Since 2016, the Government and the Société Jersiaise have operated a dolphin monitoring project using seabed hydrophones deployed around the island that record dolphins passing within one kilometre.

This indicator measures the number of dolphin encounters per day at a control site on Jersey’s east coast (an encounter being a continuous recording separated from the next recording by at least ten minutes). It is a baseline indicator for dolphin activity, monitoring site usage by dolphins rather than their abundance or diversity. Any significant deviation is likely to indicate changes in the behaviour and distribution of Jersey’s marine mammals.

One such deviation appeared to occur in 2019. Normally, dolphins (and the occasional porpoise) ‘commute’ past the east coast hydrophone but don’t stay around. Prior to November, daily encounters averaged 0.79 a day – similar to previous years. Then, prolonged poor weather may have caused porpoises to stay close inshore – leading to a significant increase in hydrophone recordings and visual reports. 

The 2020 figure is not an indication of less dolphins – it's an index of the number usage of the dolphin spotting app.