374 OCEANOGRAPHY IN THE UNITED STATES 



fishes that inhabit the same waters. Major sardine spawning areas 

 are in the Gulf of California, off the lower California coast, and 

 off southern California. We have not studied the Gulf of California 

 intensively because the sardines there belong to a distinct subpopu- 

 lation that does not intermingle with the subpopulations on the ocean 

 coast. In the first 10 years of the surveys most spawning took place 

 in the southern area, but in 1957 and 1958, as we have already said, 

 the pattern changed, and about 80 percent of the spawning has been 

 in the northern area. At the same time, the abundance of sardines 

 off California has increased, so that the 1958 catch was the greatest 

 since 1951, and could have been greater if the fishery had not been 

 restricted. 



Spawning areas and nursery grounds of other important species 

 have been discovered by these surveys. Hake, anchovy, and jack 

 mackerel inhabit the same waters as the sardine, and compete with 

 each other for food. The eggs and larvae are small and delicate; for 

 example, the newly hatched sardine or anchovy is only about one-tenth 

 inch long. It must be very sensitive to changes in oceanographic 

 conditions, and, of course, is prey to a host of diseases and predators, 

 and subject to changes in abundance of its own food, too. 



SUMMARY 



These shreds of knowledge emphasize the fact that oceanography 

 is important in fishery investigations. How large are the tuna re- 

 sources of the world, and where and how can they be fished most 

 profitably? Wliat governs the movements of North American and 

 Asian salmon across the Pacific, and how can we prevent overfishing ? 

 What causes the great variations in success of Pacific sardine spawn- 

 ing, so that some spawnings produce as much as 100 times as many fish 

 as others ? How do menhaden and shrimp find their way inshore so 

 soon after hatching, and what oceanographic conditions affect their 

 survival? Why are some ocean regions rich in marine life, others 

 poor? These are only a few of the questions that oceanographic re- 

 search can answer. 



The wind pattern over the North Pacific has changed in the past 

 decade with stronger winds off the California coast and weaker winds 

 over the Bering Sea. What relation does this bear to the decline of 

 the sardine fishery, and changes in other Pacific fisheries? 



The temperature of the North Atlantic has increased substantially 

 in the past 100 years. Early records sliowed that mackerel landings 

 increased in warm periods, but catches dropped abruptly about 1890 

 and the fishery has failed to recover. Is the water now too warm 

 for mackerel? 



On a recent cruise off Georges Bank, our biologists found large 

 numbers of dead fish larvae in plankton samples. These dead were 

 all cold-water forms, and they were taken in an area where warm 

 and cold water met, with a 20° change in water temperature in 10 

 miles. Warm-water species in this same area were not affected. 

 These kills, if they occur at certain times, can affect fishing at some 

 later date. 



Studies of shrimp migrations in tlie Tortugas area, using a newly 

 developed method of marking with dyes, have shown tliat these ani- 



