Distribution of jack mackerel (Trachurus japonicus) larvae and juveniles in the East China Sea, with special reference to the larval transport by the Kuroshio Current

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.     

Transport and survival processes of eggs and larvae of jack mackerel <Emphasis Type="Italic">Trachurus japonicus</Emphasis> in the East China Sea

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.     

Transport and survival of larvae of pelagic fishes in Kuroshio system region estimated with Lagrangian drifters

ABSTRACT:   Transport and survival of larvae of pelagic fishes in the Kuroshio system region were studied using Lagrangian drifter data recorded from 1990 to 2003. A large portion of the drifters from the Kuroshio area south of Japan spread around the Kuroshio Extension up to 170°E, while some moved south to the offshore area of the Kuroshio because of a recirculation gyre. The monthly mean eastward movement from areas south of Japan was approximately 800–900 km, which was smaller than previous numerical estimates. The results of a survival model assuming optimal temperatures for larvae suggest that surface waters during the observation period were too warm for larval Japanese sardine, which has an optimal temperature of 16°C, and the adult abundances did not increase during the observation period. In contrast, the spawning ground temperatures and transport conditions from an area south-west of Japan in April–June matched the requirement for the larval Japanese anchovy, which has an optimal temperature of 22°C. The combined effects of temperature variations due to seasonality and water mass mixing are suggested to play an important role in determining the environmental temperatures that occur in an area.     

Advection of anchovy (Engraulis encrasicolus) larvae along the Catalan continental slope (NW Mediterranean)

The Gulf of Lions is one of the main anchovy (Engraulis encrasicolus) spawning areas in the NW Mediterranean. During the spring, low‐salinity surface water from the outflow of the Rhône is advected by the shelf‐slope current along the continental slope off the Catalan coast. In June 2000, a Lagrangian experiment tracking these low‐salinity surface waters was conducted to assess the importance of this transport mechanism for anchovy larvae and to determine the suitability of the tracked surface waters for survival of anchovy larvae. The experiment consisted of sampling the tracked water parcel for 10 days with three drifters launched at the core of the shelf‐slope current where low‐salinity surface waters were detected. The survey was completed by sampling the surrounding waters. Anchovy larvae from the spawning area in the Gulf of Lions were advected towards the south in the low‐salinity waters. The size increase of anchovy larvae throughout the Lagrangian tracking closely followed the general growth rate calculated by otolith analysis (0.65 mm day⁻¹). However, advection by the current was not the only mechanism of anchovy larval transport. A series of anticyclonic eddies, originated in the Gulf of Lions and advected southwards, seemed to play a complementary role in the transport of larvae from the spawning ground towards the nursery areas. These eddies not only contributed to larval transport but also prevented their dispersion. These transport and aggregation mechanisms may be important for anchovy populations along the Catalan coast and require further study.     

Larval Japanese eel (Anguilla japonica) as sub‐surface current bio‐tracers on the East Asia continental shelf

Larval Japanese eel (leptocephali) are passively transported from their spawning sites of the North Equatorial Current to the Kuroshio and its branch waters for 4–6 months before reaching the East Asian coasts. The larvae mainly stay within water depths between 50–150 m. The dispersal dynamics of larvae thus should reflect the sub‐surface oceanic currents on the East Asia continental shelf. An analysis of Japanese glass eel catch data in East Asian countries during 1985 to 2009, and for Taiwan from 1968 to 2008, indicates that the overall annual catch is generally correlated across countries of East Asia, and between north and west areas of Taiwan. The Kuroshio and its branch waters disperse glass eels throughout East Asian habitats, and the glass eel distribution matches the flow directionality of oceanic currents. Recruitment in western Taiwan occurs with a sequential southwestern to northwestern direction, suggesting that the Taiwan Strait Current penetrates the western coast of Taiwan in the sub‐surface layer in winter. The monthly averaged sub‐surface 50 m circulation pattern in the vicinity of Taiwan and modeled tracer experiments also support the northward winter sub‐surface current in Taiwan Strait. These results suggest that the larval Japanese eel could serve as a valuable bio‐tracer of sub‐surface currents, and the earlier recruitment dynamics of Japanese glass eels in Taiwan could be a good predictor for the subsequent catch in other East Asia areas.     

