REBUILDING THE EASTERN BALTIC COD STOCK UNDER ENVIRONMENTAL CHANGE–A PRELIMINARY APPROACH USING STOCK,ENVIRONMENTAL, AND MANAGEMENT CONSTRAINTS

ABSTRACT. . The population dynamics of the Eastern Baltic cod (Gadus morhua callarias L.), unlike many other stocks, shows a strong dependency on environmental conditions. To test the implications of different management policies on the stock and the fishery in a system of global environmental change, we apply a spatially disaggregated, discrete time, age‐structured model of the Eastern Baltic cod stock in 50 year simulation analyses. The simulation provides an analysis of stock, yield, and revenue development under various management policies and environmental scenarios. The policy analysis, focusing on different regulations of fishing mortality, is embedded into three environmental scenarios, assuming low, medium, or high climate and environmental change. The environmental assumptions are based on simulation results from a coupled atmosphere‐ocean regional climate model, which project salinity in the Baltic Sea to decrease by 7–47% in the period 2071–2100 relative to the reference period 1961 1990. Our simulation results show that a significant reduction in fishing mortality is necessary for achieving high long‐term economic yields. Moreover, under the environmental scenarios presented, a stock collapse cannot be prevented. It can, however, be postponed by the establishment of a marine reserve in ICES subdivision 25.     

On Greenberg's Two-Step Model of Criminal Recidivism

With more than two million people currently incarcerated in U.S. prisons and jails, many of them repeat offenders, there is widespread agreement that criminal recidivism is a serious and costly problem in both human and economic terms. In this article, a stochastic model, which is a somewhat simplified version of a model first proposed by Greenberg, is discussed. An argument for the model is made based on recent theoretical and empirical studies that demonstrate the importance of social bonds in both the commission of and the abstinence from crime. This argument provides a stronger theoretical basis for the model, since it suggests that the model's trichotomization of a cohort of released prisoners reflects truly discrete differences and not just a convenient simplification imposed on a continuous variable. The model is shown to fit trial data sets very well, enabling the measurement of asymptotic recidivism—the ultimate percentage of a release cohort who will recidivate.     

Supermolecular liquid crystal dendrimers based on the octasilsesquioxane core

Liquid crystalline dendrimers are proving to be a fascinating class of materials that possess unusual physical properties. The self-assembling process involved in the formation of the mesomorphic state apparently deforms the spherical disposition of the supermolecular dendrimers to give rod-like entities that pack together to yield disordered Smectic A and smectic C mesophases.     

Replacing targeted compassion with multidimensional compassion: an essential paradigm shift to achieve sustainability

We are in the midst of a national, arguably global, debate about hunting and other means of controlling populations of deer and other animals that have greatly exceeded the carrying capacity of local and regional habitat. At one extreme are those who feel that, since humans have eliminated the large, natural predators, we are obligated to keep game species in balance with their environment. At the other extreme are those who value the lives of individual wild creatures and seek to prevent their destruction. Keeping in balance with nature is the essence of sustainability. This would permit the largest number of humans to occupy the planet over a long period of time. Properly managed sustainability should concomitantly make the planet more habitable for other species. The position taken in this discussion is that targeted compassion is inappropriate for sustainable use of the planet because it will not leave a habitable world for future generations.     

INDIVIDUAL‐BASED MODELS AND THE MANAGEMENT OF SHOREBIRD POPULATIONS

Abstract Individual‐based models (IBMs) predict how animal populations will be affected by changes in their environment by modeling the responses of fitness‐maximizing individuals to environmental change and by calculating how their aggregate responses change the average fitness of individuals and thus the demographic rates, and therefore size of the population. This paper describes how the need to develop a new approach to make such predictions was identified in the mid‐1970s following work done to predict the effect of building a freshwater reservoir on part of the intertidal feeding areas of the shorebirds Charadrii that overwinter on the Wash, a large embayment on the east coast of England. The paper describes how the approach was developed and tested over 20 years (1976–1995) on a population of European oystercatchers Haematopus ostralegus eating mussels Mytilus edulis on the Exe estuary in Devon, England. The paper goes on to describe how individual‐based modeling has been applied over the last 10 years to a wide range of environmental issues and to many species of shorebirds and wildfowl in a number of European countries. Although it took 20 years to develop the approach for 1 bird species on 1 estuary, ways have been found by which it can now be applied quite rapidly to a wide range of species, at spatial scales ranging from 1 estuary to the whole continent of Europe. This can now be done within the time period typically allotted to environmental impact assessments involving coastal bird populations in Europe. The models are being used routinely to predict the impact on the fitness of coastal shorebirds and wildfowl of habitat loss from (i) development, such as building a port over intertidal flats; (ii) disturbance from people, raptors, and aircraft; (iii) harvesting shellfish; and (iv) climate change and any associated rise in sea level. The model has also been used to evaluate the probable effectiveness of mitigation measures aimed at ameliorating the impact of such environmental changes on the birds. The first steps are now being taken to extend the approach to diving sea ducks and farmland birds during the nonbreeding season. The models have been successful in predicting the observed behavior and mortality rates in winter of shorebirds on a number of European estuaries, and some of the most important of these tests are described. These successful tests of model predictions raise confidence that the model can be used to advise policy makers concerned with the management of the coast and its important bird populations.     

HUMAN FERTILITY DECISIONS AND COMMON PROPERTY RESOURCES: A DYNAMIC ANALYSIS

ABSTRACT. In rural areas of developing countries, parental decisions on number of offspring may be made on the basis of the role of children in harvesting local common property renewable resources. It has been argued that this may lead to a cycle of human over‐population and resource over‐exploitation. To investigate the plausibility of this argument, we present a discrete dynamic model with two state variables representing human population level N and resource stock level S. The model is similar to one given by Nerlove and Meyer but differs in several important respects. It is assumed that, in each over‐lapping generation of parents and children, parents decide how many children to have based on their resulting share of the local resource harvest and the costs associated with child‐rearing. Using simulation and analytical methods, the long term steady state population and resource stock levels for this dynamic noncooperative game are contrasted with the steady state when parental fertility decisions are made in a cooperative manner.     

Stabilizability of Discrete-Time Nonlinear Systems

This work deals with the property of stabilizing a nonlineardiscrete-time control system to a specified equilibrium pointby appropriate state feedback. For the most part, this paperpresents Lyapunov-like sufficient conditions for stabilizabilityof discrete-time systems that are affine in control. Stabilizationresults for general nonlinear discrete-time systems are alsoincluded.