Résumé
Heterogeneous data collection in the marine environment has led to large
gaps in our knowledge of marine species distributions. To fill these gaps,
models calibrated on existing data may be used to predict species
distributions in unsampled areas, given that available data are
sufficiently representative. Our objective was to evaluate the feasibility
of mapping cetacean densities across the entire Mediterranean Sea using
models calibrated on available survey data and various environmental
covariates. We aggregated 302,481 km of line transect survey effort
conducted in the Mediterranean Sea within the past 20 years by many
organisations. Survey coverage was highly heterogeneous geographically and
seasonally: large data gaps were present in the eastern and southern
Mediterranean and in non-summer months. We mapped the extent of
interpolation versus extrapolation and the proportion of data nearby in
environmental space when models calibrated on existing survey data were
used for prediction across the entire Mediterranean Sea. Using model
predictions to map cetacean densities in the eastern and southern
Mediterranean, characterised by warmer, less productive waters, and more
intense eddy activity, would lead to potentially unreliable
extrapolations. We stress the need for systematic surveys of cetaceans in
these environmentally unique Mediterranean waters, particularly in
non-summer months.