Auxiliary and focal assessment models: a proof-of-concept involving time-varying catchability and fishery stock-status evaluation

Abstract Thorson, J. T. 2011. Auxiliary and focal assessment models: a proof-of-concept involving time-varying catchability and fishery stock-status evaluation. – ICES Journal of Marine Science, 68: 2264–2276. Many assessment models evaluate stock status, and biases can arise when time-varying processes are modelled as being time-invariant. An “auxiliary/focal” assessment process is presented, where an “auxiliary” assessment model estimates functional parameters that are used in a “focal” assessment of stock status. This process is evaluated in two steps. First, estimates of density-dependent catchability from single- or multispecies auxiliary models are compared, confirming that multispecies auxiliary models are more accurate when catch-at-age data are abundant. Possible output from the multispecies auxiliary assessment is then used in a focal model, and the results are compared with four other methods: (i) assuming that catchability is constant, (ii) ignoring fishery-dependent indices, (iii) a random-walk catchability model, and (iv) estimating density-dependent catchability without prior information. Results show that the constant catchability model leads to non-conservative biases in stock-status estimates, and a random-walk model decreases bias and has high precision when age data are available. The auxiliary/focal procedure performs best when fishery indices are used without age data, and the density-dependent model without prior information performs well with fishery and survey indices, but without age data. Different methods are optimal, therefore, depending on data availability, and the auxiliary/focal assessment process performs best of the available methods when using just fishery-dependent indices.

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Can 'Time-Invariant' Hedges Estimated from Time-Varying Hedge Models Outperform Time-Invariant Hedges Even During Period of Financial Crisis? An Empirical Investigation of Indian Futures Market

SSRN Electronic Journal ◽

10.2139/ssrn.1914385 ◽

2011 ◽

Author(s):

Sanjay Kumar Thakur ◽

S. V. D. Nageswara Rao

Keyword(s):

Financial Crisis ◽

Empirical Investigation ◽

Futures Market ◽

Time Varying ◽

Time Invariant

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Time-Varying Convergences of Environmental Footprint Levels between European Countries

Energies ◽

10.3390/en14071813 ◽

2021 ◽

Vol 14 (7) ◽

pp. 1813

Author(s):

Durmuş Çağrı Yıldırım ◽

Seda Yıldırım ◽

Seyfettin Erdoğan ◽

Işıl Demirtaş ◽

Gualter Couto ◽

...

Keyword(s):

Ecological Footprint ◽

Unit Root Test ◽

Data Availability ◽

European Countries ◽

Time Varying ◽

Cross Sectional ◽

Ecological Footprints ◽

Window Method ◽

International Policies ◽

Rolling Window

This study proposes the time-varying nonlinear panel unit root test to investigate the convergence of ecological foot prints between the EU and candidate countries. Sixteen European countries (such as Albania, Austria, Belgium, Denmark, France, Germany, Greece, Italy, Luxembourg, Netherlands, Poland, Portugal, Romania, Spain, Sweden and Turkey) and analysis periods are selected according to data availability. This study proposes a cross-sectional Panel KSS with Fourier to test the convergence of the ecological footprints. Then, we combine this methodology with the rolling window method to take into account the time-varying stationarity of series. This study evaluated sub-components of ecological footprints separately and provided more comprehensive findings for the ecological footprint. According to empirical findings, this study proves that convergence or divergence does not show continuity over time. On the other side, this study points out the presence of divergence draws attention when considering the properties of the sub-components in general. As a result, this study shows that international policies by EU countries are generally accepted as successful to reduce ecological footprint, but these are not sufficient as expected. In this point, it is suggested to keep national policies to support international policies in the long term.

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Depleted marine fish stocks and ecosystem-based management: on the road to recovery, we need to be precautionary

ICES Journal of Marine Science ◽

10.1093/icesjms/fsq158 ◽

2010 ◽

Vol 68 (1) ◽

pp. 212-220 ◽

Cited By ~ 14

Author(s):

Anna Gårdmark ◽

Anders Nielsen ◽

Jens Floeter ◽

Christian Möllmann

Keyword(s):

Fisheries Management ◽

Marine Fish ◽

Assessment Model ◽

Fishing Mortality ◽

Fish Stocks ◽

The Road ◽

Stock Status ◽

Ecosystem Based Management ◽

Management Plans ◽

On The Road

Abstract Gårdmark, A., Nielsen, A., Floeter, J., and Möllmann, C. 2011. Depleted marine fish stocks and ecosystem-based management: on the road to recovery, we need to be precautionary. – ICES Journal of Marine Science, 68: 212–220. Precautionary management for fish stocks in need of recovery requires that likely stock increases can be distinguished from model artefacts and that the uncertainty of stock status can be handled. Yet, ICES stock assessments are predominantly deterministic and many EC management plans are designed for deterministic advice. Using the eastern Baltic cod (Gadus morhua) stock as an example, we show how deterministic scientific advice can lead to illusive certainty of a rapid stock recovery and management decisions taken in unawareness of large uncertainties in stock status. By (i) performing sensitivity analyses of key assessment model assumptions, (ii) quantifying the uncertainty of the estimates due to data uncertainty, and (iii) developing alternative stock and ecosystem indicators, we demonstrate that estimates of recent fishing mortality and recruitment of this stock were highly uncertain and show that these uncertainties are crucial when combined with management plans based on fixed reference points of fishing mortality. We therefore call for fisheries management that does not neglect uncertainty. To this end, we outline a four-step approach to handle uncertainty of stock status in advice and management. We argue that it is time to use these four steps towards an ecosystem-based approach to fisheries management.

