The Pacific sardine resource, which once supported an important American fishery, declined abruptly in the late 1940's and early 1950's, and the fishery is now defunct. Scientific research during the peak of the sardine fishery and subsequent to the decline has demonstrated fairly clearly that the cause was overfishing, fluctuations in abundance from natural causes, and invasion of the vacated niche by the Pacific northern anchovy. It has been concluded that it may not be possible to harvest a sustainable yield from a highly fluctuating resource like the Pacific sardine, for the reduced population will yield available energy to other ecologically similar species. Thus, the concept of a broad resource base made up of several species may be essential to the economic viability of most fishing industries. Perhaps the best documented example of the effect of selective fishing on the ecology of a large body of water is the history of the fishery resources of Lake Michigan (SMITH 1968). About twenty years later the Atlantic menhaden fishery went through a remarkably similar cycle. The northern fishery is virtually defunct, but the southern fishery is still in operation. The total annual catch now is a little more than one-third as large as the average catch from 1953 to 1962. Although it has not been demonstrated that the Atlantic menhaden resource is overfished, it might be prudent to borrow from the experience of the sardine industry and develop management plans accordingly. An important consideration would be to determine as soon as possible which species in the environment of the menhaden are utilizing the energy released by the decline of the resource. It is unlikely that fishery management in the ocean will ever be generally successful if action is postponed until absolute proof of overfishing is available.