In this final episode, Mhairi talks with Dr Denise Risch from the Scottish Association for Marine Science. Denise is a marine mammal ecologist who studies underwater sounds and sonic marine enviroments to investigate how marine species use and are impacted by sound. During the conversation Denise plays a number of marine animal sounds and explains why sound is such an important sense, and vital for survival. Human sounds are also talked about, and how this anthropogenic noise is rapidly becoming a major threat to the ecology of our seas.