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The Swing Control of Cranes with Variable Rope Length Based on Linear Time Varying System Theory

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.461.763 ◽

2012 ◽

Vol 461 ◽

pp. 763-767

Author(s):

Li Fu Wang ◽

Zhi Kong ◽

Xin Gang Wang ◽

Zhao Xia Wu

Keyword(s):

State Feedback ◽

Closed Loop ◽

Linear Time ◽

Feedback Stabilization ◽

Time Varying ◽

Closed Loop System ◽

Overhead Cranes ◽

Time Varying Systems ◽

Time Invariant ◽

Time Invariant System

In this paper, following the state-feedback stabilization for time-varying systems proposed by Wolovich, a controller is designed for the overhead cranes with a linearized parameter-varying model. The resulting closed-loop system is equivalent, via a Lyapunov transformation, to a stable time-invariant system of assigned eigenvalues. The simulation results show the validity of this method.

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Correcting density-dependent effects in abundance estimates from bottom-trawl surveys

ICES Journal of Marine Science ◽

10.1093/icesjms/fst208 ◽

2014 ◽

Vol 71 (5) ◽

pp. 1107-1116 ◽

Cited By ~ 12

Author(s):

Stan Kotwicki ◽

James N. Ianelli ◽

André E. Punt

Keyword(s):

Stock Assessment ◽

Dead Zone ◽

Walleye Pollock ◽

Assessment Model ◽

Bottom Trawl ◽

Trawl Survey ◽

Negative Consequences ◽

Catch Per Unit Effort ◽

Density Dependent ◽

Index Of Abundance

Abstract Indices of abundance are important for estimating population trends in stock assessment and ideally should be based on fishery-independent surveys to avoid problems associated with the hyperstability of the commercial catch per unit effort (cpue) data. However, recent studies indicate that the efficiency of the survey bottom trawl (BT) for some species can be density-dependent, which could affect the reliability of survey-derived indices of abundance. A function qe∼f(u), where qe is the BT efficiency and u the catch rate, was derived using experimentally derived acoustic dead-zone correction and BT efficiency parameters obtained from combining a subset of BT catch data with synchronously collected acoustic data from walleye pollock (Theragra chalcogramma) in the eastern Bering Sea (EBS). We found that qe decreased with increasing BT catches resulting in hyperstability of the index of abundance derived from BT survey. Density-dependent qe resulted in spatially and temporarily variable bias in survey cpue and biased population age structure derived from survey data. We used the relationship qe∼f(u) to correct the EBS trawl survey index of abundance for density-dependence. We also obtained a variance–covariance matrix for a new index that accounted for sampling variability and the uncertainty associated with the qe. We found that incorporating estimates of the new index of abundance changed outputs from the walleye pollock stock assessment model. Although changes were minor, we advocate incorporating estimates of density-dependent qe into the walleye pollock stock assessment as a precautionary measure that should be undertaken to avoid negative consequences of the density-dependent qe.

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Modeling of linear time-varying systems by linear time-invariant systems of lower order

IEEE Transactions on Automatic Control ◽

10.1109/tac.1973.1100207 ◽

1973 ◽

Vol 18 (1) ◽

pp. 50-52 ◽

Cited By ~ 9

Author(s):

H. Nosrati ◽

H. Meadows

Keyword(s):

Lower Order ◽

Linear Time ◽

Time Varying ◽

Linear Time Invariant ◽

Time Varying Systems ◽

Linear Time Invariant Systems ◽

Time Invariant

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FE Analysis of Communications Systems for Drive-Thru Restaurants in a Business Dispute Over Specifications and Design Process

Journal of the National Academy of Forensic Engineers ◽

10.51501/jotnafe.v38i1.106 ◽

2021 ◽

Vol 38 (1) ◽

Author(s):

Robert Peruzzi

Keyword(s):

Communication System ◽

Communication Systems ◽

Linear Time ◽

Forensic Analysis ◽

Time Varying ◽

Audio Quality ◽

Linear Time Invariant ◽

Linear Time Invariant Systems ◽

Quick Service ◽

Time Invariant

Forensic analysis in this case involves the design of a communication system intended for use in Quick Service Restaurant (QSR) drive-thru lanes. This paper provides an overview of QSR communication system components and operation and introduces communication systems and channels. This paper provides an overview of non-linear, time-varying system design as contrasted with linear, time-invariant systems and discusses best design practices. It also provides the details of how audio quality was defined and compared for two potentially competing systems. Conclusions include that one of the systems was clearly inferior to the other — mainly due to not following design techniques that were available at the time of the project.

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