Origins of Cod on Georges Bank: Contributions of Early Developmental Stages from the Scotian Shelf

乔治海岸鳕鱼的起源：斯科舍大陆架早期发育阶段的贡献最近在缅因州地区的乔治海岸-海湾地区的工作已经记录了从新斯科舍大陆架到乔治海岸的斯科舍大陆架水（SSW）的显著和明显的间歇性通量。SSW是一种相对较冷的淡水团，其中很大一部分来自圣劳伦斯河，通常可以通过水文数据的T-S分析和海面温度的卫星图像来识别。1997年3月，卫星图像和Georges Bank的船上水文采样观测到一次这样的通量事件。对三月巡游中取样的浮游鱼的海上定性分析显示，在卵的丰度和SSW分布之间存在着显著的紧密联系，这表明，连同其他证据，这些卵大多数是在苏格兰大陆架上产卵的，并与SSW水团一起平流到乔治海岸。由此产生了一个基本问题：在多大程度上，乔治海岸的鳕鱼是在早期开发阶段通过加拿大水域向东的平流输送到英格兰银行的？这项研究的目的就是要回答这个问题。该方法将分为两层：(1)对存档的幼虫鳕鱼样本的耳石进行回顾性元素分析，以及1998年和1999年收集的浮游鱼样本，作为乔治银行GLOBEC项目的一部分，使用x射线电子显微探针和元素“指纹”分析它们的Sr/Ca比率，使用紫外线激光烧蚀电感耦合等离子体质谱（ICPMS）；(2)利用核DNA微卫星技术对来自乔治滩和苏格兰陆架的幼虫和成虫群体的遗传特性进行评估。

Origins of Cod on Georges Bank: Contribution of Early Developmental Stages from the Scotian ShelfRecent work in the Georges Bank-Gulf of Maine area has documented significant, and apparently episodic, fluxes of Scotian Shelf Water (SSW) from the Nova Scotian continental shelf to Georges Bank. SSW is a relatively cold and fresh water mass with a significant component from the St. Lawrence River, and is commonly identifiable with T-S analyses of hydrographic data and in satellite images of sea surface temperature. One such flux episode was observed March 1997 in satellite imagery and from shipboard hydrographic sampling on Georges Bank. Qualitative at-sea analyses of ichthyoplankton sampled on the March cruise revealed a remarkably tight association between abundances of gadid eggs and the distribution of SSW suggesting, along with other lines of evidence, that most of those eggs were spawned on the Scotian Shelf and were advected with the SSW water mass to Georges Bank. The fundamental question thus arises: to what extent are cod on Georges Bank imported to the Bank as early development stages by advection from Canadian waters to the east? The goal of this research is to answer this question. The approach will be two tiered: (1) performing retrospective elemental analyses of otoliths from archived larval cod samples, as well as of ichthyoplankton samples to be collected in 1998 and 1999 as part of the continuing Georges Bank GLOBEC project, analyzing them for Sr/Ca ratios, using an X-ray electron microprobe, and elemental "fingerprints", using UV lazer ablation inductively coupled plasma mass spectroscopy (ICPMS); and (2) assessing the genetic identity of the larvae relative to larval and adult populations from Georges Bank and from the Scotian Shelf using nuclear DNA microsatellite techniques.