2.2 Contributions of pelagic and demersal fish

Figure 3 shows the trends in landings of pelagic³, demersal⁴ and unspecified marine fish species. Production from marine fish species has risen from about 14 million tonnes in 1950 to about 73 million tonnes in 1994, 10% of which is unspecified marine fish which is usually landed unsorted and some of which goes for reduction to oil or meal. In quantity terms, the proportion of the total marine fish landings which is accounted for by pelagic fish has risen from about 50% in 1950 to over 60% in 1994. The production of pelagics has increased continuously, with large oscillations reflecting natural variations of resources productivity as well as boom and bust fishing strategies. In terms of value, pelagic production is much less important than demersal production, but its relative importance has been increasing and in 1993 pelagic production accounted for about 40% of the total value of the marine fish landings compared to 50% for demersal fish and 10% for unspecified marine fish. Demersal fish production showed an increasing trend until the mid-1970s and has generally levelled off, with some oscillations, since then. The production of the unspecified fish has continued to increase throughout the whole time period considered and this represents a major shortcoming of the data set.

³ Pelagic fish species are here defined as those belonging to ISSCAAP groups 34-37 which include jacks, mullets, sauries, herrings, sardines, anchovies, tunas, bonitos, billfishes, mackerels, snooks and cutlassfishes.

⁴ Demersal fish species are here defined as those belonging to ISSCAAP groups 31-33 and 38 which include flounders, halibuts, soles, cods, hakes, haddocks, redfishes, basses, congers, sharks, rays and chimaeras.

The distribution of landings among the species mentioned above is highly skewed. For example, 50% of the average total pelagic landings of 186 species items for the period 1950-1994 is represented by only seven top species (anchoveta, Atlantic herring, Japanese pilchard, South American pilchard, chub mackerel, capelin, and Chilean jack mackerel) which account for a major part of the overall variation in landings (Figure 4). A further striking feature of Figure 4 is that once a few major and highly fluctuating species are excluded, there is a smooth and continuous increase in total landings of about 180 remaining pelagic species.

Figure 4. World landings of the top pelagic marine fish species and total

Figure 5 shows the global trend in marine demersal landings with the major species identified. Once the two major species, Alaska pollock and Atlantic cod, are excluded, a consistent trend is established which shows that for the remaining 403 resource items, landings increased up to the early 1970s and have remained fairly stable since then.

Figure 5. World landings of the top demersal marine fish species and total

Because the landings data set contains considerable quantities of marine fish for which species are not specified (although most landings of unspecified species are probably demersal), comparisons of landings of pelagic and demersal fish should be treated with caution. Nevertheless, such comparisons can give indications of gross differences in fishery characteristics among oceans. The ratio of pelagic fish (small and large) to demersal fish (taken to include unspecified species) landings from 1950 to 1994 for each ocean and the Mediterranean Sea is plotted in Figure 6 and the average proportion for pelagic fish for the period is given in Table 1. It is apparent that pelagic species are particularly dominant in the Mediterranean Sea but comprise a low proportion in the Indian Ocean. Specific points of note are:

(a) In the Atlantic Ocean, pelagic fish represent on average about half of marine fish landings and this proportion has been extremely stable since 1954, despite the large variations in the landings of herring in the Norwegian and North Seas, of sardine off Namibia, and of small pelagic resources off west Africa.

(b) In the Pacific Ocean, pelagic fish comprise on average about 59% of the total landings but the proportion has fluctuated greatly in relation to large oscillations of pelagic resources such as Peruvian anchoveta and Chilean sardine, as well as “demersal” resources such as the Alaska Pollock.

(c) In the Mediterranean Sea, pelagic fish dominate the landings and their proportion increased steadily from the 1960s before collapsing in the late 1980s. The progression is remarkably sustained, possibly reflecting a shift in the ecosystem due to eutrophication. While nutrient enrichment might potentially benefit all fishery production, it may have selectively enhanced pelagic fish stocks because associated bottom anoxia, together with high fishing intensity, may have impeded the development of demersal fish stocks (Caddy et al. 1995). The collapse of the landings in the 1990s, clearly related to the collapse of the Black Sea resources and fisheries under environmental stress and overfishing (Caddy et al., 1995), tends to confirm this hypothesis.

(d) In the Indian Ocean, pelagic fish account for less than half of all fish landings, indicating a relative deficiency of pelagic production compared to other oceans. Bakun et al. (1996) related the lack of fisheries on small pelagic fish in the western Indian Ocean to the extreme strength and turbulence of the Indian Ocean system of upwellings combined with extremely dynamic offshore advection, all factors very unfavourable to the survival of small pelagic resources.

Table 1: Mean annual percentage of pelagic fish in marine fish landings for 1950-1994

Ocean	% Pelagic fish in marine fish landings
Atlantic	51
Pacific	59
Indian	45
Mediterranean	67