Fisheries Oceanography最新文献

Early growth rate in small pelagic fish is influenced by both exogenous and endogenous factors, and faster growth within a cohort is generally associated with higher survival and successful recruitment. In the central Seto Inland Sea, Hiuchi-Nada, western Japan, recruitment of Japanese anchovy (Engraulis japonicus) has markedly decreased over the past decade due to reduced early-life survival. This study assessed the link between early growth rate and recruitment indices by comparing growth rates of recruits between periods of high (2002–2006) and low (2013 and 2015–2019) recruitment. Growth rates were significantly lower during the low recruitment period, with fish exhibiting only about 80% of the growth rate observed during the high recruitment period at a given temperature. A time-series analysis revealed that prey biomass per spawning female, maternal condition factor, and nauplius density per larval density declined over the study period, while temperature increased. During the low recruitment period, recruits generally exhibited higher early growth rates than larvae (original population) of the same age, suggesting that faster growing individuals were more likely to survive. However, in 2017, the highest growth rate among recruits coincided with the lowest recruitment and survival indices, implying that the elevated growth may have resulted from growth-selective mortality favoring a small subset of rapid-growing individuals under intense top-down pressures. These findings suggest that the recent decline in early growth rates may be attributable to deteriorating maternal conditions and increased intracohort competition for prey under warming conditions, while year-specific growth-selective mortality may further shape recruitment outcomes.

Deterministic biotic interactions and abiotic conditions define species distributions and abundance, with plankton underpinning food webs to spatially structure predator distributions through bottom-up processes. However, characterizing the mechanism underlying species abundance formation in an oceanic system remains challenging. We applied piecewise structural equation models to examine plankton abundance and environmental conditions in nekton assembly, combined with joint species distribution models to investigate the distribution associations between nekton and plankton in the high-seas area of northwest Pacific. Results revealed that nekton distribution (fish and squid) showed significant associations with plankton abundance, where zooplankton correlations markedly surpassed phytoplankton associations. The fluctuations of plankton abundance directly influence nekton abundance, whereas the effects of environmental conditions were mediated indirectly through effects on plankton. These findings affirm the primacy of plankton abundance in driving nekton distribution and advance understanding of how bottom-up trophic pathways modulate nekton distribution dynamics in pelagic ecosystems.

Pacific bluefin tuna (Thunnus orientalis, PBF) are highly migratory, with a single Pacific-wide stock facing complex management challenges due to extensive transoceanic movements and a recent population recovery. This study addresses persistent knowledge gaps regarding the quantitative contributions of different natal origins to key feeding grounds and the proportions of trans-Pacific migrants in spawning grounds. We used stable isotope analysis of otoliths (δ¹⁸O_oto and δ¹³C_oto) to investigate natal origins and migratory patterns of PBF collected from three key locations: the Philippine Sea–East China Sea (PS-ECS), the Sea of Japan (SoJ), and the California Current Large Marine Ecosystem (CCLME). Our analysis of δ¹⁸O_oto values effectively discriminated natal origins, revealing a strong dominance of PS-ECS-origin fish in catches across all areas. Specifically, 91% of PBF captured in the CCLME originated from the PS-ECS spawning grounds, a proportion that surpassed estimates from those captured in SoJ and PS-ECS. Additionally, the δ¹³C_oto analysis successfully distinguished between trans-Pacific migrants and resident individuals, confirming that a substantial proportion (87%) of adult PBF caught in the PS-ECS spawning grounds have previously migrated to the CCLME. These results confirm the high connectivity of PBF across the Pacific and support its management as a single stock. The high proportion of PS-ECS-origin fish utilizing the CCLME as a critical feeding ground underscores the necessity of managing juvenile exploitation in Eastern Pacific waters to ensure sufficient survivorship and maximize the reproductive output of the adult spawning stock in the Western Pacific. The quantitative estimates of natal origins and migratory patterns derived from this study provide crucial data for future stock assessments and the development of improved spatially explicit management models.

The largehead hairtail (Trichiurus japonicus), a key commercial species in China Seas, has undergone life-history modifications including earlier maturation and decreased body size, attributed to prolonged overharvesting and environmental changes. However, spatial patterns of Age at first maturity (AFM) across its distribution range remain systematically uncharacterized. This study compared AFM between the Bohai Sea (temperate) and the East China Sea (subtropical) populations through otolith microstructure analysis and probabilistic maturation reaction norms (PMRNs). Daily age distributions showed no regional structural differences (independent t-test, p > 0.05), enabling construction of a unified PMRN model. The model identified a baseline maturation threshold at 178 days and showed the presence of population-specific deviations, with 50% maturity occurred at 176 days in Bohai specimens versus 181 days in East China Sea. Gradient forest analysis revealed sea bottom temperature (SBT) as the primary environmental factor influencing AFM difference. Comparative quantification demonstrated that specimens from warmer habitats exhibited systematically earlier maturation than those in cooler regions, with SBT variations accounting for the observed 5-day interpopulation difference. The methodological integration of PMRNs with environmental covariates provides a replicable framework for predicting climate-mediated shifts in fishery species phenology. Results advocate for regionally adaptive management protocols that account for temperature-dependent maturation plasticity to stabilize recruitment in spatially heterogeneous marine environments.

Understanding the trophic ecology of large pelagic fishes is essential to assess their ecological role in marine ecosystems and to develop effective conservation strategies. In the present study, we aimed to provide new information on the trophic ecology of eight large pelagic fish species (Thunnus atlanticus (blackfin tuna), Thunnus albacares (yellowfin tuna), Katsuwonus pelamis (skipjack tuna), Sarda sarda (Atlantic bonito), Euthynnus alletteratus (little tunny), Coryphaena hippurus (dolphinfish), Istiophorus albicans (Atlantic sailfish), and Kajikia albida (white marlin)) using carbon and nitrogen stable isotope analysis. The isotopic data were used to determine the foraging range and trophic position of the species and to assess the isotopic niche widths and resource partitioning between them. Pelagic fish samples (N = 163) were acquired from the Cabo Frio commercial fleet, Rio de Janeiro, Brazil, between February 2009 and January 2010. We found significant differences in both δ¹³C and δ¹⁵N values among the species. S. sarda appears to feed at higher trophic levels and shows isotopic niche segregation with the species analyzed. However, there was a high degree of niche overlap between the other species, with the exception of the genus Thunnus. The isotopic niche width varied among species, with C. hippurus and E. alletteratus showing the widest niches, while S. sarda had the narrowest. These results highlight relevant aspects of the trophic dynamics of species of high commercial value in a region that has not been previously studied. The information contained here can serve as a basis for future conservation and management strategies for these species in the southwest Atlantic.

A generalized additive model (GAM), incorporating sea surface temperature (SST) as a predictor of catch per unit effort (CPUE; tons per hour) from commercial fishing, has been used for the assessment of the major stock of walleye pollock in the Okhotsk Sea. We evaluated 47 GAM configurations and 5 generalized linear model (GLM) configurations for commercial CPUE standardization, including SST and Lagrangian indicators (LIs) as explanatory variables. Incorporating LIs as a regression spline in the GAM improved model performance. Moreover, the vector autoregressive spatiotemporal model (VAST) and generalized additive mixed model (GAMM) including SST and/or LIs were tested to standardize total stock biomass (TSB), based on area-swept data (t/km²) from scientific surveys. The stock assessment model using standardized TSB outperformed models without the standardized TSB with respect to retrospective analysis and model convergence. These findings highlight the importance of SST and LIs in standardized indices for biomass estimation using cohort models, thereby improving the stock assessments of walleye pollock in the Okhotsk Sea.