FAO regularly publishes the Yearbook of Fishery Statistics – Catches and Landings, which provides annual statistics on nominal catches of fish, crustaceans, mollusks and other aquatic animals, residues and plants (cf. FAO 1995). The statistics comprise reported national data from commercial, industrial and small-scale fisheries, carried out in inland, coastal and high seas fishing areas, but not recreational fishery. They also include statistics for mariculture, aquaculture and other kinds of fish farming. The data summarized by FAO represent the live weight equivalent of the landed quantities caught during the annual period covered (except for marine mammals, which are reported in numbers).

Though FAO makes every effort to gather reliable information on the catches worldwide, it has to be kept in mind that the data presented in its annual statistics are influenced by the abilities of contributing countries to collect accurate and timely information from their respective fishery sector. As the conditions for such an endeavor vary between countries, the catch statistics have to be used with some caution (see Mariott 1984 for an irreverent account of fisheries statisticians’ plight).

Aquaculture production statistics have been compiled by FAO since 1984 and published in the FAO Fisheries Circular No. 815. Now in its 9^th revision, this publication summarizes the quantity and value of aquaculture production for the period 1984-1995 (FAO 1997). Data presented are the production by various categories such as species item, country and environment (i.e., brackish water culture, freshwater culture, mariculture). The information originates from national statistics, or¾ where missing¾ has been supplemented by information from other sources such as specialist literature, academic reviews and consultants’ reports.

In order to properly differentiate catch and landing statistics from aquaculture production data, the following definition of aquaculture and its products should be considered:

"Aquaculture is the farming of aquatic organisms, including fish, mollusks, crustaceans and aquatic plants. Farming implies some form of intervention in the rearing process to enhance production, such as regular stocking, feeding, protection from predators, etc. Farming also implies individual or corporate ownership of the stock being cultivated. For statistical purposes, aquatic organisms which are harvested by an individual or corporate body which has owned them throughout their rearing period contribute to aquaculture, while aquatic organisms which are exploitable by the public as a common property resource, with or without appropriate licenses, are the harvest of fisheries" (FAO 1997).

FAO distributes the software packages FISHSTAT PC and AQUACULT PC, which contain and analyze the reported catch statistics and production figures for the years 1950 to 1998, and 1984 to 1998, respectively. These data were extracted and included in the FishBase FAOCATCH and FAOAQUACULT tables.

There are different ways to visualize the catch data incorporated in FishBase, mainly from FAO statistics. One of these is through our plot of catches vs. latitude (Fig. 12), documenting the relative importance of temperate vs. tropical fish and fisheries. However, its key features and their implications must be understood before the patterns generated by this graph can be interpreted correctly. Only fish for which the catch is reported on a single-species basis, either by FAO (see FAO catches) or as a range of catches in the SPECIES table, and for which a latitudinal range is available in FishBase, are included. The FAO catches used here are the means of the last 5 years for which data are available (generally 1992-1996) and include the 600 finfish for which FAO reports catches on a per species basis.

The data from the SPECIES table are used only for species without FAO catches and consist of geometric midranges (e.g., 3,000 t·year^-1 for a range of 1,000 to 10,000 t·year^-1). Presently, they refer to only 62 species. However, we expect these numbers to increase as the ‘Catches’ field of the SPECIES table is gradually filled in for more species.

This is important as the FAO catches are based on country reports which usually ignore discarded by-catch (a staggering figure of about 27 million tons per year; see Alverson et al. 1994), and illegal or unreported catches, and which does not identify species for nearly 50% of the world catches, especially at low latitudes.

A correct graph, accounting for these effects, would probably have a bulge in the latitude from 20°N to 20°S, contrary to the present graph, whose maximum occurs at 60°-30°N. We hope that the future development of FishBase will lead to the gradual emergence of such a corrected graph, reflecting the importance of tropical species in world fisheries.

Reference

Alverson, D.L., M.H. Freeberg, S.A. Murawski and J.G. Pope. 1994. A global assessment of fisheries by catch and discards. FAO Fish. Tech. Pap. 339, 233 p.

Daniel Pauly

Fig. 12. Latitudinal distribution of nominal catches by species. See Box 10 for interpretation of this graph.

The basic category used in the FAO statistics is the ‘species item’, which represents an aquatic animal or plant either at the species, genus, family or the suborder level. There are over 1,000 of such statistical categories, arranged in 51 groups of species that constitute the nine divisions of the FAO International Standard Statistical Classification of Aquatic Animals and Plants (ISSCAAP).

It should be noted, therefore, that it is only when a ‘species item’ refers to a single fish species that this category corresponds with a species as defined in FishBase.

Species items can be selected using any of the four choices provided by FAO: scientific, English, French or Spanish name. (For a list of FAO common and scientific names of species see FAO 1996). Information is also available on statistical entities such as FAO Area or definition of ISSCAAP codes, information typically provided in the FAO Fishery Statistics Yearbook.

Much of fisheries research has been devoted, in the last 50 years, to the dynamics of fish species targeted by various fisheries, and particularly to the change in age and size structure resulting from exploitation. If a fishery is to be sustainable, such annual changes in catch composition should have no trend.

However, the exploitation of multispecies communities has the effect of changing the relative abundance of the different functional groups in the ecosystem supporting these communities (Fig. 13). Notably, large long-lived species with high trophic levels tend to be replaced by smaller, short-lived species feeding at lower trophic levels. These trends will ultimately be reflected in catches.

