The thinlip grey mullet (Chelon ramada Risso, 1827) is a catadromous fish that performs massive migrations to freshwater habitats for feeding purposes that can assume a structuring role on riverine ecology due to the biomass involved in these movements. Seasonal movements of thinlip grey mullet through a vertical slot fish pass located in River Mondego (Portugal) were continuously monitored between 2013 and 2017. The extent of trophic migration, population size structure, biomass and the environmental triggers of bi-directional species' migratory activity were analysed. Between March and November of 2013/2014, ~2 million and 1 million movements were respectively recorded. From a subsampling approach, the upstream movements between 2015 and 2017 were estimated. Annually, around five hundred thousand upstream movements can occur to provide species access to the upstream freshwater reaches. Movements are exclusively diurnal, and the population composed by young adults in their first year of maturity, yet juveniles and larger fish were present (TL range: 90–540 mm). Upstream movements increased with temperatures above 15°C, reaching a peak at around 20°C coupled with a photoperiod of 15 h. Downstream movements attained the higher rates when temperature dropped from 22°C to 20°C and photoperiod to 13 h. However, under wetter hydrological conditions (as in 2014), discharge flows have a higher influence.

中文翻译：

---

淡水中薄唇鲻鱼迁移的时间模式

薄唇鲻鱼 ( Chelon ramadaRisso, 1827) 是一种流域鱼类，为了觅食而大规模迁徙到淡水栖息地，由于这些迁徙涉及生物量，因此可以在河流生态中发挥结构性作用。2013 年至 2017 年期间，持续监测了薄鳍鲻鱼通过位于 Mondego 河（葡萄牙）的垂直槽鱼道的季节性运动。营养迁移的程度、种群规模结构、生物量和双向物种迁移活动的环境触发因素进行了分析。2013/2014 年 3 月至 11 月期间，分别记录了约 200 万和 100 万次移动。通过二次抽样方法，估计了 2015 年至 2017 年之间的上游移动。每年，可能会发生大约 50 万次上游移动，为物种提供进入上游淡水河段的通道。运动完全是昼夜活动，种群由成熟第一年的年轻成鱼组成，但存在幼鱼和较大的鱼（TL 范围：90-540 毫米）。随着温度超过 15°C，上游运动增加，在 20°C 左右达到峰值，同时光周期为 15 小时。当温度从 22°C 降至 20°C 且光周期降至 13 小时时，下游运动达到更高的速率。然而，在更潮湿的水文条件下（如 2014 年），排放流量具有更大的影响。随着温度超过 15°C，上游运动增加，在 20°C 左右达到峰值，同时光周期为 15 小时。当温度从 22°C 降至 20°C 且光周期降至 13 小时时，下游运动达到更高的速率。然而，在更潮湿的水文条件下（如 2014 年），排放流量具有更大的影响。随着温度超过 15°C，上游运动增加，在 20°C 左右达到峰值，同时光周期为 15 小时。当温度从 22°C 降至 20°C 且光周期降至 13 小时时，下游运动达到更高的速率。然而，在更潮湿的水文条件下（如 2014 年），排放流量具有更大的影响。