. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography "V*1"-":- J^4i^^ seraa .; vv'V rely upon fish and shellfish to convert the algae into food usable for man. On land we derive our food primarily at the first trophic level. That is, we eat starches and sugars derived directly from plants. Only the more wealthy nations such as the United States can afford to obtain much of its nourish- ment at the second trophic level—that is, eat cattle which, in turn, have fed on grass. But when we ea
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography "V*1"-":- J^4i^^ seraa .; vv'V rely upon fish and shellfish to convert the algae into food usable for man. On land we derive our food primarily at the first trophic level. That is, we eat starches and sugars derived directly from plants. Only the more wealthy nations such as the United States can afford to obtain much of its nourish- ment at the second trophic level—that is, eat cattle which, in turn, have fed on grass. But when we eat tuna, we are being nour- ished at the fifth trophic level. Tuna feed upon small fish, which feed upon euphausiids, which feed upon copepods, which feed upon algae (diatoms). There is a factor of ten loss of food value at each succeeding higher trophic level. Thus ten thousand pounds of algae are needed to generate one pound of tuna. For diis reason, the seas can never supply an abundance of inexpensive food. It can only supplement our basic carbohydrate diet with an excellent source of low-fat protein. Contrary to expectation, it apparendy is easy to overfish the oceans. Fishing grounds are highly localized, and most of the ocean is a biological desert. Examples of disastrous de- clines in fisheries are legion. A case in point was the virtual disappear- ance of the California sardine (actually a pil- chard) fishery after World War II. Overfishing was apparently an important factor in this disaster, but an ultimate understanding re- mains elusive. Studies by John Isaacs of the Scripps In- stitution of Oceanography have shown a re- markable fluctuation in fossil pilchard scales and teeth in the sediments of the basins off California. This indicates there may be a natural cycle of changing pilchard abundance. In the past few years there has been a cata- strophic drop in the catch of large bluefin tuna in the North Atlantic. These, the largest of all the tuna, sometimes weigh i
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