2.3 Production peaks in demersal fisheries

It was noted above that the underlying trend in global demersal fish production, unlike that of its pelagic counterpart, has not shown any increase since the early 1970s. If the cessation of development is due to stocks becoming fully-fished or over-fished, it is to be expected that regional differences in the development of fisheries would be reflected in the sequence in which peak demersal fish production was reached in each area.

The development of the demersal fisheries was investigated for each major fishing area. The results are summarised in Table 2 which shows the sequence of attainment of peak demersal fish landings in smoothed time series of landings as defined by five-year running means. The sequence of peaks is generally as would be expected from a knowledge of world fisheries development. Landings peaked first in the Atlantic (between the late 1960s and the early 1970s), then in the Pacific (between the mid 1970s and the late 1980s) and, finally in the Indian Ocean (in the early 1990s). The case of the Mediterranean, one of the oldest and most intensively exploited marine systems is a paradox as many of its resources have been declared overfished for decades although production continues to rise slowly, probably in response to eutrophication, except for the Black Sea where pollution, species introduction and overfishing have played a part (Caddy et al, 1995).

Table 2: Development of demersal fisheries by region as shown by sequence of peak landings and a comparison of recent landings (1991) with peak landings, all based on five-year running-means. (Note 1991 is the last data point available in the running-mean series and 1 in the last column does not mean that landings are stabilised but that they are still increasing.)

Fishing Area	Recent landings (103t)	Max. landings (103t)	Year of Max. landing	Recent/max landing
Atlantic, Northwest	1007	2588	1967	0.39
Antarctic	28	189	1971	0.15
Atlantic, Southeast	312	962	1972	0.32
Atlantic, Western Central	162	181	1974	0.89
Atlantic, Eastern Central	320	481	1974	0.67
Pacific, Eastern Central	76	93	1975	0.81
Atlantic, Northeast	4575	5745	1976	0.80
Pacific, Northwest	5661	6940	1987	0.82
Pacific, Northeast	2337	2556	1988	0.91
Atlantic, Southwest	967	1000	1989	0.97
Pacific, Southwest	498	498	1990	1.00
Pacific, Southeast	459	508	1990	0.90
Mediterranean	284	284	1991	1.00
Indian Ocean, Western	822	822	1991	1.00
Indian Ocean, Eastern	379	379	1991	1.00
Pacific, Western Central	833	833	1991	1.00
Sum	18720	24059		0.78

The final column of Table 2 shows how recent landings compare to the peak landings. In two thirds of the areas, the present landings are less than the historical peak landings. In 30% of the areas, the landings are still increasing. Apart from the Antarctic where resources have been explored, developed, and overfished, and catches have now been limited by management, the major decreases have been seen in the Southeast and Northwest Atlantic where landings have fallen by over 60% in the last two decades. Declines in other areas have been much less marked or absent; the Pacific areas showed declines of less than 20% and landings from the Indian Ocean areas and Mediterranean Sea are still increasing. Although environmental changes have almost certainly played a part in some declines (e.g. the Northwest Atlantic), overfishing has been a major factor in most cases.

The difference between peak and current landings must be interpreted with caution. Peaks in smoothed production probably give an indication of the average long-term yield (ALTY) that the species assemblage in a given area may be able to produce sustainably in the future, with proper management. However, in the case of demersal stocks sensitive to regime shifts on a decadal scale, peak harvests resulting from transient favourable environmental situations bear little relation to the average long-term yield. The smoothing procedure applied to the raw data, however, should have reduced the potential impact of the above problems. As a consequence, the difference between the sum of peak landings and current ones (bottom line of Table 2), which amounts to about 5 million tonnes, may represent a potential benefit from improved management of demersal stocks, assuming, as usual, that the stock declines are reversible. In this regard, however, it is acknowledged that historical trends are also the result of environmental changes and biological interactions, and declines may reflect potentially irreversible situations created by fishing and climatic changes in the exploited ecosystem, although there is evidence that sustained intensive fishing pressure does not necessarily lead to changes in the structure and composition of species assemblages (Greenstreet and Hall, 1996).