On the occurrence of ocean sunfish Mola mola and slender sunfish Ranzania laevis in the Adriatic Sea

Abstract

Presence and habitat preference of two pelagic fish species—Mola mola and Ranzania laevis—are investigated from all available records obtained in the Adriatic from 1781 up to today. Absence of systematic investigations is overcome by relating their occurrences to the long-term meteorological and oceanographic data sets representing local conditions and processes. Seasonal and interannual distributions of these two species are significantly different and point to a possible different causes of their appearance. On the seasonal scale almost all findings of M. mola, with only a few exceptions, are from the warm part of the year, whereas R. laevis is appearing throughout the year with the highest number of individuals in December. Analysis of the interannual meteorological and oceanographic conditions indicates that occurrence of M. mola coincides with the sea warming, whereas the oceanographic conditions favourable for appearance of R. laevis are more complex and could be related to the abrupt change in the large scale atmospheric conditions. Changeable atmospheric conditions coincided with increased productivity in the Adriatic and increased number of zooplankton and small pelagic fish, which are the main food for R. laevis.