Fish Population Dynamic and Stock Assessment

10.4.4.1. Conservation

Since the occurrence of widespread public acceptance of the facts that fishery resources are exhaustible and that controlled fishing is essential for conservation, fishery scientists have been asked how much and what kind of fishing should be allowed. They have been studying the dynamics of wild animal populations since early in this century. The most useful concept they have developed is that of Maximum Sustainable Yield (MSY), a value that can be calculated in various ways if the fish stock is assumed to be in a steady state.

After successful application of MSY’s to some relatively stable fisheries, the concept was widely accepted as an objective for fishery regulation. But regulation according to the MSY concept does not always protect the stock or satisfy the users. Some very large stocks have collapsed while being regulated under the concept; the assumption of a steady state was invalid. Some commercial fisheries have become uneconomical even though the stocks have been sustained at maximum levels. And maximum catches do not reflect the concept of a quality experience for most groups of recreational fishermen.

The objective of regulating fisheries for MSY has been abandoned, although MSY continues to be a useful computation during the assessment of the condition of fish stocks. Instead, MSY is modified by biological, economic, social and political values in order to produce the maximum benefit to society (Roedel, 1975). The resulting objective, called optimum yield (OY) may be (1) equal to MSY in some stable commercial fisheries used entirely for food, (2) zero catch for an endangered species or a species in a fragile environment, (3) near zero if the species is an essential food for a more desirable species, (4) a moderate fraction of MSY in order to produce fish for a recreational stock, and (5) a catch rate greater than MSY if the species is an unavoidable component of a multispecies fishery.

International acceptance of OY as the meaning of conservation came about at the Convention of Fishing and Conservation of the Living Resources of the High Seas that was negotiated at Geneva in 1958, but this was only one step toward a comprehensive Law of the Sea that required many more years to negotiate.

Throughout the decade of the 1970s a new and comprehensive Law of Sea was negotiated, and the fishery provisions of that law have been widely accepted. The major thrust of the law gives coastal states authority over fishing and fishery resources out to 200 mi and the obligation to conserve the resources on the basis of scientific studies and in collaboration with neighboring states.

National fishery laws preceded the New Law of the Sea by thousands of years, with many objectives other than conservation. The conservation objectives that have been developed around the concept of OY in the Law of the Sea have been or will be adopted by most countries. But the other objectives of fishery regulation are constantly before the fishery agencies and may be their major activity.