Cold offshore area provides a favorable feeding ground with lipid-rich foods for juvenile Japanese sardine

Japanese sardine (Sardinops melanostictus) in the Sea of Japan expanded their distribution from the coast to offshore with an increase in population biomass; however, little is known about the suitability of the offshore habitat for this species. Using lipid analysis, this study compared the body condition of juvenile sardine between an area off the Noto Peninsula (offshore) and the Tsushima Strait (coast), with respect to habitat conditions during the summer, from 2015 to 2017. Sardine in the offshore area had larger bodies and higher lipid contents than those in the coastal area. Regarding the sardine diet, lipid content of the offshore zooplankton was clearly higher than that of the coastal zooplankton. Hence, we found a positive effect of this dietary lipid content on sardine lipid content, suggesting that these lipid measurements could explain the trophic relationship between sardine and zooplankton. The higher lipid content in offshore zooplankton was mainly attributed to the abundance of large-sized copepods and lower water temperatures. Such lipid measurements might involve habitat-specific characteristics of zooplankton assemblage. In conclusion, compared to the coastal area, the offshore area is considered a more favorable habitat for the sardine in terms of lipid availability.

Automated summary

The study revealed that Japanese sardine in the Sea of Japan have larger bodies and higher lipid contents in offshore habitats compared to coastal areas. Offshore zooplankton also showed significantly higher lipid contents than coastal zooplankton, which positively influenced the lipid content of sardines. This suggests that offshore habitats may provide a more favorable environment for sardines in terms of lipid availability.