中华鲟自然繁殖及早期胚胎发育河床质适合度研究

As one of the first national protected animals in China , Chinese sturgeon Acipenser sinensis had been listed as Critical Endangered species in the IUCN Red List since 2010. The last spawning ground of Chinese sturgeon was formed just downstream the Gezhouba dam after its construction, and thus, it is essentially important to keep the availability of last spawning ground for the sustainability of the species. Based on the long-term investigation of ecological factors linked with natural spawning and especially the observation of the spawning substrate characteristics in nearly recent years, the arrangement and structure of bottom substrate of the spawning ground have been found greatly changed from the erosion of cleaner water impounded in the Three gorge reservoir. At same time, the acute spawning site as well as spawning scale have also changed. While, it is still not well documented about the ecological effects of the bottom substrate to the spawning success and embryos development of Chinese sturgeon. The proposal thus aims at 1) learning the ecological adaptability of fertilized eggs and embryos of Chinese sturgeon to the bottom substrate and the microhabitat environment it created with artificially established substrate models in laboratory,thus,to explain the reproduction mechanism of Chinese sturgeon to the complicated bottom substrates as a cobble-spawning species; 2) learning the fitness of bottom substrate size and structure to the natural reproduction and embryo development with in-situ investigation on the last spawning ground in order to learn the status of the substrate suitability of the last spawning ground and explain the ecological process and result of the erosion of the clean water from the Three gorge reservoir. It will consummate the ecological demands of natural reproduction of Chinese sturgeon to the spawning substrate parameters and will be contributable for rehabilitation and amendment of the last spawning ground and for artificial construction of a new spawning ground in future.

中华鲟为国家一级重点保护动物，IUCN极危级（CR）物种，目前仅存葛洲坝下唯一一处自然产卵场。维持现有产卵场的有效功能对中华鲟物种延续具有极重要意义。本项目基于申请人对中华鲟自然繁殖生态需求多年调查研究结果，特别是近年来对中华鲟产卵场河床质的连续观测结果，发现三峡蓄水冲刷作用已导致产卵场河床质布局发生明显改变；同时，产卵位点也发生迁移，繁殖效果显著下降。而河床质改变对中华鲟自然繁殖及胚胎发育的生态影响尚缺乏深入研究。因此，本项目拟通过人工构建河床质模型，研究中华鲟受精卵和胚胎发育对不同河床质及河床微生境的适应性，以揭示中华鲟作为底层产粘性卵鱼类的繁殖对策；结合产卵场原位观测，获得中华鲟自然繁殖和胚胎发育期河床质适合度曲线，评估三峡蓄水冲刷作用的生态影响过程和程度。项目实施将填补和完善中华鲟自然产卵基质需求方面的生态参数，可为产卵场生态修复、改良和人工建造等保护措施提供技术支撑。

中华鲟为江底产粘性卵鱼类，产卵场河床质布局特征对自然繁殖及胚胎发育成活极为重要，三峡工程蓄水导致的清水下泄正在改变着葛洲坝下中华鲟产卵场的河床质布局特征，其对中华鲟自然繁殖的生态影响也不得而知。本项目从实验生物学角度通过人工构建河床质实验单元来模拟评估不同河床质对中华鲟受精卵粘附特性和胚胎发育成活的影响，同时结合自然产卵场原位生态观测评估三峡蓄水冲刷对自然产卵场河床质适合度的影响及其对中华鲟自然繁殖的生态影响。主要研究结果如下：1）实验和观测表明，中华鲟自然产卵繁殖依赖于长江中卵石河床（粒径中位值范围5-30 cm）。卵石河床为中华鲟受精卵提供了稳定的基质和供应受精卵粘附的表面、卵石夹缝和孔洞。受精卵在砂质河床相对于卵石河床质中因水流冲刷导致出现脱落时间提前、脱落的比例增高、受精卵被包埋的可能性增高，最终胚胎发育成活率显著降低。2）实验观测到随着卵石缝隙增加，自然受精卵聚集密度增加（估算达15-20ind/mL），会导致中华鲟受精卵耗氧总量上升而单位个体耗氧率下降，产生的氨氮总量和单位个体产生氨氮率都呈明显增加。观测了高密度聚集的中华鲟胚胎发育成活率的下降。3）长江中普遍存在的砂质河床质通过包埋、填充等方式影响着卵石河床的充塞度，决定着卵石缝隙的大小，影响着中华鲟受精卵的粘附稳定性、散布空间和粘附容量。因此，由砂质河床质决定的河床充塞度才是影响中华鲟产卵河床质适合度的关键。4）建立了水下视频观测的河床充塞度与水声学观测的河床粗糙度和硬度的关联，并基于2007年来水下视频观测数据和2004年以来水声学调查数据对比分析表明，中华鲟自然繁殖发生需要适中的河床充塞度，河床硬度和粗糙度。河床质充塞度的显著下降可能是中华鲟下产卵区消失（2004-2007年仅在下产卵区产卵，2008-2012仅在上产卵区产卵）的原因。5）三峡工程蓄水带来的清水下泄使得砂质河床质的向下游推移，葛洲坝下中华鲟自然产卵场的卵石缝隙和孔洞增加，河床硬度和粗糙度明显上升，从而导致现有产卵场河床质适合度的总体下降。三峡清水冲刷作用是现有产卵场功能下降（2004-2012年）或丧失（2013-2015年）的主要原因。同时，三峡蓄水清水下泄也为下游江段卵石河床暴露、形成新的产卵场提供了可能。项目研究完善了中华鲟自然繁殖生态需求模型，可为产卵场修复或重建，新产卵场探测，栖息地保护等中华鲟物种保护措施提供支撑。