The relationship between summer aggregation of fin whales and satellite-derived environmental conditions in the northwestern Mediterranean Sea

Few studies have tried to explain the summer distribution pattern of fin whales (Balaenoptera physalus) in the northwestern Mediterranean Sea, an area characterized with heterogeneous and transient hydrobiological features. Satellite imagery was used to gain knowledge on primary biomass over large time and space scales and to process environmental variables of significance to the problem of fin whale distribution. Fin whale distribution was obtained from survey data and expressed into sightings per unit of effort. Net primary production (g C/m2/day), NPP, can be estimated with a model by processing remote-sensed measurements of chlorophyll concentration, provided by SeaWIFS DAAC. NPP was integrated over different temporal scales, related to primary production cycles in the area. Additional variables were derived from sea surface temperature (AVHRR/NOAA sensors). Multiple cross-correlation coefficients were calculated between these environmental parameters and the fin whale summer distribution from 1998 to 2002. A predictive model, the potential grouping index, was developed from this statistical approach. This study improves our understanding of the variability of fin whale distribution in summer. While food availability at a particular time and place is a function of environmental conditions in the previous months, this study provides evidence that whales adapt their movements and group size directly to food availability rather than to instantaneous environmental conditions.