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

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.     

Entrainment of larval fish assemblages from the inner shelf into the East Australian Current and into the western Tasman Front

Entrainment and transport of larval fish assemblages by the East Australian Current (EAC) were examined from the coastal waters of northern New South Wales (NSW) to the western Tasman Front, via the separation of the EAC from the coast, during the austral spring of 2004. Shore‐normal transects from the coast to the EAC off northern NSW revealed an inner shelf assemblage of near‐shore families (Clupeidae, Engraulidae, Platycephalidae and Triglidae), an EAC assemblage dominated by Myctophidae and Gonostomatidae, and a broadly distributed assemblage over the continental shelf dominated by Scombridae and Carangidae. Further south and after the EAC had separated from the coast, we observed a western Tasman Front assemblage of inner shelf and shelf families (Clupeidae, Engraulidae, Serranidae, Scombridae, Carangidae, Bothidae and Macroramphosidae). The abundance of these families declined with distance from the coast. Surprisingly, there was no distinctive or abundant larval fish assemblage in the chlorophyll‐ and zooplankton‐enriched waters of the Tasman Sea. Water type properties (temperature‐salinity, T‐S), the larval fish assemblages and family‐specific T‐S signatures revealed the western Tasman Front to be an entrained mix of EAC and coastal water types. We found an abundance of commercially important species including larval sardine (Sardinops sagax, Clupeidae), blue mackerel (Scomber australasicus, Scombridae) and anchovy (Engraulis australis, Engraulidae). The entrainment and transport of larval fish from the northern inner shelf to the western Tasman Front by the EAC reflects similar processes with the Gulf Stream Front and the Kuroshio Extension.     

Habitat use and movement patterns of small (age‐0) juvenile Pacific bluefin tuna (Thunnus orientalis) relative to the Kuroshio

The habitat use of Pacific bluefin tuna (Thunnus orientalis; PBF) in nursery waters off the southern coast of Japan was investigated using archival tags over a 3 year study period (2012–2015), and the data were used to examine the free‐ranging habitat preferences of PBF and the relationship between their horizontal movements and the path of the Kuroshio off the Pacific coast of Japan. The path of the Kuroshio fluctuated seasonally, leading to changes in water temperature that strongly influenced the habitat use of small PBF (2–3 months after hatching). Most PBF were present in coastal waters inshore of the path of the current, and their habitat use changed in response to the distance of the current from the coast. The Kuroshio typically flowed along the coast from summer to autumn, and PBF remained in the coastal waters off Kochi Prefecture during this period. In contrast, PBF quickly moved eastward in winter when the current moved away from the coast. Throughout the winter and spring, the area of habitat use extended widely from the eastern end of the southern coast of Japan (the Boso Peninsula) to the offshore Kuroshio‐Oyashio transition region. These findings suggest that the seasonal habitat use and movement behavior of juvenile PBF are influenced by the distance of the Kuroshio axis from the coast, and the ultimate drivers are likely variations in oceanographic conditions and prey availability along the southern coast of Japan.     

