This manual deals with the practical implementation of a routine data collection programme. The data collection programme is developed through a top-down approach, from the identification of the objectives down to the practical recording and management of data obtained from the fishery. The issues are dealth with both through detailed discussion and by using simple examples. The examples are mostly based on situations in tropical fisheries, and in particular, experience has been drawn from developing a data collection programme in Viet Nam. The main questions addressed i n the manual are which fisheries data to collect, where and when to collect them. Only data from commercial marine capture fisheries are considered. The methodologies used are mainly appropriate for a tropical, developing county, with many small (artisanal) vessels and a few large (industrial) vessels. The methodology is the "sample-based approach". The data collection methodology presented attempts to utilize whatever information can be obtained in practice in a developing country.

The main objective of this manual is to present the basic and standard concepts of sampling methods applied to fisheries science. In order to ensure sound fisheries research, it is essential to have reliable data from landing ports, fishery stocks and research surveys. A rational management of fishing resources can then be established to ensure a sustainable exploitation rate and responsible fisheries management, providing long-term benefits for all. This document provides an introduction to sampling theory and introduces the theory of the three worlds (population, sample and sampling), as well as a short revision of probability concepts. It also provides an overview of the simple random, random stratified, cluster and two-stage sampling methods. The expressions for estimating the mean and total of the populations, their sampling distributions, the expected values, the sampling variances and their estimates are included and justified for each of the sampling designs. The document also contains a case study of biological sampling from landing ports and exercises that should be used to further understanding of the objectives of sampling and its advantages for fishery resource studies.