首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 125 毫秒
1.
We have numerically modeled the advection and diffusion of sardine eggs and larvae to investigate the larval transport processes of Japanese sardine from the spawning grounds by the Kuroshio.
The results indicated that the offshore drift current induced by the winter monsoon and the location of the spawning ground have significant effects on the survival of the Japanese sardine. The contribution of the drift current, the distance of the spawning ground from the Kuroshio axis, and the eddy diffusivity to the larval retention in the coastal area is approximately expressed by the following equation: where R is the retention rate in the coastal area, a the variance of initial distribution of eggs, T the time after the eggs were spawned, – V0 the velocity of the wind-induced offshore current, y0 the distance of the center of the spawning area from the Kuroshio axis, and K the coefficient of horizontal eddy diffusivity.
The year-to-year variation in larval survival rates stimulated by the two-dimensional model are consistent with those estimated previously by using field data of egg and larval abundance during 1978–1988.  相似文献   

2.
Stock level of Japanese sardine (Sardinops melanostictus) was high from 1980s to early 1990s and low from late 1990s to 2000s. The warm and cold water masses in the vicinity of the Kuroshio axis from winter to early spring used to be critical for the recruitment in the high‐stock period, because most of the larvae were distributed there. However, the environmental fluctuation might not affect the recruitment in the low‐stock period. Some studies reported that spawning location and spawning season, and hence the larval habitat, differ depending on the stock level. Three points were investigated in this study: (a) how spawning location and spawning season shifted from the late 1990s, (b) confirmation of the distribution area of larvae in the recent low‐stock period and (c) whether the water temperature in the vicinity of the Kuroshio axis was still related to the recruitment in the low‐stock period. The spawning location and spawning season clearly changed after 1995. Consequently, particle tracking experiments suggested that the larvae appeared in the vicinity of the Kuroshio axis from winter to early spring decreased. Nevertheless, only the ambient temperature of larvae that appeared in the vicinity of the Kuroshio axis from winter had a significant negative correlation with an index of the recruitment in the low‐stock period. It is suggested that the warm and cold masses in the vicinity of the Kuroshio axis are critical for the recruitment regardless of the stock level.  相似文献   

3.
We constructed a numerical model reproducing the transport, survival and individual growth of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan during 1978–93. The causes of early life stage mortality, including the influence of the effects of the spatial relationship between the spawning grounds and the Kuroshio on the mortality rate, were investigated. Survival and transport from egg stage to 60 days after spawning were modelled daily in a 1 × 1 degree mesh cell and individual growth in the period was modelled in each region (Kuroshio, Inshore, Offshore and Transition regions). Individual growth and survival from 60 to 180 days after spawning were modelled daily in the Transition region. Environmental data were taken from outside the model system. Our simulation indicates that survival variability in the larval stage (5–25 mm in standard length) is the key factor in determining the year‐class strength. The simulation revealed that strong year classes occurred with good survival in the spawning ground and whilst entrained in the Kuroshio current being transported to the main feeding grounds in the Transition region. The simulation also indicated that survival rates in 1988–93 were low in the Inshore, Kuroshio and Offshore regions, which depressed the year‐class strength during that period.  相似文献   

4.
Winter‐to‐spring variability in sea surface temperature (SST) and mixed layer depth (MLD) around the Kuroshio current system and its relationship to the survival rate (ln [recruit per spawning stock biomass], LNRPS) of Japanese sardine (Sardinops melanostictus) were investigated based on a correlation analysis of data from 1980 to 1995. The data were from a high‐resolution ocean general circulation model using the ‘Kuroshio axis coordinates’, in which the meridional positions are relocated to a latitude relative to the Kuroshio axis at each longitude, rather than the geographically fixed coordinates. A significant positive (negative) correlation between LNRPS and winter MLD (winter–spring SST) was detected near the Kuroshio axis from areas south of Japan (where eggs are spawned) to the Kuroshio Extension (where larvae are transported). This result is in contrast to previous studies using geographically fixed coordinates, which showed a significant correlation predominantly in the area south of the Kuroshio Extension in winter, where at this time few larvae have been found. From the late 1980s to early 1990s, when the survival rate was remarkably low, MLD around the axis was shallow and SST was high. Although MLD and SST show a significant correlation, significant partial correlations were also observed between February MLD and LNRPS when the contribution of SST was excluded, and between March SST and LNRPS when the contribution of MLD was excluded. We presume that MLD shoaling reduced the nutrient supply from deep layers, resulting in less productivity in the spring, and SST warming could have a negative influence on larval growth.  相似文献   

