CAREY and ROBISON: DAILY PATTERNS IN ACTIVITIES OF SWORDFISH 



FlGLlRE 7. — Satellite infrared image of the Atlantic east of Cape Hatteras, N.C. (left center), with track of swordfish no. 7 

 superimposed. Light areas indicate cold water and dark areas warm water. The Gulf Stream moving past Cape Hatteras pulls off a 

 streamer of cold shelf water. Swordfish no. 7 was tagged on the north side of this streamer, swam under it (see Figure 8), and crossed the 

 Gulf .Stream into the Sargasso Sea. 



and may at times have been resting on it. Sword- 

 fish commonly feed on bottomfish ( Scott and Tibbo 

 1968), and this location may have allowed them to 

 prey on demersal fish moving on and off the bank. 

 In the evening no. 2 and 3 swam rapidly offshore 

 and spent the night moving slowly in positions 

 about 20 km from the coast (Figures 2, 3). A 

 different area was visited each night, but they 

 returned to the same spot on the bank every day. 

 Squid, which were abundant on the surface at 

 night, came to our lights in large numbers when 

 we stopped. It is likely that the swordfish moved 

 offshore to feed on the squid and other vertically 

 migrating fauna which concentrate near the sur- 

 face at night. The onshore-offshore movements 

 which we observed may have been a feeding 

 routine which allowed the swordfish to prey on 



demersal fish available in a prescribed spot on 

 the bank during the day and to feed on squid and 

 other prey wherever they were found over deep 

 water at night. 



In an area near Hawaii, Yuen (1970) used an 

 acoustic transmitter to follow a skipjack tuna, 

 Katsuwonus pelamis, for an 8-d period. He found 

 that the fish remained with its school which spent 

 the day on a bank and moved out over deep water 

 at night. The nighttime positions were 20-100 km 

 away from the bank, and like swordfish no. 2 and 

 3, a different area was visited each night. The 

 behavior of the school during the day suggested to 

 Yuen that the fish were foraging. A diel inshore- 

 offshore movement cycle in the blue shark, Pri- 

 onace glauca, near Catalina Island was reported 

 by Sciarrotta and Nelson (1977). This cycle was 



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