138 EIGHTH PACIFIC SCIENCE CONGRESS 



ILLUSTRATIONS 



Figure 1. — Hydrogi-aphic stations occupied by the U.S. Fish and Wildlife 

 Service vessel HUGH M. smith for the investigation of equatorial cir- 

 culation, January 1950 to February 1953. 



Figure 2. — Longline fishing stations occupied by the U.S. Fish and Wildlife 

 Service vessels HUGH M. smith, John r. manning, and Charles h. gil- 

 bert, and the m/v cavalieri (chartered) for investigating the distribu- 

 tion of tuna, October 1950 to March 1953. 



Figure 3. — Direction of current transport (Small solid arrows), which would 

 exist near the equator under various wind conditions, were there no 

 pressure gradient force acting. The current magnitude is drawn every- 

 where constant (small solid arrows) . For e,ach wind condition (large 

 solid arrows) the meridional components of the current transport (dotted 

 arrows) are drawn to emphasize the regions of meridional divergence 

 (Div.) and convergence (Conv.). From Cromwell's ms. Figure 6. 



Figure 4. — The Fish ^and Wildlife Service research vessel hugh m. smith, 

 a tuna-clipper type to which have been added laboratory, winches, and 

 other special instruments for oceanographic research. 



Figure 5. — Location of the hydrographic and the fishing stations of hugh 

 M. smith Cruise 11, August 20 to October 6, 1951. 



Figure 6. — Diagrams of certain data resulting- from the southbound passage 

 on HUGH M. smith Cruise 11 along the 150th west meridian, August 

 24 to September 25, 1951. A. Temperature section showing the water 

 layer warmer than 26.7°C (unshaded), between 26.7°C and 15.6°C 

 (shaded) and colder than 15.6°C (black), as taken from bathythermo- 

 graphs. B. Direction of drift of longline gear at each fishing station. C. 

 Volume of zooplankton taken in a plankton net of one meter in diameter 

 at the mouth and towed obliquely for approximately one-half hour through 

 the upper 200 meters of water in the daytime. Volumes were measured 

 by displacement and adjusted to a standard quantity of 1000 cubic meters 

 of water strained based on flow determined by a current meter installed 

 in the mouth of the net. D. Eate of catching yellowfin in number per 

 hundred hooks per day fishing as determined by fishing 40 baskets of gear 

 each comprised of 210 fathoms of longline suspended by 10-fathom float- 

 lines and bearing 6 hooks spaced 30 fathoms apart and suspended by 

 10-fathom droppers. 



Figure 7. — Diagrams of certain data resulting from the northbound passage 

 on HUGH M. smith Cruise 11 along the 150th west meridian, Septem- 

 ber 25 to October 4, 1951. A. Temperature at the sea surface. B. Tem- 

 perature section showing the water layer warmer than 26.7 °C (un- 

 shaded), between 26.7°C and 15.6"C (shaded) ,and colder than IS.e^C 

 (black), as taken from bathythermographs. C. Phosphate section show- 

 ing water with less than 0.4 microgram atoms per liter (unshaded) be- 

 tween 0.4 and 1.0 microgram atoms per liter (shaded) ,and more than 

 1.0 microgram atoms per liter (black). D. Volume of zooplankton taken 

 and treated as stated in the title of Figure 6, except that the hauls were 

 made ,at various hours of the day and night and received further ad- 

 justment for diurnal variation according to the foi*mula: V^ = antilog 



