Recruitment Processes of Anchovy in Chesapeake Bay: Predation Effects, Spawning Sites and Larval Transport

成鱼丰度的波动是由不同的补充水平引起的，这是早期生命阶段高而可变的死亡率的结果。切萨皮克湾海湾凤尾鱼Anchoa mitchilli卵和仔鱼死亡率高的原因被认为主要是由于大量水母的捕食，这些水母在时间和空间上都是零星的。假设在低捕食压力下，凤尾鱼群可以在“窗口”中发育，以提供一种成功招募的机制。一个概念模型预测，通过河口水动力，凤尾鱼幼体将被输送到海湾上游，进入潮汐支流。这一模型和相关假设将在本次调查中得到检验。环湾巡游将绘制凤尾鱼卵、幼虫和捕食者的丰富地图，将它们与可能影响生存、生长和分布的环境梯度联系起来。将根据幼虫耳石的每日增量估计特定地区的年龄-频率分布、生长速度和死亡率。后期幼体和幼体的起源区域和可能的运输轨迹将通过分析锶与钙的比率从耳石微观化学中确定，这应该表明幼虫孵化的盐度区域。在环境条件下的大型漂流中，捕食率的直接测量将被获得。切萨皮克湾是一个吸引人的生态系统，可以在其中研究招聘过程。大量的海湾凤尾鱼鱼卵和幼虫在捕食者丰度、食物可获得性和良好描述的河口环流模式方面具有广泛的时间和空间变异性。这里的海湾分析将为影响鱼类生存和补充潜力的机制提供新的信息。

Fluctuations in adult fish abundance are caused by variable recruitment levels, a consequence of high and variable mortality during the early life stages. Causes of high mortality of bay anchovy Anchoa mitchilli eggs and larvae in Chesapeake Bay are believed to be primarily from predation by abundant jellyfish, which are both temporally and spatially patchy. "Windows" in which anchovy cohorts can develop under low predation pressure are hypothesized to provide a mechanism for successful recruitment. A conceptual model predicts that anchovy larvae will be transported up-bay and into the tidal tributaries by estuarine hydrodynamics. This model and related hypotheses will be tested in this investigation. Bay-wide cruises will map abundances of anchovy eggs, larvae and predators, relating them to environmental gradients that may affect survival, growth and distribution. Area- specific age-frequency distributions, growth rates and mortality rates will be estimated from daily increments in larval otoliths. Areas of origin, and probable transport trajectories of late-stage larvae and juveniles will be determined from otolith microchemistry by analysis of strontium:calcium ratios, which should indicate salinity zones where larvae hatched. Direct measures of predation rates will be obtained in large drifting mesocosms under ambient environmental conditions. Chesapeake Bay is an appealing ecosystem within which to study recruitment processes. Abundant cohorts of bay anchovy eggs and larvae are presented with wide ranges of temporal and spatial variability in predator abundances, food availability and well- described estuarine circulation patterns. The bay-wide analysis here will provide new information of mechanisms that affect survival and recruitment potential of fishes.