A series of large scale surveys for cetaceans in European Atlantic waters was initiated in 1994 (SCANS; Hammond et al. 2002) and continued in 2005 (SCANS-II; Hammond et al. 2013) and 2007 (CODA 2009). The third such survey, SCANS-III, is took place in 2016.

In the 1990s, the killing of thousands of harbour porpoises in fishing nets (known as bycatch), particularly in the North Sea and adjacent waters, was a great cause for concern.  At that time, there was no information on the size of the porpoise populations in these waters.  The original motivation for the surveys was thus to provide estimates of abundance of porpoise (and other whale and dolphin populations) so that the impact of this bycatch could be assessed.

There are multiple pressures on cetaceans and their populations may change over time. Most populations of whales, dolphins and porpoises inhabit large areas of sea. Thus, surveys at a large spatial scale are needed at regular intervals to provide biologically appropriate information to keep assessments up to date.

European governments have responsibilities to conserve cetacean populations and Member States of the EU must report regularly on the status of these species. SCANS-III will provide information essential to assessments of Favourable Conservation Status of species under the Habitats Directive and to assessments of Good Environmental Status (GES) under the Marine Strategy Framework Directive (MSFD).