Drones help researchers evaluate effect of boat noise on whales
A recent study in eLife led by Dr. Kate Sprogis examines the effects of boat noise level on whales. The research team explored whale responses to boat noise using behavioral observations captured with a multirotor drone.
Whale-watching is an increasing multi-million-dollar industry, and it was initial thought to be benign and a good alternative to whaling. However, as boat-based whale-watching targets populations and spends a large amount of time with whales and dolphins, researchers have shown that whale-watching can have both short-term and long-term disturbance effects on individuals and the populations. To reduce this disturbance on animals, whale-watching guidelines have been put in place that stipulate boat speeds (e.g. <8 knts) and distance (e.g. 100 m) limits when approaching animals. These guidelines are presuming that distance is the key way to reduce disturbance. However, whales, dolphins and porpoise use hearing as their primary way of sensing their environment (whereas most humans use their eyes foremost). Thus, the animals are more likely to hear the boat approaching long before they see it.
With this in mind, the researchers set out to test if noise level (e.g. a quiet boat vs. a loud boat) approaching an animal at the same speed and distance evoked behavioural changes. Humpback whales were used as a model species, as they are found globally and are the number one target in the whale-watching industry. During controlled exposure experiments, to record the behaviour of the whales a small drone (DJI Phantom quadcopter) was flown at 25-30 m altitude above the whales. The drone video recording provided details on the number of times the whales took a breath (respiration rate), the behaviours that occurred (e.g. dives, rolls, breaches), and the swim speed (calculated from the drone GPS flight records). These metrics were compared to before the vessel approached, during the vessel approach, and after the vessel departed. To provide a near-continuous recording of the whales, two drones were flown consecutively. They were launched and retrieved by hand from the front of the research vessel.
The drones are an excellent tool to collect behavioural data, and they are non-invasive as the noise from the multicopters does not penetrate the water efficiently or cause behavioural reactions (Christiansen et al. 2016, Christiansen et al. 2020). Ultimately, drones have been an excellent tool for behavioural studies on whales by providing a new aerial perspective (e.g. able to view behaviours through the water in which could not be examined from the perspective of a boat), video data which can be examined post-hoc (and re-examined for multiple studies) and are non-invasive with a great range of flight (allowing for studies to be conducted with a research vessel as greater distance away from the focal animals).
For more on the research see (Sprogis et al. 2020 – link above) which is free to download.
UAV operations were conducted under a UAV Operator’s Certificate (CASA.ReOC.0075) and a remotely piloted aircraft system licences (K. Sprogis) in accordance with regulations by the Australian Civil Aviation Safety Authority.
Christiansen F, Nielsen MLK, Charlton C, Bejder L, Madsen PT (2020) Southern right whales show no behavioural response to low noise levels from a nearby unmanned aerial vehicle. Mar Mamm Sci
Christiansen F, Rojano-Doñate L, Madsen PT, Bejder L (2016) Noise levels of multi-rotor unmanned aerial vehicles with implications for potential underwater impacts on marine mammals. Frontiers in Marine Science 3:277
Sprogis KR, Videsen S, Madsen PT (2020) Vessel noise levels drive behavioural responses of humpback whales with implications for whale-watching. eLife 9:e56760