Box 24A Definitions, data availability and quality

The Food and Agricultural Organisation of the United Nations (FAO) explains clearly the various definitions used in fishing (FAO, 1993a). The gross catch is 'the total live weight of fish caught'. The concept of 'landings' refers to the 'quantities landed on a landed weight basis' (ie, what is actually recorded at shore). From this are derived the 'nominal catches' ­ 'the live weight equivalent of the landings' (ie, landings of each species adjusted for on-board processing such as gutting, filleting and drying). The data on nominal catches may or may not be the same as landings. Every year the FAO publishes, with a two-year delay, data on nominal catches of freshwater and marine animals (mainly fish species), by species, fishing area and country (FAO, 1993a). These data normally relate to commercial fishing rather than recreational fisheries. Eurostat also publishes a yearly report on fishing statistics (eg, CEC, 1992).

There are four broad groups of species which are of economic importance for fishing:

For the marine environment, the FAO analyses the world's seas by statistical areas. In the European area these are the northeast Atlantic (area 27) and the Mediterranean and Black Sea (area 37). The International Council for the Exploration of the Sea (ICES), through its Cooperative Research Report series and Statistical Bulletins, provides more detailed data for the northeast Atlantic on fish catches and assessment of fish stocks (eg, ICES, 1992a; ICES 1993a). ICES, for example, holds time-series data for the North Sea from the beginning of the century onwards (Figure 24.1). For the purposes of this report the principal sources of data for the marine environment are FAO and ICES. Data on inland fishing are available from the FAO for Europe, for two zones: Europe (area 04) and part of the former USSR (area 07) (FAO, 1992b). Aquaculture production is often included in marine and inland catch data.

The increasing adoption of production quotas as a means of managing fish stocks is a contributory factor in the growing decline in the quality of data on fish catches submitted to FAO (UNEP, 1989). Further, total catch data are not reliable due to unreported catches or to the misreporting of fish species: for example, herring (Clupea harengus) are often declared as sprat (Sprattus sprattus), and mackerel (Scomber spp) as horse mackerel (Trachurus mediterraneus). The data available are also often not environmentally relevant, referring to administrative units rather than natural areas, and they monitor landings of commercially exploited species, which do not always include all species of importance in the food-chain.

While data are available on fish catches, data on fish stocks are harder to come by. Stock assessment involves the estimation of a variety of population parameters, in particular mortality due to fishing (from fish catches, accidental kills during fishing and natural mortality), numbers of fish in different age classes (differences between years reflecting rates of recruitment) and spawning stock biomass (SSB). Such analytical assessments are hindered by the reliability of the catch data and a lack of knowledge of the biology of the species concerned. Stock data are only meaningful in the context of historical trends and assessment of the long-term potential of stocks. Thus, in the long term, the SSB and recruitment are more useful indicators of a given species than the total stock. Stock estimation is further complicated by the fact that fishing targeted at one stock has an impact on other stocks in the same area, and ecological interactions between fish and shellfish stocks (ICES, 1992b, annex 3). Stock assessments from ICES are considered in the conservation measures adopted in policies (eg the EC Common Fisheries Policy) and by regional fisheries commissions in the northeast Atlantic area. The lack of reliable fishing statistics (stocks and catches) for the Mediterranean is a serious handicap in its management. Modern techniques for stock assessment are based on acoustic methods, and remote sensing may be particularly useful in the Mediterranean.

Few data are available on aspects such as trends in fishing techniques, employment levels and productivity. Those which are available are not particularly reliable. For example, productivity (measured, for example, as landings/fisherman/year) can be a misleading indicator because, although the total catch of a fleet may be increasing, productivity and catch per unit effort (CPUE) may be decreasing as fish stocks decline because of overexploitation. This is attributable partly to the lack of international standardisation on data collection and parameter definition (Cross, 1989).