646 



Fishery Bulletin 90(4), 1992 



Results 



A total of 16 longline sets caught 149 fish in 1989 

 and 22 sets caught 401 fish in 1990. Fishing ef- 

 fort totaled 14,410 hooks including 10,236 hooks 

 with timers. There were 14 taxa for which more 

 than 3 fish were caught (Table 2). 



Achieving deep sets when intended was some- 

 times difficult. Backlash of the main line into the 

 hydraulic line thrower created problems at high 

 thrower speeds, and ship speed through the water 

 was sometimes underestimated, reducing the 

 shortening rate. Wind and currents reduced set 

 depth by dragging floats and parts of the line in 

 opposing directions. In particular, current shear 

 between the surface and the waters below the 

 thermocline, observed with an acoustic Doppler 

 current profiler, seemed to prevent deep sets. 

 Observed set depths were highly variable and 

 usually less than the predicted depths (Table 1, 

 Fig. 2). For example, at a predicted depth of 

 about 490 m, observed depths were 200-400 m 

 (Fig. 2). Sets averaged only 54% and 68% of the 

 predicted depths in 1989 and 1990, respectively. 

 For the first three sets in 1989, the TDRs failed, 

 so depth was estimated as a percentage of the 

 predicted depth based on the average percentage 

 (49.3%) obtained from the next three sets with 

 similar configurations. 



Capture depths 



Capture depths were confirmed for those fish caught 

 >0.5h after deployment and >0.5h before retrieval, 



because the TDR records showed that the main line 

 usually took 0.5 h to sink to within about 90% of its 

 settled depth and about 0.5 h to rise to the surface dur- 

 ing retrieval (Fig. 3). Records of settled depth some- 

 times varied <100m for the deep sets (e.g., set 14; 



