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Trace element analysis of otoliths from core to edge was used to reveal differences in habitats of larvae and early juveniles of Japanese jack mackerel (Trachurus japonicus) caught in the East China Sea (ECS), Pacific Ocean, and Sea of Japan. Multi‐element signatures (Sr:Ca, Mg:Ca, Na:Ca, K:Ca, and Ba:Ca) were analyzed with multivariate statistics to determine whether these element signatures provide insight into regional population structure. The median values of elements: Ca ratios in otolith core region differed significantly among areas, with most elements between the ECS and the Pacific Ocean or Sea of Japan showing significant differences. The Sr:Ca ratios exhibited a V‐shaped trend from the otolith core to the edge, which was likely related to the vertical habitat layer shift of larvae and early juveniles of T. japonicus. Canonical analysis of principal coordinates using the element: Ca ratios and the hatching day were re‐classified according to the sampling area with higher accuracy in the ECS (88–95%) and the Sea of Japan (76–83%) compared to the Pacific Ocean (69–72%). These results indicate that the proportion of eggs, larvae, and early juveniles transported by the Kuroshio Current from the southern ECS—the main spawning ground—to the Pacific Ocean or the Sea of Japan is low and that juveniles distributed in the coastal waters off southwestern Japan may have originated from local spawners. These results suggest that determining the elemental composition of larvae and juveniles of T. japonicus is effective in determining the habitat differences of this species in the three regions. These findings will help to understand population structure and recruitment process of this species around Japan. [ABSTRACT FROM AUTHOR]

A large fraction of the carbon dioxide added to the atmosphere by human activity enters the sea, causing ocean acidification. We show that otoliths (aragonitic ear bones) of young fish grown under high CO2 (low pH) conditions are larger than normal, contrary to expectation. We hypothesize that CO2 moves freely through the epithelium around the otoliths in young fish, accelerating otolith growth while the local pH is controlled. This is the converse of the effect reported for structural biominerals.

Recruitment of Japanese jack mackerel (Trachurus japonicus) has been decreasing continuously since 2000 in the Pacific coastal waters of Japan. The reasons and mechanisms for this phenomenon are still unclear. Particle‐tracking experiments were performed using a data assimilation model to elucidate the effect of a current system on the transportation processes of T. japonicus from the main spawning ground in the southern East China Sea to the Pacific coastal waters. The experiments demonstrated that T. japonicus were transported from the southern East China Sea to the Pacific waters around western Japan through the Tokara Strait, and the number of particles transported to the Pacific decreased from 2000 to 2017. The particles passing through the northwest Tokara Strait tended to be transported to the Pacific side during 2000–2005 and to the Sea of Japan during 2006–2017. The bifurcation toward the Sea of Japan was due to an amplification of the northward current where the Tsushima Warm Current originates (west of Kyushu). This change was induced by a rising sea level west of Kyushu due to Kuroshio's northward shift along the western Pacific coast of Japan, which induced the Tsushima Strait through flow to strengthen. The decrease in larval transportation due to the current system change can be one of the causes for the recruitment decline of T. japonicus along the Pacific coast. [ABSTRACT FROM AUTHOR]

Diaphus fulgens is a diel vertical migrant myctophid, occurring abundantly in the Kuroshio waters of the East China Sea. They are multiple batch spawners with a short interspawn period, resulting in high egg productivity. Multiple spawning would be supported by feeding during their spawning season; however, there is no information on the feeding habits of this species. The present study examined the diet composition, diel feeding periodicity and daily ration of mature adult D. fulgens collected at different periods of the day during February to March. The most prevalent item was appendicularians and their mucus houses, which dominated the stomach contents in both number and weight. Additionally, various species of copepods were predated, with a prevalence, by weight, of the large-sized Pleuromamma piseki. Diaphus fulgens feeds actively in the epipelagic layer at night and moves down to the mesopelagic layer in the early morning, and digests most of the consumed food by the late afternoon, showing a typical nocturnal feeding pattern. Based on diel changes in the stomach content index and instantaneous gastric evacuation rate estimated in this study (0.118–0.129 h−1), the daily ration was calculated to be 4.0–4.2% of body weight, equivalent to a daily caloric intake of 21.2–22.3 cal day−1. Since the caloric value to produce a batch of oocytes was estimated to be 8.2–11.5 cal day−1, on an energetic basis, D. fulgens can maintain the multiple spawning at a cost of approximately 37–54% of its daily caloric intake. [ABSTRACT FROM AUTHOR]

