Optimum Escapements in the Face of Alternative Recruitment Hypotheses

1981 ◽  
Vol 38 (6) ◽  
pp. 678-689 ◽  
Author(s):  
Carl J. Walters
Keyword(s):  
Dynamic Programming ◽  
Adaptive Management ◽  
Stochastic Models ◽  
Value Of Information ◽  
Fishery Management ◽  
Historical Experience ◽  
Active Probing ◽  
Adaptive Policy ◽  
The Face ◽  
Stock Recruitment

Available data are often inadequate to discriminate among alternative models that make different predictions about the consequences of allowing escapements outside the range of recent historical experience. Dynamic programming is used to show that the optimum policy in such situations can involve active probing or experimentation with escapements. The optimum adaptive policy is usually difficult to compute, but generally may be closely approximated by a "Bayes equivalent" policy that is simpler to estimate but does not account explicitly for the value of information associated with allowing more extreme escapements. While there are various practical difficulties in estimating and implementing an optimum policy, it is concluded that regular probing experiments should be included in every fishery management plan.Key words: stock-recruitment, optimization, adaptive management, stochastic models

scholarly journals Assessing the Capacity of Adaptive Policy Pathways to Adapt on Time by Mapping Trigger Values to Their Outcomes

2019 ◽  
Vol 11 (6) ◽  
pp. 1716 ◽  
Author(s):  
Luciano Raso ◽  
Jan Kwakkel ◽  
Jos Timmermans
Keyword(s):  
Monitoring System ◽  
Decision Makers ◽  
Level Of Confidence ◽  
Adaptive Policy ◽  
Misclassification Errors ◽  
The Future ◽  
Adaptive Action ◽  
The Face

Climate change raises serious concerns for policymakers that want to ensure the success of long-term policies. To guarantee satisfactory decisions in the face of deep uncertainties, adaptive policy pathways might be used. Adaptive policy pathways are designed to take actions according to how the future will actually unfold. In adaptive pathways, a monitoring system collects the evidence required for activating the next adaptive action. This monitoring system is made of signposts and triggers. Signposts are indicators that track the performance of the pathway. When signposts reach pre-specified trigger values, the next action on the pathway is implemented. The effectiveness of the monitoring system is pivotal to the success of adaptive policy pathways, therefore the decision-makers would like to have sufficient confidence about the future capacity to adapt on time. “On time” means activating the next action on a pathway neither so early that it incurs unnecessary costs, nor so late that it incurs avoidable damages. In this paper, we show how mapping the relations between triggers and the probability of misclassification errors inform the level of confidence that a monitoring system for adaptive policy pathways can provide. Specifically, we present the “trigger-probability” mapping and the “trigger-consequences” mappings. The former mapping displays the interplay between trigger values for a given signpost and the level of confidence regarding whether change occurs and adaptation is needed. The latter mapping displays the interplay between trigger values for a given signpost and the consequences of misclassification errors for both adapting the policy or not. In a case study, we illustrate how these mappings can be used to test the effectiveness of a monitoring system, and how they can be integrated into the process of designing an adaptive policy.

The Quest for the Holy Grail and the Dutch Integrated Approach to Nitrogen: How to Align Adaptive Management Strategies with the EU Nature Directives?

2018 ◽  
Vol 15 (2) ◽  
pp. 171-217
Author(s):  
Hendrik Schoukens
Keyword(s):  
Adaptive Management ◽  
Environmental Law ◽  
Management Strategies ◽  
Integrated Approach ◽  
Natura 2000 ◽  
Nitrogen Emissions ◽  
Management Actions ◽  
The Face ◽  
Experimental Management ◽  
Economic Developments

The concept of adaptive management is generally defined as a flexible decision-making process that can be adjusted in the face of uncertainties as outcomes of management actions and other events become better understood. These experimental management strategies, which may grant permit agencies more discretion to authorise economic developments, have become increasingly popular as tools to overcome deadlock scenarios in the context of the EU Nature Directives. One notable application is the Dutch Programmatic Approach to Nitrogen (Programma Aanpak Stikstof – PAS ), which puts forward a more reconciliatory and integrated approach towards permitting additional nitrogen emissions in the vicinity of Natura 2000 sites. The purpose of this paper is to use the Dutch PAS as a benchmark to explore the margins available within the EU Nature Directives to implement more flexible adaptive management strategies. This paper argues that the Dutch PAS, especially taking into account the immediate trade-off that is provided between future restoration actions and ongoing harmful effects, appears to stand at odds with the substantive underpinning of the EU Nature Directives. As a result, its concrete application might be stalled through legal actions which advocate for a more restrictive approach to the authorization of additional impacts on vulnerable EU protected nature. It therefore remains highly doubtful whether the Dutch PAS is to be presented as a textbook example of a genuine sustainable management strategy within the context of EU environmental law.

scholarly journals Non-linearity in stock–recruitment relationships of Atlantic cod: insights from a multi-model approach

2019 ◽  
Vol 77 (4) ◽  
pp. 1492-1502 ◽  
Author(s):  
Camilla Sguotti ◽  
Saskia A Otto ◽  
Xochitl Cormon ◽  
Karl M Werner ◽  
Ethan Deyle ◽  
...  
Keyword(s):  
Environmental Variables ◽  
Gadus Morhua ◽  
Fishery Management ◽  
Atlantic Cod ◽  
Stock Assessment ◽  
Fish Stock ◽  
Recovery Potential ◽  
Stock Recruitment ◽  
Model Approach ◽  
Non Parametric

