520 



Fishery Bulletin 101(3) 



Real depth (m) 



Figure 4 



An example of observed deterioration in a pressure sensor 

 of an archival tag in a postdeployment recalibration. The 

 horizontal axis shows the test pressure, vertical axis is pres- 

 sure recorded by the tag. Dots are observed data. The solid 

 line bent at 25 m of real depth is formed from two regres- 

 sion lines, one fitted to data below and one to data above 

 25 m depth. This approximation to the deteriorated sensor 

 characteristic was used to correct pressure data for this tag. 

 Pressure values are converted to depth in meters. A broken 

 line is that of observed depth equal to real depth. 



o 

 m 



and the monthly average growth rates of tagged fish with 

 wild fish, and also by evidence of feeding to be found in the 

 records returned in the tags. 



The bodies of two fish among 30 recoveries were avail- 

 able for observation. One fish recaptured 27 days after 

 release still had a scar on its skin but no trace of the tag 

 insertion surgery was found in its belly muscle. Another 

 fish recaptured 200 days after release had no trace of sur- 

 gery either on its skin or in its belly muscle. Surface skin 

 around tag stalks was ulcerated in both fish. The stalks 

 were immobilized in the belly muscle. The cylindrical bod- 

 ies of both tags were covered with membrane and located 

 between the stomach and the pyloric caeca. No infection 

 or necrosis was observed in the visceral organs around tag 

 bodies or in the muscle around tag stalks. 



Body weights of all recaptured fish that were measured 

 (^=8, 17-203 days after release) were within the range of 

 those of wild fish of the same fork length (Fig. 5). An average 

 growth rate of recaptured fish was 1.4 ±0.5 cm per month 

 (n=6, three fish recaptured at short durations of liberty that 

 showed no or negative growth were excluded). A subgroup of 

 four fish recaptured after more than 5 months from release, 

 i.e. fish at liberty during the summer when growth might 

 be expected to be faster, had an average growth rate of 1.3 

 ±0.6 cm — similar to that from all durations. 



The average number of daily feeding events, which were 

 found by specific changes of visceral temperature ( Itoh et 

 al., 2003), increased linearly from no feeding on the day of 

 release up to a steady rate beginning about 30 days after 

 release. Thus, it appeared that fish did not feed normally 

 during this initial period (Fig. 6). 



40 



50 



60 



Fork length (cm) 



70 



80 



Figure 5 



Comparison of weight at length of young Pacific bluefin tuna between 

 recaptured fish tagged with archival tags and wild (untagged) fish. 

 Numerals show days at liberty. An average (thick solid line) and upper 

 and lower 95'7f confidence limits (thin solid lines) are derived from 

 11,777 wild fish from 40 to 80 cm in fork length caught in 1995 and 

 1996 around Japan. Equations for average is H''=2.844x 10''xL-'"", 

 upper 95% limit is W=.3.028x lO^'x/-^^™, and lower 95% limit is 

 W=2.745xl0'^xL2 906 where L = fork length in cm and VV = body 

 weight in kg. 



Horizontal movement 



Estimated tracks of all fish that traveled out 

 of the East China Sea along with one fish that 

 remained in the East China Sea are shown in 

 Figure 7 and Figure 8. All of these fish were 

 released off Tsushima in November or Decem- 

 ber and remained in the East China Sea at least 

 90 days. After that, four fish entered the Sea of 

 Japan and moved northward from April to July 

 (Fig. 7, A-D). Two of them moved southward in 

 November one year after release (Fig. 7, C and D), 

 and one of the two fish returned to the region off 

 Tsushima where the fish were released (Fig. 7C). 

 One fish remained and was recaptured within 

 the East China Sea in November, one year after 

 release, although it had moved to the east coast 

 of the Korea Peninsula for a period in August and 

 September (Fig. 7E). Ten fish remained within 

 the East China Sea for more than five months 

 and were recaptured from May to June, five to 

 seven months after release (Fig. 7F). 



Two fish moved to the Pacific Ocean (Fig. 7G 

 and Fig. 8). One of these fish entered the Pacific 

 Ocean on 7 March 1996, and then traveled east- 

 ward straight from a position off the south coast 

 of Kyushu (31°N, 131°E) to one off the east coast 

 of Choshi (36°N, 142°E), then stayed for a while 



