Invasions of two estuarine gobiid species interactively induced from water diversion and saltwater intrusion

The East Route of South-to-North Water Transfer Project of China (ESNT) uses the Grand Canal as the main pathway for water conveyance from the Yangtze River upstream to northern China and links five major lakes that serve as water storages along the route. The ESNT was completed in 2013. It was expanded from the existing Northern Jiangsu Water Transfer Project (NJWT), which had been in place since the 1960s. We observed invasions of two estuarine gobiids, Taenioides cirratus (Blyth, 1860) and Tridentiger bifasciatus (Steindachner, 1881), into the linked lakes. Taenioides cirratus was first reported in Luoma Lake in 2005 and Nansi Lake in 2011. Tridentiger bifasciatus was first observed in Luoma and Nansi lakes in 2015 and in Dongping Lake in 2016. Invasion of T. cirratus was probably associated with the operation of the NJWT, and then enhanced by operation of the ESNT. Invasion of T. bifasciatus was associated with operation of the ESNT. The ESNT/NJWT is mainly operated during winter and spring when the Yangtze River is at the annual minimum discharge. Impoundment of reservoirs at the upper Yangtze River and its tributaries has dramatically reduced river discharge, which induces saltwater intrusion upstream to the donor area of the ESNT. Thus, estuarine gobiids can reach the donor region, and be dispersed upstream through water diversion. There are several other fish species in the Yangtze Estuary that have life history traits similar to these two gobiids and can also live in a wide range of salinities. It is important to evaluate their invasive risks in the future.