Abstract The stock–recruitment relationship is the basis of any stock prediction and thus fundamental for fishery management. Traditional parametric stock–recruitment models often poorly fit empirical data, nevertheless they are still the rule in fish stock assessment procedures. We here apply a multi-model approach to predict recruitment of 20 Atlantic cod (Gadus morhua) stocks as a function of adult biomass and environmental variables. We compare the traditional Ricker model with two non-parametric approaches: (i) the stochastic cusp model from catastrophe theory and (ii) multivariate simplex projections, based on attractor state-space reconstruction. We show that the performance of each model is contingent on the historical dynamics of individual stocks, and that stocks which experienced abrupt and state-dependent dynamics are best modelled using non-parametric approaches. These dynamics are pervasive in Western stocks highlighting a geographical distinction between cod stocks, which have implications for their recovery potential. Furthermore, the addition of environmental variables always improved the models’ predictive power indicating that they should be considered in stock assessment and management routines. Using our multi-model approach, we demonstrate that we should be more flexible when modelling recruitment and tailor our approaches to the dynamical properties of each individual stock.

scholarly journals Impact of climate change on adaptive management decisions in the face of water scarcity

2020 ◽  
Vol 588 ◽  
pp. 125015 ◽  
Author(s):  
Y.C. Ethan Yang ◽  
Kyongho Son ◽  
Fengwei Hung ◽  
Vincent Tidwell
Keyword(s):  
Climate Change ◽  
Adaptive Management ◽  
Water Scarcity ◽  
Management Decisions ◽  
Impact Of Climate Change ◽  
The Face

scholarly journals Flood Risk and Resilience in the Netherlands: In Search of an Adaptive Governance Approach

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2563
Author(s):  
Astrid Molenveld ◽  
Arwin van Buuren
Keyword(s):  
The Netherlands ◽  
Flood Risk ◽  
Flood Management ◽  
Adaptive Governance ◽  
Risk And Resilience ◽  
Policy Regime ◽  
Adaptive Policy ◽  
The Face ◽  
The Government ◽  
Institutional Analysis And Development

In the Netherlands, dealing with the risk of flooding in the face of the current climate change requires a governance approach that is less based upon the long-standing tradition of prevention and protection, and more oriented toward ideas of resilience and adaptivity. Such an approach is assumed to be more resilient compared to static approaches and better equipped to deal with the indeterminate character of a problem like flood risk. This article presents the Dutch attempt to introduce a more polycentric and adaptive governance approach in flood management, called multilayered safety (MLS). We studied this approach via interviews and an extensive document study, and analyzed the institutions governing the issue using the Institutional Analysis and Development (IAD) framework of Elinor Ostrom. For years, the issue was in the hands of a small network of actors, mainly occupied by water experts and governed by a strong lead organization and permanent bodies. While introducing a new, more adaptive policy concept the government encountered both resistance and inability within the existing policy regime. This article shows that the issue of flood safety was successfully ‘tamed’ for decades. Adopting a more adaptive and polycentric approach necessitates ‘untaming’ the issue of flood safety.

The Value of Information in Fishery Management

Fisheries ◽  
2008 ◽  
Vol 33 (7) ◽  
pp. 340-348 ◽  
Author(s):  
Gretchen J. A. Hansen ◽  
Michael L. Jones
Keyword(s):  
Value Of Information ◽  
Fishery Management

scholarly journals Adaptive Control of Fishing Systems

1976 ◽  
Vol 33 (1) ◽  
pp. 145-159 ◽  
Author(s):  
Carl J. Walters ◽  
Ray Hilborn
Keyword(s):  
Sockeye Salmon ◽  
Optimization Methods ◽  
Fishing Effort ◽  
Model Parameters ◽  
Fraser River ◽  
The Face ◽  
Stock Recruitment ◽  
Best Fitting ◽  
Uncertainty Parameter ◽  
Recruitment Model

This paper discusses some formal techniques for deciding how harvesting policies should be modified in the face of uncertainty. Parameter estimation and dynamic optimization methods are combined for the Ricker stock-recruitment model to show how exploitation rates should be manipulated to give more information about the model parameters; in general, harvesting rates should be lower than would be predicted by the best fitting recruitment curve unless this curve predicts that the stock is very productive. A decision procedure is developed for comparing alternative stock-recruitment models; when applied to the Fraser River sockeye salmon (Oncorhynchus nerka), the procedure indicates that an experimental increase in escapements would be quite worthwhile. It appears that there is considerable promise for extending these methods and procedures to cases where the stock size is unknown and where fishing effort is poorly controlled.

scholarly journals Optimal Exploitation of Multiple Stocks by a Common Fishery: A New Methodology

1976 ◽  
Vol 33 (1) ◽  
pp. 1-5 ◽  
Author(s):  
R. Hilborn
Keyword(s):  
Dynamic Programming ◽  
Stochastic Dynamic Programming ◽  
Stochastic Dynamic ◽  
Recruitment Curve ◽  
Optimal Exploitation ◽  
Optimal Harvest ◽  
Stock Recruitment ◽  
Programming Solution ◽  
Parameter Values ◽  
Dynamic Programming Solution

Optimal harvest rates for mixed stocks of fish are calculated using stochastic dynamic programming. This technique is shown to be superior to the best methods currently described in the literature. The Ricker stock recruitment curve is assumed for two stocks harvested by the same fishery. The optimal harvest rates are calculated as a function of the size of each stock, for a series of possible parameter values. The dynamic programming solution is similar to the fixed escapement policy only when the two stocks have similar Ricker parameters, or when the two stocks are of equal size. Normally, one should harvest harder than calculated from fixed escapement analysis.

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