Helping Hawaiian spinner dolphins rest

In this post Julian Tyne discusses his paper ‘The importance of spinner dolphin (Stenella longirostris) resting habitat: implications for management

Coastal dolphin populations are exposed to non-consumptive human activities that can pose conservation challenges. Consequently, effective management strategies, using rigorous scientific assessments of exposed populations and their habitats, are needed to mitigate potential negative impacts of these activities. Key habitats may function as critical for population viability by providing optimal resources such as shelter or prey. To quantify potential negative impacts of human disturbance on animal populations, important areas can be identified by linking habitat characteristics to either animal presence and/or important life functional behaviours such as foraging, breeding, nursing and resting.

Human Interactions
Swimmers surrounding a spinner dolphin in one of the resting bays along the Kona Coast.

The Hawaii Island associated spinner dolphins (Stenella longirostris) have long been known to exploit four sheltered bays (Makako Bay, Kealakekua Bay, Honaunau Bay and Kauhako Bay) along the Kona Coast to socialise and rest during the day, following a night of cooperative feeding offshore. This temporal partitioning of behaviours allows the dolphins to maximize their foraging efficiency while minimizing predation risk during periods of rest in the sheltered bays. However, their predictable behavioural pattern makes the dolphins vulnerable to perturbation during rest, especially if they are unable to compensate for disrupted resting periods. This spinner dolphin population may be especially vulnerable to human disturbance because their resting habitats are subject to considerable human activity; the population is small and genetically-isolated from other populations.

Dolphins resting.
Synchronised surfacing of a group of spinner dolphins during a resting bout within Kealakekua Bay, Hawaii Island.

In our study ‘The importance of spinner dolphin (Stenella longirostris) resting habitat: implications for management’ a novel integration of boat-based and land-based group focal follow data collected inside and outside of the sheltered bays, and the development of three gradient boosting Generalised Additive Models (GAMs) were used to identify habitat features that contribute to the occurrence of resting spinner dolphins in coastal waters off Hawaii Island. Our results illustrate that should spinner dolphins be displaced from resting bays, they are unlikely to engage in rest behaviour elsewhere. These findings provide further information that the four sheltered bays along the Kona Coast are important resting habitat for spinner dolphins during daylight hours.

The US National Oceanic and Atmospheric Administration (NOAA) is considering several management strategies to mitigate the negative effects of human–spinner dolphin interactions, including the use of area closures to reduce the number and intensity of interactions during dolphin resting periods. This strategy proposes to identify specific areas that are important to the population’s survival and restricting human access.

Our results provide important information that can support management actions for an effective mitigation approach to reduce human access to the preferred dolphin resting areas during important resting periods. Interactions between human activities and marine megafauna are often negative, and the approach presented in this paper, where models explicitly link behaviour with habitat characteristics to identify important areas for protection, is much needed. This approach is applicable to ongoing conservation conflicts, but could also be incorporated into recovery plans for depleted species. Such models could help identify future conflicts as animals recover from previous exploitation and reoccupy portions of their ranges.

Spinning dolphin.
A spinner dolphin leaps and spins in Makako Bay, Kona Coast, Hawaii Island.

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