背景:Anadromy包括对鲑鱼的成功生命周期适应,海洋迁徙提供了改善的喂养机会,从而改善了生长。这些奖励与来自增加的能量消耗和死亡风险的成本相平衡。人为引起的环境变化,减少移民利益和/或增加移民成本,例如,水产养殖和水力发电,因此,可能会导致适应性不利于anadromy。我们标记了棕色鳟鱼(Salmotrutta)smots(N=175)和资深移民(N=342),来自索格内夫乔登的五个相邻河流种群,最长的挪威峡湾系统,支持无缘褐鳟鱼种群(209公里)。四年多,部署了138个声学遥测接收器,以跟踪被标记的个体从淡水和整个Sognefjorden的迁移。检测到的运动用于拟合每个生命阶段的生存和运动的迁移模型和多状态标记重新捕获模型。对Seaward迁移距离进行了建模,以检查替代迁移策略的适应性后果,这些模型用于模拟个体和伴随生长的峡湾使用程度,繁殖力和生存后果。我们将这些发现与水产养殖和水电开发之前收集的重新捕获数据进行了比较。
结果:遥测数据显示,所有人群都使用了最外层峡湾区域,尽管很少有人使用。然而,历史上的夺回位于离河口更远的地方(87.7±70.3公里),与当今对应物的最大迁移距离(58.6±54.9km)相比。起源河影响了观察到的迁徙行为,并估计了每个种群和生命阶段的差异生存率。基于遥测数据模型的模拟显示,smots和资深移民的人口之间的生存率差异分别为30%和23%,分别。在个人层面,长距离迁移策略获得了繁殖力增强的奖励。然而,对人口繁殖力的主要贡献绝大多数来自中距离移民,由于较高的死亡率和有限的远程移民。
结论:我们得出的结论是,当今的无性系是不稳定的,但是潜在的风险在生命阶段和人群之间差异很大,即使在一个单一的峡湾系统。我们的研究结果表明,选择延长移民面临压力,因此,我们强调监测和管理行动的重要性,以确保遗传变异与保持anadromy的健康收益有关。
BACKGROUND: Anadromy comprises a successful life-cycle adaptation for salmonids, with marine migration providing improved feeding opportunities and thus improved growth. These rewards are balanced against costs from increased energy expenditure and mortality risk. Anthropogenic-induced environmental changes that reduce benefits and/or increase costs of migration e.g., aquaculture and hydropower, may therefore result in adaptations disfavouring anadromy. We tagged brown trout (Salmo trutta) smolts (N = 175) and veteran migrants (N = 342), from five adjacent riverine populations located in Sognefjorden, the longest Norwegian fjord-system supporting anadromous brown trout populations (209 km). Over four years, 138 acoustic telemetry receivers were deployed to track migrations of tagged individuals from freshwater and throughout Sognefjorden. Detected movements were used to fit migration models and multi-state mark-recapture models of survival and movement for each life-stage. Seaward migration distance was modelled to examine the fitness consequences from alternate migration strategies, with these models used to simulate the extent of fjord-use by individuals and accompanying growth, fecundity and survival consequences. We compared these findings with mark-recapture data collected prior to aquaculture and hydropower development.
RESULTS: The telemetry data revealed that the outermost-fjord region was utilised by all populations albeit by few individuals. However, historical recaptures were located at a greater distance from the river mouth (87.7 ± 70.3 km), when compared to maximum migration distances of present-day counterparts (58.6 ± 54.9 km). River of origin influenced observed migratory behaviour and differential survival was estimated for each population and life-stage. The simulations based on telemetry-data models revealed a 30% and 23% difference in survival among populations for smolts and veteran migrants, respectively. At the individual-level, a long-distance migration strategy was rewarded with enhanced fecundity. However, the main contribution to population-level fecundity was overwhelmingly derived from middle-distance migrants, due to higher mortality rates and limited numbers of long-distant migrants.
CONCLUSIONS: We conclude that present-day anadromy is precarious, but potential risk varies considerably between life-stages and populations, even within a single fjord system. Our findings suggest that selection for extended migration is under pressure, we therefore stress the importance of monitoring and management actions to secure genetic variation pertinent to preserve fitness gains of anadromy.