SCIARROTTA and NELSON: DIEL BEHAVIOR OF BLUE SHARK 



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© twilight 

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100 meters 



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SANTA 



CATALINA ISLAND 



TIME OF DAY 



18 20 



TIME OF DAY 



FIGURE 2. — Data from two individual trackings of blue sharks typical of the late March to early June period. Top, shark positions at 

 approximately 0.5-h intervals. Bottom, telemetered sensor data. Note the characteristic evening-twilight migration towards the 

 island, the initial plunge occurring immediately after transmitter application, and the close correlation between temperature and 

 depth. Depths in excess of 110 m (the sensor limit) are indicated by x x. 



changes. During the dusk transition, rate of 

 movement most closely matched swimming speed, 

 indicating the greatest consistency in swimming 



direction. In timing, this coincides with the rela- 

 tively oriented shoreward migrations of from late 

 March to early June. The greatest disparity be- 



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