Social responses of travelling finless porpoises to boat traffic risk in Misumi West Port, Ariake Sound, Japan

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.

Assessing the Behavioural Responses of Small Cetaceans to Unmanned Aerial Vehicles

“…Notwithstanding, VTOL UAVs are an excellent platform for aerial studies of marine mammals, having been used in studies of morphometrics, behaviour, demographics and relative abundance [6][7][8][9][10][11][12]. While many of these studies have focused on pinnipeds [2,10,11], others have also focused on cetaceans including humpback whales (Megaptera novaeangliae) [13,14]; grey whales (Eschrichtius robustus) [15]; southern right whales (Eubalaena australis) [16]; blue (Balaenoptera musculus), fin (B. physalus) and sperm (Physeter macrocephalus) whales [17]; killer whales (Orcinus orca) [12]; bottlenose dolphins (Tursiops truncatus) [18]; dusky dolphins (Lagenorhynchus obscurus) [7] and finless porpoise (Neophocaena asiaeorientalis) [19].…”

Unmanned Aerial Vehicles (UAVs) in Marine Mammal Research: A Review of Current Applications and Challenges

“…UAVs have been used to carry out ethological studies related to social relationships [48,50,67,102], collaborative hunting [65] and foraging behaviours [33][34][35]47], kinematic studies and movement patterns [28,32,76,143], respiratory dynamics [93], energy expenditure and behavioural events involving mother-calf pairs [29,50,51], the effects of micropredators [30,75], the impact of swimmer approaches during in-water tourism activities [45], responses to boat traffic [100], responses to sound playback experiments [73], responses to the presence of naval sonar in military training areas [131,132], responses to pinger exposure [69], and comparisons with simultaneous underwater acoustic recordings [68,77].…”

Habitat preference of two sympatric coastal cetaceans in Langkawi, Malaysia, as determined by passive acoustic monitoring

“…A distance of 100 m was used, as it greatly reduces the influences of the presence and cavitation noise of the research vessel on the acoustic detection of porpoises and dolphins. Previous studies have reported that finless porpoises and humpback dolphins may avoid vessels (Ng & Leung 2003, Li et al 2008, Morimura & Mori 2019, Piwetz et al 2021. The detection range of the A-tag was ~450 m, based on the sound intensity and propagation of the clicks emitted by dolphins and porpoises (Fisher & Simmons 1977, Fang et al 2015.…”