The importance of spinner dolphin (Stenella longirostris) resting habitat: Implications for management

Summary 1. Linking key ecological characteristics with animal behaviour is essential for identifying and protecting important habitats that support life functions. Spinner dolphins display a predictable diurnal behavioural pattern where they forage offshore at night and return to sheltered bays during daytime to rest. These bays, which are also subject to considerable use by humans, have long been recognized as key habitats for this species although the extent to which dolphins rely on specific characteristics of these habitats for rest has not been quantified. 2. An integration of boat-based and land-based group focal follow sampling regimes and three gradient boosting generalized additive models were developed to identify habitat features that contribute to the occurrence of resting spinner dolphins in coastal waters off Hawai'i Island. Two ‘in-bay’ models used data collected within bays, and a third ‘coastal’ model (near-shore, outside of bays) used data collected both inside and outside of bays. 3. The coastal model identified that spinner dolphins were unlikely to rest outside sheltered bays. In-bay models showed that dolphins rested throughout daylight hours within bays with a peak resting period between 10.00 h to 14.00 h. The models also identified bottom-substrate-type as an important predictor of rest. Pseudo R2 values of 0·61 and 0·70 for the in-bay models and 0·66 for the coastal model showed that these models provided a good fit to the behavioural data for the occurrence of resting spinner dolphins. 4. Synthesis and application. To date, studies evaluating spinner dolphin resting habitat have focussed on areas inside bays only. Here, we combined data collected inside and outside bays, and illustrate that should resting spinner dolphins be displaced from resting bays, they are unlikely to engage in resting behaviour elsewhere. Results provide further information on the importance of bays as important habitat for resting spinner dolphins. To mitigate the disturbance from human interactions during important rest periods, we recommend that management keep the spinner dolphin resting areas free from human activities. Our quantitative approach where models explicitly link behaviour with habitat characteristics is applicable to identify important habitats for protection of other taxa