Confirmation of the presence of harbour porpoise (Phocoena phocoena) within the tidal Thames and Thames Estuary.

This study documents the presence of harbour porpoise (Phocoena phocoena, Linnaeus 1758) in the tidal Thames from strandings, dedicated surveys and opportunistic sightings. In March 2015, a visual and acoustic vessel survey for harbour porpoises was conducted; 17 sightings and 45 acoustic detections of porpoise groups were documented. A conservative acoustic encounter rate of 4.2 animals/100 km surveyed is estimated, comparable to results from acoustic surveys in other important European porpoise habitats. Presented with data from opportunistic sightings records, porpoises are reported in the tidal Thames during all months, with peak presence in spring and late summer. Results support the need for further studies in this significant habitat, and that harbour porpoises must be considered when planning future activities and developments within the estuary.