长江上游鲢幼鱼空间分布特征及其关键环境因子判别

Spatial Distribution Characteristics and Identification of Key Environmental Factors for Juvenile Silver Carp in Upper Reaches of Yangtze River

鲢(Hypophthalmichthys molitrix)是长江重要的中上层经济鱼类,为了解长江上游鲢幼鱼空间分布变化与环境因子之间的关系。根据2019年9月至2020年1月在长江上游至三峡库区开展的渔业资源调查和水文环境数据,并利用广义可加模型(GAM)筛选影响其分布特征的主要环境因子。结果显示,长江上游鲢幼鱼资源密度具有显著的空间分布差异,主要分布于三峡库区丰都江段;影响鲢幼鱼资源密度分布的主要环境因子为流速、浮游生物密度、离坝距离和水温,其中流速偏差解释率最大为57.7%。随着流速增大,鲢幼鱼资源密度整体呈现降低的趋势,集中分布于0.10~0.55 m/s流速范围内;浮游生物密度和离坝距离与鲢资源密度具有显著的线性关系,即随着浮游生物密度增加和距离大坝越远,其鲢幼鱼资源密度呈现上升趋势;随着水温的升高,鲢幼鱼资源密度整体呈现缓慢上升的趋势,集中分布在18℃~21.5℃水温范围内。本研究揭示了长江上游流速、浮游生物密度、离坝距离和水温变化对鲢幼鱼空间分布特征的影响。在长江十年禁渔背景下,应加强缓流生境库区和干支流汇合处的生境保护,为鲢种群资源量恢复构建重要栖息地。

The silver carp(Hypophthalmichthys molitrix)is an important economic fish in the Yangtze River's middle and upper layers.Based on the survey data of fishery resources and environmental data collected from the upper Reaches of the Yangtze River to the Three Gorges reservoir area in 2019-2020,we analyzed the spatial distribution characteristics of resource density of juvenile silver carp,as well as the environmental factors influencing its spatial distribution using the generalized additive model(GAM).The environmental factors were selected using Pearson’s correlation analysis to determine whether they were significantly correlated and to verify that the variables in the model were independent.Thereafter,the best model was determined by a minimum Akaike information criterion(AIC).The results show that the resource density of juvenile silver carp in the upper reaches of the Yangtze River has obvious spatial distribution characteristics,mainly concentrated in the Fengdu River section at the tail of the Three Gorges Reservoir.GAM analysis revealed that the main factors influencing the resource density and distribution of juvenile silver carp were flow velocity,plankton density,distance from the dam and water temperature in the upper Reaches of the Yangtze River,and the flow velocity having the highest deviance explained(57.7%).The resource density of juvenile silver carp shows a decreasing trend with increasing flow velocity,and is mostly distributed in the range of 0.10-0.55 m/s.The resource density of juvenile silver carp increases with increasing plankton density and distance from the dam,indicating a significant linear relationship between these variables and the resource density of silver carp.There was a multi-peak nonlinear relationship between the resource density of juvenile silver carp and the water temperature.With the increase of water temperature,the resource density of juvenile silver carp showed a slow upward trend,and the resource density of juvenile silver carp was mainly distributed in the range of 18℃-21.5℃.This result reveals the effects of flow velocity,plankton density,distance from the dam and water temperature in the upper reaches of the Yangtze River on the density distribution of juvenile silver carp.Therefore,it is necessary to strengthen the habitat protection of slow-flowing habitats at the tail of the reservoir and the confluence of trunk and tributaries to provide the basis for the recovery of silver carp population resources.