Species dispersal through the raw water transfer invasion pathway

Raw water transfers (RWTs) are a globally occurring freshwater invasion pathway. Recently, the need to better understand the invasion risk posed by RWTs and develop pathway management strategies has been recognised. However, as a complex and challenging pathway to study, few direct investigations of RWTs have been carried out previously, and a detailed understanding of pathway activity is currently lacking. We therefore carried out a preliminary investigation of three separate enclosed RWTs in the northeast of England to obtain direct evidence of species dispersal. In total, viable specimens of 24 different species, including the non-native Crangonyx sp . and New Zealand mud snail ( P. antipodarum ) were dispersed, though the introduction capacity of each RWT varied substantially. This study sheds light on the role of RWTs in the secondary spread of diverse species, and demonstrates that different pathway characteristics may influence the species introduction capacity of individual RWTs. The study also highlights that given the complexity and variation inherent within the RWT pathway, risk-based approaches to pathway management may be inefficient for meeting this global management challenge.