Guano
Peruvian guano beds are currently being managed on a sustained-yield basis; the harvest, as in the days of the Incas, depends entirely on the amount of guano deposited each year. Conservation and management policies have resulted in a steady increase in the amount extracted, from around 20,000 tons in 1900 to over 200,000 tons in 1971 (Lockley 1973).
The islands off south and southwest Africa are also commercial producers of guano. The annual yield from these breeding colonies averaged 3,971 tons in the 12-year period, 1961-72. In 1969, guano brought 4.75 Rands (equivalent to $7.11) per 200-pound bag. South African gannets are apparently depositing guano that is worth twice as much as the fish they consume to produce it (Jarvis 1971).
Indirect Commercial Benefits
Marine birds also play significant roles in the economies of the world's oceans, where algae, invertebrates, fish, seabirds, mammals, and man interact in complex ways. The bioenergetics and nutrient cycling in ocean ecosystems is even less well understood than the contributions seabirds make to man's dollar economies.
Sanger (1972) has conservatively estimated that in the subarctic Pacific region alone, birds consume from 0.6 to 1.2 million tons of food and return from 0.12 million to 0.24 million tons of feces each year.
Marine bird excrement is especially rich in nitrates and phosphates, which phytoplankton, the basis of ocean food pyramids, requires. Marine birds then, at least to some extent, help to sustain the northern commercial, recreational, and subsistence fishing industries. The fisheries in turn sustain seals and certain other mammals which are also essential elements of northern subsistence and recreational economies. Thus, marine birds contribute economic benefits indirectly as well as directly by serving as critical links in ecosystem food chains (Tuck 1960).
Subsistence Uses
The use of marine birds and their products does not have to be commercial to be economic. Economics is the science of the allocation of scarce resources. Any resource, regardless of whether it is bought or sold, has value to people and is therefore an economic commodity. Thus, any society has an economy whether or not it uses cash, and when the meat, feathers, or oil of marine birds are used, the birds have economic value. The problem, of course, is that of trying to determine just what this value is when a cash medium does not exist.