5.
Numerical particle-tracking experiments were performed to investigate the transport and variability in environmental temperature experienced by eggs and larvae of Pacific stocks of the Japanese anchovy ( Engraulis japonicus ) and Japanese sardine ( Sardinops melanostictus ) using high-resolution outputs of the Ocean General Circulation Model for the Earth Simulator (OFES) and the observed distributions of eggs collected from 1978 to 2004. The modeled anchovy individuals tend to be trapped in coastal waters or transported to the Kuroshio–Oyashio transition region. In contrast, a large proportion of the sardines are transported to the Kuroshio Extension. The egg density-weighted mean environmental temperature until day 30 of the experiment was 20–24°C for the anchovy and 17–20°C for the sardine, which can be explained by spawning areas and seasons, and interannual oceanic variability. Regression analyses revealed that the contribution of environmental temperature to the logarithm of recruitment per spawning (expected to have a negative relationship with the mean mortality coefficient) was significant for both the anchovy and sardine, especially until day 30, which can be regarded as the initial stages of their life cycles. The relationship was quadratic for the anchovy, with an optimal temperature of 21–22°C, and linear for the sardine, with a negative coefficient. Differences in habitat areas and temperature responses between the sardine and anchovy are suggested to be important factors in controlling the dramatic out-of-phase fluctuations of these species.  相似文献   

6.
In the mid 1970s, the fishery catch of postlarval Japanese anchovy (Engraulis japonica) in a shelf region of the Enshu‐nada Sea, off the central Pacific coast of Japan, started to decline corresponding to a rapid increase of postlarval sardine (Sardinops melanostictus). In late 1980s, sardine started to decline, and it was replaced by anchovy in the 1990s. This alternating dominance of postlarval sardine and anchovy corresponded to the alternation in egg abundance of these two species in the spawning habitat of this sea. It was also noteworthy that during the period of sardine decline, sardine spawning occurred in April–May, a delay of two months compared with spawning in the late 1970s. The implication of oceanographic changes in the spawning habitat for the alternating dominance of sardine and anchovy eggs was explored using time‐series data obtained in 1975–1998, focusing on the effect of the Kuroshio meander. Large meanders of the Kuroshio may have enhanced the onshore intrusion of the warm water into the shelf region and contributed to an increase in temperature in the spawning habitat. This might favour sardine, because its egg abundance in the shelf region was more dependent on the temperature in early spring than was that of anchovy. In addition, enhanced onshore intrusion could contribute to transport of sardine larvae from upstream spawning grounds of the Kuroshio region. On the other hand, anchovy egg abundance was more closely related to lower transparency at the shelf edge, which may indicate the prevalence and prolonged residence of the coastal water, and therefore higher food availability, frequently accompanying non‐meandering Kuroshio. The expansion/shrinkage of the spawning habitat of sardine and anchovy in the shelf region, apparently responding to the change in the Kuroshio, possibly makes the alternation in dominance of postlarval sardine and anchovy most prominent in the Enshu‐nada Sea, in combination with changes in the abundance of spawning adults, which occurred almost simultaneously in the overall Kuroshio region. The implication of this rather regional feature for the alternating dominance of sardine and anchovy populations on a larger spatial scale is also discussed.  相似文献   

