Abstract
Anthropogenic effects have created various risks for wild animals. Boat traffic is one of the most fatal risks for marine mammals. Individual behavioral responses of cetaceans, including diving behavior such as changing swimming direction and lengthing inter-breath interval, to passing boats is relatively well known; however, the social function of cetacean responses to boat traffic in a natural setting remains poorly understood. We focused on describing the behavioral responses of single and aggregated finless porpoises to boats passing at Misumi West Port, Ariake Sound, Japan, by using a drone characterized with a high-precision bird’s-eye angle. During the study period, we collected 25 episodes of finless porpoise responses to boats passing by. A mean (± SEM) of 5.1 ± 1.0 individuals were observed for each episode. The primary response to passing boats was avoidance by dive, which implies boat traffic is a substantial disturbance to finless porpoises that travel along the seawater surface daily. The diving duration decreased significantly with an increase in the number of aggregated individuals. The diving and floating reaction times were 10.9 ± 2.3 s and 18.7 ± 5.0 s, respectively. There was no significant difference between the reaction times indicating that each individual was motivated to keep the group cohesion consistent when floating even after the risk had dissolved, which is comparable to the behavior of porpoises that dive when riskier conditions are present, such as when a boat approaches an aggregation. Our findings provide new insights on the sociality of finless porpoises even though there were limitations, like an inability to identify a specific individual. The drone enabled us to observe the social behavior of finless porpoises and other cetaceans at an unprecedented resolution, which may lead to a better understanding of the evolutionary diversity of intelligence and sociality and the bridge to human evolution.
Highlights
Anthropogenic impacts have created a variety of risks for non-human animals in the wild [1, 2, 3]
The most common response to the passing of boats was avoidance, which implies that the boats passing disturbed the finless porpoises that travelled at the seawater surface
Even though the methods employed during this study had limitations, like an inability to identify a specific individual, our findings identified the social responses of wild finless porpoises to boat traffic around the Misumi West Port
Summary
Anthropogenic impacts have created a variety of risks for non-human animals (hereafter “animals”) in the wild [1, 2, 3]. Traffic accidents are one of the major causes of death for both terrestrial and marine mammals inhabiting areas close to anthropogenic activities. Roadkill can lead to wildlife mortality that exceeds natural rates [4]. In 2002, 31.1% of all known manatee.
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