What is overfishing?

Three quarters of all marine fish stocks worldwide are deemed fully exploited or overfished. Overfishing means in any case that over time fishing yields are lower than they could be. Several fish stocks have even collapsed under fishing pressure, that means, despite very great fishing effort hardly any fish can be caught. Researchers expect that more stocks may collapse unless fisheries management and policy change substantially.

Overfishing leads to high yields only in the very short run. In the long run, an overfished stock yields only few and small fishes, for two reasons. Firstly, fish are harvested before they are mature and can reproduce, and secondly, an overfished, thus smaller, stock reproduces more slowly than a stock that is fished to a lesser extent and hence bigger. Under better management the oceans could contribute much more to the human food supply than they presently do. In a report, published in 2008 the World Bank estimates that, with better management, marine fisheries worldwide could generate an additional benefit of US$50 billion annually over the long run.

Better management could increase long-run yields
The basic problem that leads to overfishing is that fishes in the oceans belong to nobody. Thus, fishermen have an economic incentive to catch as large a share of the decreasing yields as possible. For that sake they spend a very high effort (vessels, fishing gears, labor) by which (i) too many and too small fishes are caught, (ii) marine ecosystems are damaged to a greater extent than necessary and (iii) on top of that is economically much more expensive than efficient.

More stocks will collapse unless policy changes to the better
Some stocks have been fished so heavily that they will not recover in the long-run – they are collapsed. A prominent example is the formerly very large stock of cod off the east cost of Newfoundland. These stock collapsed in the early 1990th and did not recover since then. Hence, they do not generate fishing yields any more. The Newfoundland cod fishery has been closed completely in 2003 (http://www.millenniumassessment.org/). It is estimated that a further stocks are close to collapse, as with highly efficient fishing technologies it is profitable to harvest those fishes even at very small stocks. This holds in particular for schooling fishes like, e.g., herring or anchovies.

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