Kuroshio Oyashio Transition Region Research Articles

Diving behavior of immature, feeding Pacific bluefin tuna (Thunnus thynnus orientalis) in relation to season and area: the East China Sea and the Kuroshio–Oyashio transition region

AbstractTwenty‐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.

Newly designed quantitative frame trawl for sampling larval and juvenile pelagic fish

A newly designed frame trawl with a 5 m2 mouth area was constructed for quantitative sampling of larval and juvenile pelagic fishes and its performance was tested in the ocean. Towing depth of the trawl was easily controlled by adjusting the warp length, and the stability at depth increased with decreasing weight of the net in water. Larval and juvenile fishes were sampled using the trawl at stations in the Kuroshio-Oyashio transition region from 29 May to 24 June 1998. A total of 44 oblique tows were conducted and towing depths of the frame trawl had a high degree of stability despite the various sea conditions and the fluctuations in the ship speed. Larvae and juveniles of Japanese anchovy Engraulis japonicus and Myctophidae made up the majority of the specimens. It was concluded that the newly constructed trawl was appropriate for the quantitative sampling of pelagic fish larvae and juveniles.

Growth rate-dependent recruitment of Japanese anchovy Engraulis japonicus in the Kuroshio-Oyashio transitional waters

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 266:227-238 (2004) - doi:10.3354/meps266227 Growth rate-dependent recruitment of Japanese anchovy Engraulis japonicus in the Kuroshio-Oyashio transitional waters Motomitsu Takahashi1,*, Yoshiro Watanabe2 1National Research Institute of Fisheries Science, Fisheries Research Agency, 2-12-4 Fukuura, Kanazawa-ku, Yokohama, Kanagawa 236-8648, Japan 2Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164-8639, Japan *Email: takahamt@fra.affrc.go.jp ABSTRACT: Based on the relationship between otolith and somatic growth rates, we examined the effect of growth and developmental rates on survival during larval and early juvenile stages in Japanese anchovy Engraulis japonicus collected in the Kuroshio-Oyashio transition region in the western North Pacific. Mean daily otolith increment width (IW) positively correlated with mean growth and developmental rates in rearing experiments. In the Kuroshio-Oyashio transition region, faster-growing larvae with larger IWs attained completion of metamorphosis at younger ages than slower-growing larvae. The minimum IWs in the recruited adults collected in 1999 greatly increased from 4.8 µm at 40 d after hatching to 11.0 µm at 60 d, while the minimum IWs in the pre-recruits collected in 1998 was less than 5.0 µm at 60 d, and accounted for ca. 60% of the total pre-recruit population. Based on the positive relationship between IWs and growth rates in the rearing experiments, an IW of 11.0 µm is estimated to correspond to 0.41 mm d-1 in growth rate. It was concluded that pre-recruits with growth rates <0.41 mm d-1 at 60 d have a negligible probability of survival to recruitment. Mortality dependent on growth and developmental rates occurred in the metamorphosing stage of E. japonicus in the Kuroshio-Oyashio transition region. Since environmental conditions in the transition region are variable, and these conditions affect growth and developmental rates of larvae, the rates in the metamorphosing stage could determine the abundance of recruited 1 yr old E. japonicus in the transition region. KEY WORDS: Growth rate · Survival · Otolith increment width · Metamorphosis · Japanese anchovy Full article in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 266. Online publication date: January 30, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Developmental and growth rates of Japanese anchovy Engraulis japonicus during metamorphosis in the Kuroshio-Oyashio transitional waters

Stage duration and growth rate during the late larval stage can be key parameters of recruitment dynamics in the Japanese anchovy Engraulis japonicus in the Kuroshio-Oyashio transi- tion region of the western North Pacific. The developmental rate was defined as a reciprocal of the duration in days of the metamorphosing stage, and was a positive function of the growth rate after the onset of metamorphosis. The growth rate after the onset of metamorphosis in the early juvenile stage fish corresponded with higher growth rates in the early metamorphosing stage fish. The results indicate that larvae with a faster growth rate during the late larval stage metamorphosed at a younger age than the larvae with a slower growth rate. Developmental and growth rates were faster in the southwestern waters than in the northern and eastern waters in the Kuroshio-Oyashio transi- tion region. Survival during metamorphosis depends on the developmental and growth rates, and we conclude that the larvae with faster developmental and growth rates in the southwestern waters had a higher probability of successful metamorphosis and recruitment to the spawning stock, and con- stituted the major part of the population of E. japonicus in the Kuroshio-Oyashio transition region.

Importance of the Shatsky Rise Area in the Kuroshio Extension as an offshore nursery ground for Japanese anchovy (Engraulis japonicus) and sardine (Sardinops melanostictus)

AbstractRecent findings suggest that recruitment of Japanese anchovy (Engraulis japonicus) and sardine (Sardinops melanostictus) depends on survival during not only the first feeding larval stage in the Japanese coastal waters and the Kuroshio front but also during the post‐larval and juvenile stages in the Kuroshio Extension. Spatial distributions of juvenile anchovy and sardine around the Shatsky Rise area in the Kuroshio Extension region and the Kuroshio–Oyashio transition region are described, based on a field survey in the late spring using a newly developed mid‐water trawl for sampling juveniles. All stages of anchovy from post‐larvae to juveniles were obtained in the northern Shatsky Rise area. The Kuroshio Extension bifurcates west of the Shatsky Rise area and eddies are generated, leading to higher chlorophyll concentrations than in the surrounding regions in April and May. When Japanese anchovy and sardine spawn near the Kuroshio front or the coastal waters south‐east of Japan, their larvae are transported by the Kuroshio Extension and are retained in the Shatsky Rise area, which forms an important offshore nursery ground, especially during periods of high stock abundance.

