Investigating the Diel Occurrence of Odontocetes Around the Maui Nui Region Using Passive Acoustic Techniques

The distribution of odontocetes on a daily scale is largely driven by bottom-up processes that in turn influence foraging opportunities. Environmental variables such as bathymetry may help indicate productive foraging regions and serve as useful tools when assessing dolphin spatial and temporal patterns. To begin to understand daily spatial patterns of different odontocete species relative to heterogeneous benthic habitat, passive acoustic monitoring was conducted near an understudied basin of the Hawaiian Islands, the Maui Nui region (Maui, Lāna'i, Kaho'olawe, Moloka'i). Results showed that the acoustic activity of smaller species was stronger at night than day, particularly closer to shelf waters. In contrast, the acoustic activity of less common larger species tended not to follow a diel pattern, except at sites of a moderate proximity to shelf waters. These findings support previous research showing that smaller odontocetes, such as spinner dolphins (Stenella longirostris), track and feed upon the daily vertically migrating mesopelagic boundary community at night, while larger odontocetes, such as false killer whales (Pseudorca crassidens), may forage across most of the region during both the day and night. This information will help inform best management practices that account for interspecies variation in use of the Maui Nui basin.