A Policy Failure Analysis of Salmon Enhancement Programs

Hilborn, R. (1975). A Policy Failure Analysis of Salmon Enhancement Programs. IIASA Working Paper. IIASA, Laxenburg, Austria: WP-75-011

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Abstract

The Canadian government has established a policy of enhancing natural salmon runs on the west coast. The basic concept of enhancement for commercial species is to provide additional artificial spawning grounds. In effect this creates new salmon stocks. The Fulton River spawning channels are the best example currently in operation; more such developments are being considered. There are several potential problems with such stock enhancement facilities. In this paper I wish to consider long range problems associated with achieving an optimal exploitation of both enhanced and natural stocks. I have discussed this problem earlier and used a deterministic model to find what would happen to a natural salmon stock being harvested simultaneously with an enhanced stock with a higher productivity. Briefly, the problem is that in order to optimally harvest the combined stocks, the natural stock (with a lower productivity) would be kept at lower stock levels, thus subjecting it to a higher probability of random extinction. This concept is summarized in figure 1, which shows the equilibrium stock level of the natural stock when a combination of natural and enhanced stocks are harvested at maximum sustained yield. The larger and more productive the enhanced stock is made, the lower is the equilibrium size of the natural stock.

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