FISHERY BULLETIN: VOL. 79, NO. 2 



37° 



FIGURE 6.— Track of swordfish no. 7 in the Atlantic near Cape Hatteras, N.C. 1) Dotted line indicates position of longline gear where 

 this fish was caught. 2) The swordfish moved beneath a layer of cold surface water at 1000 h on 9 November. 3) It emerged from beneath 

 the cold surface layer at 2000 h on 9 November. 4) By 0500 h 10 November, it was in the Gulf Stream. 51 At 1500 h 11 November, it had 

 crossed the Gulf Stream and entered the Sargasso Sea. Dots represent sunset; circles represent sunrise. Ticks at 1-h intervals, bottom 

 contour lines in fathoms. 



During the first day, the vertical movements of 

 no. 7 were complex. On the second and third day 

 however, it followed a clear pattern of moving 

 near the surface at night and going deep during 

 the day. An hour before dawn on 10 November it 

 was in 27° C water at a depth of 20 m (Figure 8). It 

 began to descend and was in 8° C water at 400 m 

 2 h after sunrise. An hour before sunset it started 

 back toward the surface and was at 20 m at 

 twilight. No. 7 spent the night at about 20 m 

 with four brief excursions to 100 m. Some of these 

 were caused by our tracking vessel, for swordfish 

 would often dive when we drove the boat over 

 them and would do this even at night when 

 the ship was darkened. The depth pattern on 

 11 November was similar to the previous day. 

 Leaving the surface 1 h before dawn, it descended 

 rapidly and was at 450 m shortly after sunrise. It 

 continued to descend, reaching 617 m at noon. 



then starting back up, slowly at first, then more 

 rapidly around sunset. 



A continuous recording of the final ascent, made 

 with the phase lock receiver, shows that it was 

 done in steps with a rapid rise of 20-80 m, a 

 pause for several minutes, then another rapid rise 

 (Figure 8). 



DISCUSSION 



Horizontal Movements 



Swordfish no. 2 and 3 showed clear cycles of 

 movement between deep water and an inshore 

 bank. During the day they occupied a rather 

 narrow region, perhaps 8 by 1.5 km, along the 50- 

 fathom (91 m) contour on the bank where the 

 bottom fell off to the south and east (Figure 3). 

 They stayed close to the bottom, moving slowly. 



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