Timing and duration of spawning migration of Pacific herring is known to vary by fish age and length. Older fish mature earlier, but there are few verified examples of differences in the pre-spawning migration of individuals varying in age or size. Here we use sonic tagging to examine the fluctuations in age, fish length and maturity throughout the migration of herring in Akkeshi, Japan. We tracked the horizontal and vertical movement of individual fish using acoustic telemetry and biologging methodology. In Akkeshi Lake, older, larger individuals migrated early, reached peak maturity and remained in the lake until early April, after spawning. The timing and duration of the stay in Akkeshi Lake coincided with the freezing and melting of the surface layer of the lake. Fish tracking indicated no differences in herring in different length classes migrated to and from Akkeshi Lake and offshore and stayed in Akkeshi Bay. For the vertical movement, larger, older herring occupied a wide depth range during diurnal vertical movements as they moved to Akkeshi Lake and to offshore. In contrast, the smaller group occurred frequently in depths shallower than 5 m throughout the day and night. Greater depth variation could result in beneficial effects in predator avoidance and increased prey encounter opportunities though vertical migration. In contrast, smaller herring that were more confined to surface waters could experience more frequent sensing of the environmental cues of spawning grounds such as low-salinity water and olfactory stimulation near the surface. Therefore, there are differences in the benefits and risks during migration for each fish length, which may result in superior spawning grounds and individual mortality in this area.

已知太平洋鲱鱼产卵洄游的时间和持续时间因鱼龄和长度而异。年龄较大的鱼成熟得更早，但几乎没有经过验证的例子表明不同年龄或大小的个体在产卵前迁移存在差异。在这里，我们使用声音标记来检查在日本Akkeshi整个鲱鱼迁移过程中年龄，鱼类长度和成熟度的波动。我们使用声学遥测和生物记录方法跟踪了单个鱼的水平和垂直运动。在厚岸湖，年龄较大、体型较大的个体较早迁徙，达到成熟高峰，并在产卵后一直留在湖中直到 4 月初。在厚岸湖停留的时间和时间恰逢湖面结冰融化。鱼的追踪表明，在从阿克西施湖和近海迁移并停留在阿克西施湾的不同长度等级的鲱鱼没有差异。对于垂直运动，较大、较老的鲱鱼在昼夜垂直运动中占据了较宽的深度范围，因为它们向厚岸湖和近海移动。相比之下，较小的群体在白天和黑夜中频繁出现在深度小于 5 m 的地方。更大的深度变化可能会在避免捕食者方面产生有益影响，并通过垂直迁移增加遇到猎物的机会。相比之下，更局限于地表水域的较小鲱鱼可以更频繁地感知产卵场的环境线索，例如低盐度水和靠近地表的嗅觉刺激。所以，