Leptocephalus larvae of Pterothrissus gissu collected from the Kuroshio-Oyashio transition region of the western North Pacific, with comments on its metamorphosis

Pterothrissus gissu is a rare albulid fish that is distributed in deep water off Japan. This fish is known to pass through a leptocephalus larval stage, but only metamorphosed (after reaching the fully grown stage) specimens have been available. In this study, the premetamorphosis (before fully grown stage) leptocephalus larva of P. gissu is first described from 45 specimens (117.2–194.5 mm SL) collected by a pelagic otter trawl in the Kuroshio–Oyashio transition region of the western North Pacific in May 1995. Premetamorphosis leptocephalus larvae are characterized by having poorly developed fin rays except for the caudal fin, a translucent body, branched melanophores beneath the eye, and punctuate melanophores on the dorsal edge of the gut from the throat to the anus. Previously fully grown leptocephali were estimated to reach about 130 mm SL based on the size distributions of metamorphosing specimens. However, the present specimens show that fully grown leptocephali of P. gissu exceed 180 mm SL.

Growth rates of larval stage of Japanese anchovy &lt;i&gt;Engraulis japonicus&lt;/i&gt; and environmental factors in the Kuroshio Extension and Kuroshio-Oyashio transition regions, western North Pacific Ocean

Recent studies of Japanese anchovy Engraulis japonicus have shown that they are distributed and spawn widely off the Pacific coast of eastern Honshu, Japan, with increasing stock size. Larvae are considered to be transported offshore and migrate, influenced by physically complicated process with warm and cold waters derived from the Kuroshio and Oyashio currents respectively. Survival mechanism during early life history stages in such offshore waters could be a missing link for population dynamics of Japanese anchovy. In this study, we examined the growth rates of larval stage of Japanese anchovy, which were collected in the Kuroshio Extension and Kuroshio-Oyashio transition regions, western North Pacific Ocean, by sagittal otolith microstructure analysis. Our objectives are to determine the principal environmental factor affecting larval growth rates and to find out a survival mechanism in relation to transport and migration of larvae.

Behavior of Warm-Core Rings in a Double-Gyre Wind-Driven Ocean Circulation Model

Numerical experiments have been performed to understand the movement of warm-core rings in the Kuroshio-Oyashio Transition region, considering the double-gyre ocean circulation represented by a 2.5-layer primitive equation model. Rings, eddies, and frontal disturbances are simulated, and analytical descriptions of warm-core ring behavior are examined. Warm-core rings are usually generated at the south of the zero wind stress curl line (ZWCL), either off-shore or near-shore, and a near-shore ring gradually moves northward along the coast, supplied with energy from the sub-tropical front and other rings. When they approach the ZWCL, two different types of movements occur, which is affected by the intensity of the rings and controlled by the wind stresses. In case the ring intensity is strong, it moves northward along the coast against the subarctic western boundary current system and cold-core rings, whereas a moderate ring is advected by them to the northeastward. The advection process of moderate rings seems to be important for northeastward movement of the Kuroshio warm-core rings in the middle of the Oyashio current system. The mechanism of large-scale forcing dynamics influences the cross-shore location of rings and implications for the fishing ground formation of the Pacific saury are described.

Dispersal of larvae and juveniles of Japanese anchovy Engraulis japonicus in the Kuroshio Extension and Kuroshio–Oyashio transition regions, western North Pacific Ocean

A sampling survey for Japanese anchovy Engraulis japonicus larvae and juveniles was carried out using two types of sampling gear for capturing a wide size range of fish in the Kuroshio Extension and Kuroshio–Oyashio transition regions in August 1996. Anchovy larvae were found widely far offshore. Total lengths (TLs) of the fish ranged mostly from 6 to 40 mm, which corresponded to 5–50 days after their hatching in July. The number of anchovy collected varied with sampling sites, but it was not clear what factors accounted for the variation. While the mean lengths of larvae taken in the Kuroshio Extension area tended to be smaller offshore, those in the transition area significantly increased in size as the distance offshore increased, perhaps because larger larvae migrated northward into the transition region. The mean growth rate of otolith-aged larvae was 0.63 mm per day, which was similar to those previously reported in the coastal waters. The daily mortality coefficient, which was estimated based on age–frequency distribution converted from length–frequency distribution, ranged from 0.362 to 0.136 per day. The mortality rates decreased with growth, being lowest for larger larvae offshore.

The Dependence of Yearly Recruitment of Japanese Sardine &lt;i&gt;Sardinops melanostictus&lt;/i&gt; on Survival in the Kuroshio-Oyashio Transition Region

The Dependence of Yearly Recruitment of Japanese Sardine &lt;i&gt;Sardinops melanostictus&lt;/i&gt; on Survival in the Kuroshio-Oyashio Transition Region