铜陵长江大桥对豚类栖息地的影响

The Impact of Tongling Yangtze Bridge on the Dolphins' Habitats

根据 1 987～ 2 0 0 1年在铜陵江段所进行的 1 8次豚类生态考察 ,统计历年考察记录中 ,在成德洲 -梅埂段 (以下称大桥河段 )工作的天数及观察到的白豚和长江江豚数量 ,分别计算其 SPUE值 (Sightings perunitof effort,以头 /d计 )。并于 1 989、2 0 0 1年 ,在长江水位 8.5 m左右 (吴淞高程 )测定了大桥河段断面 A、B、C、D的深度 (m)及流速 (m/s)。根据汊道最大河宽 (B)、转折角 (α)、曲折率 (S/L)、以及汊道宽长比 (B/S)的变化 ,分析河道与沙洲的变动对白豚和长江江豚栖息地的影响。研究结果表明大桥建成后 ,河段平面变形小 ,汊道分流比稳定 ,滩槽很少变动 ,流态稳定 ,水势复杂多样 ,仍具备豚类栖息活动必要的水文条件。但铜陵大桥对其上下河道、沙洲也产生了一定的影响 ,主要表现为近期和悦洲与成德洲附近的滩槽冲淤明显 ,汇、分流区主流摆动不确定 ,不能形成稳定的水区 ,导致成德洲附近的白豚和长江江豚活动次数明显减少。特别是白豚的活动路线中 (太阳洲→梅埂 )的羊山矶 ,历次考察中未观察到白豚。总而言之 ,白豚在大桥河段的 SPUE值降低与其种群急剧下降是一致的 ,但在梅埂活动的次数下降不明显 ;长江江豚在局部水域 (梅埂、横港 )的SPUE值有上升趋势 。

The Tongling River Section, with many zigzag river channel and well developed sandbars, is one of the few river sections of the Yangtze River where the Baiji (\%Lipotes vexillifer\%) can be found usually, and Yangtze finless porpoise (\%Neophocaena phocaenoides asaeorientalis\%) concentrated with relatively high density. However, along with the increase and expansion of human activities, especially the construction of anti flood, main dams and bridges, the habitat of the Yangtze dolphins has been fragmented and isolated. In order to preserve the critically endangered Baiji endemic to China, in situ conservation must be enforced besides ex situ conservation effort, based on the experience and lessons from the domestic and foreign conservation practices of endangered animals. According to 18 ecological surveys in the Tongling River Section from 1987 to 2001, the sighting per unit of effort (individual/day) in river section Chengdezhou Meigeng (henceafter the Bridge Section) was estimated based on the survey days and individual numbers observed. The water depth (m) and velocity (m/s) in the Bridge Sections when the water level was 8.5 m at Gaocheng, Wushong, were measured in 1989 and 2001. The influences of the alteration of river channel and sandbars on the Baiji and the Yangtze finless porpoises were analyzed according to the change of the maximum width, angles, refractive index, and ratio of width/length of the branch stream.\;Our studies showed that there was only a small change in the water surface, branch streams, beaches, and water flows after bridge construction. Thus, the Bridge River Section still has the necessary water conditions for the dolphins' inhabiting. However, the Tongling Yangtze Bridge slightly affected the river channel and sandbars in the upper stream and downstream of the Bridge waters. There are many newly silted beaches, and the difference between water convergence and diffluence became unclear. For this reason, the discovery rates of Baiji and finless porpoises in this river section decreased significantly. No Baiji was found around the water of Yangshanji and Heyue islet as surveying in field, where Baiji was feeding along Taiyangzhou to Meigeng. To sum up, the decrease of SPUE in the Bridge Section for the Baiji is consistent with the rapid population decline for Baiji, however, the derease in the Meigeng is not obvious. Rather, in some sections, e.g. Meigeng and Henggang, the SPUE of Yangtze finless porpoise increased to some degree, which is probably in relation to the change of riverbed and water flow caused by the bridge piers. In order to preserve the Baiji and the Yangtze finless porpoises and their habitat in the core area in the Tongling River Dolphins Reserve (i.e.Meigeng and Henggang), it is urgently need to prohibit any illegal activities of fishing operations and sand pickings, and the speed of ships and boats in this waters must be restricted strictly.