长江南京江段长颌鲚生境履历的反演

Inversion of habitat history for the long-jaw ecotype Coilia nasus collected from Nanjing section of the Yangtze River

利用电子探针显微分析技术(EPMA),对2009年和2014年采自长江南京段的长颌鲚耳石微化学进行了研究,反演了其生境履历。结果显示,这些长颌鲚耳石上元素Sr/Ca值的动态可分为两类。一类Sr/Ca值出现显著波动,不仅具有对应淡水生境的低值(1.87±0.36),而且有对应于河口半咸水生境的较高值(4.80±0.80),甚至出现了外海高盐度生境的高值(7.85±0.57),反映了溯河洄游的生境履历特征。另一类Sr/Ca值稳定3.0以下(14NJC09和14NJCE10),仅反映出在淡水生境中生活的履历。上述结果均得到了耳石Sr面分布的验证。上述"反演"的结果首次发现,传统上认为的一定是溯河洄游的长颌鲚,也可能存在有淡水定居个体。单纯利用上颌骨的长短并不能作为有效判别长江刀鲚资源群体中溯河洄游个体和淡水定居个体的标准。

The estuarine tapertail anchovy Coilia nasus is a highly valued fish in the Yangtze River, however, its resources have drastically declined due to anthropogenic impacts, e.g., overfishing, habitat degradation, water pollution. This small anchovy has been recently proposed for listing as a Class II protected species by the plan for adjustment on China＇s List of Wildlife under Special State Protection. The long-jaw （supermaxilla） estuarine tapertail anchovy is believed to be an anadromous ecotype of C. nasus with a length ratio of upperjaw to head〉l. Anadromous C. nasus has much higher commercial value than that of another freshwater residen tecotype of this species with a length ratio of upper jaw to head〈l. In order to understand the migration characteristics of the long- jaw C. nasus, an electronic probe microanalyzer （EPMA） was applied to analyze the microchemistry patterns of element Sr and Ca in otoliths often C. nasus of this ecotype collected form Nanjing section of the Yangtze River in 2009 and 2014. The results of line transect analyses showed that the Sr：Ca ratio （i.e., Sr/Ca×103） in the otolith of the anchovies could be divided into two patterns： ① Sr/Ca ratio fluctuated between low （〈3.0） and high （〉3.0） phases in the otolith, suggesting the individuals were typical anadromous ecotype which experienced not only the freshwater, but also the brackish water, even the sea water habitats at different stages in their life history. ② Sr/Ca ratio was consistently at low phase （〈3.0） throughout the otolith, indicating that the individuals only experienced freshwater habitat during its whole life history. These evidences were supported by the Sr mapping analyses of EPMA. The results showed, for the first time, that the habitat use of long-jaw grenadier anchovy was much more flexible, and furthermore, freshwater resident individual could even be found in long-jaw grenadier anchovies, although it is traditionally believed that every individual of long-jaw C. nasus in the Yangtze River is diadromous ecotype. Therefore, anadromous and freshwater resident C. nasus cannot be effectively distinguished only by the length ratio of upper jaw to head. However, otolith microchemistry analysis can provide an objective approach to solve successfully this problem of C. nasus fishery management.