Identifying spinner dolphin Stenella longirostris longirostris movement and behavioral patterns to inform conservation strategies in Maui Nui, Hawai‘i

Abstract

Spinner dolphins Stenella longirostris longirostris in Hawai‘i exhibit a predictable diurnal behavioral pattern which makes them vulnerable to human disturbance: feeding at night in offshore waters and resting during daytime in bays. There is concern that human activity, such as swimming with and viewing wild dolphins from vessels, is altering their natural behavioral patterns and preventing them from having adequate rest. In light of this, state and federal management agencies are proposing enhanced protection measures. Research on spinner dolphins has largely focused off Hawai‘i Island and there are insufficient data from Maui Nui (Maui, Lāna‘i, Kaho‘olawe, and Moloka‘i) to inform appropriate management measures for the genetically distinct stock that resides around these islands. Using location data from 316 encounters between 1996 and 2019, we identified 2 hotspots for spinner dolphins within the region, located along west Maui and south Lāna‘i. The predominant behavior observed was traveling, and there was little resting behavior documented throughout the study period, with no resting behavior observed along the coastline of Maui. Our findings revealed that spinner dolphins use a wide variety of available habitat in Maui Nui and were observed resting both near the shore of Lāna‘i and in the channels between islands. Based upon these findings, the proposed lone area for closure in south Maui is inadequate for providing protection to spinner dolphins during resting hours, and we propose that the identified hotspots be considered as additional sites for closures, in addition to an approach limit for vessels transiting Maui Nui.

Tourism informing conservation: The distribution of four dolphin species varies with calf presence and increases their vulnerability to vessel traffic in the four‐island region of Maui, Hawai‘i

“…Areas with these physical characteristics are popular with recreational vessels offering snorkel or diving experiences. This supports the need for management of areas wider than that proposed area in south Maui, in order to successfully provide protection for spinner dolphin from adverse impacts of disturbance (Stack et al, 2020).…”

“…Quantifying either of these can be difficult due to the dynamic nature of the marine environment, particularly when trying to establish the drivers of species distribution whilst incorporating individual movement patterns (Thorson et al., 2017). This lends additional complexity to attempts to assess the degree of spatio‐temporal overlap of marine populations with anthropogenic activity, which is essential to inform effective management (Stack et al., 2020; Thorson, Jannot, & Somers, 2017). The management of explicit spatial areas can be an effective tool for reducing the pressures on mobile species (CBD, 2008), such as the approach used by NOAA in establishing the Main Hawaiian Islands longline fishing prohibited area and Southern Exclusion Zone in order to manage the impact of mortality from interaction with the longline fishery (NOAA, 2012).…”

“…We should explore whether decreasing anthropogenic pressures in areas where calves are observed more could increase the resilience of the population. The spatio‐temporal variation in exposure to anthropogenic pressure also needs further exploration, alongside investigations into any variations in sensitivity to such pressures, as is present in spinner dolphins during resting periods (Stack et al., 2020). This study also highlights that resting bays are not the only locations where spinner dolphins are exposed to anthropogenic pressures (Tyne et al., 2015) and that the management of non‐lethal anthropogenic stressors on this species should include a more comprehensive spatial management plan (Stack et al., 2020) which incorporates the spatio‐temporal variations in the overlap of target species with anthropogenic activity (Thorson et al., 2017).…”

Better educational signage could reduce disturbance of resting dolphins

“…This conclusion applies to most of the west side of Hawai‘i Island and other locations where spinners rest during the day, spinners rest in bays, bays are directly accessible by land, and unguided visitors are abundant. Some Hawaiian sites may fail to meet the first criterion (e.g., west coast of Maui, [ 41 ]), the second criterion (e.g., west coast of Maui, [ 41 ]), or the third criterion (Makako Bay on Hawai‘i Island). Therefore, the utility of signs will vary in a predictable manner across the Hawaiian archipelago.…”

Rapid weight loss in free ranging pygmy killer whales (Feresa attenuata) and the implications for anthropogenic disturbance of odontocetes

“…With an estimated 80% of the 9.9 million people visiting Hawaii each year partaking in marine tourism 34 , the potential for interactions between humans and odontocetes in nearshore environments is high 35 . The lucrative nature of these interactions for some species 36 is particularly problematic 37 , 38 , with high rates of disturbance observed in spinner dolphins ( Stenella longirostris ) targeted for close-up encounters 38 , 39 . This highlights the need to effectively predict and monitor potential consequences of disturbance to minimize the impacts of marine tourism on various odontocete species.…”