There is evidence of a rather wide vari- 

 ation in the depth of the deepest hooks among 

 sets within cruises. Although the method of 

 setting and retrieving the gear was standard on 

 cruise 2 7 of the JohnR. Manning, it can be seen 

 that the deepest hooks reached greater depths at 

 5° to 6°N. than near 1 "N. latitude (fig. 4). This 

 difference possibly resulted from the shear 

 between the westerly South Equatorial Current 

 at the surface and the easterly Equatorial Under- 

 current beneath. The Equatorial Undercurrent 

 is usually encountered within approximately 2 

 degrees of latitude of the Equator in the central 

 Pacific (Cromwell et al. 1954). These conclu- 

 sions are supported by the observed drift of the 

 gear and vessels on fishing stations. 



Differences in the depth of the deepest 

 hooks are as large as 40 fm. from north to south. 

 During October and November 1952, at stations 

 between 7 ° and 9 °N. latitude, Murphy and Shomur a 

 (1955) found mean depths for the deepest hooks 

 at about 300 ft., as measured by the echo-sounding 

 method, whereas we obtained a figure closer to 

 500 ft., employing sounding tubes in October 

 1955. At stations near the Equator we both found 

 the mean depth to be approximately 200 ft. Murphy 

 and Shomur a (195 3b, table 1 6) present data obtained 

 with "pressure gauges" on longline sets along 



NORTH LATITUDE 



CO 



Figure 4. --Latitudinjil variation in depth of the 

 deepest hook on longline sets, as determined 

 by sounding tubes, 157''48'W. - 161'57'W. 

 longitude, John R. Manning cruise 27, 

 October 1955, 



MAR APR 



MAY 



JUN 



JUL AUG SEP OCT NOV DEC 

 1955 



JAN FEB 



1956 



Figure 5. --Variation in average depth of the deepest hooks on longline sets in 

 relation to time of year, 1955-5 6. 



