allometric relationship and reproduction is ignored, then another model gives a slightly different slope (higher by roughly 0.03). If the same assumptions are used in both models, however, they give compatible results. Some simple equations are suggested for routine application in size spectrum analysis of biomass and production data.

scholarly journals Evaluation of Fish Communities in Daya Bay Using Biomass Size Spectrum and ABC Curve

2021 ◽  
Vol 9 ◽  
Author(s):  
Shannan Xu ◽  
Jianzhong Guo ◽  
Yong Liu ◽  
Jiangtao Fan ◽  
Yayuan Xiao ◽  
...  
Keyword(s):  
Fish Communities ◽  
Breeding Population ◽  
Trophic Levels ◽  
Daya Bay ◽  
Size Spectrum ◽  
The Status ◽  
Unimodal Pattern ◽  
Severe Disturbance ◽  
Main Factor ◽  
Biomass Size Spectrum

Based on the data collected by four trawl surveys during 2016–2017, we applied biomass size spectrum (BSS) and abundance–biomass comparison (ABC) curve to assess the status of fish communities’ status in Daya Bay, China. Our findings indicated a unimodal pattern and biomass size ranged from −2 to 10 grain levels and the pattern of the Sheldon-type BSS of fish in Daya Bay. Moreover, fishes in the range of four to eight size class were relatively abundant. The highest peak belonged to the two to four grain level (log2 size bins), mainly consisting of Leiognathus brevirostris, Callionymus meridionalis, Callionymus koreanus, Evynnis cardinalis, Trachurus japonicus, and other small fishes. The curves of the BSS in spring and winter were relatively flat and comprised a large curvature. The summer and autumn curves were comparatively steep, and the seasonal curvature was small. The curvatures of the curve were mainly related to a large number of small Evynnis cardinalis and a small number of large-sized Harpadon nehereus and Leiognathus ruconius. In our study, it was observed that the number and the size of the breeding population, trophic levels, migration habits, and other life history characteristics, as well as anthropogenic disturbances (especially overfishing), significantly affected the peak shape, slope, or curvature of the fish BSS, with overfishing being the main factor. The ABC curve exhibited that Daya Bay was in a critical state of disturbance throughout the year. The spring, summer, and autumn were in severe disturbance, while the winter was in moderate disturbance.

scholarly journals Theoretical Considerations on the Dynamics of Normal Galactic Nuclei

1980 ◽  
Vol 5 ◽  
pp. 197-204
Author(s):  
Robert H. Sanders
Keyword(s):  
Spatial Distribution ◽  
Gravitational Field ◽  
Mass Distribution ◽  
Rotation Curve ◽  
Spiral Galaxies ◽  
Neutral Hydrogen ◽  
Galactic Nuclei ◽  
The Galaxy ◽  
Theoretical Considerations ◽  
Normal Spiral

I want to discuss the origin of non-circular gas motions observed in the nuclei of normal spiral galaxies and the possibility that recurring violent activity in normal nuclei excites such motion. But first, let us review several basic aspects of the nearest normal galactic nucleus — the nucleus of our own Galaxy.The rotation curve as observed in the 21-cm line of neutral hydrogen gives some indication of the form of the gravitational field in the central region of the Galaxy. Figure 1 is a smooth fit to the rotation curve in the inner few kiloparsecs (solid line) taken essentially from the data of Rougoor and Oort (1960) and Simonson and Mader (1973). This rotation curve, within 1 kpc of the centre, is completely accounted for by the mass distribution implied by the extended 2.2-μ emission (Becklin and Neugebauer 1968, Oort 1971). Moreover, there is little doubt that this centrally condensed mass distribution should be identified with the bulge or spheroidal component of the Galaxy, because the spatial distribution of the 2.2-μ intensity is practically identical to the distribution of visible starlight in the bulge of M31 (Sandage, Becklin, and Neugebauer 1969). The conclusion is that the bulge overwhelmingly dominates the gravitational field inside of 1 kpc.

scholarly journals Electrical Properties Tomography: A Methodological Review

Diagnostics ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 176
Author(s):  
Reijer Leijsen ◽  
Wyger Brink ◽  
Cornelis van den Berg ◽  
Andrew Webb ◽  
Rob Remis
Keyword(s):  
Machine Learning ◽  
Spatial Distribution ◽  
Electrical Properties ◽  
Single Type ◽  
Imaging Method ◽  
Methodological Review ◽  
Matlab Code ◽  
Integral Methods ◽  
Data Requirements ◽  
Insight Into

Electrical properties tomography (EPT) is an imaging method that uses a magnetic resonance (MR) system to non-invasively determine the spatial distribution of the conductivity and permittivity of the imaged object. This manuscript starts by providing clear definitions about the data required for, and acquired in, EPT, followed by comprehensively formulating the physical equations underlying a large number of analytical EPT techniques. This thorough mathematical overview of EPT harmonizes several EPT techniques in a single type of formulation and gives insight into how they act on the data and what their data requirements are. Furthermore, the review describes machine learning-based algorithms. Matlab code of several differential and iterative integral methods is available upon request.

scholarly journals Why Italy First? Health, Geographical and Planning aspects of the Covid-19 outbreak

2020 ◽  
Author(s):  
Beniamino Murgante ◽  
Giuseppe Borruso ◽  
Ginevra Balletto ◽  
Paolo Castiglia ◽  
Marco Dettori
Keyword(s):  
Spatial Distribution ◽  
Spatial Association ◽  
Analytical Techniques ◽  
Ecological Approach ◽  
Po Valley ◽  
Containment Measures ◽  
Points Of View ◽  
Socio Economic Variables ◽  
Valley Area ◽  
Related Mortality

The Covid-19 has hit Italy in February 2020 after its outbreak in China at the beginning of January. But why Italy first among Western countries? What are the conditions that made Italy more vulnerable and the first target of such disease? What characteristics and what diffusion patterns could be highlighted and hypothesized, from the outbreak to the end of March 2020, after containment measures - including a national lock down – were introduced? In this paper we try to provide some answers to these questions, analyzing the issue from the medical, geographical and planning points of view. In particular, we started from a hypothesis of very similar economic, geographical, climatic and environmental conditions of the areas of Wuhan – in Hubei Province in China, the outbreak of the epidemics – and the Po Valley area – in Italy – where most cases and deaths were registered. Adopting an ecological approach, we compared the spatial distribution and pattern of Covid-19-related mortality in Italy with several geographical, environmental and socio-economic variables at Provincial level, analyzing them by means of spatial analytical techniques as LISA – Local Indicators of Spatial Association. Possible evidence relating Covid-19 cases and Nitrogen-related pollutants and land take arise, particularly in the Po Valley area.

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