VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

FISH POPULATION

• Capture fishery refers to all kinds of harvesting of naturally occurring living resources in both marine and freshwater environments.
• Fish Stock Assessment or FSA is a method of determining presence and stocking of fish in any particular area regardless of its species, volume, fishing ground, weather, size, age or maturity. The aim of Fish Stock Assessment is to establish the status of a resource and to determine the level at which it may be sustainably exploited . Stock assessments provide fisheries managers with the information that is used in the regulation of a fish stock. Biological and fisheries data are collected in a stock assessment. The following are necessary to assess a fish stock:
  • The appropriate data bases
  • Analyses of the available data for exploitation
  • Short and long-term projections of the yield and biomass
  • To determine long-term biological reference points and to estimate the short and long-term effects on yield and biomass of different strategies of the fishery exploitation
• Population is termed as the naturally occurring stock (group of individuals) of races  or a certain race of fish which occupy a certain area of space, and behave as a biological unit.
• Population density is the population size per unit of space ( area or volume). For example 300 pounds of fish per acre of water surface. This density also called abundance when expressed in terms of number of individuals in the stock or weight of the stock per unit of an ecosystem (a lake) or per unit of area of water body.

Certain characteristics develop in a population which are density dependent

• Density-dependent recruitment: The abundance of the adult stock in a population affects recruitment to the population. If adult density is low the recruitment will be low. If it is high the recruitment will also be high. This relation between the adult density and subsequent recruitment may not be holding true always. Fecundity (number of eggs laid) is directly proportional to the adult density. But the recruitment is also limited largely by the food availability.
• Density-dependent growth: The more the density of a population slower is the rate of growth . At low density the growth is faster. Over population often leads to stunted individuals.
• Density-dependent mortality: In case of young fish or eggs (before the age of recruitment), natural mortality is found to be linearly related to numbers, in general, there is no effect of density on the natural mortality.