Forecasting Pacific saury (Cololabis saira) fishing grounds off Japan using a migration model driven by an ocean circulation model

Draft genome sequence and tissue expression panel of Pacific saury (Cololabis saira)

Pacific saury (Cololabis saira) is an important fish in several countries. Notably, the catch of this fish has markedly decreased recently, which might be due to environmental changes, including feeding habitat changes. However, no clear correlation has been observed. Therefore, the physiological basis of Pacific saury in relation to possible environmental factors must be understood. We sequenced the genome of Pacific saury and extracted RNA from nine tissues (brain, eye, gill, anterior/posterior guts, kidney, liver, muscle, and ovary). In 1.09 Gb assembled genome sequences, a total of 26,775 protein-coding genes were predicted, of which 26,241 genes were similar to known genes in a public database. Transcriptome analysis revealed that 24,254 genes were expressed in at least one of the nine tissues, and 7,495 were highly expressed in specific tissues. Based on the similarity of the expression profiles to those of model organisms, the transcriptome obtained was validated to reflect the characteristics of each tissue. Thus, the present genomic and transcriptomic data serve as useful resources for molecular studies on Pacific saury. In particular, we emphasize that the gene expression data, which serve as the tissue expression panel of this species, can be employed in comparative transcriptomics on marine environmental responses.

Effects of oceanographic environment on the distribution and migration of Pacific saury (Cololabis saira) during main fishing season

The Pacific saury (Cololabis saira) is one of the most commercially important pelagic fishes in Asia–Pacific countries. The oceanographic environment, especially the Oyashio Current, significantly affects the distribution of Pacific saury, and may lead to variations in their migration route and the formation of fishing grounds in Japanese coastal region and the high seas. In this study, six oceanographic factors, sea surface temperature (SST), sea surface chlorophyll-a concentration (SSC), sea surface salinity (SSS), sea surface height (SSH), mixed layer depth (MLD), and eddy kinetic energy (EKE), were associated with the monthly catch per unit effort 1 (monthly CPUE₁, ton/vessel) and the monthly CPUE₂ (ton/day) of Pacific saury from Chinese fishing vessels during the optimal fishing periods (September–November) in 2014–2017. The gradient forest analysis showed that the performance of monthly CPUE₁ was higher than monthly CPUE₂ and SST was the most important oceanographic factor influencing monthly CPUE₁, followed by EKE. The generalized additive model indicated that SST, SSH, and EKE negatively affected monthly CPUE₁, whereas SSC, SSS, and MLD induced dome-shaped increases in monthly CPUE₁. The distributions of fishing locations are likely to form along Offshore Oyashio current and meanders, especially in October and November. Synchronous trends in the relationship between the intrusion area of the Oyashio and relative abundance variation index suggest that an increase in the intrusion area of the Oyashio causes more Pacific saury to migrate to the Japanese coastal region, and vice versa. These findings extend our understanding of the effects of the oceanographic environment on Pacific saury.