Urban and peri-urban aquaculture as an immediate source of food fish: Perspectives of Dhaka City,Bangladesh

This paper describes the present status of aquaculture activities in Dhaka City and its surrounding areas including the system of fish marketing and distribution and environmental and socioeconomic issues. Dhaka City contains over 10 million people and is expanding day by day. Demand of fish in the last 10 years has increased as a result of increases in population and income levels. The annual per capita consumption of fish is reported to drop by 0.5 kg since 1985. The reason for this decline is increased prices and decreased supply of fish. Fish supply to the city comes from catch in the rivers-estuaries and floodlands of Dhaka district, neighboring districts, imports from other areas and aquaculture in surrounding areas of the city. Considerable quantities of fish are imported from India, Myanmar and Thailand. Seasonal patterns are common both in supply and consumption of fish. Along with traditional rural household aquaculture, in recent years, urban and peri-urban aquaculture has also been popular. Three broad types of aquaculture activities are found in and around Dhaka City; these are polyculture of carp in ponds, monoculture of catfishs in ponds, and pen and cage aquaculture in open waters. The carp includes both Indian major carp and Chinese carp and some minor carp. The catfish group includes mainly Thai pangas (Pangasius sutchi). Tilapia (Oreochromis niloticus) is also widely popular among the farmers. The technology used for aquaculture is improved extensive to semi-intensive. Increasing demand for fish in the city markets has encouraged the expansion of peri-urban aquaculture with a corresponding increase in the proportion of farmed fish in the markets.     

Optimal designs for minimising covariances among parameter estimators in a linear model

We construct approximate optimal designs for minimising absolute covariances between least‐squares estimators of the parameters (or linear functions of the parameters) of a linear model, thereby rendering relevant parameter estimators approximately uncorrelated with each other. In particular, we consider first the case of the covariance between two linear combinations. We also consider the case of two such covariances. For this we first set up a compound optimisation problem which we transform to one of maximising two functions of the design weights simultaneously. The approaches are formulated for a general regression model and are explored through some examples including one practical problem arising in chemistry.     

Birth-interval dynamics in rural Bangladesh and maternal weight

This article reports on the results of a study conducted in rural Bangladesh on the influence of maternal weight on the components of birth intervals, including gestation and intrauterine mortality, the duration of postpartum amenorrhea, and the duration of waiting time to conception (the menstrual interval). When biological factors (including maternal age, parity, and supplementation practices) and behavioral variables, including religion, education, and occupation, were controlled, maternal weight was found to be related to the risk of intrauterine mortality and to the probability of resuming menses in the postpartum period. The implications of these findings for policies and programs in developing countries are discussed.     

Climate-related migration in rural Bangladesh: a behavioural model

Research into the climate change and migration nexus has often focussed solely on how people move in response to the impacts of variability and change in climate. This notion often ignores the nature of migration as a tried and tested livelihood choice amid a variety of socio-economic and environmental opportunities and limitations. This paper closely looks at the behavioural aspects of migration decision-making in Bangladesh in the context of changes in its economy, and, increasingly, exposure to the impacts of climate variability and change. We find that villagers in areas particularly affected by increasing climatic stresses and shocks are diversifying their traditional livelihood strategies by migrating. Environmental factors, including climatic stresses and shocks, often make such shifts even more necessary. Although the migrants’ primary motivation is better income, in effect, migration becomes an effective form of adaptation. Based on a qualitative study in three geographically distinct places of Bangladesh, we propose that migration is a socially acceptable behaviour that occurs in the context of perceived environmental change and climate variability. Migration decisions are mediated by a set of ‘behavioural factors’ that assesses the efficacy of different responses to opportunities and challenges, their socio-cultural acceptance and the ability to respond successfully. This understanding has policy relevance for climate change adaptation, in terms of both how migrants are perceived and how their movements are planned for.     

