LAURS ET AL.: SMALL-SCALE MOVEMENTS OF ALBACORE 



FIGURE 6. — Movements of albacore number 5 as 

 indicated by ultrasonic tracking and the dis- 

 tribution of surface chlorophyll in milligrams per 

 cubic meter. 



chlorophyll a, as much as three to four times lower 

 in waters where upwelling had been taking place 

 on 17 August (Figure 6). Also, measurements of 

 14 C uptake indicate that the rate of primary 

 production was about 33% lower, 1,014 mg C/m 2 

 per day, than it had been when fish number 4 was 

 tracked. In addition, estimates of biomass of 

 potential albacore forage organisms taken in 

 midwater trawl hauls made during tracking 

 operations for fish number 5 were less, ranging 

 from about 6 to 25 ml/1,000 m 3 of water filtered 

 (Table 4), than during tracking operations for fish 

 number 4. (Relatively low chlorophyll a values 

 (Figure 7) and albacore forage biomass values 

 (Table 4) were also observed during tracking 

 operations for fish number 6.) 



While tracking information on only two fish 

 does not provide sufficient data from which to 

 make generalizations, the results suggest that 1) 

 albacore concentrate in the vicinity of upwelling 

 fronts, presumably to feed, and 2) albacore move 

 away from the immediate area when upwelling 

 ceases and the upwelling front is no longer present 

 at the surface. Pearcy and Keene (1974) discussed 

 the possibility of albacore congregating in the 

 region of upwelling fronts. The concentration of 

 albacore in the vicinity of upwelling fronts has 

 also been indicated by high catch rates made by 

 fishing and research vessels near upwelling fronts 

 (Pearcy and Mueller 1970; Panshin 1971; Laurs 

 1973). 



Relationship of Albacore 



Movements to Other Sea Surface 



Temperature Fronts 



During the tracking operations, it appeared 

 that fish numbers 5 and 6 tended to slow down 



FIGURE 7. — Movements of albacore number 6 as indicated by 

 ultrasonic tracking and the distribution of surface chlorophyll 

 in milligrams per cubic meter. 



when crossing temperature fronts where the tem- 

 peratures on both sides of the front were within 

 the favorable range for albacore. To examine this 

 more closely, mean speeds were estimated for 

 tagged fish when they were within a 5-nmi dis- 

 tance before crossing and after crossing the tem- 

 perature front and when crossing the front. A 

 sea surface temperature front was defined as a 

 change in surface temperature of 0.5°C or larger in 

 a nautical mile (0.003°C/m). The results are sum- 

 marized in Table 5 and show that for the three 

 cases examined, 1) the mean speed was slower 

 when crossing the front than it was before 



353 



