There is a diverse range of mechanisms, processes, techniques, approaches and working concepts (collectively referred to as methodology) which have been developed to collect data from capture fisheries and aquaculture in order to manage their biological sustainability and economic and social aspects.

In the case of capture fisheries, the variables on which information is collected differ according to the overall objectives of national fishery policies and the main topics in a design of a survey would include:

1. Objective of the statistical program and an analysis of which data are required to meet the objective.
2. Reflections on the use of different data sources and collection techniques (survey or enumeration), including total survey error estimation and data analysis methods e.g. time series analysis and seasonal adjustment. The diverse economic conditions, the varying cost of systematic data collection, and the different amount of resources made available for establishing and maintaining a fishery statistical collection system or for improvements to an existing system, necessitate the adoption of firm priorities.
3. Practical design issues. Data types and variables on which information needs to be collected should be tailored to the structure of national fisheries and an overall strategy is required to decide on the data collection methods. As with other types of statistical series, the methods most commonly used include surveys, based on either complete enumeration (e.g. vessel registers, infra-structural data, aquaculture production units) or on sampling. Complete enumeration is expensive, but may be essential for certain data sets. Sampling is more cost-effective, but caution is required in designing the distribution of sampling effort in time and space. Some fisheries are small and a fully-fledged statistical program may not be justified based on costs.
4. Survey evaluation. The survey should be kept under review; a valid design may become obsolete because of changes in fishing or landing practices. In general, it is preferable to invest in the improvement of the existing system rather than to set up a new independent data collection system. Where the industry is sufficiently organized with centralized marketing facilities or auctions, it is possible to obtain reliable records of the total catch and value without the need for sampling and recording directly, except for occasional checks. Where no records are available, the collecting system must start with a complete survey to obtain the most basic information on ports, landing sites, numbers and type of vessels, and sample surveys to identify species landed and their utilization.

Experience has shown that national and regional statistical programs generally rely on census-based and sample-based schemes for data collection as well as licensing and compliance data available from fishery agencies and registries. Census-based schemes apply primarily to industrial and semi-industrial fisheries, where data are collected by the operators and reported to the relevant fishery authority, usually as part of the licensing and reporting requirements. Sample-based schemes are used for the artisanal fleets which are often characterized by ad hoc local/community based sub-sectors and a large number of fishers which are geographically dispersed, thus making it difficult to collect information covering the whole of the fishing activities.

The paucity of adequate and reliable capture fishery and aquaculture statistics for many countries, and for developing countries in particular, are issues that CWP and its member agencies address and provide guidance on the establishment of cost-effective and sustainable data collection schemes and methodologies. CWP may also be influential in motivating donor-support for fishery statistical development, projects and training.

There are a number of other issues that affect the quality of national and regional fishery statistics:

1. Data coverage. The data may be incomplete in terms of the range of variables and fishery sectors sampled. Consequently, records in the national or regional databases may include estimates which are derived from assumptions made about fishery sectors and variables which may not have been adequately sampled.
2. Differences in statistical concepts and methodologies used by national or regional authorities for collecting the data. Methodological variations often make comparability of statistics a difficult task, especially when the degree of accuracy of national or regional data varies amongst fishery authorities.
3. Quality of primary data. Although data quality assurance is the responsibility of the relevant fishery authority, it nevertheless has a strong impact on the overall quality of regional and global statistics. Thus, improving data quality and protecting the credibility of fishery statistics requires interaction with relevant fishery authorities and countries and resources invested in capacity building at the national level, including the development and improvement of logbook data collection and fishing activity information.

With regards to point (3) above, political willingness of the national authorities backed by adequate funding is needed for the adoption of measures deemed necessary to improve and maintain data quality.

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