Anchovy and sardine populations have fluctuated alternately with decadal changes in climatic and oceanic states, although the mechanisms remain unclear. In the western North Pacific, anchovy and sardine share nursery grounds in the Kuroshio-Oyashio transitional waters, where the subtropical and subarctic currents converge from the south and north, respectively. We found that northward expansion of the subtropical waters simultaneously changed the local environment in the nursery grounds to be favorable for late larvae and early juveniles of anchovy, but not for those of sardine during 1996-2002. Increased temperature enhanced growth and survival for anchovy, whereas reduced food availability diminished those for sardine. Northward expansion of the subtropical waters have been linked with wind-forced anomaly of sea-surface height in the central North Pacific. After 1988, when anchovy flourished and sardine collapsed in the western North Pacific, previous studies by other researchers documented similar changes in air-sea interaction. Our results suggest that contrasting responses in growth and survival processes to wind-forced oscillation of the current structures caused the alternate population dynamics between anchovy and sardine in the western North Pacific. Les populations d'anchois et de sardines fluctuent en alternance a l'echelle des changements decennaux de climat et d'etat oceanique, bien que les mecanismes impliques restent peu evidents. Dans l'ouest du Pacifique Nord, les anchois et les sardines partagent les memes zones de nourricerie dans les eaux de transition Kuroshio-Oyashio, ou convergent les courants subtropicaux et subarctiques, provenant respectivement du sud et du nord. L'expansion vers le nord des eaux subtropicales en 1996-2002 a en meme temps modifie l'environnement local des zones de nourricerie pour les rendre propices aux larves avancees et aux premiers stades juveniles d'anchois, mais non a ceux de sardines. L'augmentation de temperature a accru la croissance et la survie des anchois, alors qu'une reduction de la disponibilite de nourriture a restreint celles des sardines. L'expansion vers le nord des eaux subtropicales a ete associee a une anomalie de la hauteur de la surface de la mer sous l'emprise du vent dans le centre nord du Pacifique. Des changements semblables dans les interactions air-mer avaient ete observes lors d'etudes anterieures faites quand les populations d'anchois se sont developpees et celles de sardines se sont effondrees apres 1988 dans l'ouest du Pacifique Nord. Nos resultats laissent croire que les reactions opposees des processus de croissance et de survie aux oscillations des structures de courant sous l'influence du vent expliquent l'alternance des dynamiques de population des anchois et des sardines dans l'ouest du Pacifique Nord. [Traduit par la Redaction], Introduction Fish populations in marine ecosystems have fluctuated with decadal changes in climatic and oceanic states (Chavez et al. 2003; Hsieh et al. 2005; Yatsu et al. 2008). Anchovy and [...]

Abstract: Growth trajectories during larval to early juvenile stages in Japanese sardine (Sardinops melanostictus) were backcalculated based on the widths of otolith daily increments from 1996 to 2003 in the [...]

Growth traits of juvenile Japanese jack mackerel (Trachurus japonicus) were estimated based on otolith daily increments in spring during 2011–2016 in the southwestern part of the Sea of Japan (SWSJ). Spatial variability in growth traits was examined between the western and eastern areas of the study area. Back‐calculated body length at 50 days post hatch varied among areas and years between 26 and 40 mm. Body lengths at age in the eastern area were significantly smaller than those in the western area. Slower growth rate in the eastern area was associated with the lower ambient temperature in the eastern area than in the western area. In the eastern area, interannual variations in the instantaneous growth rate positively correlated with ambient temperature. Furthermore, interannual variations in back‐calculated body length during the late larval and early juvenile stages positively correlated with the juvenile abundance. These results suggest that the thermal conditions in the eastern area are indicative of the growth rate and abundance of juvenile T. japonicus in SWSJ. We further examined relationships between juvenile abundance and thermal conditions during 2003–2019 using archived data of this survey and found that the ambient temperature in the eastern area positively correlated with the juvenile abundance and also the strength of the Tsushima Warm Current. Thus, higher temperatures derived from the Tsushima Warm Current result in a faster growth rate during the late larval and early juvenile stages and subsequently higher abundance of T. japonicus juveniles in SWSJ. [ABSTRACT FROM AUTHOR]