Satellite tracking of a fin whale (Balaenoptera physalus) in the north-western Mediterranean Sea and fractal analysis of its trajectory

Abstract

Satellite tracking of whales was the aim of the ARGOCET program in the western Mediterranean Sea. With the tracking technology and the development of telemetry, we can study large mammals under natural conditions. In 1991, a satellite tracking during 42 days on a fin whale (Balaenoptera physalus) was obtained. The Argos system allowed us to know the location of this tagged fin whale 263 times. In this study, we can distinguish two kinds of movements: linear segments and tortuous segments with loops drawn in a clockwise direction. Such loops may be superficial oscillations of inertia due to the inertia of the water mass combined with earth's rotation. With this trial study, which is the best we have obtained, we can estimate the fractal dimension d of this trajectory at different observation scales. These d values seem to be scale-independent, so the fin whale path is fractal-like or scale-independent. Fractal dimension, which is a scale-independent measure, summarizes interactions between an organism and its ecosystem and depends on the heterogeneity of the whale's environment (exogeneous factors) and the whale's ability to perceive it (endogeneous factors). For the fin whale trajectory we calculated d = 1.03 +/−0.01 with the divider method. The aggregated distribution of available resources for the fin whale in the western Mediterranean Sea can explain this result close to 1. The heterogeneity of this food resources is not a `measured heterogeneity' but is a `functional heterogeneity'. The low fractal dimension also points to the low probability that the tagged fin whale and the zooplankton aggregates will meet in the western Mediterranean Sea so the fin whale must cover long straight lines from one patch of available zooplankton to another.