Age-specific fecundity of Pacific saury

We estimate number of eggs spawned per fish per day (NESFD) of age-0 by winter field sampling in 2015, 2020, 2021, and 2022 as the index of fecundity. Estimated NESFDs of age-0 were compared with those of age-1 provided by previous studies to understand the difference in fecundity among ages. Estimated NESFD of age-0 in winter (80-460 eggs/day/fish, 220 eggs/day/fish in average) was lower than those of age-1 in winter estimated by the previous study (650-830 eggs/day/fish, 740 eggs/day/fish in average). Given the age-specific body weight in winter, NESFD per body weight of age-0 was also lower than age-1, suggesting the non-proportional fecundity to spawning stock biomass. These results stem from the lower spawning frequency and smaller amount of batch fecundity of age-0 than age-1. Assuming the general rule that larger or older fish have longer spawning seasons, we considered that age-1 spawn more eggs per fish per spawning period than age-0. This study recommended to not to assume the equal fecundity for age-0 and age-1 when stock assessment of Pacific saury is conducted by the age structured models.