Late winter larval mesopelagic fish assemblage in the Kuroshio waters of the western North Pacific

The larval mesopelagic fish assemblage and its distribution patterns were investigated in the Kuroshio region off southern Japan in late winter. A total of 8690 fish larvae was collected, 85.8% of which were mesopelagic fish larvae. Mesopelagic fish larvae were significantly more abundant in the area east of the Kuroshio axis than west of the Kuroshio axis (660.6 versus 194.5 ind 10 m^?2). Sigmops gracile, Bathylagus ochotensis, Notoscopelus japonicus, Diaphus slender type and Myctophum asperum were the five most abundant larvae and accounted for 16.9, 16.4, 15.2, 13.9 and 9.3% of the total catch in numbers, respectively. We conclude that these larvae were transported by the Kuroshio Current to the more productive transition waters, where they spend their juvenile stage from spring to early summer. The possibility of expatriation and southward long‐distance spawning migrations of N. japonicus and B. ochotensis are discussed, based on the geographic distribution patterns of their larvae, juveniles and adults.     

Egg and larval distributions of seven fish species in north-east Atlantic waters

The distribution of egg and larvae of mackerel, horse mackerel, sardine, hake, megrim, blue whiting and anchovy along the European Atlantic waters (south Portugal to Scotland) during 1998 is described. Time of the year, sea surface temperature and bottom depth are used to define the spawning habitat of the different species. Mackerel, horse mackerel, and sardine eggs and larvae presented the widest distribution, whereas megrim and anchovy showed a limited distribution, restricted to the Celtic Sea and the Bay of Biscay respectively. Correspondingly mackerel, horse mackerel and sardine showed the highest aggregation indices. Blue whiting larvae were found at the lowest temperatures, whereas anchovy eggs and larvae were found in the warmest waters. The analysis is a basis for evaluation of ongoing changes in the pelagic ecosystem of the north‐east Atlantic.     

Seasonal and interannual variations of oceanographic conditions off Mangalore coast (Karnataka, India) in the Malabar upwelling system during 1995–2004 and their influences on the pelagic fishery

Mangalore coast is well known for its multi‐species and multi‐gear fisheries and the fishery and oceanographic features of this region is a true representation of the Malabar upwelling system. Ten years of study (1995–2004) of oceanographic parameters has been carried out from the inshore waters off Mangalore to understand their seasonal and interannual variations and influences on the pelagic fishery of the region. Attempt has been also made to understand the influence of local and global environmental conditions on the alternating patterns of abundance between the Indian mackerel and oil sardine from the area. Field‐ and satellite‐derived oceanographic data have shown that coastal upwelling occurs during July–September with a peak in August resulting in high nutrient concentrations and biological productivity along the coast. Nearly 70% of the pelagic fish catch, dominated by oil sardine and mackerel, was obtained during September–December, during or immediately after the upwelling season. Catches of scombroid fishes were significantly related to cold Sea Surface Temperature, while such relationships were not observed for sardines and anchovies. Significant positive correlations were observed between the ENSO events (MEI) and seawater temperature from the study area. The extreme oceanographic events associated with the cold La Niña, which preceded the exceptional 1997–98 El Niño event, were responsible for the collapse of the pelagic fishery, especially the mackerel fishery along the southwest coast of India (Malabar upwelling system). Coinciding with the collapse of the mackerel fishery, oil sardine populations revived during 1999–2000 all along the southwest coast of India. Tolerance of oil sardine to El Niño / La Niña events and the low predatory pressure experienced by their eggs and larvae due to the collapse of mackerel population might have resulted in its population revival.     

Identifying potential habitat distribution of the neon flying squid (Ommastrephes bartramii) off the eastern coast of Japan in winter

