25 



returns for these years are being published in a Fish and 

 Wildlife Service Special Scientific Report. These releases 

 and recoveries reflect the lower winter velocity of the surface 

 current system near the Hawaiian Islands and the predominant 

 drift to the northwest which prevails in winter. The seasonal 

 changes Indicated coincide with seasonal changes in the 

 strength of the trade-wind system. 



Drift card returns showed certain interesting and important 

 features of the currents near the islands, such as a large eddy 

 to the southeast of Oahu. Such eddies have profound effects 

 on the distributions of temperature and other properties of 

 the water, as well as on the movements of the small organisms 

 that form the major sources of food tor the commercially 

 valuable tunas. 



To learn more about these eddies, two cruises were made 

 in 1963 in which the currents were measured directly by the 

 Laboratory research vessel Charles H. Gilbert . This was 

 done by attaching a parachute, which acts as a sea anchor, to 

 a surface float equipped with lights and a radar reflector. 

 Nine such drogues were put out during the cruise made in 



FtAKlBntHMiSKlLF 



RELEASES & LONG-RANGE RECOVERIES 

 OF DRIFT BOTTLES & CARDS 



/ 





April (fig. 33). The drogues were placed in the northern part 

 of what is clearly alarge counterclockwise eddy. The drogues 

 toward the outer edge of the eddy moved at speeds of almost 

 2 knots, while those near the center moved at half a knot or 

 less. The eddy appeared to rotate at the rate of 1 revolution 

 in about 8 days and to move westward at about 7 miles a day. 

 The eddy was at least 50 miles in diameter. In August 1963, 

 an eddy of about the same size was found 100 miles farther 

 east and followed with drogues. It rotated more rapidly, 

 making about 1 revolution in 5 days, and its center appeared 

 to be stationary. 



A topographic scale model of the Hawaiian Islands and the 

 ocean floor surrounding them was designed and used to study 

 eddies near the islands and other phenomena associated with 

 the effects of the islands on the ocean nearby. The model is 

 4 feet wide, 8 feet long, and 1 foot high. It is placed in a large 



RELEASES t RECOVERIES OF 



DRIFT BOTTLES t CARDS 



JANUARY - MARCH 



Figure 31. — Long-distance releases and recoveries 

 of drift bottles. 



Figure 32. — Releases and recoveries of drift cards 

 and drift bottles near the Hawaiian Islands, 

 January through March in 1961, 1962, and 1963. 



