384 



Fishery Bulletin 105(3) 



23 nl (13 (IS 07 04 



II 13 15 



Time (local) 



Figure 3 



Depth and temperature records for a skipjack tuna (Katsuwonus pelamis) 

 with an implanted archival tag (no. 4930) on 18 April 2004. (A) Skipjack 

 tuna exhibiting unassociated repetitive bounce diving behavior. (B) Delta 

 T's (differences between peritoneal cavity and ambient temperature) for 

 the same time period as in (A). 



CI=00:25 h) (Fig. 4A), the mean number of dives made 

 per day was 21.2 (95% CI = 4.9) (Fig. 4B), the mean 

 duration of dives was 10.0 min (95% CI=0.9 min), and 

 the mean depth of all dives was 230 m (95% CI=5.7) 

 (Fig. 4C). 



One skipjack tuna (tag no. 4885) made an extraordi- 

 nary dive below the thermocline that lasted 119 min at 

 1700 h on 19 April 2004. From a depth of 36 m (22.3°C) 

 with a peritoneal cavity temperature of 24.1°C, the fish 

 dived to about 180 m (13.7°C) where it presumably for- 

 aged for 1 h 12 min. The fish then dived fairly rapidly 

 to a maximum depth of 330 m (10.5°C) from which 

 it gradually ascended toward the surface, remaining 

 below the thermocline for another 47 min. From echo- 

 sounder data collected aboard the vessel, it appeared 

 that this fish was tracking the slowly ascending DSL 



and foraging on prey during this period. The minimum 

 peritoneal cavity temperature observed in this study 

 of 15.9°C was recorded continuously over a period of 

 7 mintes as this skipjack tuna ascended from 197 to 

 105 m depth. 



Deep diving behavior 



Only one of the five skipjack tuna (tag no. 4930) dived 

 in excess of 500 m on 13 April 2004, beginning at 12:16 

 (Fig. 5). The maximum depth was 596 m, with a dura- 

 tion of 14 min in excess of 300 m (11.0°C), and 1 min 

 52 seconds in excess of 500 m (8.3°C). The dive pro- 

 file shows that the fish dived initially to about 300 m 

 where it remained for 4 minutes before continuing to 

 596 m and returning after about 2 minutes to between 



