A prior for steepness in stock-recruitment relationships, based on an evolutionary persistence principle

Priors are existing information or beliefs that are needed in Bayesian analysis. Informative priors are important in obtaining the Bayesian posterior distributions for estimated parameters in stock assessment. In the case of the steepness parameter (h), the need for an informative prior is particularly important because it determines the stock-recruitment relationships in the model. However, specifications of the priors for the h parameter are often subjective. We used a simple population model to derive h priors based on life history considerations. The model was based on the evolutionary principle that persistence of any species, given its life history (i.e., natural mortality rate) and its exposure to recruitment variability, requires a minimum recruitment compensation that enables the species to rebound consistently from low critical abundances (Nc). Using the model, we derived the prior probability distributions of the h parameter for fish species that have a range of natural mortality, recruitment variabilities, and Nt values.

Community-based aquaculture in India: strengths, weaknesses, opportunities and threats

Community-based aquaculture founded on the principles of common interest groups working together regardless of sex and age has been an effective tool for implementing scientific aquaculture programs in India. Water bodies that do not interset villagers are targeted for use to avoid communal problems. Farmers who share common interests are identified and organized and a team leader chosen among them. An inventory of resources using the SWOT analysis is made. A participatory approach to identify major problems, socioeconomic and biophysical constraints is used and appropriate interventions are planned. This process is then evaluated and the results of the impact assessment are provided to research/extension /policy planners for setting directions and priorities for further improvement. The potential for expanding community aquaculture for generating self-employment and improving food security of the rural poor as well as improving the environmental conditions of the villages in India can be further tapped.