I.AUKS KT AL.: SMALL-SCALE MOVEMENTS OF ALBACORE 



from the surface to a depth of approximately 175 

 m at a ship speed of about 5 knots. The volumes of 

 water strained were estimated from data obtained 

 by a TSK 6 depth-distance recorder mounted in'the 

 mouth of the trawl. The Formalin-preserved 

 IKMT catches were sorted into several categories 

 of fishes, cephalopods, crustaceans, and other 

 animals, and the displacement volume of each of 

 these kinds of animals was measured and stan- 

 dardized in ml/1,000 m 3 of water filtered for each 

 haul. The standardized values of 1) larval and 

 juvenile fishes, 2) epipelagic fishes, 3) cephalo- 

 pods, and 4) crustaceans were summed for each 

 haul and collectively regarded as potential alba- 

 core forage. Analysis of stomach contents of 

 albacore has shown that these categories of 

 organisms are important in the diet of albacore 

 (Pinkas et al. 1971) in this area. 



Oceanographic Observations Made 

 by Aircraft 



A Coast Guard aircraft equipped with a Barnes 

 PRT-5 infrared radiometer made measurements 

 of sea surface temperature for evaluation of the 

 small-scale features and changes in the distribu- 

 tion of sea surface temperature. 



RESULTS AND DISCUSSION 



Six albacore were tagged and tracked with 

 ultrasonic equipment for periods ranging 

 from about 2 to 50 h and distances ranging from 

 6.5 to 150.7 km (3.5 to 81.3 nmi). Results will be 

 presented for fish numbers 4, 5, and 6, which were 

 tracked for 27.8, 41.4, and 50.0 h, respectively. 

 There are too few data for discussion for fish 

 numbers 1, 2, and 3 because of the short periods 

 that the fish were tracked. A summary of the 

 tracking date and time, tagging location, distance 

 tracked, and fork length offish for fish numbers 4, 

 5, and 6 is given in Table 1. 



Tagged fish rejoined untagged albacore after 

 being returned to the water, and tended to remain 

 in their company. Surface "boils" characteristic of 

 albacore were frequently sighted close by Linda, 

 and approximately 30 fish of the same general size 

 as fish tagged with ultrasonic transmitters were 

 caught by the crew while tracking was in 

 progress. Also, one tagged fish "lost" the previous 

 day was heard intermittently over a 4-h period 



TABLE 1. — Summary of tracking date and time, fork length of 

 albacore, location of tagging, and distance tracked. 



Fork Tagging location 



No Date Time length Lat. Long. Distance 



84 cm 36 49.8'N,122°19.1'W 41 6 nmi 



(77.1 km) 



87 cm 36"50.3'N,122'13.6 W 61 .4 nmi 



(113.8 km) 



85 cm 35°20.0'N, 12122 0'W 81 3 nmi 



(150.7 km) 



during the track that followed. We were able to 

 distinguish between the two fish because of 

 slightly different signals from the tags. 



Speed of Albacore Movements 



Swimming speeds for albacore were estimated 

 from straight-line calculations using position of 

 the tracking vessel. The average swimming speed, 

 based on the total distance and time that the fish 

 were tracked, for fish numbers 4, 5, and 6 was 

 about 1.6 knots (82 cm/s). Speeds calculated from 

 hourly ship positions for each fish ranged from 0.1 

 to 3.6 knots (5 to 185 cm/s). Table 2 shows the 

 percentage of time each fish spent at various 

 swimming speeds. There were day-night differ- 

 ences in the rate of movement, with fish exhibit- 

 ing faster swimming speeds during hours of 

 daylight (0500 to 1900 h) than during hours of 

 darkness. The average speed during daylight for 

 fish numbers 4 and 5 was 1.7 knots (88 cm/s) and 

 for number 6 was 2.1 knots (108 cm/s). The 

 average speed during nighttime for fish numbers 



4 and 6 was 1.3 knots (67 cm/s) and for fish number 



5 was 1.0 knot (51 cm/s). Table 3 gives a summary 

 of time, distance, and mean speeds. 



Moonlight also appeared to influence the rate of 

 movement offish number 5. This fish, which had 

 been moving steadily at about 2.0 knots ( 103 cm/s) 

 for about 3 h after moonrise and following a course 

 about 20° west of the full moon, came to a near stop 



TABLE 2. — Percent of time each albacore spent at various swim- 

 ming speeds. 



Speed 



Fish 

 no. 4 



Fish 

 no. 5 



Fish 

 no. 6 



knots 



cm/sec 



Percent 



G Tsurumi Seiki Kosakusho Co., Ltd., Yokohama, Japan. 



349 



