Fisheries, decline

Each of the two important prewar fisheries, the herring and the flatfish fishery reached at its best years in the late 1930s a magnitude of about 100 0001. Thereafter the flatfish fishery declined rapidly, remains on a comparatively low level (Fig. 18.3) and has never regained its former importance again. 

Hrabik TR, Watras CJ. 2002. Recent declines in mercury concentration in a freshwater fishery isolating the effects of de-acidification and decreased atmospheric mercury deposition in Little Rock Lake. Sci Total Environ 297 229-237. 

World productiai of aquatic life excluding whale doubled twice in the decades between 1950 and 1970. Growth in world fishery producticxi throughout the seventies however was lower than the rate of growth in population. Consequently on a worldwide basis the contributicxi of fish to human nutritiai has declined (16). 

Malley, D. F. Chang, P. S. S. Schindler, D. W. Decline of Zooplankton Populations following Eutrophication of Lake 227, Experimental Lakes Area, Ontario 1969-1974 Dept. Fisheries Oceans, Freshwater Institute, Winnipeg, Manitoba, 1977. 

Through this exciting period the dietary intake of fish in western society had declined as other modem foods were easier to produce, store, and distribute. Fish were also beginning to be more scarce as fisheries were overexploited and fish populations diminished or were even wiped out. 

Once recovery of cod to (above) safe biological biomass has occurred (presently defined as 240000 tonnes or precautionary spawner biomass ICES, 2006), the fishery could be re-opened but at a lower more sustainable level. The minimum legal size of cod should also be increased to allow many more cod to have a chance of spawning at least once during their lifetime. Present minimum sizes allow targeted and bycatch capture of many juveniles (ICES, 2006). Implementation of these measures would reduce the risk of population decline in future. 

As the world s fisheries have declined, attention has turned to aquaculture. For it to be sustainable in the future, current problems of replacement of mangroves by ponds, use of wild fish as feed, pollution from wastes, escapes of exotic species or varieties, and the short lifetimes of ponds, must be solved.87 Shrimp and salmon farming have many of these problems. It would be better to farm herbivorous fish. 

Coastal eutrophication caused by high nutrient loads reduces the productivity of wetlands and fisheries. It is estimated that the Danube contributes about half of the total river load of nutrients to the Black Sea. The shallow north-western shelf of the sea into which the Danube discharges is where the damage is most evident. Fisheries have been drastically reduced biodiversity has suffered and the quality of the beaches has declined because of excessive growth of algae and jellyfish (Suciu, Constantinescu, David, 2002). 

An increase in nutrient availability results in an increase of fisheries yield to a maximal point then there are declines in various compartments of the fishery as further increases in nutrients lead to seasonal hypoxia and permanent anoxia in semi-enclosed seas. Documenting loss of fisheries related... 

Figure 6.1. The response of secondary production and fishery yield in coastal marine ecosystems to increased nutrient loads (primarily nitrogen). Note the nonlinear responses, with production at all trophic levels increasing as nutrient inputs increase at lower levels of loading, but declines in secondary production and fishery yields at higher nutrient loads. Demersal fisheries (those that are dependent upon the bottom waters and sediment) decline before fish dependent on zooplankton in the water column for their food. Modified from Caddy (1993)...

Mussel capture fisheries peaked in 1992 (276 tons) and 2000 (262 tons), hi 2003, mussel catches dropped drastically to 17% and 23% from 2004 to 2005. The decline was caused by lower production in Denmark. Nevertheless, Denmark continues to be, so far, the main capturing country, accounting for about half of the mussel catch (69,155 tons). Other important producers of wild mussels include Italy (35,065 tons), Turkey (12,362 tons), the United Kingdom (11,158 tons), and the United States (10,566 tons) in 2004. 

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