The seamless use of acoustics between freshwater and saltwater, combined with non-lethal tagging and gentle handling, makes our approach ideal to answer large scale questions. This is especially true when dealing with threatened stocks potentially under pressure from man-made structures, pollution, climate changing climate, fish farms.  Many such migratory fish (the term anadramous is used to describe fish that have different parts of their life cycle in freshwater and oceans) appear to be under population stress, and trying to understand the root of this has only enforced the need for a better understanding of both the river, and in particular the marine, stages of these stocks.