Smolt lengths are increasingly recognised as an important determinant of salmonid marine survival rates. Overwintering growth rates could thus strongly influence adult return rates. In Atlantic salmon Salmo salar, most overwintering studies focus on rivers in harsh climates with minimal growth, yet in more southerly rivers, overwintering growth rates can be relatively high. Here, the factors influencing annual overwinter growth rates were tested for juvenile S. salar in a temperate chalk stream in southern England over 13 years, where over 10,000 salmon parr were tagged annually in autumn and a proportion recaptured the following spring during smolt emigration. Winters of higher and more variable water temperatures, with longer periods of high flows, showed increased overwintering growth rates. Faster growth rates were recorded from sites further upstream and that had lower parr densities; smaller individuals also grew more than expected for their initial size. These results suggest that a range of factors influences overwintering salmonid growth rates and can be used to inform management decisions to maximise the quality of emigrating smolts.

中文翻译：

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环境和生物因素对英国白垩流中大西洋鲑鱼的越冬生长率的影响

幼鱼的长度越来越被认为是鲑鱼海洋存活率的重要决定因素。因此，越冬增长率可能会强烈影响成虫的返回率。在大西洋鲑鲑鱼盐沼中，大多数越冬研究集中在生长速度极慢的恶劣气候中的河流，但在更偏南的河流中，越冬增长率可能相对较高。在这里，13 年来在英格兰南部的温带白垩溪流中测试了影响年度越冬增长率的因素，其中每年秋季有超过 10,000 条鲑鱼被标记，并且在次年春天在幼鲑迁徙期间重新捕获了一部分。冬季水温更高、变化更大，高流量时间更长，显示越冬增长率增加。从更远的上游站点记录到更快的增长率并且具有较低的parr密度；体型较小的个体也比其初始体型增长得更多。这些结果表明，一系列因素会影响越冬鲑鱼的生长速度，并可用于为管理决策提供信息，以最大限度地提高迁徙的小鲑鱼的质量。