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TIME AT LIBERTY (h) 



50 



Figure 7. — Movement of tagged spotted dolphins, Stenella attenuata, 

 recaptured within 48 h of release. When more than one dolphin was 

 tagged and recovered from the same school at the same time, the 

 number is indicated in parentheses. Dashed line is linear regression 

 line fitted to unweighted data points. 



n.mi. area than in the 250-n.mi. area. This result shows 

 that the pattern in Figure 8 of apparent annual migra- 

 tion or dispersal of at least some of the tagged animals is 

 real and not an artifact of the distribution of recapture 

 effort. 



The net direction of movements of <300 n.mi. was es- 

 sentially random, but movements >300 n.mi. had a very 

 strong east-west component (Fig. 9). This apparent pre- 

 dominance of longitudinal movement in long-distance 

 returns is probably not due to chance. If it is assumed 

 that the distribution of deviations in Figure 8 would be 

 random, given that neither longitudinal nor latitudinal 

 movement predominate, the probability that all seven of 

 the over 300 n.mi. net movements would have devi- 

 ations of <20° is described by a binomial probability 

 distribution. If n = 1 and P = 90, then the probability is 

 2.6 X 10~ 5 . The data, therefore, show that, if seasonal mi- 

 gration or dispersal does indeed exist, it is primarily 

 onshore-offshore. The time-of-year data for the few tag 

 returns indicating movements >300 n.mi. indicate that 

 movement may be generally onshore (E) in fall and 

 winter and offshore (W) in late spring and summer 



Table 7. — Estimated catch of yellowfin tuna within 250 n.mi. and 

 within 250-600 n.mi. of point of tag release for 12 tagged dolphins 

 recovered between 50 and 200 days after release and traveling up to 

 582 mi (average 174 mi) and 15 tagged dolphins recovered between 

 200 and 400 days after release and traveling <223 mi (average 93 

 mi). Catches for the first group are between 50 days after release and 

 before recapture and for the second group between 200 days and 

 recapture. 







Estimated yellowfin tuna catch 





Within 250 n.mi. 



Within 250-600 n.mi. 



Tag returns 





(short tons) 



(short tons) 



Group 1 









(50-200 days): 



1. 



886 



14,041 





2. 



9,363 



25,908 





3. 



4,858 



35,508 





4. 



4,728 



30,119 





5. 



76 



657 





6. 



2,065 



11,906 





7. 



2,365 



4,562 





8. 



745 



1,529 





9. 



516 



1,501 





10. 



1,202 



7,885 





11. 



1,436 



4,497 





12. 



4,737 



6,605 



Group 2 









(200-400 days): 



1. 



5,108 



6,224 





2. 



2,396 



26,142 





3. 



470 



6,325 





4. 



4,656 



14,737 





5. 



4,523 



16,180 





6. 



3,277 



12,389 





7. 



3,893 



14,452 





8. 



3,893 



13,126 





9. 



4,485 



13,573 





10. 



1,955 



3,177 





11. 



3,051 



6,746 





12. 



952 



3,611 





13. 



3,214 



6,377 





14. 



5,390 



13,312 





15. 



759 



3,944 



Table 8. — Time of year at liberty and net direction of 

 movement for seven tagged spotted dolphins, Stenella 

 attenuata, traveling more than 300 n.mi. before 

 recapture. 





Net movement 







Distance 



At liberty 



Direction 



(n.mi.) 



1. Jan-May 



W 



572 



2. Aug-Feb 



E 



568 



3. Sept 



E 



390 



4. Nov-Mar 



ENE 



435 



5. Nov-Apr 



ESE 



582 



6.' Dec-Feb 



E 



363 



■Two dolphins. 



(Table 8). This hypothesis must be considered as highly 

 tentative, however, pending availability of more data. 



In summary, home range at any particular season is 

 roughly circular, on the order of 200 to 300 n.mi. in 

 diameter, and may move seasonally several hundred 

 miles onshore (possibly in fall and winter) and offshore 

 (possibly in spring and summer). Average short-term net 

 movement is on the order of 30 to 50 n.mi./day. 



12 



