Animal groups are known to exhibit collective behaviours that allow for effective responses to predators and environmental factors. Habitats with high levels of structural complexity have been shown to influence the collective tendencies of these animal aggregations. However, the effect of anthropogenically induced habitat complexity on collective tendency is still unknown. We examined the effect of a water control structure (WCS), located in an estuarine salt marsh system, on the collective behaviours of free ranging juvenile Gulf menhaden (Brevoortia patronus), a schooling forage fish. Using an acoustic imaging sonar, behavioural observations prior to and during predator attacks were collected in an open marsh canal as well as in the vicinity of the WCS. We found that fish in schools responded to the WCS by swimming in a less aligned and cohesive manner, while maintaining an increased ability to transfer social information. Our results demonstrate that collective tendency in schooling fish is affected by the presence of anthropogenically introduced habitat complexity, prior to and during predator attack. Our study, thus, strengthens the idea that the complex environmental conditions induced by the presence of man-made structures may play a large role in structuring collective behaviour and trophic interactions in aquatic environments.

众所周知，动物群体表现出集体行为，可以对捕食者和环境因素做出有效反应。具有高度结构复杂性的栖息地已被证明会影响这些动物聚集的集体趋势。然而，人为引起的栖息地复杂性对集体趋势的影响仍然未知。我们研究了位于河口盐沼系统中的水控制结构 (WCS) 对自由放养的海湾鲱鱼幼鱼（Brevoortia pauseus）的集体行为的影响)，一种教育饲料鱼。使用声学成像声纳，在开放的沼泽运河以及 WCS 附近收集捕食者攻击之前和期间的行为观察。我们发现学校里的鱼通过以不那么一致和凝聚力的方式游动来响应 WCS，同时保持增强的社会信息传递能力。我们的结果表明，在捕食者攻击之前和期间，鱼群的集体趋势受到人为引入的栖息地复杂性的影响。因此，我们的研究强化了这样一种观点，即由人造结构的存在引起的复杂环境条件可能在构建水生环境中的集体行为和营养相互作用方面发挥重要作用。