IT has been argued that the reason for going into space is to obtain a better look at our own planet. One of the specific projects of NASA will be remote measurement of phytoplankton chlorophyll in the world's oceans, the practical use of this measurement most often mentioned relating to pelagic fisheries. A proponent is Dr Maurice Blackburn of Scripps Institution of Oceanography, who argues that the detection of phytoplankton concentrations by the measurement of chlorophyll may increase the efficiency of the tuna fisheries by reducing the scouting time necessary for the fishing fleet. Blackburn's arguments are based on a rather simple hypothesis that the distribution of a pelagic fish such as the tuna is controlled by water temperature and the availability of food1. His group has tested this hypothesis in an area off Baja, California, where large schools of tuna concentrate, feeding primarily on a red crustacean. The crustaceans in turn feed at least partially on the phytoplankton, which are abundant in this area. There is some feeling among fishery biologists that the Baja case may be an exception. Also, if the energy change through the food web is higher than the generally accepted value of 10%, small fluctuations in primary production observed in the open ocean may be too small to explain the yield of a particular fish or its distribution2. As Blackburn points out, tests with pelagic fishes are not easily arranged. The opportunity for testing the hypothesis in the Atlantic Ocean occurred when the research vessel Delaware made an exploratory fishing cruise across the North Atlantic Ocean, roughly between the Azores and the North American coast3.