Twenty-four archival tags were recovered from Pacific bluefin tuna previously released off Tsushima Island in the East China Sea. By analysis of the time-series data of the pressure and the ambient and internal temperature from the 24 tags, we examined the relationship between the tuna's pattern of diving and the thermocline depth. In the East China Sea, diving and feeding events occurred throughout almost the entire day in both winter and summer, suggesting that the purpose of diving is for feeding. In summer, the feeding frequency was greater than that in winter, which corresponds to the fact that growth is more rapid in summer than in winter. During summer in the Kuroshio-Oyashio transition region, on the other hand, feeding events were much more frequent than those in the East China Sea, in spite of a lower diving frequency. The mean horizontal distance traveled was also significantly higher and it seems that in this area they may move horizontally to feed on prey accumulated at the surface. We conclude that, in addition to the ambient temperature structure, the vertical and horizontal distribution of prey species plays an important role in the feeding behavior of Pacific bluefin tuna. One bluefin tuna migrated to the Oyashio frontal area, where both the horizontal and the vertical thermal gradients are much steeper. The fish spent most of the time on the warmer side of the front and often traveled horizontally to the colder side during the day, perhaps to feed. This implies that there is a thermal barrier effect, in this case from the Oyashio front, on their behavior. The frequency of feeding events was low, although all the monitored fish dived every dawn and dusk, irrespective of the seasons or location. It is possible that these twice-daily diving patterns occurred in response to the change in ambient light at sunrise and sunset.

Hydrogen peroxide (H 2 O 2 ) in the range of several tens to several hundreds of micromoles per liter is usually added to the process water in advanced oxidation processes (AOPs). In this study, a spectrophotometric method using copper(II) ion and 2,9-dimethyl-1,10-phenanthroline (DMP) for measuring H 2 O 2 concentration was compared with other methods [i.e., spectrophotometric methods using titanium oxalate and N,N-diethyl-p-phenylenediamine (DPD) and a fluorometric method using p-hydroxyphenyl acetic acid (POHPAA)]. Particular attention was paid to sensitivities and effects of coexisting substances. The most sensitive method was the fluorometric method, followed in order by DPD, DMP, and the titanium oxalate colorimetric method; their detection limits in 1-cm cells were 0.16, 0.77, 0.80, and 29 µM, respectively. Therefore, the DMP method was found to be reasonably sensitive when applied to AOPs. Also, the DMP reagent is commercially available, and the absorbance of Cu(DMP) 2 + , a reaction product of the DMP method, was not affected by reaction time. In the DMP method, copper(II)-DMP complexes react with humic acid, and colored chemicals are produced. However, the slopes of the calibration curves of H 2 O 2 containing up to 10 mg of C L -1 from humic acid did not change significantly as compared to that in ultrapure water. The effect of chlorine on the DMP method was not observed up to at least 23 µM (0.8 mg of Cl L -1 ) of free chlorine, although the DPD and fluorometric methods are known to be interfered by chlorine. From this study, it was concluded that the DMP method is suitable to be used in AOPs.

To estimate the survival process of Pacific bluefin tuna Thunnus orientalis during the larval period, estimated growth histories were compared between larvae collected in late spring and juveniles collected in the boreal summer of 2004, which were considered to be survivors of the larval cohorts. Larval tuna (3.3 to 9.6 mm standard length, SL) were collected from mid-May to early June around the Ryukyu Islands, northwestern Pacific Ocean, and juvenile tuna were collected offshore of Kochi and Nagasaki prefectures in July-August. Preflexion, flexion and postflexion larvae were collected, and their ages ranged from 4 to 18 d. Back-calculated SLs by the biological intercept method showed that larval tuna in the postflexion phase were larger-at-age than preflexion and flexion larvae, suggesting that only larger and faster growing larvae were able to survive to the postflexion phase. The logarithms of otolith radii (ln OR: proportional to SL) of larvae with slower growth and development were smaller than the minimum ln OR of surviving juvenile tuna, which indicated the smallest possible size required for larvae to successfully recruit to the fishery. These results indicate that the survival of larvae of Pacific bluefin tuna depends largely on size and growth rates during early life history.KEY WORDS: Growth · Survival · Recruitment · Otolith · Pacific bluefin tuna Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 319: [225][226][227][228][229][230][231][232][233][234][235] 2006 higher tolerance to starvation and a greater ability to escape from predators than smaller larvae (Anderson 1988, Miller et al. 1988, Bailey & Houde 1989. The target species in these studies were flatfish, cod, coral reef fishes and clupeoids, which have relatively low growth rates and a long pelagic period in their early life stages, with the exception of larval bluefish Pomatomus saltatrix that has a relatively high growth potential (Hare & Cowen 1997). Scombrid fishes including Pacific bluefin tuna are generally considered to have survival strategies in the early life stages characterized by large prey and fast growth (Hunter 1981. Scombrids have a high growth rate in the larval stages, and this growth is potentially variable depending on water temperature and food availability, implying that small variations in larval growth may induce broad variations in cumulative mortality and recruitment of the stock. We examined the hypothesis that growth during the early larval period is a key factor in the survival process of Pacific bluefin tuna larvae.Growth history of individual fish is recorded in the otolith (Degens et al. 1969, Dunkelberger et al. 1980, Watanabe et al. 1982, Mugiya 1987. In this study, individual growth histories of larval bluefin tuna were back-calculated from the otolith increment width and compared to growth histories of juvenile bluefin tuna collected in the coastal zone of Japan. These juvenile bluefin tuna were considered to be survivors of the sampled larval pop...

No abstract

Immature Pacific bluefin tuna Thunnus orientalis, tagged with archival tags, were released near Tsushima Island in the East China Sea during the winters of 1995 through 1998. Timeseries data for ambient and peritoneal cavity temperatures, recorded every 128 or 256 s for 23 fish recovered, were analyzed. The objective of this study was to clarify the process of development of thermoconservation ability with growth in relation to adaptive mechanisms to cooler temperate waters. According to the results, mean ambient temperatures ranged from 14.9 to 20.7°C, which is almost within the optimum temperature range according to previous reports. Mean peritoneal temperatures were higher than ambient temperatures (19.7-27.3°C), but never reached 35°C, which would induce overheating. Although the mean thermal differences between peritoneal and ambient temperatures increased with body size, the rate of increase decreased with body size. A heat budget model suggests that as the insulation of the body develops, the estimated mean values of internal heat production decrease with body size. This is probably due to the allometric scale effect and explains why the thermal difference does not increase quickly with body size. It is likely that Pacific bluefin tuna inhabit cooler temperate waters in mid-latitude regions to avoid overheating.KEY WORDS: archival tag, bluefin tuna, internal heat production, thermal adaptation, wholebody heat-transfer coefficient.