DataSheet1_The Interannual Variability of the Fall Size of Young-of-The-Year Chub (Squalius cephalus): Influence of Phenology, Growth Patterns and Abiotic Factors.docx

Long-term surveys confirm the rapidity of environmental and biological changes undergone by endangered species but that also concerned relatively “tolerant” species, especially common rheophilic species such as European chub (Squalius cephalus, Linnaeus 1758). As many organisms, fish are highly vulnerable during their first life stages. Body size is a determinant factor for ecosystem functioning and for fish to survive to predators or to winter conditions. While numerous studies has already demonstrated the large variability of autumnal size of fish hatched during the year, few have focused on the factors explaining these interannual variations and on the growth patterns underlying these distributions. Using otoliths of young-of-the-year (YOY), we studied how the interannual variability in fall sizes of chub might be related to varying phenology, temperature, hydrology and growth patterns. YOY were sampled in three sections of the same reach of the Rhône River with contrasted hydrological regime: an artificial deep lotic channel (the tailrace of Bollène), a bypassed section with both lotic and lentic areas (former river channel before dam construction) and a reservoir with lentic deep waters. Sampling was performed on each sector during two thermally distinct years. Temperature had an important effect on both phenology and growth rate but it was not expressed similarly among river sections. Fish hatched earlier in the warmer year. Fish sizes were positively correlated with growing degree-days, but with distinct relationships between years and sections. The growth was faster in the warmer year, and in the warmer section, but differences in growth patterns varied between sections. In the bypassed section, the difference was slight, almost not significant, even if temperatures were very different between the 2 years considered. Autumnal variations in size could be explained either by an earlier phenology or by a faster growth due to higher temperatures occurring during the final part of the growing period. Our results were in accordance with general theory’s predictions relating individual growth to temperature, but they also showed that other factors might mitigate the influence of temperature on fish early life stages.

长期监测调查证实，濒危物种所经历的环境与生物变化速率极快，而此类变化同样波及相对“耐受型”物种，尤以欧洲欧鳊（Squalius cephalus，林奈1758）这类常见喜流性（rheophilic）物种为甚。与多数生物类似，鱼类在早期生活史阶段极易受到外界影响。个体体型是决定生态系统功能的关键因素，同时也是鱼类躲避捕食者、顺利越冬的核心条件。尽管已有大量研究证实当年孵化幼鱼的秋季体型存在显著变异，但鲜有研究聚焦于解释这类年际变异的影响因子，以及驱动该体型分布的生长模式。本研究借助当年生幼鱼（young-of-the-year, YOY）的耳石，探究了欧鳊秋季体型的年际变异与物候变化、水温、水文条件及生长模式之间的关联。研究对象采自罗讷河同一河段的三个水文特征差异显著的断面：分别为人工深水急流通道（博莱讷尾水渠）、兼具急流与静水生境的绕流河段（大坝修建前的原河道）以及拥有深水静水环境的水库。研究在两个热条件差异显著的年份对各断面开展了采样工作。水温对物候与生长速率均有显著影响，但该影响在不同河段的表现并不一致。在水温更高的年份，鱼类的孵化时间更早。幼鱼体型与生长度日呈正相关关系，但该相关关系在不同年份与河段间存在显著差异。水温更高的年份以及水温更高的河段，幼鱼生长速率更快，但不同河段的生长模式差异各有不同。在绕流河段中，即便两年间的水温差异显著，幼鱼生长速率的差异却极小，几乎不具备统计学显著性。幼鱼秋季体型的年际变异，既可以归因于更早的孵化物候，也可以归因于生长末期更高水温所带来的更快生长速率。本研究结果既符合“个体生长与水温相关”的通用理论预测，同时也表明其他因素可能会削弱水温对鱼类早期生活史阶段的影响。