Dual effects of reversed winter–spring temperatures on year‐to‐year variation in the recruitment of chub mackerel (Scomber japonicus)

To clarify the effects of temperature on the recruitment of chub mackerel (Scomber japonicus) in the North Pacific, we investigated the influence of winter surface temperature (WST) on spawners at the time of maturity around the spawning grounds and the influence of ambient spring temperature on larvae using estimated temperature (ET) obtained from particle tracking experiments. We found a significant positive correlation between ET approximately 10 days following hatching and the recruitment per spawning stock biomass (RPS) after 2000. The closer (more meandering) the Kuroshio Current (KC) axis was in relation to the spawning ground, the higher (lower) the spring surface temperature and the higher (lower) RPS was in the spawning ground. In contrast, WST inside KC near the maturity/spawning ground was significantly negatively correlated with RPS. A significant negative correlation between the temperatures in winter and spring was detected in the area after 2000, when the conditions of the Pacific decadal oscillation index and the stability of the Kuroshio Extension were synchronous, indicating that KC shifted northward during this time. The reversed temperature pattern was consistent with the winter–spring movement of KC axis in the offshore direction and was correlated with the winter–spring difference in the intensity of the Aleutian low. These results suggest that the annual variation in chub mackerel recruitment after 2000 was strongly affected by the combined effects of ambient temperature because of the reversal of conditions that occurred between winter and spring around the maturity/spawning ground, which was related to the KC path.     

Winter monsoon promotes the transport of Japanese temperate bass Lateolabrax japonicus eggs and larvae toward the innermost part of Tango Bay,the Sea of Japan

Northwesterly cold winds characteristic of the East Asian Winter Monsoon (EAWM) dictate winter climatic conditions over the Japanese Archipelago. Japanese temperate bass Lateolabrax japonicus is a commercially important coastal fish that spawns offshore in winter and uses shallow waters as nursery habitats. To investigate the effects of EAWM on the planktonic period of L. japonicus, eggs, larvae, and juveniles were quantitatively collected in Tango Bay on the Sea of Japan side in winter and spring from 2007 to 2017. Although eggs occurred close to the mouth of the bay, planktonic larvae occurred further inside as they developed. The horizontal distribution of planktonic larvae, combined with water velocity data obtained from mooring observations, indicated that planktonic larvae are transported south‐ to westward through Ekman current and an anticyclonic circulation, which are driven by northwesterly winds. To evaluate survival during the planktonic period in each year class, the abundance of benthic larvae/juveniles was divided by winter total landings of Lateolabrax spp. (proxy of the spawning stock size). This survival index exhibited a positive correlation with the northwesterly component of winter winds, and a negative correlation with winter air temperature (average from December to February, Spearman's correlation, p < .05). There was, however, no significant correlation with winter water temperature or winter freshwater discharge in the bay. We conclude that northwesterly cold winds of EAWM play a critical role in transporting L. japonicus eggs and larvae toward nursery habitats, specifically beaches and estuaries fringing the innermost part of Tango Bay.     

Modeling the growth,transport, and feeding migration of age-0 Pacific saury Cololabis saira

Fisheries Science - In this study, we developed an individual-based model for age-0 Pacific saury Cololabis saira focusing on the winter-spawned cohort to advance our understanding of the dynamic...     

Transport and survival of Japanese sardine (Sardinops melanostictus) eggs and larvae via particle‐tracking experiments

Particle‐tracking experiments were performed to infer the distribution of larvae of the Japanese sardine (Sardinops melanostictus) and to detect effects of transport environment on sardine recruitment, using the output of a high‐resolution ocean general circulation model and observed data of sardine spawning grounds during 1978–2004. By the 60th day following spawning, approximately 50% of the larvae had been transported to the Kuroshio Extension (KE). Whereas the spawning period and grounds changed markedly in relation to the stock level, the proportion of larvae transported to the KE remained relatively constant and no significant correlations were found between sardine recruitment and the transport proportion. Instead, the recruitment was found to be correlated with physical parameters including the mixed layer depth and the sea surface temperature along several major transport trajectories of sardine larvae. The correlations were most significant for the trajectories in the region 0.5° south to 1° north of the Kuroshio axis (defined as the location of velocity maxima at each longitude) and for larvae spawned in February and March during the high stock period (1978–94), and for larvae spawned in March and April during the low stock period (1995–2004).     

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.     

Modeling the coastal ecosystem complex: present situation and challenges

To enhance numerical modeling of the coastal ecosystem complex (CEC), we reviewed the CEC and related concepts along with the current coastal ecosystem model framework in this study. We identified two model implementation paths from the initial objectives to numerical models: specific model building, and the use of existing model frameworks. As the CEC is still at the conceptual stage, both paths are possible. Four important ecological features of CEC modeling (population connectivity, habitat heterogeneity, ontogeny of organisms, and trophic interactions) were also identified. Models for population connectivity, species distributions, life histories, and food webs were categorized using these features. We found that some previously established concepts (between–habitat interactions, coastal ecosystem mosaic, and seascape nursery) overlap with the CEC concept. Several existing integrated model frameworks were reviewed, focusing on their potential to simulate CEC processes. Building specific models for the CEC at the current conceptual stage will be challenging, and modification of existing models will be needed if they are to be used for CEC modeling. Habitat function, ontogenetic development in early life stages, and recruitment variability are important factors when modifying existing models for the development of CEC models. Although model complexity should become high to reproduce observed ecoclogical processes, an intermediate level of model ccomplexity is feasible to decrease parameter uncertainty in models for fisheries management.