370 OCEANOGRAPHY IN THE UNITED STATES 



the marine resources of the North Pacific, characterized by the im- 

 portant salmon stocks of northern waters and the tuna resources of 

 the tropical Pacific. 



The Bureau's tuna investigations based in the Hawaiian Islands 

 have made some significant contributions to fishery oceanography. 

 For example, early cruises discovered a region of divergence near the 

 equator in midocean along which an upwelling of nutrient-rich water 

 from mid-depths occurred. Biological investigations showed that this 

 water was rich in plankton, and it was concluded that exploratory 

 longline fishing for tuna might be profitable here. Exploratory cruises 

 located deep-swimming yellowfin tuna in commercial quantities in the 

 region between the equator and the equatorial countercurrent. 



Of even more far-reaching importance was the recent discovery of 

 a major ocean current in the Pacific equatorial region. The existence 

 of this current was first realized by a Bureau scientist in attempting to 

 explain the contrary drift of a ship and its experimental fishing gear. 

 Subsequent surveys revealed that this hitherto unsuspected current 

 is one of the major oceanic currents, ranking with the Kuroshio and the 

 Gulf Stream in magnitude. More than 3,000 miles long, flowing at 

 more than 3 knots in its center, at a depth of 300 feet, and carrying 

 more than a thousand times the volume of water discharged by the 

 Mississippi River, this deep ocean river is not evident at the surface. 

 Its discovery will lead to a vast improvement in our understanding 

 of the circulation of the Noi-th Pacific Ocean, and so to a better knowl- 

 edge of the movements and distribution of the major fishery resources. 

 In honor of its discoverer, this has been nam«d the Cromwell Current. 



But there is much that we do not know about the effect of currents 

 on marine life. Our work has shown, for example, that salmon from 

 Alaska spread throughout almost this whole region north of the 

 Aleutian drift, intermingling with salmon from Asian streams. Yet 

 by some unknown sense, when spawning time approaches, they un- 

 erringly find their way back in opposite directions, over thousands of 

 miles of ocean, to streams on opposite sides of the Pacific. We are 

 entirely ignorant of the part currents play in this almost incredible 

 countermigration. 



In the Atlantic and Gulf of Mexico, we have some equally fascinat- 

 ing problems. Perhaps the most famous is the story of the American 

 and European eels, which undergo migrations even more striking than 

 Pacific salmon. Both eels spawn in the open Atlantic in the region 

 of the Sargasso Sea. Then, as delicate, transparent larvae, their 

 progeny find their way back to coastal rivers and streams, one species 

 to American shores, one to Europe — presumably carried by the clock- 

 wise current system. Their rates of development are so adjusted to 

 the timing of the current drift that the American species transforms 

 to the elver stage just as it reaches American streams. The European 

 species, on the other hand, takes much longer to reach its native 

 streams, and its larval development is extended accordingly. From 

 beginning to end of this journey, the larval eels drift with the major 

 ocean currents. 



Equally interesting^ are the migrations of shrimp, menhaden, and 

 many other coastal fishery resources of the South Atlantic and gulf 

 coasts. These species are similar in that they spaAvn in the ocean, 

 usually not far offshore, and the delicate transparent young somehow 



