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-scattering 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 differed 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. Comparing the observed patterns to the phylogeny of these diverse species could provide insights into the evolution of behavior in delphinids.

Interaction between bottlenose dolphin (Tursiops truncatus) and trammel nets in the Archipelago de La Maddalena, Italy

“…Hernandez-Milian et al (2008) showed significant positive relationships between moon phase and sightings of short-beaked common dolphin (Delphinus delphis, Linnaeus, 1758) and Atlantic spotted dolphin (Stenella frontalis, Cuvier, 1829) in the Azores. Although previous studies suggest that moon phase is likely to be important in determining behaviour of the many delphinid species that forage on vertically migrating prey (Hernandez-Milian et al, 2008;Benoit-Bird et al, 2009), our results show that the lunar phase is not correlated with dolphin interaction in these waters.…”

Prey in oceanic sound scattering layers organize to get a little help from their friends

“…Risso's dolphins, Grampus griseus , a squid predator (Baird ), were detected frequently throughout the study area both visually and from the active acoustics. The unique echo characteristics of marine mammals (Benoit‐Bird et al ) make them easy to distinguish in echograms (Fig. D).…”

“…Single targets were extracted from both the 38 kHz and 120 kHz data. Echoes consistent with marine mammals were identified based on their frequency response, intensity, and morphology (Benoit‐Bird et al ), their positions noted, and their echoes removed from the dataset for further analyses of the scattering layer (Fig. A).…”

The diet of a nocturnal pelagic predator, the Bulwer’s petrel, across the lunar cycle

“…However, species of the deep scattering layers also react to changes in moonlight intensity, migrating closer to the surface during new moons than during full moons 8–11 . Such cyclical responses of mesopelagic organisms to moonlight are thought to induce significantly different foraging strategies in predators.…”