7.
We compared a wide range of environmental data with measures of recruitment and stock production for Japanese sardine Sardinops melanostictus and chub mackerel Scomber japonicus to examine factors potentially responsible for fishery regimes (periods of high or low recruitment and productivity). Environmental factors fall into two groups based on principal component analyses. The first principal component group was determined by the Pacific Decadal Oscillation Index and was dominated by variables associated with the Southern Oscillation Index and Kuroshio Sverdrup transport. The second was led by the Arctic Oscillation and dominated by variables associated with Kuroshio geostrophic transport. Instantaneous surplus production rates (ISPR) and log recruitment residuals (LNRR) changed within several years of environmental regime shifts and then stabilized due, we hypothesize, to rapid changes in carrying capacity and relaxation of density dependent effects. Like ISPR, LNRR appears more useful than fluctuation in commercial catch data for identifying the onset of fishery regime shifts. The extended Ricker models indicate spawning stock biomass and sea surface temperatures (SST) affect recruitment of sardine while spawning stock biomass, SST and sardine biomass affect recruitment of chub mackerel. Environmental conditions were favorable for sardine during 1969–87 and unfavorable during 1951–67 and after 1988. There were apparent shifts from favorable to unfavorable conditions for chub mackerel during 1976–77 and 1985–88, and from unfavorable to favorable during 1969–70 and 1988–92. Environmental effects on recruitment and surplus production are important but fishing effects are also influential. For example, chub mackerel may have shifted into a new favorable fishery regime in 1992 if fishing mortality had been lower. We suggest that managers consider to shift fishing effort in response to the changing stock productivity, and protect strong year classes by which we may detect new favorable regimes.  相似文献   

8.
ABSTRACT:   Recent surveys showed substantial aggregation of larvae of jack mackerel in the southern East China Sea, indicating intensive spawning grounds near Taiwan. A numerical model was applied to investigate transport and survival processes of eggs and larvae of jack mackerel from the spawning area to the nurseries. The results show that: (i) the distributions of larvae simulated by the model agreed well with those obtained by field survey; (ii) the stock of jack mackerel in the Sea of Japan is composed of both groups from north of Taiwan and from the western coast of Kyushu. It takes more than two months for the former to reach the Sea of Japan, while it is within 40 days for the latter; and (iii) large proportions of the eggs and larvae spawned off the north of Taiwan are transported rapidly to the Pacific side of Kyushu by the Kuroshio Current, and the rest slowly to the east or north-east along the continental slope in the East China Sea. In contrast to the larval flux, survivors are more abundant in the northern East China Sea than in the Pacific Ocean, indicating that survival in the northern East China Sea would determine the jack mackerel stock in Japan.  相似文献   

9.
Recent 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.  相似文献   

10.
Horizontal distribution patterns of jack mackerel (Trachurus japonicus) larvae and juveniles were investigated in the East China Sea between 4 February and 30 April 2001. A total of 1549 larvae and juveniles were collected by bongo and neuston nets at 357 stations. The larvae were concentrated in the frontal area between the Kuroshio Current and shelf waters in the upstream region of the Kuroshio. The abundance of small larvae (<3 mm notochord length) was highest in the southern East China Sea (SECS) south of 28°N, suggesting that the principal spawning ground is formed in the SECS from late winter to spring. Jack mackerel also spawned in the northern and central East China Sea (NECS and CECS, respectively), as some small larvae were also collected in these areas. In the SECS, the abundance of small larvae was highest in February and gradually decreased from March to April. The habitat temperature of small larvae in the SECS and CECS (20–26°C) was higher than that in the NECS (15–21°C), suggesting higher growth rates in the SECS and CECS than in the NECS. The juveniles (10‐ to 30‐mm standard length) became abundant in the NECS off the west coast of Kyushu Island and CECS in April and were collected in association with scyphozoans typical of the Kuroshio waters. However, juveniles were rarely collected in the SECS, where the small larvae were concentrated. Considering the current systems in the study area, a large number of the eggs and larvae spawned and hatched in the SECS would be transported northeastward by the Kuroshio and its branches into the jack mackerels’ nursery grounds, such as the shallow waters off the west coast of Kyushu and the Pacific coast of southern Japan.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号