FISHERY BULLETIN: VOL. 75, NO. 2 



Infrared radiation temperature measurements 

 made during an overflight by the Coast Guard 

 aircraft on 16 August showed that the water on 

 the cold side of the front continued to decrease 

 toward shore to values below 13.0°C. 



Fish number 4 traveled in about an 8 x 8 nmi 

 area on the warm side of the upwelling front and 

 in close proximity to it for nearly the total time 

 the fish was tracked. Subsequently, high winds 

 and rough seas made tracking difficult and the 

 signal from the fish was lost during hour 27 of 

 tracking. 



Fish number 5 exhibited a much different 

 pattern of movement than did number 4 (compare 

 Figures 2 and 3). It moved many miles from the 

 location where it had been tagged, in a general 

 northwesterly direction, rather than remaining in 

 the local vicinity as fish number 4 had done. 



Examination of oceanograhic data revealed 

 that marked changes in the distribution of sea 

 surface temperature had occurred between 17 and 

 19 August (compare Figures 2 and 3). Upwelling 

 had subsided, the upwelling temperature front 

 was no longer present on 19 August, and the 

 temperature over much of the area had increased 

 by about 1.5°C. The breakdown of the upwelling 

 front and warming was due to a slackening and 

 shifting of the winds to a westerly-southwesterly 

 direction which allowed a thin layer of warmer 

 offshore water to flow toward the coast. 



It is presumed that the school offish with which 

 fish number 4 was traveling remained in the 

 vicinity of the upwelling front to feed in the highly 

 productive water associated with the upwelling. 

 Measurements of chlorophyll were high in the 

 tracking area and showed a very strong positive 

 gradient on the cold side of the upwelling front 

 (Figure 5). Measurements of 14 C uptake indicated 

 a primary production rate integrated over the 

 euphotic zone (0 to 36 m) of 1 ,5 1 1 mg C/m 2 per day. 

 The biomass of potential albacore food organisms 

 was also high, ranging from about 20 to 56 

 ml/1,000 m 3 water strained, in midwater trawl 

 collections made at night in the nearby area 

 where tracking took place (Table 4). 



Albacore were frequently seen boiling in the 

 area nearby the upwelling front by personnel 

 aboard Linda and David Starr Jordan. Also, 

 observers aboard the Coast Guard aircraft noted 

 about 25 to 30 commercial albacore jig boats 

 fishing immediately on the warm side of the front 

 in water warmer than 15.0°C. High biological 

 production in the area of the upwelling front was 



q ystf 



FIGURE 5. — Movements of albacore number 4 as indicated by 

 ultrasonic tracking and the distribution of surface chlorophyll 

 in milligrams per cubic meter. 



TABLE 4. — Summary of dates, times, positions, and estimates of 

 potential albacore forage, 1972. 



Fish IKMT 



no. no. Date 



Time 



Lat. 

 (N) 



Long. 



(Wj 



Forage 



biomass 



(ml/1,000 m 3 ) 



also indicated by large numbers of sea birds and 

 numerous sightings of marine mammals, includ- 

 ing blue whales and other whales. 



It is possible that fish number 5 and the school it 

 was traveling with left the immediate area where 

 it had been tagged because food organisms were 

 no longer concentrated there due to the break- 

 down of the upwelling front. This explanation is 

 supported by the observation on 19 August of an 

 overall reduction in the concentration of surface 



352 



