Abstract
BACKGROUND: The Azores islands have been historically linked to cetaceans, becoming an example of a successful transition from whaling to whale watching. Twenty-eight cetacean species have been sighted in these waters, making the archipelago one of the most recognised whale and dolphin watching destinations worldwide. The business is well-established in the region, operates in four of the nine islands year-round or seasonally and provides an excellent opportunity to collect long term information on cetacean distribution and abundance in an affordable way. Continuous monitoring is indeed essential to establish baseline knowledge and to evaluate cetacean response to potential natural or anthropogenic impacts. Opportunistic data greatly complement traditional dedicated surveys, providing additional support for appropriate management plans. NEW INFORMATION: The MONICET platform has been running continuously since 2009 as a collaborative instrument to collect, store, organise and disseminate cetacean data voluntarily collected by whale watching companies in the Azores. In the period covered by this dataset (2009-2020), 11 whale watching companies have voluntarily provided data from the four islands of the archipelago where whale watching takes place. The dataset contains more than 37,000 sightings of 25 species (22 cetaceans and three turtles). This manuscript presents the first long-term whale watching cetacean occurrence dataset openly available for the Azores. We explain the methodology used for data collection and address the potential biases and limitations inherent to the opportunistic nature of the dataset to maximise its usability by external users.