The works for the recording of the lionfish populations in Crete were initiated in June 2021. Initially, a survey in SW Crete was conducted in order to choose the most appropriate sampling sites, based on criteria such as, known presence, substrate characteristics (type, depth range) and the frequency of human presence (remote areas, infrequently visited by amateur speargun fishers or professional fishers were preferred). Visual census was the sampling technique chosen as the most effective, considering the particularities of the specific study and the advantages of this technique, and the sampling method applied was the stratified random sampling. Each sampling area was subdivided into two strata, 0-10 and 10-25 m. The contour of the chosen sites and strata were delineated on surface with continuous GPS and depth readings and in a second stage, data regarding the physical characteristics of each sampling site and stratum (substrate rugosity and slope) were collected by underwater in situ measurements. For all of the above works the inflatable boat «MAKRES» was used.