Upstream passage of Galaxias maculatus and Galaxias brevipinnis: comparative behavioural assessment for improved fish pass design

Abstract 1. Customized fish passage solutions enhance the upstream passage of fish through low-head instream structures. These solutions are designed based on the behaviour of benchmark species, with the hope that they will also perform well for other species. Across species, suitability can be supported by establishing similarity in passage behaviour. However, for small-bodied fish species, such comparative behavioural assessments are largely missing. 2. With respect to spoiler baffle-based passage design for Southern Hemisphere small-bodied fish species, Galaxias maculatus are typically considered as a benchmark species. In order to characterise the upstream passage of G. maculatus with a view to extending it to other species, here the behaviour of G. maculatus and Galaxias brevipinnis were recorded for three different spoiler baffle designs. Hydrodynamic preferences during upstream swimming and resting, including pathway assessment, were analysed. 3. Both species show increased preference to swim at locations with streamwise velocities similar to the known sustained swimming capacity threshold of G. maculatus, whilst resting locations align with minimal streamwise velocities. Preferred pathways were observed to be influenced by the streamwise water velocity and turbulent kinetic energy, with both species showing increased preference to move towards locations with similar streamwise velocities, by avoiding locations with higher turbulent kinetic energy. 4. The study further shows that both species' passage behaviour is more dependent on space availability than individual behaviour alone. The spatial distribution of fine-scale hydrodynamics influences observed swimming and resting behaviour, with both species showing similar passage behaviour for all three tested designs. 5. Synthesis and applications: Similarities, for both passage behaviour and pathway selection, suggest that spoiler baffle-based passage designs are a suitable management option for both species. Both species were observed to use different fine-scale hydrodynamic regions for resting and subsequent swimming. Among the patches, patch P2 provided increased resting and low-velocity swimming cells for both species, which are shown to be important ecological indicators of successful passage applications, supporting further evaluation for possible application of culvert retrofitting, allowing for varying flow rates, slopes and fish species. <br>

摘要1. 定制化过鱼设施可提升鱼类穿越低水头河道内构筑物的上行过流能力。此类设施基于基准物种的行为特征设计，以期对其他鱼类物种同样适用。通过验证过流行为的相似性，可支撑跨物种的过鱼适宜性评估。然而，针对小型鱼类类群，此类比较行为学评估仍较为匮乏。
2. 针对南半球小型鱼类的扰流板（spoiler baffle）式过流设计，通常以南乳鱼（Galaxias maculatus）作为基准物种。为表征南乳鱼的上行过流行为并将研究结论推广至其他鱼类物种，本研究针对三种不同的扰流板设计，记录了南乳鱼与短鳍南乳鱼（Galaxias brevipinnis）的行为表现，并分析了二者在上行游泳与休憩阶段的水动力学偏好，包括行进路径选择行为。
3. 两种鱼类均表现出对顺流流速接近已知南乳鱼持续游泳能力阈值区域的游泳偏好，而休憩区域则对应顺流流速最小的区域。研究观测到，鱼类偏好的行进路径受顺流流速与湍流动能的共同影响：两种鱼类均倾向于选择流速相近的区域，并主动规避湍流动能较高的区域。
4. 本研究进一步表明，相较于单纯的个体行为，两种鱼类的过流行为更多依赖于空间可利用性。精细尺度水动力学的空间分布会影响鱼类的游泳与休憩行为，且两种鱼类在三种测试设计下均表现出相似的过流行为。
5. 综合与应用：两种鱼类在过流行为与路径选择上的相似性表明，基于扰流板的过流设计对这两个物种均为适宜的管理方案。观测发现，两种鱼类会利用不同的精细尺度水动力学区域进行休憩与后续游泳。在各流场斑块中，斑块P2为两种鱼类提供了更多休憩与低流速游泳的区域，而此类区域已被证实是过流设施成功应用的重要生态指标，这为涵洞（culvert）改造的进一步评估提供了支撑，使其可适配不同流速、坡度与鱼类物种。