These changes present a risk to both human health and the marine ecosystem, for example, due to the accumulation of toxic trace metals in fish stocks from these areas. The results of various mussel watch programmes, which are co-ordinated by the Sea Fisheries Research Institute , show that trace metals are accumulating in mussels on the west coast. By comparison, changes to the environment as a result of other effluent discharges have been found to be surprisingly low and are generally limited to the immediate vicinity of the discharge. Table 4.3 illustrates the pattern of fish harvesting per species in South African waters during the period from 1938 to 1997. The peak harvest is highlighted in bold.
Trends indicating the levelling of stock are also apparent and are indicated in italics.
Demersal fish stocks quantified in Table 4.3 exhibit a stable pattern of resource harvesting throughout the time series. This can in part be attributed to the effective control and management of the fishery within South Africa's Exclusive Economic Zone. The pilchard, anchovy and redeye exhibit a decreasing trend of catches over the years which is caused by over- fishing coupled with adverse environmental conditions. The great fluctuation in the anchovy catch is a feature of the species which reaches sexual maturity within the first year of its life. As a result, annual catches have decreased from 6930 tonnes in 1978 to 2582 tonnes in 1997.