航道整治期间长江江豚临时庇护所建设及效果评估

航道整治期间为受扰动江豚提供临时庇护所,是在就地保护和迁地保护之外的一种尝试。2020年1月至2021年12月,在长江干线武汉至安庆段6 m水深航道整治过程中,选取马当圆水道建设长江江豚临时庇护所,通过禁止渔业捕捞,增殖放流和通航引导等措施来提升庇护所质量。监测结果表明,庇护所设立后其作为长江江豚栖息地的质量得到提高:夏季鱼类密度从(3361.2±1991.7)条/hm²上升到(12439.1±10734.5)条/hm²,冬季鱼类密度从(501.3±381.8)条/hm²上升至(1684.4±3770.9)条/hm²。通航船舶显著减少,水下噪声低于长江干流的平均水平。长江江豚临时庇护所建立后,枯水期庇护所水域内长江江豚的平均目击次数(4.3±0.6)、观察头次(6)和群体大小(1.4±0.5)都要显著高于庇护所建设前(P<0.05),丰水期则无显著性差异(P>0.05),说明庇护所在枯水期发挥了对长江江豚的保护作用。但长江江豚对庇护所的利用主要集中在进出水道两端,可能是枯水期部分水域过浅限制了江豚对庇护所的利用。分析认为,航道整治等涉水工程施工期间为江豚提供临时庇护所是一项可行措施,但要充分发挥庇护所对江豚的保护作用,必须全面考虑江豚对各项生态因子的需求,防止因关键因子带来的"木桶效应"制约庇护所的整体适合度。

Construction and protection efficacy evaluation of temporary shelter for Yangtze finless porpoise during waterway regulation

Providing temporary shelter for disturbed Yangtze finless porpoises during waterway regulation is an attempt to go beyond in situ and ex situ conservation. Madangyuan waterway was selected to build a temporary shelter for Yangtze finless porpoise during the regulation of the waterway from Wuhan to Anqing of the Yangtze River between January 2020 and December 2021. The temporary shelter for the Yangtze finless porpoise was set up with several measures include fishing ban, enhancement and releasing, guiding navigation, etc. The monitoring results showed that the quality of the habitat of the Yangtze finless porpoise has improved. Fish abundance increased noticeably as average fish density increased from (3361.2±1991.7) ind./hm² to (12439.1±10734.5) ind./hm² in summer,and increased from (501.3±381.8) ind./hm² to (1684.4±3770.9) ind./hm² in winter. Meanwhile, transportation decreased significantly (P<0.05) from (15.3±10.6) ships per day before the temporary shelter was set up to (0.8±0.7) ships per day in flood period, and (0.4±0.5) ships per day in dry period after the temporary shelter was build. And underwater noise reduced and kept at low level ((130.6±3.7) dB re 1 μpa), which is lower than the mean underwater noise level in the mainstream of the Yangtze river, It was proof that fishing banning, enhancement and releasing, and limit the number of ships can improve the quality of the habitat of the Yangtze finless porpoise in short time. As result, the mean sightings (4.3±0.6), observed number (6) and group size (1.4±0.5) of the Yangtze finless porpoise in each surveys in low-water seasons was significantly higher than the shelter was set up before (P<0.05). However, the is no difference in high flow period before and after the shelter was set up (P>0.05). These results indicate that protective effect of the shelter on the Yangtze finless porpoise is mainly in the dry season. However, most of the Yangtze finless porpoises was observed concentrated at the inlet and outlet of the waterway. One possible reason is that the water level decreased during the dry season, which makes some waters too shallow for the Yangtze finless porpoise and that limited their utilization of the temporary shelter. Based on the integration of the upwards research, we concluded that providing temporary shelter for the Yangtze finless porpoise during waterway regulation is a feasible measure. Nevertheless, the demand for the ecological factors of the Yangtze finless porpoise should be fully considered to guarantee for the protection efficiency, or else the habitat suitability will be influenced by the key factors.