Unmanned aerial vehicles (UAVs) represent a novel and cost effective research tool to investigate cetacean behaviour, as conventional aircraft are expensive, limited in the altitude they can fly at and potentially disturb sensitive wildlife. In addition, the aerial observation from the UAVs allows assessment of cetacean behaviour from an advantageous perspective and can collect high spatial and temporal resolution data, providing the opportunity to gather accurate data about group size, age class and subsurface behaviour. However, concerns have been raised about the potential risks of disturbance to animals caused by the UAV’s visual and acoustic stimuli. Boat-based surveys were conducted to assess the short-term behavioural responses of resting bottlenose dolphins (Tursiops truncatus) to a lightweight Vertical take-off and landing (VTOL) UAV flown at 10, 25, and 40 m altitude. Changes in group swim direction and frequencies of surface and aerial behavioural events were recorded from an anchored research vessel before (control) and during the aerial survey. The number of reorientation and tail slap events increased significantly between controls and flights when the UAV was flown at 10 m over the animals. In contrast, no significant differences were detected when the aircraft was flown at 25 and 40 m altitude. However, a precautionary approach is recommended for research applications requiring lower flight altitudes, with further research recommended to assess how different cetacean species and age class may respond to the UAV presence.

Unmanned aerial vehicles (UAVs; or drones) are an emerging tool to provide a safer, cheaper, and quieter alternative to traditional methods of studying marine megafauna in a natural environment. The UFES Nectology Laboratory team developed a drone-monitoring to assess the impacts on megafauna related to the Fundão dam mining tailings disaster in the Southeast Brazilian coast. We have developed a systematic pattern to optimize the available resources by covering the largest possible area. The fauna observer can monitor the environment from a privileged angle with virtual reality and subsequently analyzes each video captured in 4k, allowing to deepening behavioral ecology knowledge. Applying the drone-monitoring method, we have observed an increasing detectability by adjusting the camera angle, height, orientation, and speed of the UAV; which saved time and resources for monitoring turtles, sea birds, large fish, and especially small cetaceans efficiently and comparably.

Measuring and monitoring the behavior and biomedical condition of free-ranging whales remains a fundamental challenge in cetacean science and conservation. Advances in unoccupied aerial systems (UAS) and infrared thermography (IRT) create unprecedented opportunities to fill these knowledge gaps and advance our understanding of how cetaceans interact with the environment. Here, we show that non-invasive UAS-IRT systems, deployed from shore-based positions in a humpback whale (Megaptera novaeangliae) calving ground, can be used to document rarely observed whale behaviors and to quantify biomedical vital signs, including blowhole and dorsal fin skin temperature, respiration rate, and heart rate. Our findings demonstrate: (1) prolonged (>3 h) logging behavior by a mother-calf pair located ∼550 m offshore; (2) that the calf’s respiration rate (∼3 breaths per minute) was six times higher than its mother’s (∼0.5 breaths per minute); (3) that the calf’s blowholes were ∼1.55°C warmer than adjacent ocean water and that the mother’s blowholes were ∼2.16°C warmer than adjacent ocean water; (4) that the mother’s dorsal fin included four infrared (IR) hot-spots, each separated by ∼20 cm in horizontal distance, that ranged between 1 and 2°C warmer than adjacent ocean water; (5) a significant (p <<0.05; wavelet analysis) temporal cyclicity in the hottest of the mother’s dorsal fin hot-spots consistent with cardiovascular blood flow pumped at an apneic heart rate of ∼9.3 beats per minute. Despite these novel results, there remain several key limitations to UAS-IRT, including its: sensitivity to environmental conditions and animal behavior; equipment costs and associated risks; potential regulatory restrictions; time-intensive nature of IR data processing; factors that can impact data quality, such as imaging angle and sensor accuracy. Future opportunities created by the UAS-IRT results we report center on the potential to couple non-invasive behavioral and physiological monitoring tools, quantify cetacean response to prolonged environmental change and acute disturbances, and extend UAS-IRT applications to cover a wider range of environmental and behavioral contexts. Considering the small sample size of the dataset we report, application of UAS-IRT to live-stranded and captive cetaceans, where environmental and cetacean conditions can be independently measured, is of paramount importance.

Generating accurate estimates of group sizes or behaviours of cetaceans from boat-based surveys can be challenging because much of their activity occurs below the water surface and observations are distorted by horizontal perspectives. Automated observation using drones is an emerging research tool for animal behavioural investigations. However, drone-based and boat-based survey methods have not been quantitatively compared for small, highly mobile cetaceans, such as Delphinidae. Here, we conduct paired concurrent boat-based and drone-based surveys, measuring the number of individuals in 21 groups and the behaviour within 13 groups of bottlenose dolphin (Tursiops truncatus). We additionally assessed the ability to detect behaviour events by the drone that would not be detectable from the boat. Drone-derived abundance counts detected 26.4% more individuals per group on average than boat-based counts (p = 0.003). Drone-based behaviour observations detected travelling 55.2% more frequently and association in subgroups 80.4% more frequently than boat-based observations (p < 0.001 for both comparisons). Whereas foraging was recorded 58.3% and resting 15.1% less frequently by the drone than by boat-based surveys, respectively (p = 0.014 and 0.024). A considerable number of underwater behaviours ranging from individual play activities to intra- and inter-species interactions (including those with humans) were observed from the drone that could not be detected from the boat. Our findings demonstrate that drone surveys can improve the accuracy of population counts and behavioural data for small cetaceans and the magnitude of the discrepancies between the two methods highlights the need for cautious interpretation of studies that have relied on boat-derived data.

Post-mortem examinations provide valuable information on sources of mortality for marine mammal populations. However, no published data exist to describe causes of death in the New Zealand population of Common Dolphin (Delphinus sp.). In order to examine the proportion of human and non-human induced mortality affecting this population, necropsies were conducted on 133 individuals that stranded around the New Zealand coastline between 1998 and 2008. Of these, 92.5% (n=123) were found as beach cast carcasses, with just 7.5% (n=10) as live strandings that subsequently died or that were euthanized on humane grounds. The sample included 54 males, 67 females and 12 animals of unknown sex from a range of age classes. Of the individuals for which cause of mortality could be established, 41.2% (n=35) were classified as human induced, with 28.2% (n=24) of carcasses exhibiting evidence of net entanglement. A further 10.6% and 32.9% of mortality was attributable to disease and natural (non-human related) causes, respectively. Few examples of disease were detected, but this may be at least partly a consequence of sampling constraints. Of the carcasses assessed, 68.6% of individuals exhibited some form of parasitism. Parasites identified were typical of the genus and considered to be present in low to moderate burdens. The proportion of beach cast carcasses exhibiting evidence of net entanglement suggests that fisheries-related mortality maybe higher than that previously considered for the New Zealand Common Dolphin population.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.