determination of salinity (Van Landingham 1957). 

 Results are incorporated in the BT sommaries. 

 A plot of surface salinities collected on cruise 

 33 of the John R. Manning and cruise 31 of the 

 Charles H. Gilbert is shown in figure 13. 



Phosphate 



Samples for inorganic phosphate determi- 

 nations were usually taken at approximately 90- 

 mile intervals.-!^ The samples were frozen at 

 sea, returned to the POFl laboratory, and ana- 

 lyzed by the hydrazine sulfate modification of 

 Deniges' method (King et al. 1957). Results (in 

 ^i.g at./L) are incorporated in the BT summaries. 



Light Penetration and Water Color 



Weather permitting, Secchi disk observa- 

 tions were made each day about local apparent 

 noon. Water color was estimated using the 

 Forel scale. Results are listed in tables 4, 7, 

 and 10. 



Photometer measurements, at 50-, 10-, 

 5-, and 1 -percent levels of transmission, were 

 made in addition to the above on JohnR. Manning 



cruise 32 and Charles H. Gilbert cruise 31.^/ 

 Results are listed in tables 4 and 10. 



Photometer Description 



The photometer— used by POFI consists of 

 a deck and sea unit, each housing a matched 

 photoelectric cell. Opal glass shields over the 

 photoelectric cells serve to diffuse the light 

 normal to the windows of the cells. The amount 

 of light incident upon a cell is registered by a 

 microammeter. 



Before lowering the sea unit into the water 

 both cells are directly exposed to sunlight on 

 deck and the ammeter readings are checked to 

 note any failing in the photoelectric cells. The 

 desired 1 e v e 1 of transmission is selected by 

 placing a metal disk, with a hole in the center, 

 over the opal glass shield of the deck cell. Disks 



— Samples were taken at approximately 

 30 -mile intervals on John R. Manning 32. 



— Except that on CharlesH. Gilbert cruise 

 31 observations were made only on the initial 

 northbound leg and measurements of the 50- 

 percent level of transnnission were not obtained. 



— Manufactured by Fred Schueler, 

 Albemarle, Massachusetts. 



with openings of various diameters are used in 

 accordance with the percentage transmission to 

 be measured. The sea unit is then lowered and 

 ammeter readings of both cells checked until 

 they are equal. The depth is determined from 

 the wire angle and the amount of wire out. 



When making observations care is taken to 

 prevent the deck cell (mounted in gimbal-rings) 

 from being shadowed by the ship's rigging and 

 superstructure. In some instances, however, 

 it was not possible to prevent the shadow cast 

 by the ship's hull from influencing the reading of 

 the sea cell. 



METEOROLOGICAL OBSERVATIONS 



Synoptic marine weather observations were 

 recorded daily at 0000, 0600, 1200, and 1800 

 GCT. The reports were transmitted to the U.S. 

 Weather Bureau at San Francisco, California, 

 or Honolulu, T. H. , as often as radio conditions 

 would permit. Observations are listed in tables 

 3, 6, and 9- 



RECORDS 



The following records were kept and are on 

 file at POFI, except as otherwise noted: 



Bait tank records [ Charles H. Gilbert 



cruise 31 only] 

 Barograph records (U. S. Weather Records 



Center, Asheville, N. C.) 

 Bathythermograph log sheet "B" (duplicates 



at U. S. N. Hydrographic Office) 

 BT slides (U. S. N. Hydrographic Office) 

 Deck log 



Field plots of BT temperatures 

 Flowmeter and plankton sampler calibra- 

 tion log 

 Gill net record sheets 

 Light station fishing log 

 Occurrence of tuna schools, birds, and 



aquatic mammals log 

 Photonneter log [ John R. Manning cruise 



32 and Charles H. Gilbert cruise 31 only] 

 Plankton log 

 Scientists' log 



Short form tuna morphometric sheets 

 Standardized surface trolling data sheet 

 Tagging record sheets 

 Thermograph records 

 Track charts 



Tuna condition - vessel report 

 U.S.W.B. Form 1210F (U. S. Weather 



Records Center, Asheville, N. C.) 



