Collaborative Research: Origins of Cods on Georges Bank: Contributions of Early Developmental Stages for the Scotian Shelf

9806712Townsend最近在乔治斯海岸-缅因湾地区的工作记录了从新斯科舍省大陆架到乔治斯海岸的Scotian Shelf Water(SSW)显著的、显然是断断续续的通量。SSW是一个相对寒冷和淡水的水团，其重要组成部分来自圣劳伦斯河，通常可以通过水文数据的温-盐度分析和海洋表面温度的卫星图像来确定。去年3月(1997年)在乔治斯海岸的卫星图像和船上的水文采样中观察到了一次这样的通量事件。对三月份邮轮上采集的浮游鱼类进行的海上定性分析显示，盖迪卵的丰度与SSW的分布之间存在着非常密切的联系，这表明，与其他证据一起，这些卵大多是在斯科特大陆架上产卵的，并与SSW水团一起平流到了乔治斯海岸。由此产生了一个基本问题：从加拿大水域向东的平流在多大程度上将乔治斯银行的鳕鱼作为早期开发阶段输入到该银行？本研究的目的就是回答上述问题。该方法将分为两个层次：(1)汤森和拉德克博士将对存档的鳕鱼幼体样本以及将于1998年和1999年收集的浮游鱼类样本进行元素分析，这些样本将作为乔治海岸GLOBEC项目的一部分，使用X射线电子探针分析它们的锶/钙比，并使用紫外线激光消融电感耦合等离子体质谱(ICPMS)分析元素“指纹”。(2)他们还将使用核DNA微卫星技术评估幼虫与乔治斯浅滩和斯科特大陆架幼虫和成虫种群的遗传身份。他们将首先验证已知在这两个地点产卵的鳕鱼幼体的耳石的元素组成。这种元素分析将与幼虫的实验室饲养实验相结合，以确定温度、盐度、摄食量和生长速度对耳石中元素含量的影响。基于DNA的技术将被用来在这些共同的花园饲养实验中识别个体。第二步将是根据通过表征核DNA微卫星产生的单个DNA图谱来确定幼体的来源，核DNA微卫星是他们用来区分乔治浅滩鳕鱼和斯科特大陆架水域的一种新的遗传标记。使用这两种不同的、独立的方法的目的是能够确定幼虫的产卵地点，并根据该区域水团的水文特征追踪其运输情况。

9806712TownsendRecent 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 temperature-salinity analyses of hydrographic data and in satellite images of sea surface temperature. One such flux episode was observed last 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 the above question. The approach will be two tiered: (1) Drs. Townsend and Radtke will perform 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). (2) They will also assess 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. They will first verify the elemental composition of otoliths from cod larvae known to have been spawned in the two locations. This elemental analyses will be combined with laboratory rearing experiments of larvae to determine the effects of temperature, salinity, feeding, and growth rates on the incorporation of elements in the otoliths. DNA based techniques will be used to identify individuals in these common-garden rearing experiments. The second step will be to identify the origin of larvae based on individual DNA profiles generated by characterizing nuclear DNA microsatellites, a new class of genetic markers that they have used to differentiate Georges Bank cod from those of Scotian Shelf waters. The intent in using the two different, independent approaches is to be able to identify the spawning locations of the larvae and track their transport in relation to hydrographic characteristics of water masses in the region.