Arula Timo, Shpilev Heli, Raid Tiit, Sepp Elor
Estonian Marine Institute, University of Tartu, Tallinn, Estonia.
PeerJ. 2019 Jul 22;7:e7345. doi: 10.7717/peerj.7345. eCollection 2019.
Baltic herring () is a total spawner with a group-synchronous ovarian organization. Age polymodality in total spawners is considered an important factor in assuring that a strong population is sustainable under an intensive harvesting regime and different climatic conditions. In the present study, we investigated the seasonal and inter-annual variation in spawner age structure and the effect of preceding winter thermal conditions on the start of the herring spawning and larvae retention period. Herring spawning season in the Gulf of Riga starts up to six weeks later after colder winters compared to milder winters. Significantly older individuals dominated at the beginning of the spawning season, and thus herring mean age gradually decreased towards the end of the spawning season from 1999-2015. On an annual scale, this pattern was obvious after cold winters, while after mild winters the pattern did not continue, indicating a more homogenous maturation cycle and spawning period, despite the age and size of the herring population in mild winters. Further, herring condition factor was studied in relation to age and spawning season following different winter thermal conditions. Young, 2- and 3- year old first-spawning herring experienced significantly lower conditions after cold winters compared to older ages, indicating an age-dependent effect of preceding winter on herring maturation cycle, condition and spawning time.
波罗的海鲱鱼（）是一种全产卵型鱼类，具有群体同步的卵巢组织。全产卵型鱼类的年龄多模态被认为是确保在密集捕捞制度和不同气候条件下强大种群可持续的一个重要因素。在本研究中，我们调查了产卵群体年龄结构的季节性和年际变化，以及前一个冬季热条件对鲱鱼产卵开始和幼鱼滞留期的影响。与较暖的冬季相比，里加湾的鲱鱼产卵季节在较冷的冬季后开始时间要晚六周。在产卵季节开始时，明显年龄较大的个体占主导地位，因此从1999年至2015年，鲱鱼的平均年龄在产卵季节结束时逐渐下降。在年度尺度上，这种模式在寒冷冬季后很明显，而在温暖冬季后这种模式不再持续，这表明尽管温暖冬季鲱鱼种群的年龄和大小不同，但成熟周期和产卵期更加均匀。此外，还研究了不同冬季热条件下鲱鱼的状况因子与年龄和产卵季节的关系。与年龄较大的鲱鱼相比，2岁和3岁首次产卵的年轻鲱鱼在寒冷冬季后的状况明显较低，这表明前一个冬季对鲱鱼成熟周期、状况和产卵时间存在年龄依赖性影响。