Habitat suitability index (HSI) models were applied to identify the potential habitat distribution of the neon flying squid (Ommastrephes bartramii) off the eastern coast of Japan during winter. We used an ocean reanalysis product, a satellite‐derived dataset, and commercial fisheries data during 2003–2008 to develop the HSI models, and illustrated the characteristics of the ocean environments at the fishing ground of the neon flying squid, focusing on a typical fishing ground formation event in 2006. The estimated HSI fields of the neon flying squid using three‐dimensional (3D) ocean environmental parameters showed a clear relationship between the squid habitat and the edge of a warm core ring south of the Oyashio water; this is considered a key characteristic of fishing ground formation, as noted in Sugimoto and Tameishi (Deep‐Sea Research, 39, 1992 and S183). This result suggests that mixing of the warm and nutrient‐poor Kuroshio water and the cold and nutrient‐rich Oyashio water at the edge of the ring could provide favorable conditions for the foraging of the neon flying squid. The warm water condition in the subsurface layers could be a further advantage to the formation of a stable fishing ground for the neon flying squid. Comparison of the Akaike Information Criteria among a satellite‐data‐based model, a reanalysis‐based model using the same parameters as the satellite‐based model, and a reanalysis‐based model using 3D ocean environmental parameters, showed an apparent improvement in the performance of the reanalysis‐based model using the 3D parameters, reproducing realistic features of the squid fishing ground during the winter of 2006.     

A basking shark (Cetorhinus maximus) tracked by satellite together with simultaneous remote sensing II: New analysis reveals orientation to a thermal front

AVHRR remote sensing data for sea surface temperature during the first successful satellite track of a basking shark, Cetorhinus maximus on 6 July 1982 is analysed using the new composite front map technique. The shark is shown to have been swimming, presumed to be filter-feeding zooplankton, in warm coastal water off the west coast of Scotland parallel to the line of a thermal front.     

Diversity and distribution of early life stages of carangid fishes in the northwestern Mediterranean: responses to environmental drivers

The diversity and distribution of the early stages of carangid fishes were investigated in relation to environmental conditions off the Catalan Coast (NW Mediterranean). Data were obtained during four oceanographic cruises conducted in spring–summer 2003 and 2004. A total of 4743 larvae from seven species and five genera were identified. Most were thermophilic species very abundant in the warm waters of the south and eastern Mediterranean. The presence of larvae and juveniles of Caranx crysos, Caranx rhonchus, Seriola dumerili and Trachinotus ovatus in the northwestern Mediterranean is reported for the first time. Except for Trachurus trachurus, which spawns in winter–spring, all species reproduce in spring–summer with a temporal succession in their spawning peaks. On average, the spatial patterns of different species (except T. trachurus) showed common features: a clear preference for spawning in coastal areas, high abundance of larvae in the south warmer zone in relation to the surface productive waters of Ebro river runoff and relatively high larval concentrations south of the thermal front and its associated anticyclonic eddy. The presence of larvae of thermophilic species of carangids in the northwestern Mediterranean indicates successful reproduction and establishment of these species in the cold part of the basin.     

Hydrographic phenomena influencing early life stages of the Sicilian Channel anchovy

The information collected from a European Union funded project on the ‘Distribution Biology and Biomass Estimates of the Sicilian Channel Anchovy (Engraulis encrasicolus)’ was used to analyse the linkage between the general circulation pattern of the Atlantic Ionian Stream (AIS) and the reproductive strategy of the Sicilian Channel anchovy. The main spawning ground is located in the NW region of the southern Sicilian coast. This region is a stable area of low current produced by the impingement towards the coast of the AIS and its bifurcation into two branches. The main branch heads towards the SE end of the Sicilian coast (Cape Passero) acting as a transport mechanism for the anchovy eggs and larvae. Along the AIS trajectory, there is a density front to the left of the current, facing downstream. This front is a consequence of the shoreward sloping of isopycnals that maintains the geostrophic flow, facilitating the mixing of deeper waters with surface layers and fertilization of coastal waters. The front enhances primary production assuring food availability for anchovy larvae during their advection by the AIS. The highest concentrations of larval anchovy were found off the SE Sicilian coast, in the area off Cape Passero. The greater average sizes of larvae found in this region, and their estimated age, support the evidence of advection by the AIS. The hydrographic features observed in this area, such as the existence of a well‐defined cyclonic vortex, implies the existence of upwelling in its centre, providing a suitable environment for sustained enhanced rates of primary production and allowing the larval population to maintain their relative position. This retention area is conceived as favourable for providing the necessary feeding conditions. The data acquired from a survey carried out to evaluate the anchovy recruitment strength confirm that larvae reach the juvenile stage in the south‐eastern coast of Sicily, since most of the young‐of‐the‐year anchovy were located in the Cape Passero region.     

