基于生态水力学的长江中游四大家鱼产卵场修复机理研究

The four famous Chinese carps, i.e. grass carp (Ctenopharyngodon idella), black carp (Mylopharyngodon piceus), silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) are the main catching and breeding species of freshwater fishery in China, the yield of which can directly influence the sustainable development of the freshwater fishery in China. After the completion of the Three Gorges Project, the spawning grounds of the four famous Chinese carps in the section from Yichang to Chenglingji were scoured by the unsaturated water flow. The hydraulic condition of the spawning grounds were changed correspondingly, which caused the range of some spawning grounds dwindled or moved. As the eco-hydraulics mechanisms of natural propagation of the four famous Chinese carps were still in the exploratory stage, now it is difficult to quantitative evaluate the damaged extent of the spawning grounds and restorate the specific grounds. In this study, we will systematacially investigate the spawning grounds of the four famous Chinese carps in the middle reaches of the Yangtze River, several advanced methods such as early resources monitor, ultrasonic telemetry, hydro acoustic survey and so on will be used to locate the spawning grounds of the four famous Chinese carps. In addition, to typical spawning grounds of the four famous Chinese carps, acoustic doppler current profilers (ADCP) will be adopted to measure the flow field and terrain actually. Based on historic information and the field prototype observation results, statistic methods of numerical simulation, data mining technology and mathematical statistics will be introduced to the study to determine the hydrodynamics characteristics of the four famous Chinese carps' spawning grounds. In our study, we use principles of some interdisciplinary fields such as eco-hydraulics, aquatic resources, hydroacoustics and so on to reveal the eco-hydraulics mechanisms of natural propagation of the four famous Chinese carps. Based on the mechanisms, a habitat evaluation model will be put forward, the production of which can provide theoretical basis to repair the spawning grounds of the four famous Chinese carps in China.

四大家鱼是我国淡水渔业的主要捕捞和养殖对象，其自然资源的丰歉直接关系到我国淡水渔业的健康发展。三峡工程建成后，下泄不饱和水流使长江中游宜昌至城陵矶江段四大家鱼产卵场受到冲刷，产卵场的水力学条件发生了改变，部分产卵场范围缩小或迁移。目前，四大家鱼自然繁殖的生态水力学机理仍处于探索阶段，难以开展四大家鱼产卵场受损程度地量化评估及针对性地生态修复。项目拟对长江中游四大家鱼产卵场开展系统调查，结合早期资源监测、超声波遥测、水声学探测等手段，准确定位四大家鱼产卵场位置，并采用流速剖面仪等测量系统，对四大家鱼典型产卵场流场和地形进行实测。基于历史资料和原型观测结果，通过数值模拟、数据挖掘和数理统计等方法确定四大家鱼产卵场的水动力特征。本项目利用生态水力学、水产资源学、水声学等多学科原理，旨在揭示长江四大家鱼自然繁殖的生态水力学机理，并建立基于该机理的栖息地评价模型，成果可为四大家鱼产卵场修复提供依据。

长江是四大家鱼主要栖息和繁殖地，近年来由于水利工程、过度捕捞等影响，四大家鱼生存空间被挤占、洄游通道被切断、产卵场遭到破坏，如三峡大坝下泄的清水将使中游江段发生长距离冲刷，可能引起鱼类产卵场的变迁。本研究采用传统采集卵苗方法、超声波遥测、水声学探测等手段定位了四大家鱼产卵场位置，并通过流速剖面仪等对产卵场流场和地形进行实测，分析了水生态水力学特征空间变异，主要研究结果如下：（1）历史上宜昌至城陵矶分布十余个四大家鱼产卵场，三峡水库蓄水后，四大家鱼产卵规模已缩小，部分产卵场范围缩小，宜昌-宜都、涴市-荆州、新厂-公安和石首-调关江段是四大家鱼的主要栖息区域，宜昌、公安、新厂、石首江段目前仍是四大家鱼主要产卵场。（2）一定范围内的流量能满足四大家鱼的产卵所需水文条件，但流量过低或者过高时则产生阻碍作用，流量的变化是四大家鱼产卵的必要条件之一。（3）基于产卵场和非产卵场的流场数据，提取了测点平均流速，非产卵场白沙洲区域的流速均值高于宜都区域和南兴洲区域，且白沙洲区域的主要流速分布范围也高于其他两个区域，流速在数据上的分布并不能作为区别产卵场和非产卵场的充分条件。（4）基于流场的断面水深数据和流速空间分布，分析了研究区域断面地形对流速分布的影响，研究发现四大家鱼的适宜流速主要分布在河道干流至河岸区域。（5）长江中游四大家鱼产卵场的断面平均涡量值主要分布区间约为0.237-0.2652s-1。断面平均涡量值与水流速度呈正相关，但这种正相关关系不一定呈线性关系。（6）断面平均涡量值具有明显的空间变异特征，其空间级差分布特征可以作为长江中游四大家鱼产卵场的水力学指示指标。在产卵高峰期，产卵场断面平均涡量值处于一个较高的水平，受河道形态、流速、河底地形等因素的相互作用，研究区域内断面平均涡量值呈明显的空间变异特征，主要变现为核心区域的断面平均涡量值有明显区域性级差变化，断面平均涡量值在水流方向上大致呈现增大趋势，但整个区域内断面平均涡量值复杂多变。（7）与家鱼产卵习性相近的铜鱼产卵场多分布在深潭浅滩较密集的江段。采用局部高程差异法推算了长江上游深潭浅滩分布情况，确定判定限度值T为3.54m。对比了铜鱼主要产卵场江段与非产卵场江段的深潭浅滩分布情况，结果发现产卵场江段每千米深潭浅滩个数为1.19个，而非产卵场江段仅为0.95个，较好的验证了学者之前的定性描述结果。