Coherent Mortality Forecasting: The Product-Ratio Method With Functional Time Series Models

When independence is assumed, forecasts of mortality for subpopulations are almost always divergent in the long term. We propose a method for coherent forecasting of mortality rates for two or more subpopulations, based on functional principal components models of simple and interpretable functions of rates. The product-ratio functional forecasting method models and forecasts the geometric mean of subpopulation rates and the ratio of subpopulation rates to product rates. Coherence is imposed by constraining the forecast ratio function through stationary time series models. The method is applied to sex-specific data for Sweden and state-specific data for Australia. Based on out-of-sample forecasts, the coherent forecasts are at least as accurate in overall terms as comparable independent forecasts, and forecast accuracy is homogenized across subpopulations.     

Underinvestment in a Profitable Technology: The Case of Seasonal Migration in Bangladesh

Hunger during pre‐harvest lean seasons is widespread in the agrarian areas of Asia and Sub‐Saharan Africa. We randomly assign an $8.50 incentive to households in rural Bangladesh to temporarily out‐migrate during the lean season. The incentive induces 22% of households to send a seasonal migrant, their consumption at the origin increases significantly, and treated households are 8–10 percentage points more likely to re‐migrate 1 and 3 years after the incentive is removed. These facts can be explained qualitatively by a model in which migration is risky, mitigating risk requires individual‐specific learning, and some migrants are sufficiently close to subsistence that failed migration is very costly. We document evidence consistent with this model using heterogeneity analysis and additional experimental variation, but calibrations with forward‐looking households that can save up to migrate suggest that it is difficult for the model to quantitatively match the data. We conclude with extensions to the model that could provide a better quantitative accounting of the behavior.     

Ecosystem services in managing residential landscapes: priorities,value dimensions,and cross-regional patterns

Although ecosystem services have been intensively examined in certain domains (e.g., forests and wetlands), little research has assessed ecosystem services for the most dominant landscape type in urban ecosystems—namely, residential yards. In this paper, we report findings of a cross-site survey of homeowners in six U.S. cities to 1) examine how residents subjectively value various ecosystem services, 2) explore distinctive dimensions of those values, and 3) test the urban homogenization hypothesis. This hypothesis posits that urbanization leads to similarities in the social-ecological dynamics across cities in diverse biomes. By extension, the thesis suggests that residents’ ecosystem service priorities for residential landscapes will be similar regardless of whether residents live in the humid East or the arid West, or the warm South or the cold North. Results underscored that cultural services were of utmost importance, particularly anthropocentric values including aesthetics, low-maintenance, and personal enjoyment. Using factor analyses, distinctive dimensions of residents’ values were found to partially align with the Millennium Ecosystem Assessment’s categories (provisioning, regulating, supporting, and cultural). Finally, residents’ ecosystem service priorities exhibited significant homogenization across regions. In particular, the traditional lawn aesthetic (neat, green, weed-free yards) was similarly important across residents of diverse U.S. cities. Only a few exceptions were found across different environmental and social contexts; for example, cooling effects were more important in the warm South, where residents also valued aesthetics more than those in the North, where low-maintenance yards were a greater priority.     

On the Dirichlet distributions on symmetric matrices

In this paper, we introduce a generalization of the Dirichlet distribution on symmetric matrices which represents the multivariate version of the Connor and Mosimann generalized real Dirichlet distribution. We establish some properties concerning this generalized distribution. We also extend to the matrix Dirichlet distribution a remarkable characterization established in the real case by Darroch and Ratcliff.     

That’s the ticket: explicit lottery randomisation and learning in Tullock contests

Theory and Decision - Most laboratory experiments studying Tullock contest games find that bids significantly exceed the risk-neutral equilibrium predictions. We test the generalisability of these...     

From Multiracial Subjects to Multicultural Citizens: Social Stratification and Ethnic and Racial Classification among Children of Immigrants in the United Kingdom

This study examines how immigrant parents’ geographic origins correspond to their adult children's ethnic and racial self‐classification; whether discrepancies are associated with socioeconomic status; and the implications of these patterns for assessing socioeconomic inequality. Using linked British census data, we identify immigrants’ children in 1971 and examine how they ethnically/racially self‐classify in 2001. We find that fluidity in classification varies across groups, but higher educational attainment is consistently associated with less white British classification. Therefore, grouping immigrants’ children by ethnic/racial self‐classification underestimates socioeconomic disadvantage for these groups. However, grouping by parental birthplace overlooks variation in racialization and disadvantage among children of immigrants from the same country of origin.