Abstract The brackish water Baltic Sea is strongly influenced by irregular saline water inflows. Fewer inflow events since the 1980s have resulted in a decrease in salinity, and will according to predicted climate change continue to decrease. The newly described Baltic flounder Platichthys solemdali has adapted to reproduction at low salinity conditions since it colonized the Baltic Sea 7000 years BP; in the area studied (ICES SD 3d 28.2) spawning occurs at 3–20 m depth at ca 7 psu. Here we monitored variability in year-class strength as newly settled 0-gr fish in three coastal nursery areas, and compared obtained recruitment indices with prevailing temperature and salinity conditions. 0-gr abundance indices varied considerably between years, from 1 to 90, 10–296 and 17–86 at the respective sampling site, and showed strong accordance with the age structure of the adult stock. Variability in temperature showed no effect, but stronger and weaker year-classes respectively were related to variability in salinity in the range 6.6–7.1 psu with stronger year-classes at >6.8 psu. This coincides with variability in spermatozoa motility, fertilization rates and early egg development at different salinities and suggests that the year-class strength may be set already at the egg stage. Thus, only small changes in salinity at spawning may affect reproductive success and ultimately stock development. The potential effects on stock abundance and distribution facing climate change call for changes in future fishing patterns as well as adaptations in management to prevent stock collapse.

中文翻译：

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波罗的海比目鱼（Platichthys solemdali）的招募变异性——盐度的影响对面临气候变化的种群发展的影响

摘要 咸水波罗的海受到不规则咸水流入的强烈影响。自 1980 年代以来较少的流入事件导致盐度下降，并且根据预测的气候变化将继续下降。新描述的波罗的海比目鱼 Platichthys solemdali 自从 7000 年前在波罗的海定居以来，已经适应了低盐度条件下的繁殖；在所研究的区域 (ICES SD 3d 28.2) 中，产卵发生在 3-20 m 深度，约 7 psu。在这里，我们监测了三个沿海育苗区新定居的 0-gr 鱼的年度强度变化，并将获得的补充指数与当时的温度和盐度条件进行了比较。0-gr 丰度指数在各个采样点的年份之间变化很大，从 1 到 90、10-296 和 17-86，并表现出与成年种群的年龄结构高度一致。温度的变化没有显示出影响，但更强和更弱的年份级别分别与 6.6-7.1 psu 范围内的盐度变化有关，而更强的年份级别在 >6.8 psu。这与不同盐度下精子活力、受精率和早期卵子发育的变异性相吻合，表明年级强度可能已经在卵子阶段设定。因此，产卵时盐度的微小变化可能会影响繁殖成功并最终影响种群发育。气候变化对种群丰度和分布的潜在影响要求改变未来的捕捞模式以及调整管理以防止种群崩溃。但更强和更弱的年份等级分别与 6.6-7.1 psu 范围内的盐度变化有关，而更强的年份等级大于 6.8 psu。这与不同盐度下精子活力、受精率和早期卵子发育的变异性相吻合，表明年级强度可能已经在卵子阶段设定。因此，产卵时盐度的微小变化可能会影响繁殖成功并最终影响种群发育。气候变化对种群丰度和分布的潜在影响要求改变未来的捕捞模式以及调整管理以防止种群崩溃。但更强和更弱的年份等级分别与 6.6-7.1 psu 范围内的盐度变化有关，而更强的年份等级大于 6.8 psu。这与不同盐度下精子活力、受精率和早期卵子发育的变异性相吻合，表明年级强度可能已经在卵子阶段设定。因此，产卵时盐度的微小变化可能会影响繁殖成功并最终影响种群发育。气候变化对种群丰度和分布的潜在影响要求改变未来的捕捞模式以及调整管理以防止种群崩溃。这与不同盐度下精子活力、受精率和早期卵子发育的变异性相吻合，表明年级强度可能已经在卵子阶段设定。因此，产卵时盐度的微小变化可能会影响繁殖成功并最终影响种群发育。气候变化对种群丰度和分布的潜在影响要求改变未来的捕捞模式以及调整管理以防止种群崩溃。这与不同盐度下精子活力、受精率和早期卵子发育的变异性相吻合，表明年级强度可能已经在卵子阶段设定。因此，产卵时盐度的微小变化可能会影响繁殖成功并最终影响种群发育。气候变化对种群丰度和分布的潜在影响要求改变未来的捕捞模式以及调整管理以防止种群崩溃。