U.S. GLOBEC Phaes III: Environmental Consequences of Tidal- Front Entrainment in Larval Fish along the Southern Flank of Georges Bank

乔治斯银行南侧潮锋诱捕仔鱼的环境后果Lough，J.Manning，E.Caldarone，L.Buckley，L.Incze，D.Townsend大陆架产卵区的一个普遍特征是，鱼类幼体可以集中在潮锋附近，即混合良好和温度分层的水域之间的过渡区，潮汐急流可以导致下行平流增加。也有可能通过跨额交换保留到浅滩育苗区，这一机制的细节尚不清楚。在桡足类丰度和产量达到峰值与幼鱼聚集一致的汇聚区，观察到幼虫的生长和存活得到了促进。然而，由于时间和空间尺度的物理过程很短，物理和各种营养水平的采样是困难的。因此，在1999年4月和5月，我们将集中于以下目标：(1)描述和量化通常在乔治斯滩南侧发现鳕鱼和黑线鳕幼体时潮锋附近的三维环流；(2)确定与物理锋面过程有关的鱼类幼体及其猎物的小尺度分布和时间变异性；(3)估计不同环境中的生命速率；以及(4)评估幼虫游动行为、生理状况和跨额交换和滞留过程的相互关系和相对重要性。现场采样策略和工具包括网格调查、跨锋横断面和漂流研究的组合，这些研究旨在测量与幼鱼及其桡足类猎物相关的时间和空间尺度。无论是鱼还是它们的猎物，都不太可能以足够的分辨率进行测量，以记录交换过程。因此，我们计划使用船载声学多普勒水流剖面仪(ADCP)高分辨率测量水流/切变场，并在采样幼鱼和猎物的同时采样水文结构、营养物质和叶绿素浓度作为水分运动的示踪剂。ADCP/CTD/荧光/营养数据不仅将提供幼鱼无法测量的尺度，而且还将在我们的巡航和GLOBEC的详细物理海洋过程研究和其他模拟组成部分之间提供一个共同的测量分母。当这些数据和过程与我们的其他采样系统(ARGOS/VHF漂移器、MOCNESS/VPP、CTD/PUMP)相结合时，我们希望能够描述潮汐锋过程与鳕鱼和黑线鳕幼体及其猎物在过渡到分层水条件之前和期间的迁移、保留和生长之间的相互作用。

Environmental Consequences of Tidal-Front Entrainment in Larval Fish Along the Southern Flank of Georges BankG. Lough, J. Manning, E. Caldarone, L. Buckley, L. Incze, D. TownsendIt is a general feature of continental shelf spawning regions that fish larvae can be concentrated in the vicinity of tidal-fronts, the transition zone between well-mixed and thermally-stratified waters, and tidal jets can result in increased downstrean advection. There also is the possibility of retention to shoal nursery areas through cross-frontal exchange, a mechanism whose details are unknown. Enhanced growth and survival of larvae have been observed in convergence zones where peak copepod abundance and production coincide with aggregations of larval fish. However, sampling of the physics and various trophic levels is difficult because of the short time- and space-scale physical processes. Therefore in April and May 1999, we will focus on the following objectives: (1) describe and quantify the three-dimensional circulation in the vicinity of the tidal front when cod and haddock larvae are normally found along the southern flank of Georges Bank; (2) determine the small-scale distribution and temporal variability of fish larvae and their prey in relation to the physical frontal processes; (3) estimate vital rates in the different environments; and (4) evaluate the interrelations and relative importance of larval swimming behavior, physiological condition, and cross-frontal exchange and retention processes.The field sampling strategy and instrumentation include a combination of grid surveys, cross-front transects, and drifter studies which have been designed to make measurements on the time- and space- scales relevant to larval fish and their copepod prey. Neither the fish nor their prey are likely, by themselves, to be measured with sufficient resolution to document the exchange process. Consequently, we plan to make high-resolution measurement of the current/shear fields with ship-mounted Acoustic Doppler Current Profiler (ADCP) and sample hydrographic structure, nutrients and chlorophyll concentrations as tracers of water movements contemporaneously with larval fish and prey sampling. Not only will the ADCP/CTD/fluorescence/nutrient data provide a scale of measurement not possible with larval fish, but they will provide a common denominator of measurement between our cruises and the detailed physical oceanographic process studies and other modeling components of GLOBEC. When these data and processes are combined with our other sampling systems (ARGOS/VHF drifters, MOCNESS/VPP, CTD/pump), we hope to be able to describe the interaction between tidal front processes and the transport, retention and growth of cod and haddock larvae and their prey prior to and during the transition to stratified water conditions.