Following a demonstration of worldwide decline in mean trophic levels (Pauly et al. 1998), reproducible as a FishBase routine (see Fig. 4), we have developed a routine which computes the average maximum size of organisms (fish & invertebrates) caught in fisheries, from 1950 to 1998, weighted by the FAO catches, for any country and FAO area or combination thereof. The routine relies on length as measure of ‘size’ in each group in the ISSCAAP table, consisting of the maximum (standard) length of each species identified as such in the FAO statistics (n = 744) and of the mean of the maximum lengths of component species in the case of composite groups (‘gadoids’, ‘perches’, etc.). For sharks, the precaudal length and for rays the width were taken as the measure best expressing ‘size’. Similarly, for invertebrates, lengths were selected which corresponded best to body length, i.e., excluding antennae or tentacles. Here also for some groups, width was used to represent body size, notably in crabs and most bivalves. References are given for all sources of maximum sizes.

As illustrated by Fig. 14, a decline in average maximum size of organism landed by various countries did occur. Moreover, the trend in Fig. 14 is probably an underestimate, given that it does not consider the reduction of mean length within species, i.e., the very trend that single-species analysis has so well documented for major commercial species.

Reference

The FAO catch data can be viewed in tables and graphs, grouped according to:

Country Nominal catch per species item, reported for a selected country.

FAO area Nominal catch per species item, per country, reported for a selected FAO statistical area.

Species item Nominal catch per country, reported for a selected species item.

ISSCAAP code Nominal catch per country, reported for a selected group of species identified by an ISSCAAP code.

We have added to each ISSCAAP category a fully referenced estimate of trophic level (abbreviated ‘troph’, see Box 22), used to derive series of mean trophic levels in fisheries catches (Pauly et al. 1998). Also, for each ISSCAAP group, an estimate of maximum length was added (standard length in fish, body length in invertebrates) which allows estimating the mean maximum length in fisheries catches (see Box 12).

The FAO fishery catch database hosted by FishBase can be used to show that the composition of these catches has changed much in the last 50 years. Notably, mean sizes have declined (see Box 12), as have the mean trophic levels of the fish landed (Fig. 14). The latter process, described as "Fishing down marine food webs" by Pauly et al. (1998) is also documented by a newly developed routine which outputs, for every time series of multispecies catches (as in Fig. 15) a ‘pyramid’ of catches per trophic level class, from troph = 2.0 (herbivores) to troph = 5.0 (see Box 23, on "Trophic levels of fishes" for detailed definitions). The routine compares two periods in a time series by plotting them as the left and right side of a trophic pyramid. In a sustainable fishery, the pyramid should be roughly symmetrical, in shape, size and composition (fish vs. invertebrates).

The approach used to construct the pyramids relies on the standard errors of the trophic levels (from the ISSCAAP table, this vol.) to define triangular distributions (base of triangle = mean trophic level of each group + 2 s.e.) to assign a catch with a given trophic level (+ s.e.) to different classes of trophic level. [Note that the trophs used here all comply with 2.0 < troph < 5.0, and that for very low and very high troph values (i.e., troph – 2 s.e. < 2.0; and troph + 2 s.e. > 5), the s.e. is set to zero, these two constraints thus limiting the range of trophs in the resulting graphs from 2.0 to 5.0].

Fig. 15 illustrates the resulting pyramid for the North Atlantic (FAO areas 21 + 27), with the left side (negative scale) documenting catches at the start of the time series (1950), while the right side (positive scale) documents the catches at the end (1996). Note the overall increase of catches in recent years, the relative and absolute decrease of top predators, the strong increase of catches in lower trophic levels, and the development of invertebrate fisheries.

Reference

You get to the FAO Catches, FAO Aquaculture, FAO Areas and ISSCAAP tables by clicking on the Reports button in the Main Menu and the FAO Statistics button in the PREDEFINED REPORTS window. Alternatively, you can access them from the Species, Countries and FAO Areas forms.

FAO fisheries and aquaculture production statistics are available in the ‘Information by Topic’ section of the ‘Search FishBase’ page if you select the FAO statistics radio button. You can also access this information in the ‘Species Summary’ page, ‘Internet sources’ section, if you click on the FAO statistics link.

FAO. 1995. FAO yearbook: Fishery statistics – Catches and landings 1993. Vol. 76. Food and Agriculture Organization of the United Nations, Rome, Italy. 687 p.

FAO. 1996. FAO standard common names and scientific names of commercial species (in alphabetical order). Fishery Information, Data and Statistics Unit. Food and Agriculture Organization of the United Nations, Rome, Italy. 143 p.

FAO. 1997. Aquaculture production statistics 1984-1995. FAO Fisheries Circular No. 815, Rev. 9, 195 p. Food and Agriculture Organization of the United Nations, Rome, Italy.

Mariott, S.P. 1984. Notes on the completion of FAO form FISHSTAT NS1 (National Summary). Fishbyte 2(2):7-8.

Pauly, D., V. Christensen, J. Dalsgaard, R. Froese and F. Torres, Jr. 1998. Fishing down marine food webs. Science 279:860-863.

Welcomme, R.L. 1988. International introductions of inland aquatic species. FAO Fish. Tech. Pap. 294, 318 p.

Jan Michael Vakily