August 1966 



COMMERCIAL FISHERIES REVIEW 



23 



other sound was named the "unh." It is "a 

 grunt-like sound that occurred when the yel- 

 lowfin flexed its body to avoid an obstacle." 

 It was believed that the "unh" nnight well be 

 used as a means of communication between 

 yellowfin. In a school about j nnile across, 

 such a signal need be relayed only 25 times 

 to cover the distance. 



The Bureau scientist who conducted the 

 experiments presented his results at a Sym- 

 posium on Marine Bio-Acoustics at the Amer- 

 ican Museum of Natural History, New York. 

 His paper was to be published in the Pro- 

 ceedings of the Symposium. These studies 

 are now being extended to other species of 

 tuna. 



Note: See Commercial Fisheries Review , July 1965 p. 20. 



* 



* * * 



OCEANOGRAPHIC RESEARCH PROJECT 

 CONDUCTED SOUTH OF 

 THE HAWAIIAN ISLANDS: 



M/V " Townsend Cromwell " Cruise 22 

 (February 10-March 5, 1966): To study the 

 wake system downstream of the Hawaiianls- 

 lands, locating the major eddies that make up 

 this system an5 determining their apparent 

 origin while studying the changes in salinity 

 and temperature distributions in the area of 

 the wake, was the main objective of this cruise 

 by the research vessel Townsend Cromwell . 

 The vessel is operated by the Bureau's Hon- 

 olulu Biological Laboratory. The area of 

 operations was south of the Hawaiian Island 

 chain, within the area bounded by latitude 17° 

 to 22° N., and longitude 156° to 162° W. 



Other objectives of the cruise were to: (1) 

 look for and record any association between 

 fish schools and bird flocks and the wake sys- 

 tem, and (2) release drift cards and bottles 

 in the cruise area. 



During the first part of the cruise, a large 

 cyclonic (counterclockwise) eddy was found 

 just west of the island of Hawaii, together 

 with 3 smaller anticyclonic eddies to the south 

 and west of Hawaii, and 1 or 2 minor, ill-de- 

 fined cyclonic eddies to the northwest. 



The second part of the cruise was devoted 

 to a detailed study of the largest eddy and its 

 smaller neighbors to the south and west. A 

 total of 26 salinity-temperature-depth (STD) 

 casts was made, to determine salinity and 

 temperature within and between these ed- 

 dies down to 1,000 meters (3,281 feet) and 



permit calculation of dynamic topography; 

 details of the thermal structure were studied 

 by means of the bathythermograph (BT). 



Watches were kept for bird flocks and fish 

 schools throughout the cruise. As in previ- 

 ous cruises of this series, no clear-cut asso- 

 ciation could be detected between the occur- 

 rence of flocks and schools and the details of 

 the eddy system. 



A total of 1,224 drift bottles and 1,250 

 drift cards were released during the cruise; 

 thermograph and barograph were operated 

 continuously; standard inarine weather ob- 

 servations were made; and pyranometer was 

 operated during daylight hours. 



The largest eddy, associated with a pro- 

 nounced dome in the thermocline, was found 

 to be stationary throughout the cruise; it was 

 probably the same eddy which was detected 

 during a January cruise by means of BT casts 

 made in the same area. If so, its lifetime 

 in its original position was at least 2 months 

 and perhaps longer, since it showed no signs 

 of either growth or dissipation during the 

 interval. 



On the other hand, the smaller cyclonic 

 eddies to the south, which are associated 

 with depressions in the therm.ocline, were 

 found to travel westward at speeds of the 

 order of 5 miles per day. Since these eddies 

 occur at regular intervals --about 120 miles 

 apart- -if the system is at or near equilibri- 

 um, one such eddy must be generated up- 

 stream every 3 weeks or so. 



The origin of the anticyclonic "domes" 

 appears to be the area in the lee of the is- 

 land of Hawaii; the vorticity represented by 

 such eddies is apparently generated by cur- 

 rents flowing west through Alenuihaha Chan- 

 nel, between Hawaii and Maui. The origin of 

 the cyclonic "troughs" is less apparent. They 

 seem to occur too far south, and east, to be 

 due to the sheltering effect of the island of 

 Hawaii. It is likely that such eddies are gen- 

 erated in the velocity shear which occurs 

 north of the core of the North Pacific Equa- 

 torial Current (NPEC); indeed, the eddies 

 may mark the northern edge of that current 

 whenever the NPEC does not intercept the 

 Hawaiian Islands. 



Marked surface currents (0.5-2.0 knots 

 or more) occurred in conjunction with each 

 of the eddies, as was evident from the drift 



