The information now available on seabird diets is largely presented in terms of the number and volume of various prey species taken. Whereas these data provide the relative importance of prey, fishery data on prey stocks are usually measured in terms of biomass. Thus, it is difficult to relate seabird data to the immense wealth of information on biological oceanography. If we are to recognize the importance of seabirds in the nutrient and energy cycling of marine ecosystems, rather than considering them merely as "yo-yo predators," we must relate them to the total marine community.
The goal of marine ornithologists should be to refine and broaden considerably in detail such studies as those by Sanger (1972), Shuntov (1974), and Laws (1977), who attempted to assess the relations between seabird populations and stocks of other marine organisms for the northern North Pacific, the world oceans, and the Antarctic, respectively. The trophic roles played by seabirds must be studied in detail at the community level year-round before those analyses can be properly refined. Another exemplary work is that done by Brownell (1974), who studied trophic relations of higher vertebrates off Uruguay, including dolphins, pinnipeds, seabirds, and some large fish. In a review study, Sanger (1974) considered the food-chain relations of similar vertebrates in the Bering Sea. These sorts of studies will serve to bring the role of seabirds into perspective with other upper trophic level feeders.
We much appreciate the opportunity to participate in the symposium at which this paper was presented. The encouragement and help given by J. C. Bartonek was indispensable. D. G. Ainley's participation in the symposium was supported by the Point Reyes Bird Observatory. This is contribution No. 124 of the Point Reyes Bird Observatory.
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