Biology: Louder petrol engine noise disrupts whale resting and nursing

Whale-watch vessels with louder petrol engines significantly disrupt short-finned pilot whale resting and nursing, according to a study published in Scientific Reports.

Previous research has found that noise produced by whale-watch vessels can affect whale behaviour. However, the impact of engine noise levels on toothed whale behaviour has been unclear and whale-watch vessel noise levels are not currently regulated.

Patricia Arranz and colleagues used drones to observe the behaviour of short-finned pilot whale mother and calf pairs off the coast of Tenerife, Spain. 13 pairs were observed without a vessel present while 23 were observed as a whale-watch vessel with either a louder petrol engine or a quieter electric engine slowly passed them from 60 metres away, in compliance with Canary Islands whale-watching guidelines. The researchers found that, compared to those not approached by a vessel, mothers who were approached by the vessel with the petrol engine spent on average 29% less time resting and 81% less time nursing their calves. Compared to whales not approached by a vessel, some decreases in nursing and resting were observed during approaches by the vessel with the electric engine, however these were not found to be significant. The researchers suggest that decreases in resting and nursing could increase the energy consumption of mothers and reduce calf energy intake, with potential negative implications for calf survival.

The findings demonstrate that, even if whale-watch vessels comply with current guidelines, louder engines can have a greater impact on whale behaviour. The authors suggest that the noise produced by whale-watch vessels be minimised and that whale-watch guidelines specify maximum engine noise levels, in order to limit disturbance to whales.