Boggs Estimating capture depths of longline-caught pelagic fish 



651 



the bigeye tuna with hook timers were caught while 

 the hoolts were moving (sinking or rising; Table 4). No 

 clear relationship existed between depth and the pro- 

 portion caught on moving hooks (Table 4). 



Yellowfin tuna were not very abundant, which is 

 typical for the winter months off Hawaii. The CPUEd 

 for yellowfin tuna was not the same in both years (Fig. 

 7), but the number of fish caught with timers was very 

 small, particularly in 1989 (Table 4). Pooled CPUEd 

 was highest at 40-200 m (Fig. 8) although no signifi- 

 cant difference in CPUEo by depth was found. The 

 40 m end of the depth range did not indicate the 

 shallowest depths preferred by any species, since no 

 hooks fished depths of <40m. 



Timer-confirmed catches by settled hooks indicated 

 the highest catch rates for striped marlin were at 

 40-120 m in both years (Fig. 7), and pooled CPUEd 

 was clearly the highest at this depth range (Fig. 8). The 

 overall proportion of striped marlin caught on moving 

 hooks was high (32%; Table 4) and increased with 



depth. At > 120 m most striped marlin were caught by 

 moving hooks, and at >200m only one was caught by 

 a settled hook (Table 4). 



For spearfish, the pattern of CPUEd vs. depth dif- 

 fered between years. In 1989, the highest CPUEp was 

 at 120- 160 m although several fish were caught as deep 

 as 280-360 m; however, in 1990 the highest CPUEq 

 was at 40-80 m, and no confirmed capture depths were 

 recorded at >200m (Fig. 7). Pooled data suggested that 

 spearfish were more abundant at <120m, but the 

 CPUEd at 40-120 m was not significantly different 

 from that at 120-200 m (Fig. 8). In 1989, a large pro- 

 portion (43%) of the spearfish were caught on moving 

 hooks, but none were caught on moving hooks in 1990 

 (Table 4). Furthermore, for each of the major species, 

 a higher proportion of fish were caught on moving 

 hooks in 1989 than in 1990 (Table 4). An early report 

 (Boggs 1990) on this research was based on 1990 data 

 (Table 4) wherein only 12% of the tuna and billfish 

 (combined) were caught on moving hooks. 



