Source, Trophic Opportunities and Fate of Billfish Larvae in the Diverse Pelagic Habitats of the Straits of Florida

长嘴鱼是一种复杂的大型远洋鱼类，生活在世界海洋的热带和亚热带水域。它们是远洋食物网的顶级捕食者，同时也是咸水垂钓者最喜爱的鱼类。这些海洋“巨人”支撑着价值数百万美元的钓鱼运动产业，并构成了金枪鱼延绳钓的重要副渔获物。不幸的是，人类活动导致长嘴鱼种群数量大幅下降；据认为，蓝马林鱼的数量还不到维持最高可持续捕鱼量所需的40%。尽管它们具有重要的生态地位，但关于这些生物的生物学信息极其有限。关注长嘴鱼的早期生活史阶段是获得有价值的生物学数据的一种容易处理的方法。例如，早期幼虫阶段的收集可与循环数据结合使用，作为确定产卵发生的时间和地点的一种手段。研究与长嘴鱼幼虫发生相关的上层生境变量，可以为了解产卵和早期生存所需的环境条件提供见解。即使在它们的早期生活史中，长嘴鱼也可能是远洋食物链的重要组成部分，尤其是作为浮游动物和幼鱼的捕食者。本研究的总体目标是在佛罗里达海峡复杂的环境中，对长嘴鱼产卵、幼虫生长、摄食和运输的年周期有一个季节性的理解。作为顶级捕食者，长嘴鱼在远洋食物网中扮演着一个至关重要但尚未确定的角色。在这里，我们在佛罗里达海峡（SSF）的海洋学背景下研究长嘴鱼的早期生活史。SSF是一个由离散的、相互作用的水团和远洋环境组成的复杂系统。初步数据表明，长嘴鱼的幼虫可以预见地出现在整个南太平洋海域的三个不同的斑块上。该项目的目的是：1)确定三种不同的长嘴鱼幼体的来源；2)确定这些斑块在长嘴鱼幼鱼的营养和生长环境方面的差异；3)研究不同斑块长嘴鱼幼体的运输命运。田野调查分为三个独立的研究部分：第一项研究将探讨海峡两岸特征的时间性质（即水体质量分布、长嘴鱼幼虫斑块和浮游动物群落结构）。每月取样（包括浮游鱼和浮游动物拖带、CTD、荧光测定法和ADCP测量）为期两年，将通过耳石老化研究和循环模式与产卵地点的估计联系起来。进一步的关于幼虫生长速率的耳石研究将与浮游动物群落组成和动态的研究相结合，以确定斑块之间的营养动力学差异。第二项研究将扩大我们的空间尺度，以研究海峡两岸与长嘴鱼幼虫斑块的形成、维持和命运有关的动态。将在第二年进行一次巡航，并将包括上述相同的一套测量以及argos跟踪的漂船测量。第三年的研究将采用拉格朗日技术，从假设的产卵地点通过佛罗里达海峡系统跟踪长嘴鱼幼虫，将这些轨迹与观察到的海峡两岸空间斑块和离散斑块的最终命运联系起来。采样将包括在与一组漂流者的轨道垂直的站点进行的一套类似的测量。该研究结果将为这些重要的远洋捕食者的早期生活史和生态学，以及不同水团之间的相互作用和远洋食物网的营养动力学提供重要的新信息。进一步了解特定chl的形成、维持和命运。A /浮游动物/幼鱼斑块也将为理解上升流和跨越锋面边界和浅滩的水团交换的作用提供见解。

Billfishes are a complex of large pelagic fishes that occur in the tropical and subtropical waters of the world's oceans. They are top predators in the pelagic food web and, simultaneously, the most sought-after fishes for saltwater anglers. These oceanic "giants" support a multi-million dollar sportfishing industry and comprise a significant bycatch of tuna longline efforts. Unfortunately, human activities have led to significant declines in billfish stocks; blue marlin are thought to be at less than 40% of that necessary to sustain fishing at maximum sustainable yields. Despite their critical ecological status, the biological information available on these organisms is extremely limited. Focusing on the early life history stages of billfishes is a tractable means of obtaining valuable biological data. For example, collection of early larval stages can be used, in conjunction with data on circulation, as a means of determining when and where spawning occurs. Investigation of the pelagic habitat variables associated with the occurrence of billfish larvae may provide insight into environmental conditions required for spawning and early survival. Even in their early life history, billfishes are likely important constituents of the pelagic food chain, especially as predators on zooplankton and larval fishes. The overall objective of this study is a seasonally resolved understanding of the annual cycle of billfish spawning, larval growth, feeding, and transport within the complex environment of the Straits of Florida. As top predators, billfishes play a critical yet undefined role in the pelagic food web. Here we examine the early life history of billfishes within the oceanographic context of the Straits of Florida (SSF). The SSF is a complex system of discrete, interacting water masses and pelagic environments. Preliminary data suggest that billfish larvae occur predictably in three distinct patches across the SSF. The project is designed to 1) identify the sources of the three distinct larval billfish patches within the SSF; 2) determine how the these patches differ in terms of the trophic and growth environment of the billfish larvae; and 3) investigate the transport fates of larval billfishes from these different patches. The fieldwork is divided into three separate study components: The first study will address the temporal qualities of cross-Strait features (i.e., water mass distribution, larval billfish patches, and zooplankton community structure). Monthly sampling (consisting of ichthyoplankton and zooplankton tows, CTD, fluorometry, and ADCP measurements) over two years will be linked via otolith aging studies and circulation patterns to estimates of spawning locations. Further otolith work on larval growth rates will be coupled to zooplankton work on community composition and dynamics to identify trophodynamic differences among patches. The second study will expand the spatial scale of our efforts to examine the along-Strait dynamics relating to the formation, maintenance, and fate of larval billfish patches. A single cruise will be made during the second year and will include the same suite of measurements as above as well as ARGOS-tracked drifter measurements. The third study during year 3 will incorporate Lagrangian techniques to track larval billfishes from hypothesized spawning sites through the Straits of Florida system to link these trajectories to the observed cross-Strait spatial patchiness and ultimate fate of the discrete patches. Sampling will consist of a similar set of measurements conducted at stations normal to the track of a group of drifters. Results of the proposed study will provide critical new information regarding the early life history and ecology of these important pelagic predators as well as the interaction between different water masses and the trophodynamics of pelagic food webs. A further understanding of the formation, maintenance and fate of particular chl. a/zooplankton/larval fish patches also will provide insights into understanding the role of upwelling and water mass exchange across frontal boundaries and shallow banks.