MEPS 629:193-206 (2019)  -  DOI: https://doi.org/10.3354/meps13123

ABSTRACT: The availability of light, both solar and lunar, is likely to influence the behavior of vertically migrating aquatic animals and their predators. However, the influence of light level on the diving behavior and habitat use of deep-diving cetaceans is not well understood. We used data from 28 depth-transmitting satellite tags deployed on short-finned pilot whales Globicephala macrorhynchus around the main Hawaiian Islands to examine movements and diving behavior in relation to lunar cycles and oceanographic season. During a full moon, dives were deeper (48.1%) and longer (16.7%) than during a new moon. This change appeared to be driven primarily by an increase (25.2%) in the depth of deep dives (>200 m) completed at night and an increase in the proportion of deeper daytime and twilight dives during a full moon. Dives occurred a mean of 18.3 km farther offshore (more than twice as far from shore) during a full moon compared to a new moon. During the oceanographic season with the shortest day length (fall), dives were shallower (25.4%) and shorter (14.2%) than seasons with longer days (summer). This suggests that changes in light level, both solar and lunar, affect the depth of prey targeted by pilot whales, which in turn influences pilot whale diving behavior and distribution. Future research should determine how these changes influence the feeding success and energetics of pilot whales.

KEY WORDS: Diel migration · Foraging · Globicephala macrorhynchus · Lunar cycle · Oceanographic season · Solar cycle · Spatial use · Tagging · Temporal variability