Analytical and numerical investigation of optimal harvest with a continuously age-structured model
An age-structured bioeconomic model, which is completely continuous in age and time, is developed in order to compare with traditional discrete models. Both types have advantages and disadvantages. The continuous framework complements discrete models as it allows for deeper and more transparent analytical study and leads to analytical results that would be difficult to achieve within a discrete framework. To make the model realistic, a nonlinear recruitment function is introduced and steady state solutions and constant-effort optimal fishing are studied analytically. In addition, the framework has been used for numerical analysis. Simulations are used to investigate how optimal harvesting patterns vary with parameter values.
This article presents a detailed analysis of various ways of informal private environmental management at fisheries in the context of control practices by representatives of the local executive power. In the light of uncovered strategies by which inspectors construct instances of “reference offense” and thus stigmatize potential violators, as well as of techniques of conspiracy and play based on mutual mythologization, one can argue that a new field of interactions is being formed. But this interaction is organized not according to the logic of confrontation and resistance to the state. The community as a significant agent changes the balance of power relations and embeds the partnership with entities exercising control on behalf of the state within the system of exchange, services, and mutual obligations. Drawing on the micro-anthropological analysis of situational actions, rhetorical practices, and narratives, I examine the complex structure based on the alternation of processes of creation and termination of temporary alliances.
According to the US Energy Information Administration (EIA), 10% of the USA total energy consumption and 13% of electricity generation was coming from renewable resources in 2015. The International Renewable Energy Agency (IRENA) estimates that if renewable resources reached 27% of the US energy mix, it would save the US economy between $30 and $140 billion a year in terms of reduced health effects and CO2 emissions.
We model the evolution of a trans-boundary marine fishery, which is based on the harvesting of a single “highly-migratory” stock and is beginning to be impacted by regional oceanic-climate changes. The fish-stock’s range will be composed of a number of jurisdictional zones: namely, its intersection with the EEZ of each coastal country for which that intersection is non-trivial. There may also be a zone within international waters of the high seas. We also assume that management of the fishery is vested in a Regional Fishery Management Organization, whose members are countries that are “direct stakeholders” in the fishery—being either one of the above countries with jurisdictional authority in a zone or a country that has registered fishing vessels that are licensed to harvest in the fishery, or both.
A model for organizing cargo transportation between two node stations connected by a railway line which contains a certain number of intermediate stations is considered. The movement of cargo is in one direction. Such a situation may occur, for example, if one of the node stations is located in a region which produce raw material for manufacturing industry located in another region, and there is another node station. The organization of freight traﬃc is performed by means of a number of technologies. These technologies determine the rules for taking on cargo at the initial node station, the rules of interaction between neighboring stations, as well as the rule of distribution of cargo to the ﬁnal node stations. The process of cargo transportation is followed by the set rule of control. For such a model, one must determine possible modes of cargo transportation and describe their properties. This model is described by a ﬁnite-dimensional system of diﬀerential equations with nonlocal linear restrictions. The class of the solution satisfying nonlocal linear restrictions is extremely narrow. It results in the need for the “correct” extension of solutions of a system of diﬀerential equations to a class of quasi-solutions having the distinctive feature of gaps in a countable number of points. It was possible numerically using the Runge–Kutta method of the fourth order to build these quasi-solutions and determine their rate of growth. Let us note that in the technical plan the main complexity consisted in obtaining quasi-solutions satisfying the nonlocal linear restrictions. Furthermore, we investigated the dependence of quasi-solutions and, in particular, sizes of gaps (jumps) of solutions on a number of parameters of the model characterizing a rule of control, technologies for transportation of cargo and intensity of giving of cargo on a node station.