Fisheries and Aquaculture

One of the greatest long-term threats to the viability of commercial and recreational fisheries is the continuing loss of marine, estuarine, and other aquatic habitats. Habitat considerations should receive increased attention for the conservation and management of fishery resources.....(US Congress). The conservation of fish habitat is an important component of building and maintaining sustainable fisheries.

A number of land-based waste products, notably nutrients and toxic pollutants, exert a direct effect on economically or culturally important fish-stocks. In most cases this is a negative impact, with reduced productivity, or losses of certain species, associated with declines in habitats , deoxygenation of the waters, or replacement of species with others of lower commercial value. In a few cases increases in nutrients have been reported to improve productivity: although evidence is still not clear, increased nutrient loading has been used to explain the continued high yields from the Mediterranean over the last century. The physiological impacts of some toxins on commercially important species are also a point of concern, notably the impacts of endocrine disruptors . (Pollution image courtesy of J. Everett)

Pathogens, toxic waste and toxins from Harmful Aquatic Blooms (HABs) have a major impact on fisheries, not only from the impact on human health, but from the closure of fisheries in contaminated areas. The losses in areas which are permanently polluted is hard to measure, however during periods of HABs, the economic losses have been calculated for a number of locations. A red tide in Hong Kong in 1998 caused losses of US$32 million from the closure of fish farms, whilst an algal bloom in Korea in 1991-2 was estimated to cost US$133 million. Solid waste also has an impact on fisheries, and is a regular source of complaint, notably from bottom trawlers who have to disentangle materials from their nets. The constant trawling and dredging operations have significant impact on the sea floor. It is similar to farming in that areas are cleared of rocks and obstacles, the terrain is leveled, and each succeeding year gear passess easier over the bottom. At the same time though, just as fields of wheat replace forests, trawlable bottom replaces coral heads and rock piles. The ecology of plants and animals is greatly changed. Some species gain an advantage and others lose. It is an issue being faced by an increasing number of countries.

 

Most concern is with inshore and coastal waters such as estuaries and bays. The open ocean is in relatively good condition. Nevertheless, one cannot travel far without seeing floating human debris, or picking up discarded materials off the sea-floor in a bottom trawl.