National reports are the main but not the only source of data used by FAO to maintain its fishery statistics database. In cases where data are missing or are considered unreliable, FAO includes estimates based on the best available information from any source, such as regional fishery organizations, project documents, industry magazines, or statistical interpolations.
For fleet statistics, FAO crosschecks data submitted by countries with data from other sources, such as international shipping registers. International trade statistics are obtained from countries and supplemented through a comprehensive network of regional inter-governmental institutions created by FAO (the GLOBEFISH system).
In the 1990s, FAO completely revised the fishery production statistics time series, computerizing them back to 1950, including estimates where data were missing, disaggregating data by fishing areas, taking account of political changes (e.g. emergence of new countries), adjusting species identification (as taxonomy evolves), and improving the discrimination between aquaculture and capture fisheries production. The resulting data sets, as used in numerous analyses outside and within FAO, have been made widely available on the Web (as FishStat Plus).
Global reviews of the state of stocks elaborated and published by FAO are not based on catch statistics as primary source of information because there are often more direct indicators of the state of resources than the catch. Primary information used is obtained directly from the working groups of the FAO and non-FAO regional fishery organizations (RFOs) and other formal arrangements, scientific literature (scientific journals, theses, etc.), supplemented by information from industry magazines, and fishery-independent information such as trade data. Where RFOs do not exist, such as in the Northwest Pacific, there are bilateral assessment processes (e.g. among China, Japan and Republic of Korea) which can be built upon.
Where data do not exist, on discards for instance, estimates are made on a one-off basis, using consultant experts or through dedicated expert consultations. In the areas in which FAO has not yet had the means to work effectively e.g. production from illegal fishing, there is no information at all at global level. However, all such data are only available for certain areas or certain years. The great advantage of FAO's catch statistics is that they are global in coverage, have complete time series since 1950 and are regularly updated, and so they are used to provide overview trends in fisheries by region and to provide resource status indicators when other data are lacking.
Problems faced in collecting data
During the last decade, financial support for the development and maintenance of national fishery statistical systems has decreased sharply in real terms, while information needs have been increasing dramatically for by-catch and discards, fishing capacity, illegal fishing, vessels authorized to fish in the high seas, economic data (expenditures, revenues, prices, subsidies), employment, management systems, inventories of stocks and fisheries, aquaculture, etc.
Despite FAO's efforts, the fishery data available are not fully reliable. The outcome is far from perfect in terms of coverage, timeliness, and quality. Data are submitted to FAO often with one or two years of delay. The proportion of catch identified at the level of individual species has tended to decrease with time, and the percentage of "unidentified fish" in the declarations has increased as fisheries diversified and large stocks were depleted. Stock assessment working groups provide a good means for screening catch data, but the frequency of stock assessment in many developing regions has dropped for want of human and financial resources.
The general availability of data has not really improved during the last two decades. Statistics from artisanal and subsistence fisheries are still a concern and many key statistics are missing at the global level, e.g. economic and social data, discards, fishing capacity. The result is that the general trends are probably reliably reflected by the available statistics as shown by the good relations observed with global development trends or climatic changes but the annual figures and the assessments involve a certain degree of uncertainty and small changes from year to year are probably not statistically significant.
The FAO Fisheries Department believes that working with the countries is the only way to improve fishery statistics, primarily to meet national needs with regard to food security and fisheries management, but also those of regional fishery bodies and FAO. Without reliable statistics, effective fisheries management and policy-making are impossible, with serious negative implications at the national and regional levels. Unfortunately, the rehabilitation of major national data collection schemes to provide reliable statistics is necessarily a slow process.