200 300 400 



BATHYTHERMOGRAPH DEPTH IN FEET 



Figure 6. --Calibration of chemical sounding tubes with bathythermo- 

 graph on John R. Manning cruises 22 and 23. Each point denotes 

 readings obteiined frona one lowering of the BT with sounding tube 

 attached. 



attached to the proximal end of the deepest branch 

 line (number 7) on 2 to 4 baskets at 31 stations 

 during Manning cruises 22 and 23. They were 

 placed on centrally located baskets of the 5- and 

 15-fathom floatline gear in order to avoid atypi- 

 cal measurements from the end baskets. 



Table 7 (a, b) gives the depths recorded 

 on the two cruises for both the 5- and 16-fathom 

 floatline gear. On^ cruise 22 the maxinnum depth 

 for the 5-fathom gear ranged from 306 to 504 feet 

 and averaged 405 feet. The 15-fathom gear fished 

 deeper, averaging 432 feet with a range of depths 

 from 336 to 450 feet. On cruise 23 the difference 

 was more pronounced, principally because the 5- 

 fathom gear was set without the usual slack. The 

 5-fathom gear averaged 328 feet and ranged from 

 222 to 504 feet. The 15-fathom gear fished about 

 80 feet deeper, averaging 410 feet and ranging 

 from 288 to 522 feet. 



The sdbacore catches by relative depths 

 of capture are given in table 8. In general, alba- 

 core were caught in approximately equcil numbers 



throughout the range of fishing depths, a dif- 

 ferent situation from that in the equatorial 

 region, where they are taken in the greatest 

 numbers on the deepest hooks (Murphy and 

 Shomura 1953b). This difference in the ver- 

 tical distribution of the North Pacific albacore 

 and equatorial albacore may be associated with 

 the difference in water temperatures between 

 the two areas. The water temperatures which 

 occur at the surface in the North Pacific are 

 found in the deeper layers near the Equator; 

 e.g., the 60 F. isotherm which is at or near 

 the surface in the North Pacific is located at 

 depths exceeding 500 feet in equatorial waters 

 (Murphy and Shomura 1953a, b). Thus even 

 near the Equator, where albacore exist in size- 

 able numbers, they appear to occupy a similar 

 environment temperature-wise as they do in 

 the northern region. 



A comparison of the maximum depth of 

 fishing, the depth of the thermocline, and the 

 albacore distribution by relative hook depth 

 indicates that albacore may possibly be foraging 



13 



