Gill nets were employed successfully by 

 the Gilbert (cruise 23) on the first leg of the 

 cruise, on 165°W. longitude, but their use was 

 restricted by bad weather on the second leg, on 

 145'W. longitude (fig. 3). Of four catches made 

 only one contained more than a single albacore 

 and this consisted of 8 fish taken at 43°22'N, 

 latitude, 164°40'W. longitude. All of the fish 

 except one were properly gilled in the nets. Bad 

 weather also restricted longlining on the second 

 leg of the cruise, allowing only 3 sets; all were 

 either north or south of what is considered "alba- 

 core water." A single deep-swimming albacore 

 was taken at 41''40'N, latitude, 164'29'W. longi- 

 tude (fig. 3). 



Briefly, within the areas surveyed (table 

 1, figs. 1, 2, eind 3) albacore were scarce in 

 the central and eastern North Pacific during the 

 late spring and were abundant during the late 

 summer. The summer distribution was probably 

 discontinuous, with concentrations in the central 

 and eastern North Pacific sectors and a lack of 

 fish in between. During the fall albacore were 

 relatively abundant in this intervening area, 

 suggesting that the discontinuity was either a 

 transient condition or had diminished somewhat 

 with the change in season. 



ENVIRONMENTAL CONDITIONS 



a more southerly latitude, 28''56'N.. Ug'OT'W. 

 longitude. The latter catch was considerably 

 south of the areas of low transparency, Sunnmer 

 catches showed a nnuch closer association with 

 the Polar Front in that they were within or 

 adjoining areas of relatively low transparency. 

 To the west of 155*W. longitude the front extends 

 roughly east and west in a narrow band, but 

 east of this longitude the front curves southeast 

 and loses much of its continuity. A positive 

 association of albacore surface catches and the 

 Polar Front is suggested in this instance since 

 catches to the west of 155°W, longitude were 

 made within a narrow range of latitude, while 

 those to the east showed an extended distribution. 

 Fall conditions with a drop in surface tempera- 

 ture set in during cruise 23 of the Gilbert ; 

 albacore were taken roughly between latitudes 

 42°30'N. and 46'00'N. along longitude IbS'W. 

 and from 40°00'N. to 48°00'N. along longi- 

 tude 145°W. As in previous catches, these 

 were taken along the Polar Front. 



Deep-swimming albacore were sampled 

 exclusively with longline gear. Tenaperature 

 profiles and the approximate depth of the gear 

 fished suggest that most catches were made in 

 areas of abrupt temperature change, which were 

 probably subsurface manifestations of the Polar 

 Front (figs. 5-8 of the Appendix). 



The association of albacore catches with 

 the Polar Front has been reported by Shomura 

 and Otsu (1956). This boundary or transition 

 zone between central and subarctic waters is 

 probably a more or less constant source of 

 enrichment to the surface waters (McGary and 

 Stroup 1956) as indicated by the occurrence of 

 relatively high concentrations of dissolved in- 

 organic phosphate. The relatively low trans- 

 parency of the surface waters may be evidence 

 of increased biological productivity. Super- 

 imposed on the Polar Front is a seasonal 

 latitudinal change in surface temperature. Pre- 

 vious results (Shomura and Otsu 1956) and those 

 reported below suggest that the movements of 

 surface albacore are coordinated with this shift 

 in temperature, particularly about isotherm 

 SS'F. to 65°F. 



Figures 1, 2, and 3 show that albacore 

 taken at the surface during the spring, summer, 

 and fall cruises were clustered about isotherms 

 55'F. to 65''F. and, especially during the latter 

 two seasons, were within or adjacent to areas 

 of relatively low transparency. In the spring, 

 the Manning (cruise 25) took a single albacore 

 along the 65°F. isotherm at 35°38'N. latitude, 

 165"W. longitude, and the Smith (cruise 29) 

 also took one along the same isotherm, but at 



SIZE COMPOSITION 



A comparison of size frequencies of 

 surface -caught albacore taken in the central and 

 eastern sectors of the North Pacific shows (fig, 

 4) that the same size ranges were sampled on 

 either side of the discontinuity in distribution 

 noted above. During the late summer at least 

 three size groups were present in both areas, 

 with modes at 50-55 cm. , 60-65 cm. , and 75- 

 80 cm. The Smith (cruise 30) captured only 7 

 albacore; their size range agrees roughly with 

 those taken by the Manning (cruise 26). While 

 the number taken by the Smith is too small for 

 adequate comparison, the size range of 52 alba- 

 core (fig. 4) captured at the surface in gill nets 

 west of 160°W. longitude by the Mitkof agrees 

 well with that of the Manning 's catch. A similar 

 agreement is indicated in the fall catches, where 

 the same three size groups are represented in 

 the eastern and central sectors of the North 

 Pacific, 



The size range of albacore taken in gill 

 nets by the Mitkof corresponds closely to those 

 taken on troll lines by POFI vessels. Such a 

 similarity between gill-netted and troll-caught 

 albacore is also evident in catches made by the 

 John N. Cobb (Powell et al. 1952) off the Oregon 



