Schaefer and Fuller Movements, behavior, and habitat selection of Thunnus obesus 



773 



400 



Time (CTZ) 

 18 00 



-99-862 (93 cm) 



-^99-883 (116 cm) 



28 



18 



15 



H 

 h14 g 



M3 I 

 •13 O 

 •13 

 •12 

 12 



B 



18 00 



Time (CTZ) 



18 00 



Figure 4 



Simultaneous depth and temperature records for two bigeye tuna carrying 

 archival tags, exhibiting unassociated type-1 behavior. 23-25 April 2000. 

 Approximate area. 0°N 96°W. is based on geolocation estimates from the 

 archival tags. (A) Depth and ambient temperature records (B) delta T's (dif- 

 ferences between peritoneal cavity and ambient temperature) for the same 

 time period as in A above. CTZ = central time zone. 



surrounding the autumn equinox because there was very 

 little variation in day length near the spring and autumn 

 equinoxes (Hill and Braun, 2001). 



Movements 



The movements of 8 bigeye tuna at liberty for 76 to 340 

 days are plotted in Figure 9. A-D. No bigeye tuna went 

 farther west than about 110°W and most spent the major- 

 ity of time between QCW to 105°W and 5°N to 5°S. Data 

 for the estimated movement paths of 22 fish, derived from 

 the filtered geolocation estimates, are given in Table 4. The 



estimated mean speeds ranged from 76 to 165 km/d (grand 

 mean=116.6 km/d. 95^7^ CI=10.0 km/d). The hypothesis 

 that the observed movement path is random was rejected 

 for 17 of the 22 fish (Table 4). A significant positive cor- 

 relation (r=0.61, P<0.05) was found between the number 

 of days at liberty and their corresponding 95*7^ utilization 

 distributions (Tables 1 and 4). 



The areas encompassed by the 95^f probability ellipses 

 for the geolocation estimates of unassociated behavior and 

 behavior associated with floating objects (Fig. 10), for the 

 22 bigeye tuna at liberty for 30 d or more (Table 4). were 

 3.9 and 3.1 x 10*' km-, respectively. The difference between 



