FAO Fisheries Circular No. 920 FIRM/C920
REVIEW OF THE STATE OF WORLD FISHERY RESOURCES: MARINE FISHERIES
Marine Resources Service,
Fishery Resources Division,
FAO, Rome, Italy
As more and more experience of long-period variability in fish populations accumulates, a remarkable pattern seems to be emerging. Many of the largest fish stocks of the world seem to be growing and declining rhythmically, with a high degree of synchrony between them. The simultaneous rise and fall of sardine (pilchard) populations in widely separate areas of the Pacific Ocean was first pointed out by Kawasaki (1983) at the major FAO Expert Consultation held that year (Sharp and Csirke, eds., 1983). Since Kawasaki's paper appeared, the pattern he reported has continued to hold, including an additional episode of quite simultaneous change of trend from population growth to abrupt decline in the ensuing period (Figure C3.A).
Many other similar impressive examples can be cited. For example, the Peruvian anchoveta, which grew to support the largest fishery that has ever existed, the Southern African pilchard fisheries (Figure C3.B), as well as the Japanese flying squid (Bakun, 1989), all rose and peaked between the late 1950s and early 1970s during which period the large Pacific pilchard stocks essentially vanished.
The early period from the 1970s to the mid-1980s, which saw the massive rises in population sizes of the sardine stocks in the Pacific, and the collapses of the Peruvian anchoveta in the Pacific and the Southern African pilchard in the Atlantic, was also remarkable as a period of global average temperature rise, suggesting the likelihood that climatic variability may be the driving force linking these variations (Kawasaki and Omori, 1988). However, it seems unlikely that temperature alone could be the major causal agent, since the sea temperatures on the eastern and western sides of the Pacific Ocean tend to vary out of phase rather than in phase. This has also been a period of enhanced El Niño conditions, marked by a long-period progressive collapse of the Southern Oscillation Index (Bakun, 1996), commencing with the 1972 El Niño and culminating in the major 1982-83 El Niño episode. It is well known that El Niño Southern Oscillation (ENSO) is the dominant driving force for short-period climatic variability throughout the world.
For reasons not well understood, the 1972 El Niño did not have a substantial impact in the North Pacific. Thus the period seems to have commenced a little later there, where as the 1976 El Niño had a relatively much greater effect. Accordingly, one sees the large North Pacific salmon populations rising dramatically from the mid-1970s to the mid-1980s (Figure C3.C).
|Figure C3.D||Figure C3.E|
Clearly, no one is yet sure that these ostensible patterns are anything more than fortuitous happenstance, nor has a comprehensive objective analysis been produced. However, there is no doubt that if there does exist a truly effective climatic linkage mechanism which acts to synchronize variability in many of the largest and most important fish populations of the world, it has very interesting and important connotations for management of the global fish supply and for understanding, and even predicting, fishery resource variability.
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Bakun, A. 1989. Recruitment in fishery resources and its relation to environment: Accessible pathways to greater insight, pp. 25-34. In Memorias del Simposio Internacional de los Recursos Vivos y las Pesquerías en el Pacífico Sudeste. Viña del Mar, 9-13 Mayo 1988. Rev. Pacífico Sur (Número Especial). Comisión Permanente del Pacífico Sur (CPPS).
Csirke, J. 1995. Fluctuations in abundance of small and midsize pelagics. Sci. Mar. 59: 481-492. In C. Bas, J.J. Castro and J.M. Lorenzo (eds.), Int. Symp. on Middle-Sized Pelagic Fish. (see also erratum: Sci. Mar. 60: p. 431)
Kawasaki, T. 1983. Why do some pelagic fishes have wide fluctuations in their numbers? - biological basis of fluctuation from the viewpoint of evolutionary ecology., p. 1065-1080. In G.D. Sharp and J. Csirke (eds.), Reports of the Expert Consultation to Examine Changes in Abundance and Species Composition of Neritic Fish Resources. FAO Fish. Rep. 291 (2, 3): 1224 p.
Kawasaki, T., and M. Omori. 1988. Fluctuations in the three major sardine stocks in the Pacific and the global trend in mean temperature, p. 273-290. In T. Wyatt and M.G. Larrañeta (eds.), Int. Symp. on Long Term Changes in Marine Fish Populations, Vigo, Spain..
Sharp, G.D., and J. Csirke (eds.), Reports of the Expert Consultation to Examine Changes in Abundance and Species Composition of Neritic Fish Resources. FAO Fish. Rep. 291 (2, 3): 1224 p.
Lluch-Belda, D., R.J.M. Crawford, T. Kawasaki, A.D. MacCall, R.H. Parrish, R.A. Schwartzlose and P.E. Smith, 1989. World-wide fluctuations of sardine and anchovy stocks: the regime problem. S. Afr. J. mar. Sci. 8: 195-205.
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Wespestad, V. 1996. Trends in North Pacific pollock and cod fisheries (presentation to the NORFISH Symposium). NOAA-NMFS Alaska Fisheries Science Center. REFM Stock Assessment Home Page (www.wrc.noaa.gov/-jianelli/home.html).