Retrospective analysis of dispersive and retentive behaviors of young-of-the-year fishes: Are fish otoliths environmental chronometers

海洋鱼类的空间行为是对气候变化、开发模式和环境退化的主要生态反应。然而，几乎没有量化和概念性的工具来开发与种群内迁徙和栖息地使用模式变化相关的假设。偶发结构(分散和保持行为中的种群内形态)被认为是一种测量和分类空间行为变异的有效手段，并在种群和集合种群水平上评估变异的后果。利用鱼耳石中的锶、多元素和同位素示踪剂，已经在不同的河口和沿海鱼类中证明了偶发结构。这项研究项目将测试几个导致权变结构的因素，并评估切萨皮克湾内依赖河口的美洲波罗鱼种群权变结构的种群水平后果。过去得到国家科学基金会支持的研究发现，存在两个独立的少年特遣队，被归类为留守(淡水)或分散(咸水)个人。此外，在大样本成人中，观察到了青少年的偶发行为，以决定人口水平上的增长和招募速度。切萨皮克湾白鲈的偶然性结构是评估将偶然性结构(空间行为)与生长、补充、丰度、生活史和环境环境联系起来的重要假说的独特机会。维持特遣队结构的假设机制在很大程度上借鉴了关于留守和迁徙鲑鱼生态形态的文献，这些文献强调留守和分散特遣队之间的早期增长率和新陈代谢差异。对于这一研究项目，将进行密集的浮游鱼场研究和幼体队列分析，以将幼体的生长、死亡和环境条件与随后的幼体临时结构联系起来。将在野外和实验室对少年特遣队进行抽样，并进行生物能量研究，以测试分散的少年是否按比例分配更多的能量用于进食，而较少分配给日常新陈代谢。对于从切萨皮克湾七个主要亚河口采集的大样本成虫，将重建幼虫的分散行为，并研究权变结构作为一种塑造种群内招募和复原力的机制，以及亚种群之间可能的连通性。气候对应急结构的影响也将被调查。耳石同位素示踪剂有望成为比耳石中锶更可靠的苗圃生境示踪剂。保护基本鱼类栖息地(EFH)现在是海洋鱼类管理的任务，但EFH的概念仍然定义不清，许多对栖息地进行分级的方法缺乏严密性或站不住脚。其他研究人员提出了一种系统，根据一组托儿所栖息地招募到成年种群的幼虫数量来对托儿所栖息地进行排序。过去由美国国家科学基金会资助的关于白鲈幼年种群对成体种群贡献的研究，代表了以这种方式评估托儿所栖息地的初步努力。排名系统应该得到额外的评估，因为1)这个概念可以用过去NSF研究和其他地方开发的工具进行测试，但2)这个概念可能需要拓宽。在温带系统中，幼体栖息地使用的后果可能在很大程度上取决于气候。例如，切萨皮克湾白鲈的初步结果表明，在高流量年份，微咸水栖息地贡献了成年新兵的大部分，因此对白鲈的招募和种群增长最重要。尽管如此，在枯水年份，淡水苗圃栖息地对成体种群的贡献不成比例地重要，因此可能会增强种群在十年干旱周期中的复原力。这项研究的一个更广泛的影响是，通过对相关气候周期中的许多人口进行同时分析，对EFH概念进行全面评估。

Spatial behaviors in marine fishes serve as a principal ecological response to climate change, exploitation patterns, and environmental degradation. Yet there exist few quantitative and conceptual tools to develop hypotheses related to intra?population variations in migration and habitat use patterns. Contingent structure (intra?population modalities in dispersive and retentive behaviors) has been proposed as a useful means to measure and categorize variation in spatial behaviors, and to evaluate the consequences of variation at the population and metapopulation level. Contingent structure has been demonstrated in diverse estuarine and coastal fishes using strontium, multi?element, and isotopic tracers in fish otoliths. This research project will test several factors that lead to contingent structure and evaluate population?level consequences of contingent structure for estuarine?dependent populations of white perch, Morone americana, within the Chesapeake Bay. Past research supported by NSF uncovered the existence of two discrete juvenile contingents classified as retentive (freshwater) or dispersive (brackish water) individuals. Further, in a large sample of adults, juvenile contingent behaviors were observed to structure growth and recruitment rates at the population level. Contingent structuring in Chesapeake Bay white perch represents a unique opportunity to evaluate important hypotheses that relate contingent structure (spatial behaviors) to growth, recruitment, abundance, life history, and environmental circumstance. Hypothesized mechanisms for the maintenance of contingent structure draw heavily upon literature for resident and migratory salmon ecomorphs, which emphasizes early growth rate and metabolic differences between retentive and dispersive contingents. For this research project, intensive ichthyplankton field studies and larval cohort analyses will be conducted to link larval growth, mortality and environmental conditions to subsequent juvenile contingent structure. Juvenile contingents will be sampled in the field and in the laboratory, bioenergetic studies will be conducted to test whether dispersive juveniles allocate proportionately more energy toward feeding and less toward routine metabolism. For a large sample of adults collected from seven major Chesapeake Bay sub?estuaries, juvenile dispersive behaviors will be reconstructed, and contingent structuring investigated as a mechanism shaping recruitment and resiliency within populations, and possibly connectivity among sub?populations. Climate effects on contingent structuring will also be investigated. Otolith isotope tracers, which are expected to be more reliable tracers of nursery habitats than strontium in otoliths, will be further developed. Protection of Essential Fish Habitat (EFH) is now mandated in the management of marine fishes, yet concepts of EFH remain poorly defined and many of the approaches to rank habitats lack rigor or are untenable. Other researchers have proposed systems that rank nursery habitat according to how many juveniles from a set of nursery habitats recruit to the adult stock. Past NSF?supported research on the contribution of white perch juvenile contingents to the adult stock represents an initial effort to evaluate nursery habitats in this manner. Ranking systems deserve additional evaluation because 1) the concept is testable with tools developed in past NSF research and elsewhere, but 2) the concept may need to be broadened. In temperate systems, the consequences of juvenile habitat use may largely depend upon climate. For instance, preliminary results for Chesapeake Bay white perch indicate that in high flow years, brackish water habitats contributed a majority of adult recruits and thereby are most important for white perch recruitment and population growth. Still, during low flow years, freshwater nursery habitats made disproportionately important contributions to the adult stock and thereby may confer resiliency to the population during decadal cycles of drought. A broader impact of this research is the comprehensive evaluation of the EFH concept through simultaneous analysis of many populations across relevant climatic cycles.