FISHERY BULLETIN VOL. 79. NO. 2 



pican T-6 and T-10) which were dropped rou- 

 tinely every several hours and more frequently 

 when passing through boundaries between water 

 masses. The XBT records were used to construct 

 plots of isotherm depth. By superimposing the 

 plot of swordfish depth on the isotherms, we could 

 tell water temperature at the location of the fish 

 in those experiments where a temperature trans- 

 mitter was not used. 



RESULTS 



Swordfish No. 2, 19-24 April 1977, 

 Baja California, Mexico 



This 70 kg swordfish sounded when struck with 

 the transmitter, but quickly came up and spent 

 20 min on the surface. It appeared to be in 

 good condition and unaffected by the depth trans- 

 mitter. During a 5-d period it showed a clear 

 cyclical pattern of movement between an inshore 

 bank during the day and offshore waters at night 

 (Figure 2). Each day it occupied the same area 

 along the 50-fathom (91 m) depth contour on the 

 bank. Several hours before sunset it would move 

 offshore, going out as far as 26 km from land, and 

 remain in deep water all night. At first light of 

 dawn, 1.0-1.5 h before sunrise, it would swim 

 inshore again and return to the 50-fathom contour 

 on the bank. 



The fish remained close to the bottom while on 

 the bank, coming to the surface during daylight 

 only three times in 5 d. On 20 April it was usually 

 5-10 m up from the bottom and on the following 

 days, usually 5-20 m above it. Each evening, an 

 hour after sunset, swordfish no. 2 rose to the 

 surface and spent the night in the upper 10 m. 

 At first light, an hour before dawn, it descended 

 and moved toward shore at depth with frequent 

 vertical excursions. 



Swordfish No. 3, 26-27 April 1977, 

 Baja California, Mexico 



This 70 kg fish was found close to where no. 2 

 had been tagged and was harpooned with both 

 depth and temperature transmitters. It followed a 

 similar pattern to no. 2, moving offshore before 

 sunset and turning inshore at first light (Figure 

 3). Several hours before sunset both of these fish 

 would leave their position on the 50-fathom con- 

 tour of the bank and swim offshore into deeper 

 water. They swam twice as fast, perhaps 3 km/h. 



when moving offshore as they had while on the 

 bank. When on the surface several hours after 

 dark, swimming speed usually slowed to 1 or 2 

 km/h. The movements during the dark hours 

 showed a distinct offshore progression ending at 

 an average distance of about 19 km offshore where 

 the fish moved about slowly until first light. The 

 journey back to the bank was again at a higher 

 speed, about 3 km/h. 



From 1100 to 1800 h on the second day, no. 3 

 remained in one spot and appeared to be resting on 

 the bottom during part of this time (determined by 

 positioning the boat over the fish and noting that 

 the echo sounder depth was the same as that 

 telemetered from the fish). At sunset it rose from 

 the bottom and headed offshore. We lost it soon 

 afterward when our equipment was damaged in 

 rough water. 



Swordfish No. 4, 30 April 1977, 

 Baja California, Mexico 



This 80 kg fish was harpooned in midmorning in 

 500 m of water some 24 km off the coast. It moved 

 slowly in a westerly direction (Figure 4) staying 

 uncharacteristically near the surface, frequently 

 with its fins showing, and did not descend below 10 

 m. It was followed for only 2 h, then abandoned 

 because of technical problems. 



Swordfish No. 5, 30 April 1977, 

 Baja California, Mexico 



This fish weighed about 100 kg and was har- 

 pooned close to where we left no. 4. It also moved 

 slowly westward, covering <3 km in the first 5 h 

 (Figure 4). An hour before sunset it turned south 

 and swam offshore over San Jose Canyon at a 

 speed of 3.5 km/h. During the day it surfaced five 

 times, spending alternate periods on the surface 

 and at 100 m. Sunset marked a period of vertical 

 activity and a gradual ascent to the upper 25-50 m. 

 We lost the fish in rough weather that night as it 

 was swimming offshore on a southerly course. 



Swordfish No. 6, 3-6 May 1977, 

 Baja California, Mexico 



Swordfish no. 6 weighed about 140 kg and was 

 harpooned with depth and temperature trans- 

 mitters in an area about 24 km offshore, near 

 where no. 4 and 5 had been tagged (Figure 4). It 

 swam slowly westward as those fish had done. 



280 



