Investigating Spinner Dolphin (Stenella longirostris) Occurrence and Acoustic Activity in the Maui Nui Region

Abstract

Hawaiian spinner dolphins (Stenella longirostris) rest during the day in the islands’ coastal waters where they are susceptible to human disturbance. Due to concerns over the negative impacts of human activity, the Pacific Islands Regional Office of the National Oceanic and Atmospheric Administration (NOAA) has proposed a 50-yard approach rule for spinner dolphins and is also considering time-area closures of certain important spinner dolphin resting areas. However, gaps still persist in the understanding of how spinner dolphin populations on different Hawaiian Islands use coastal waters, raising questions about the efficacy of the proposed rules. To better understand how spinner dolphins use the waters in the Maui Nui region (Maui, Moloka‘i, Lāna‘i, and the ‘Au‘au channel), a study was conducted using a combination of passive acoustic monitoring and vessel surveys to document spinner dolphin occurrence and movements. Bottom-moored acoustic recorders were deployed at eight locations in Maui Nui, and at one previously established resting bay off west O‘ahu for comparison. The amount of whistles, clicks, and burst pulses at each location was quantified and averaged by the hour of the day. Acoustic activity was greater at the O‘ahu site than at any of the Maui Nui sites, and was greatest between sunrise and noon. Acoustic activity and vessel surveys both reveal that spinner dolphins occur and exhibit resting behaviors in the ‘Au‘au channel between Maui and Lāna‘i, and also along west Maui and southeast Lāna‘i. Spinner dolphins resting in a channel between islands appears to be unique to Maui Nui and differs from resting patterns described along Hawai‘i Island and O‘ahu. Because spinner dolphins appear to use both the coastlines and the channel to rest in Maui Nui, the 50-yard approach rule appears to be a more suitable management option for the region than time-area closures.

Fine-scale spatial and temporal acoustic occurrence of island-associated odontocetes near a mid-oceanic atoll in the northern Indian Ocean

“…Snapping shrimp activity contributed most to the ambient noise in our dataset and showed distinct day− night differences. Dolphin detections also showed distinct day−night patterns in our study, and such patterns have been reported in other studies as well (Lammers et al 2008, McElligott 2018, Cascão et al 2020, McElligott & Lammers 2021. Because ambient noise had a strong diel pattern, it is difficult to know if the diel pattern in dolphin detections we observed was caused by true diel differences in behaviour (e.g.…”

“…Additionally, we suspect that populations in our study area may be similar to populations off other isolated single-island habitats where site fidelity is high, and resident dolphin populations may be fairly isolated and therefore more vulnerable to anthropogenic disturbances (Karczmarski et al 2005). Information on the abundance, distribution, and community composition of cetaceans, such as that presented in our study, prior to large-scale tourism is critical to designing adequate regulations in this area and may act as a useful baseline with which to monitor any future trends (McElligott & Lammers 2021). We recommend further finescale visual and acoustic studies that can inform policy makers and establish no-go zones, times or seasons in upcoming tourism plans and environment impact assessments.…”

“…If, as we suspect, spinner dolphins are the dominant species contributing to our detected whistles, then we would expect day− night differences in acoustic occurrence to reflect their day−night movement patterns as well. The 2 daytime peaks in delphinid acoustic activity observed in our study may indicate periods before and after which spinner dolphins enter or exit resting states, when dolphins become more active (McElligott 2018, McElligott & Lammers 2021.…”

Seasonal and diel patterns in Pacific white‐sided dolphin (Lagenorhynchus obliquidens) pulsed calls near Barkley Canyon

“…Passive acoustic monitoring has become popular for studying dolphin diel patterns, which seem to vary across and within taxa. Several studies have found that dolphins are most vocally active at night (Deconto et al, 2016;Dede et al, 2014;Frouin-Mouy, 2022;Hodge et al, 2013), while others found that dolphins are most vocally active during the day (Gauger et al, 2022;McElligott & Lammers, 2021) or during twilight hours (Goold, 2000), or showed no observable diel pattern in vocalization rates (Philpott et al, 2007). One study found different diel patterns for different types of vocalizations (Cascão et al, 2020), while another found a nocturnal diel pattern in the vocalizations of smaller dolphin species while larger species were vocally active throughout the diel cycle (Howe & Lammers, 2021).…”

Exploring marine mammal presence across seven US national marine sanctuaries

“…In Massachusetts Bay and Stellwagen Bank the opposite was seen with likely Atlantic white-sided and/or common dolphins, with the fewest amount of whistles occurring around midday and peaks in whistle activity during the night (Silva et al, 2019b). Hawaiian spinner dolphins emit more whistles during the morning before their resting period then utilize echolocation clicks during the night for foraging on the deep scattering layer (Heenehan et al, 2016;McElligott and Lammers, 2021). The diversity in vocalization behavior and site usage observed in NMS highlights the potential importance of these areas for different aspects of the life history of numerous delphinid species.…”