The spatial structure of the oceanic spawning of jack mackerel (Trachurus murphyi) off central Chile (1998–2001)

The jack mackerel population has a widespread oceanic spawning habitat off central Chile, extending more than one thousand nautical miles offshore. In this paper, the spatial structure of jack mackerel eggs density is analyzed on the basis of four surveys carried out in oceanic waters (32°S–39°S, 75°W–92°W), from 1998 to 2001. In each survey, a grid of plankton stations was sampled through vertical hauls with WP2 plankton nets by using several purse-seine fishing ships sampling simultaneously along the E–W transects. With the aim of finding the bulk of the egg distribution within the surveyed area, an exploratory analysis between jack mackerel egg densities, latitude, longitude, and sea surface temperature (SST) was carried out. The spatial structure of the egg distribution was studied using geostatistical techniques. The bulk of the jack mackerel spawning tends to occur offshore between 80°W and 92°W, is maximal at 35°S and associated to SST warmer than 15–16 °C. All of the variograms showed clear spatial autocorrelations without anisotropy, with the range fluctuating between 125 and 252 nautical miles. The range of variograms suggests that the spawning of jack mackerel is a large scale process, probably reflected in the adult behavior of the spawning by favoring a high dispersion of eggs and/or associated with sea surface temperature characterizing the subtropical frontal zone (16–18 °C) off central Chile.     

Estimation of the spawning grounds of chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> and spotted mackerel <Emphasis Type="Italic">Scomber australasicus</Emphasis> in the East China Sea based on catch statistics and biometric data

The spawning grounds of the chub mackerel (Scomber japonicus) and spotted mackerel (Scomber australasicus) in the East China Sea were estimated based on catch statistics of the Japanese large- and medium-type purse seine fishery from 1992 to 2006. Biometric data were obtained from specimens caught by purse seiners in the East China Sea from 1998 to 2006. Gonadosomatic index (GSI) at 50% sexual maturity of chub mackerel and spotted mackerel females was 2.5 and 2.6, respectively. Using this criterion for GSI, chub mackerel larger than 275 mm and spotted mackerel larger than 310 mm in fork length were considered to be mature. Mature chub mackerel was observed in the area of 15–22°C sea surface temperature (SST), and mature spotted mackerel was observed in the area of 17–25°C SST. The spawning period of chub mackerel ranged from February to June, and that of spotted mackerel ranged from February to May in the East China Sea. The spawning grounds were estimated from the distributions of catch per unit effort (CPUE) of spawners and SST. As a result, the spawning ground of chub mackerel was estimated to be in the central and southern part of the East China Sea and the area west of Kyushu in February, March, and April, and in the central part of the East China Sea, the area west of Kyushu and Tsushima Straight in May, and in Tsushima Straight and western part of the Sea of Japan in June. The spawning ground of spotted mackerel was estimated to be in the central and southern part of the East China Sea and southern coastal area of Kyushu in February, March, and April, and the central and southern part of the East China Sea and the area west of Kyushu in May.     

Ichthyoplankton-based spawning dynamics of blue mackerel (Scomber australasicus) in south-eastern Australia: links to the East Australian Current

