FIGURE 28 - OCEANOGRAPHIC EQUIPMENT USED IN 1950 TUNA EXPLORATION. A. WATER SAMPLE 

 BOTTLE. B. SURFACE THERMOMETER HOLDER AND WATER SAMPLER. C. MESSENGER USED TO 

 TRIP THE REVERSING WATER BOTTLE. D. BATHYTHERMOGRAPH AND ACCESSORIES. E. WATER 

 BOTTLE WITH REVERSING THERMOMETER HOLDERS ATTACHED. 



Subsurface temperatures were recorded v/ith a batliythermOi;raph (see 

 fig. 28) having a vertical depth range of 450 feet. This instrument, used for 

 measuring and recording vrater temperature versus depth, is essentially a metal 

 tube housing pressure and thermal units. The thermal element is a 45-foot, coiled 

 capillary tube filled with a fluid, xylene, which reacts rapidly to any change in 

 temperature. A pen ann and a stylus are attached to the capillary tube end to re- 

 cord the temperature variations. The pressure element consists of an evacuated 

 bellows which tends to compress with increased water pressure due to increased 

 depth. In operation, a plain smoked slide is inserted in the holder at the end of 

 the bellows and below the stylus, Vi'hen the unit housing the slide is closed, the 

 stylus is depressed and a continuous record cf water temperatures at all depths 

 within the instruLient ' s range can be recorded on the slide. The bathythermograph 

 is attached to the sounding wire and loivered over the side. The operation of lower- 

 ing and raising, the instrument was usually carried out while trollingj however, 

 during choppy or roug}i v/eather the vessel's speed was slov;ed to facilitate opera- 

 tion. A bathytheriaograph cast can be completed v/ithin a few irdnutes under normal 

 circujtistances. The slide is removed after each lov;ering of the instrument and 

 lacquered to preserve it for future examination. The bathythermograph was lowered 

 by means of an electric sounding winch located en the starboard side of the upper 

 deck. The winch carried 400 fathoms of 3/32-inch steel wire, spooling 50 fathoms 

 of wire a minute. 



Surface Distribution 



Results of several years of observations by coiiimercial fishermen and re- 

 search workers indicate that the main barrier directly or indirectly influencing 

 the distribution of albacore throughout their northern range is water temperature. 



36 



