How much effort is enough? The power of citizen science to monitor trends in coastal cetacean species

Citizen scientists provide a cost-effective means of carrying out broad scale, long-term monitoring of the environment while fostering earth stewardship. In this study we investigate how much effort is required by citizen scientists to detect trends in the occurrence of a protected population of bottlenose dolphins (Tursiops truncatus). We analyse the WDC citizen science shore-based data collected over nine years (2005–2013) between April to October from within and in the vicinity of a Special Area of Conservation (SAC) for bottlenose dolphins in the Moray Firth, Scotland. Watches comprised a continuous 10 minute scan of the survey area in an hour. During peak season, around 5 watches per day were required to detect annual or between-site trends of 50% in dolphin occurrence in locations where dolphins were sighted reliably (0.1 sightings per hour). Less effort was required at higher sightings rates, and it was not possible to statistically detect trends of <30%. This study highlights the importance of power analysis in designing citizen science programmes and demonstrates their effectiveness in carrying out long term shore-based monitoring of coastal cetacean species, providing a cost-effective early warning system for changes in the marine environment.