中华鲟的死亡螺旋和改出螺旋的可能性探讨

Seeking the chance of escaping from the population depression spiral for Chinese sturgeon (Acipenser sinensis)

  • 摘要:
    目的 中华鲟是长江水生生物旗舰种之一。自1981年葛洲坝截流阻断中华鲟的传统繁殖洄游路径至今,中华鲟自然种群持续萎缩,并出现自然繁殖中断,物种岌岌可危。为有效开展中华鲟自然种群的恢复,亟需弄清楚中华鲟的种群演变机制,分析中华鲟不同拯救方案下的预期效果。
    方法 本研究提出中华鲟在葛洲坝截流之后就已陷入种群螺旋式衰退(死亡螺旋)的假设,并用基于中华鲟生活史的自然种群历史演变量化模型检验该假设,计算不同拯救方案下中华鲟自然种群改出死亡螺旋的可能性。
    结果 模型计算结果显示,葛洲坝截流导致的中华鲟对环境改变的不适应(受精率、怀卵量降低,性腺发育节律失配)已使得中华鲟自然种群陷入了死亡螺旋,三峡蓄水导致的替代产卵场水体滞温、坝下涉水工程导致的替代产卵场功能退化加速了中华鲟的自然种群萎缩、自然繁殖中断。中华鲟自然种群修复(形成可持续种群)的关键是中华鲟繁殖洄游群体能够适应葛洲坝截流导致的环境条件改变(受精率、怀卵量能够恢复,性腺发育节律能够适配),同时要完成水温调控(基本消除滞温)、产卵场修复(容量≥14尾雌鱼产卵),以及持续开展每年大于6.5万尾规格苗(5~7月龄幼鱼)的有效放流(具有高存活率)。
    结论 实践中,有效放流规模越大,出现能够适应葛洲坝截流导致的环境条件改变的洄游繁殖亲本概率越大,实现中华鲟可持续种群重建的概率也就越大。水温调控、产卵场修复,2035年前完成都不算太晚。特别建议,对放流中华鲟群体进行适应葛洲坝截流导致的环境条件改变的遗传筛选和管理,推进中华鲟可持续种群更快地重建。

     

    Abstract: Chinese sturgeon (Acipenser sinensis) are the flagship species of the Yangtze River aquatic ecosystem and the indicator species for indicating the degradation of the Yangtze River aquatic ecosystem in recent decades. The Gezhou Dam, constructed in 1981, blocked the previous spawning migration route of A. sinensis. The previous spawning fields located in the section from the upstream of the Yangtze River to the downstream of the Jinsha River (as long as more than 600 km) were squeezed into a new spawning field located in the section under the Gezhou Dam (about 4 km). It greatly affected the entire spawning migration process of A. sinensis. Subsequently, a series of river engineering projects further impacted on the natural spawning activities of A. sinensis. Although central government and local governments have taken a series of protective measures, the natural population of A. sinensis continued to decline. Natural spawning activity of A. sinensis in the wild has been interrupted in 2013, and there has been no natural spawning detected for 8 consecutive years from 2017 to 2024, making the A. sinensis natural population critically endangered. Why does A. sinensis fall in such an endangered situation? What are the key influencing factors? There has been much debate about this in the academic community. We proposed that A. sinensis may have fallen into a population depression spiral after the Gezhou Dam blocked the previous spawning migration route of A. sinensis, and the subsequent human activity disturbance further pushed A. sinensis towards extinction. Based on the life cycle of A. sinensis, we constructed a simplified parametric model to estimate the dynamic of the natural population of A. sinensis and to test this hypothesis and explore the possibility of rescuing A. sinensis from the population depression spiral. The results showed that: ① the river engineering projects that were constructed in the spawning field under the Gezhou Dam had a small contribution to the current failure of A. sinensis natural spawning (1 year ahead). ② The temperature hysteresis that was caused by the Three Gorges reservoir impounding led to A. sinensis natural spawning failure 15 years ahead. ③ Artificial propagation and release that were implemented over the past 40 years had little contribution towards keeping the A. sinensis natural spawning (delaying the failure of A. sinensis natural spawning for 1 year), but had some contributions on the spawning migration population (postponing the disappear time of spawning migration population by 31 years). ④ Assuming that water temperature regulation and spawning ground restoration can be completed in 2025 and 300 000 Chinese sturgeon juveniles are released each year, natural spawning may be reappeared in 2025, but may failures in both 2029 and 2030, and then natural spawning would be restored once again. However, natural spawning and breeding population will heavily rely on artificial release. If artificial release was stopped, natural spawning will fail again in approximately 33 years later, with a complete loss of spawning migration population after 41 years. ⑤ Assuming that water temperature regulation and spawning ground restoration can be completed in 2025, A. sinensis breeding population can adapt to the environmental changes caused by Gezhou Dam, with fertilization rate, egg production recovered, and gonadal development rhythm adapted to the Gezhou Dam, then 300 000 A. sinensis juveniles only need to be released from now to 2027, and A. sinensis can form a small-scale sustainable population. However, the size of breeding population is positively correlated with the duration of artificial release and the number of released A. sinensis individuals, but there is an inherent ceiling (♀217, ♂197) which was mainly determined by the ecological capacity of spawning ground (♀90). Moreover, there is a minimum value (♀14) for the ecological capacity of spawning ground. If the ecological capacity of spawning ground is lower than the minimum value, the sustainable wild population of A. sinensis would not appear. It is recommended to carry out the water temperature regulation and spawning ground restoration under Gezhou Dam as soon as possible (before 2035), and continue to release 300 000 (at least 65 000) A. sinensis juveniles per year. What needs to be emphasized is that more effectively released A. sinensis juveniles potentially mean higher possibility of the emergence of A. sinensis breeding individuals that can adapt to the environmental changes caused by Gezhou Dam. Of course, it is suggested that all released A. sinensis juveniles should be genetically designed for adapting to the environmental changes caused by Gezhou Dam according to adaptive genetic management.

     

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