Scientia Marina, Vol 76, No 4 (2012)

Discovering where bluefin tuna, Thunnus thynnus, might go: using environmental and fishery data to map potential tuna habitat in the eastern Mediterranean Sea

Dimitrios Damalas
Department of Biology, Section of Zoology-Marine Biology, University of Athens , Greece

Persefoni Megalofonou
Maritime Affairs Unit, Institute for the Protection and Security of the Citizen (IPSC), Joint Research Centre (JRC), European Commission , Italy


Based on a dataset derived from commercial fisheries in the eastern Mediterranean Sea in 1998-2005, we applied generalized additive models (GAMs) to investigate the relative influence of a range of environmental factors on catch rates of Atlantic bluefin tuna (Thunnus thynnus Linnaeus, 1785). GAM analyses were conducted by separately modelling (1) the probability of making a catch (encountering a school), and (2) the positive catch rates (school size). Results suggested intra-annual variations in tuna distribution and revealed interesting associations with some environmental features, lunar periodicity being the most distinctive one. Probability of encountering a school peaked in late spring months, eastwards, at water temperatures above 22°C and around the full moon. Size of school was more likely to be larger in northeasternmost regions and in the vicinity of land in late spring, when the percentage of lunar disc illumination was higher. A moderate but continuous annual decline in the probability of encountering a bluefin tuna school was detected from the models’ outputs. The models were used as an indication of preference or association for the selected environmental variables. Based on these associations, an indirect identification of the bluefin tuna potential habitat was obtained and used to map distributions in the eastern Mediterranean region.


bluefin tuna; GAM; habitat; SST; lunar index; Mediterranean; management

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