Schaefer et al.: Vertical movement patterns of Kotsuwonus pelomis in the eastern Pacific 



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Figure 2 



Depth and temperature records for a skipjack tuna iKatsuwonus pelamis) 

 with an implanted archival tag (no. 4930 i on 11 April 2004. (Al Skipjack 

 tuna exhibiting behavior associated with floating objects. (Bl Delta T's 

 (differences between peritoneal cavity and ambient temperature) for the 

 same time period as in (A). 



to spike upward, indicative of the thermal excess of 

 the peritoneal cavity in relation to the ambient tem- 

 perature. 



Behavior unassociated with floating objects 



Within 48 hours after the skipjack tuna were unas- 

 sociated with the vessel, they showed a distinct change 

 in their vertical movements and behavior, exhibiting 

 repetitive bounce diving between about 50 and 300 m 

 during the day (Figs. 1 and 3A). They remained close 

 to the surface at night, primarily within 50 m, showing 

 distinct diel differences in behavior. Figure 3A shows 

 50 dives in excess of 150 m, and an average duration of 

 6.8 min (range: 3 to 17 min). The mean depth of these 

 dives was 257 m (range: 153-355 m). During ascents 



following dives the fish returned to an average depth of 

 44 m, the approximate depth of the thermocline, before 

 undertaking another dive. The delta T values (Fig. 

 3B), corresponding to the simultaneous depth records 

 (Fig. 3A), showed an average of 1.9°C (95% CI=0.09°C, 

 range: 0.8-13.5°C) during the night when the fish were 

 primarily in the mixed layer. The delta T values during 

 the day corresponding to the maximum depths of bounce 

 dives were an average of 12.2°C (95% CI=0.3°C, range: 

 10.2-13.9°C). At the maximum depths of these bounce 

 dives, the mode of the minimum ambient temperature 

 experienced was 11.7°C and the peritoneal cavity tem- 

 perature was 25.1°C. 



For the five skipjack tuna, during days of unassoci- 

 ated repetitive bounce diving behavior, the mode for the 

 time the first dive of the day occurred was 07:10 h (95% 