We describe findings of three ichthyoplankton surveys undertaken along south‐eastern Australia during spring (October 2002, 2003) and winter (July 2004) to examine spawning habitat and dynamics of blue mackerel (Scomber australasicus). Surveys covered ～860 nautical miles between southern Queensland (Qld; 24.6°S) and southern New South Wales (NSW; 41.7°S), and were mainly centred on the outer shelf including the shelf break. Egg identifications were verified applying mtDNA barcoding techniques. Eggs (n = 2971) and larvae (n = 727; 94% preflexion) occurred both in spring and winter, and were confined to 25.0–34.6°S. Greatest abundances (numbers per 10 m²) of eggs (1214–7390) and larvae (437–1172) occurred within 10 nm shoreward from the break in northern NSW. Quotient analyses on egg abundances revealed that spawning is closely linked to a combination of bathymetric and hydrographic factors, with the outer shelf as preferred spawning area, in waters 100–125 m deep with mean temperatures of 19–20°C. Eggs and larvae in spring occurred in waters of the East Australian Current (EAC; 20.6–22.3°C) and mixed (MIX; 18.5–19.8°C) waters, with none occurring further south in the Tasman Sea (TAS; 16.0–17.0°C). Results indicate that at least some of the south‐eastern Australian blue mackerel stock spawns during winter‐spring between southern Qld and northern NSW, and that no spawning takes place south of 34.6°S due to low temperatures (<17°C). Spawning is linked to the EAC intrusion, which also facilitates the southward transport of eggs and larvae. Since spring peak egg abundances came from where the EAC deflects offshore, eggs and larvae are possibly being advected eastwards along this deflection front. This proposition is discussed based on recent data on blue mackerel larvae found apparently entrained along the Tasman Front.     

Estimation of habitat suitability for the southern form of the short‐finned pilot whale (Globicephala macrorhynchus) in the North Pacific

Habitat models were developed from dedicated sighting survey data collected during summers between 1983 and 2006 in the North Pacific Ocean. Our aim was to examine the distribution pattern of the southern form of the short‐finned pilot whale (Globicephala macrorhynchus) in relation to the physical environment. We tested two different types of analytical procedures for habitat estimation: generalized linear models (GLMs) and ecological niche factor analysis (ENFA). The area under the receiver operating characteristic curve and the Boyce index suggested that GLM defined the core habitat well, whereas ENFA estimated the suitable habitat more correctly. These models indicated the core habitat within the subtropical gyre. Among the environmental variables used to construct the habitat models, the temperature at a depth of 200 m contributed most to both GLM and ENFA. This corresponds to the fact that the species mainly feeds on mesopelagic prey and that the axis of the Kuroshio Current, in the northwestern part of the subtropical gyre, is characterized by its temperature at 200 m. Habitat suitability in the coastal waters off southern Japan also correlated with the Kuroshio meander patterns. Thus, the southern form of the short‐finned pilot whale appears to be particularly well adapted to the ecosystem of the North Pacific subtropical gyre.     

Occurrence and density of Pacific saury Cololabis saira larvae and juveniles in relation to environmental factors during the winter spawning season in the Kuroshio Current system

The occurrence and density of Pacific saury Cololabis saira larvae and juveniles were examined in relation to environmental factors during the winter spawning season in the Kuroshio Current system, based on samples from extensive surveys off the Pacific coast of Japan in 2003–2012. Dense distributions of larvae and juveniles were observed in areas around and on the offshore side of the Kuroshio axis except during a large Kuroshio meander year (2005). The relationships of larval and juvenile occurrence and density given the occurrence to sea surface temperature (SST), salinity (SSS), and chlorophyll‐a concentration (CHL) were examined by generalized additive models for 10‐mm size classes up to 40 mm. In general, the optimal SST for larval and juvenile occurrence and density given the occurrence was consistently observed at 19–20°C. The patterns were more complex for SSS, but a peak in occurrence was observed at 34.75–34.80. In contrast, there were negative relationships of occurrence and density given the occurrence to CHL. These patterns tended to be consistent among different size classes, although the patterns differed for the smallest size class depending on environmental factors. Synthetically, the window for spawning and larval and juvenile occurrence and density seems to be largely determined by physical factors, in particular temperature. The environmental conditions which larvae and juveniles encounter would be maintained while they are transported. The survival success under the physically favorable but food‐poor conditions of the Kuroshio Current system could be key to their recruitment success.