Odor transport in turbulent flows: Constraints on animal navigation

Odor plumes are common features of aquatic and terrestrial environments, forming an olfactory landscape through which animals must navigate to locate resources and avoid potential hazards. Time-averaged concentration profiles suggest that plumes consist of stable gradients in odor that animals may use for orientation. However, the lime scales necessary to generate such profiles are much longer than those typically associated with the neural or behavioral components of odor-mediated search. In contrast, plume measurements made at biologically relevant scales have indicated that turbulent plumes consist of discrete odor filaments separated by clean water. in addition, certain characteristics of individual odor filaments may vary consistently with distance from the odor source, thus providing directional information to a navigating organism. Unfortunately, there is no method to predict the distribution of these putative chemical cues, and our knowledge of odor dispersal is limited to very few laboratory flume studies. Here, we present the results of a held study during which we measured the distributions of the time-averaged concentration, properties of odor filaments, conditional statistics, and relevant hydrodynamic mixing parameters. Many of the observed odor plume characteristics have similar spatial distributions through a range of hydrodynamic conditions. The high degree of similarity in the distribution of many odor plume characteristics suggests that organisms can rely on any number of metrics to successfully orient in an odor plume. However, the temporal and spatial scales of odor dispersal may constrain the strategies used by navigating organisms and influence the efficiency of odor-mediated search. These field results should provide the basis for further empirical and theoretical work on chemosensory-mediated behavior of aquatic animals.