Growth-dependent recruitment of Pacific bluefin tuna Thunnus orientalis in the northwestern Pacific Ocean

Abstract

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...

Otolith δ18O of Pacific bluefin tuna Thunnus orientalis as an indicator of ambient water temperature

“…The primary spawning ground of this species is in the northwest region of the Philippine Sea, between eastern Tai-wan and Ryukyu Islands in the southern part of Japan (roughly the western North Pacific, Fig. 1, Bayliff 1994, Chen et al 2006, Tanaka et al 2006, Shiao et al 2010. Spawning occurs in late April to July at a sea surface temperature of 26 ± 2°C, which has been confirmed in rearing experiments ).…”

“…This difference was also observed in Pacific bluefin tuna spawning in the northwest region of the Philippine Sea, between eastern Taiwan and Ryukyu Islands located in the southern part of Japan (roughly the western North Pacific) from late April to June (Bayliff 1994, Chen et al 2006, Tanaka et al 2006, Shiao et al 2010 and in the southern Sea of Japan in late July to August (Tanaka et al 2007, Itoh 2009). These 2 areas have different temperatures and salinities.…”

“…Fish otoliths, which are composed of aragonite, a crystalline form of calcium carbonate, record environmental information as well as age (Struhsaker & Uchiyama 1976, Radtke & Dean 1982, Volk et al 1984, Tanaka et al 2006) throughout a fish's life. The chemical and isotopic compositions that accumulate on the growing surface of the otolith are permanently retained after being deposited because otoliths are acellular and metabolically inert (Campana & Neilson 1985, Mugiya 1994, Campana 1999.…”

Rapid ontogenetic shift in juvenile Pacific bluefin tuna diet

“…Subsequently, ARs increased to 6.7 on average for fish > 200 cm, which were approximately 9 yr old (Shimose et al 2009). Tanaka et al (2006) reported that 16.7− 30.0 cm PBT appeared in waters off Kochi Prefecture at 54 to 89 d of age. Therefore, taking the slope value into consideration, it is suggested that they grow rapidly and gain greater swimming ability in the 1 to 2 mo after arriving in Japanese coastal waters.…”

Impact des coupes forestières sur l'écologie des jeunes stades de vie chez la perchaude (Perca flavescens) :

“…Post & Prankevicius 1987, Hovenkamp 1992, Meekan & Fortier 1996, Sirois & Dodson 2000b, Searcy & Sponaugle 2001, Takasuka et al 2003, Meekan et al 2006, Shoji & Tanaka 2006a, Tanaka et al 2006, Robert et al 2007). However, many studies shown that the survivors were rather the slow-growing members of a cohort (e.g.…”