Using active acoustics to compare lunar effects on predator–prey behavior in two marine mammal species

Abstract

Many delphinids feed on vertically migrating sound-scattering layers. The migration of micronektonic animals in these layers is strongly affected by light, both solar and lunar. Active acoustic approaches were used to observe lunar phase effects on the diel patterns of sound-scatter- ing layers in 2 habitats and to simultaneously observe the behavior of foraging spinner dolphins Stenella longirostris in Hawaii and dusky dolphins Lagenorhynchus obscurus in New Zealand. Lunar phase was important in structuring the behavior of diurnally migrating animals in scattering layers off both New Zealand and Hawaii. While the responses of these scattering layers to lunar phase dif- fered between locations, the layers were similar in continuing to migrate to surface waters during all moon phases, in contrast to results from other locations. In both dusky and spinner dolphins, dolphin relative abundance increased with increasing lunar illumination. The dolphin response to lunar phase is not clearly explained by the observed changes in prey. However, the results suggest that lunar phase is likely to be important in driving behavior of the many delphinid species that forage on vertically migrating prey. Active acoustics can be used to simultaneously study predator and prey, elucidating the foraging behavior of other dolphin species feeding on sound-scattering layers. Com- paring the observed patterns to the phylogeny of these diverse species could provide insights into the evolution of behavior in delphinids.